Overview on the development and applications of antenna control systems

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Overview on the development and applications of antenna control systems A.A. Mulla a,∗, P.N. Vasambekar b a b

Department of Electronics, Yashwantrao Chavan College of Science, Karad 415 124, India Department of Electronics, Shivaji University, Kolhapur 416 004, India

a r t i c l e

i n f o

Article history: Received 12 August 2015 Accepted 15 November 2015 Available online xxx Keywords: Positioning control Tracking control Positioning algorithms Antenna robust control Antenna tracking system Antenna positioning system

a b s t r a c t During last three decades, the antenna control systems have been extensively developed, studied and applied in several satellite communication systems. While tracking the signal source, these systems play an important role in the alignment of antenna coordinates at receiving end. It is always needed to receive strongest, best quality and environmental effect free signal, transmitted by the transmitter. The speed, accuracy, power, cost and size are the important parameters of antenna control system. The number of control systems implement standard algorithms PI, PD, PID, PIDA, fuzzy, self-tuned fuzzy, LQG, H∞ , genetic, neural network and their combinations. Many researchers developed manual, differential, monopulse, electronic, auto-tracking, left-right, conical and step tracking methods to track signal source. In this paper the developments and applications of the antenna control systems are reviewed. The system performances of the implemented standard algorithms and tracking methods in antenna control system are discussed. The simulated and experimental results show that the advancements in algorithms have reduced major issues and increased performance of the systems. The performance is also improved with the combinations of tracking methods and/or algorithms. © 2016 International Federation of Automatic Control. Published by Elsevier Ltd. All rights reserved.

1. Introduction Satellite communication is one of the fast growing field of science and technology. It is useful to communicate the information over the globe. The antenna plays an important role of signal transmission and reception. The received signal quality (amplitude or strength) depends on the relative location of the satellite, antenna position (Gawronski, 2002) and antenna parameters. After design the antenna parameters become fixed. When the transmitted signal strength is fixed, the signal quality depends on the antenna position (in the form of coordinates). These coordinates are manually adjusted by operator/labor. The manual adjustments have limitations when the antennas are working on mobile vehicles, in antenna parameter measurement systems, in tracking or positioning systems, in antenna systems facing natural disturbances, in large size antenna systems, etc. To have lower pointing error, antenna should be aligned within one tenth of its beamwidth (Dybdal & Pidhayny, 2002). An automatic alignment of the antenna coordinates leads to receive the best quality strongest signal. The antenna control system consists of the electronic and mechanical components with control algorithm. The smallest possible pointing error,

∗

Corresponding author. Tel.: +919766633713. E-mail address: [email protected] (A.A. Mulla).

high speed, low power systems, etc. are the prime requirements of the system. The tracking and positioning systems are the important categories of antenna control systems. A tracking system continually tracks a moving object without stopping its operation. It tracks a moving signal source or object, like communication satellite, spacecraft, etc. It can select the optimum signal strength for particular step by continuous tracking. In order to receive signal efficiently from the satellite, a receiving antenna should track the target satellite precisely. The receiving antenna system does it according to the predetermined search pattern. In positioning system antenna tracks a moving object or it is in a moving mode (antenna mounted on mobile vehicle). When the strongest signal is obtained, it stops tracking and starts again when the signal goes below certain threshold level or adjusts the positioning coordinates by using sensors. Keeping this in mind researchers developed various tracking and positioning methods and algorithms using modern technology. In many systems, the correct satellite position is found by, i. Detecting the level of Automatic Gain Control (AGC) signal (Cho et al., 2003; Min et al., 20 0 0; Myeongkyun Kim et al., 2013; Van Hoi et al., 2015a,2015b). ii. RF detecting/sensing signal (Bolandhemmat et al., 2009; Brain et al., 1989; Gawronski, 2001).

http://dx.doi.org/10.1016/j.arcontrol.2016.04.012 1367-5788/© 2016 International Federation of Automatic Control. Published by Elsevier Ltd. All rights reserved.

Please cite this article as: A.A. Mulla, P.N. Vasambekar, Overview on the development and applications of antenna control systems, Annual Reviews in Control (2016), http://dx.doi.org/10.1016/j.arcontrol.2016.04.012

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iii. Using sensors (Edgar et al., 2007; Kocadag & Demirkol, 2015; Gawronski, 2002; Ito & Yamazaki, 1989; Ming et al., 2005; Myeongkyun Kim et al., 2013; Okumus et al., 2012; Soltani et al., 2011; Soltani et al., 2008; Tanaka et al., 1992; Tiezzi et al., 2012; Watanabe et al., 1996). In this communication we focus on the necessity, applications, classification, basic elements and parameters/performance of the antenna control systems. Further various important aspects such as architecture, computation, algorithms, advantages and disadvantages of the reported antenna control systems are summarized.

2. Necessity The following reasons support the necessity of antenna control systems. (a) The drifting orbital positions of satellites due to some reasons like solar, lunar, oblate shape of earth, non-uniform earth gravity and radiation pressure. This small drift can affect the quality of the received signals from the satellite (Holleboom, 1987; Pirhadi et al., 2005). (b) Every satellite has different look angles (azimuth and elevation) and certain polarization in a link. These angles are adjusted manually by labor/operator for every satellite with measurement of signal strength on TV, spectrum analyzer, field strength meter, compass or inclinometer. This manual antenna alignment is labor/operator sensitive, time consuming, different for different types of satellites and locations of receivers (Cesar et al., 2012). (c) The receiving antenna systems are affected by some natural disturbances like torque (wind pressure), rain fall and some mechanical lacuna like gusts on the antenna structures, bearing, aerodynamic disturbances and internal uncertainties (Cho et al., 2003; Dimitrijevic & Antic, 1999; Hao & Yao, 2011; Hoque & Hassan, 2015; Yalcin & Kurtulan, 2009). (d) The system sensitivity also depends on polarization of signal. The sensitivity reduces due to polarization mismatch. If signal polarization and receiving antenna polarizations are different, the system performance is degraded (Dybdal, 2004). (e) The receiving antennas on mobile vehicles require a system which has capacity to track the satellite signals precisely and accurately when vehicle is in motion (Basari et al., 2010; Bolandhemmat et al., 2009; Brain et al., 1989; Chang & Lin, 2008; Kocadag & Demirkol, 2015; Cho et al., 2003; Densmore & Jamnejad, 1993; Edgar et al., 2007; Kim et al., 2006; Lin & Chang, 2011; Min et al., 20 0 0; Ming et al., 20 05; Myeongkyun Kim et al., 2013; Noordin et al., 2008; Soltani et al., 2008, 2011; Tanaka et al., 1992; Tiezzi et al., 2012; Tseng & Teo, 1995; Watanabe et al., 1996). (f) For antenna parameter measurement, low cost, relatively simple, versatile and operator convenient automatic control systems are required (Anderson et al., 2010; Papaioannou & Langley, 1985). (g) The narrow beamwidth antenna has important requirement of significantly improved pointing accuracy (Bolandhemmat et al., 2009; Lo, 1996). (h) In high frequency band communications, to maintain precise communication link between spacecraft and ground station antenna, improved pointing precision is required (Gawronski, 2001). (i) Advanced satellite communications with narrow spot beams require an automatic antenna pointing mechanism for maintaining spot beam coverage over the specified area (Gupta et al., 2012).

3. Applications The applications of antenna control systems are listed below. (a) The communication link between mobile vehicles (ship, car, train, bus, Yachts, etc.) and satellites (Basari et al., 2010; Bolandhemmat et al., 2009; Brain et al., 1989; Chang & Lin, 20 08; Cho et al., 20 03; Densmore & Jamnejad, 1993; Edgar et al., 2007; Kocadag & Demirkol, 2015; Kim et al., 2006, 2013; Lin & Chang, 2011; Min et al., 20 0 0; Ming et al., 2005; Noordin et al., 2008; Soltani et al., 2008, 2011; Tanaka et al., 1992; Tiezzi et al., 2012; Tseng & Teo, 1995; Watanabe et al., 1996). (b) Radiosonde tracking in a radio theodolite system (Bhuiya et al., 2010). (c) Telemetry receiving antenna tracking system (Payne & Haider, 1993). (d) Tracking weather satellites (Kalliomaki & Tiuri, 1970) and (e) Tracking GEO and non-GEO satellites (Cheng et al., 2012; Pirhadi et al., 2005; Taheri et al., 2014) (f) Automatic control system for antenna parameter measurement (Anderson et al., 2010; Papaioannou & Langley, 1985) (g) Systems used in adverse weather conditions (high rain fall, wet snow), atmospheric water vapor pressure and temperature gradients (Holleboom, 1987; Kuramoto et al., 1988; Rama Rao et al., 1994) (h) Continuous spacecraft tracking (Gawronski, 2002) (i) Mobile satellite internet terminal and television reception system (Bolandhemmat et al., 2009) (j) The radio-telescope antenna positioning system (Isa & Basher, 2005) (k) Field measurement in different conditions for geostationary satellite with vehicle mounted antenna system (Basari et al., 2010) 4. Classification The antenna control systems can be designed with following two technologies. (a) Mechanical steering (b) Electrical (or Electronic) steering Both the technologies are used in directional antennas in communication links. (a) Mechanically steered systems use motors and other mechanical parts to rotate the antennas. The energy consumption in these systems is higher and the moving parts require more care and service (Cheng et al., 2012; Kalliomaki & Hilton et al., 1989; Kalliomaki & Tiuri, 1970; Tanaka et al., 1992; Van Hoi et al., 2015a). The mechanical steering can be achieved in following two ways. (i) Closed loop The system is in the closed loop (Gawronski, 2001) when the control unit receives the control signal from antenna feedback path presented in Fig. 1. In this system receiving antenna tracks the satellite by using detected satellite signal. The received satellite signal always suffers from shadowing and blocking effects of varying signal level. The system therefore requires extra action and time to search and recover. (ii) Open loop In the open loop system the feedback path presented in Fig. 1 is absent and the control unit receives control signals from positioning sensors like gyroscope. It is more suitable for a land to mobile-satellite services

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Signal Detection

Control Unit

Motor

Gears

Antenna

Sensors Fig. 1. Basic Elements of antenna control system.

(Hao & Yao, 2011; Tanaka et al., 1992). The shadowing and blocking effects are less significant in this system as the system uses positioning sensor outputs (Rama Rao et al., 1994). The system is useful for achieving precise angle positioning in land vehicles as their movements, directions and speeds change very rapidly than ships or airplanes. It does not require complexities and expenses of closed loop tracking system. It is useful for precision angle positioning (Dybdal & Pidhayny, 2002; Papaioannou & Langley, 1985; Van Hoi et al., 2015a). The combination of the closed and open loop systems gives the hybrid system. It is used for highly accurate and stable pointing (Hilton et al., 1989; Ito & Yamazaki, 1989). (b) In electronically steered technology phased array uses the phase shifters to steer antenna beam direction. The low, compact profile, high speed tracking and potential low price advantages of this technology make to use it in high gain antennas for land to mobile-satellite communications. These systems are preferred especially at fully automatic stations. The electrical steering eliminates limitations of mechanical steering related to tracking speed and accelerations. It increases considerably the Mean Time Between Failure (MTBF) of the antenna. Due to compact structures, it is more compatible in vehicle installations and requires lower production costs. It suffers from additional losses and lower efficiency (Tiezzi et al., 2012). 5. Basic elements The basic elements of the antenna control system are presented in Fig. 1. It consists of sensors, signal detector, control unit, motors, gears and antenna. 5.1. Sensors The sensors play vital role in receiving antenna tracking systems. Various types of sensors used in the system are geomagnetic, optical fiber gyro, yaw rate, synchro, hall sensor, optical encoder, GPS receiver, beam, potentiometer, GPS-gyro, electronic compass, magnetometer, accelerometer and inclinometer (Edgar et al., 2007; Gawronski, 2002; Ito & Yamazaki, 1989; Kim et al., 2013; Kocadag & Demirkol, 2015; Ming et al., 2005; Okumus et al., 2012; Soltani et al., 2008, 2011; Tanaka et al., 1992; Tiezzi et al., 2012; Watanabe et al., 1996). The angle of rotation of the antenna is measured by using potentiometer (Ming et al., 2005). For absolute direction of mobile vehicle indication geomagnetic sensor is used. However, its performance is affected by magnetic environment. For relative direction, Optical Fiber Gyroscope (OFG) is used with limitation of detection of absolute direction (Tanaka et al., 1992). The rotation of antenna in azimuth at very fast rate are detected by gyroscope (Tiezzi et al., 2012).The Gyro sensor can be used in precise attitude control (Kim et al., 2013). The rolling and pitching angles of receiving antenna are calculated by using gyro and inclinometer.

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The antenna position and pointing is in the form of latitude, longitude and altitude detected by using GPS receiver (Edgar et al., 2007; Tiezzi et al., 2012; Van Hoi et al., 2015a). Orientation of the antenna positions are determined by using Hall Effect technology digital compass with indication of the horizontal components of the earth magnetic field (Edgar et al., 2007). To determine the direction of an antenna with respect to north–south pole electronics compass is used (Tiezzi et al., 2012). Inclinometer is used to measure track profile by measuring antenna tilts in X and Y directions (Gawronski, 2002). The beam sensor is used to measure a change in the strength of the signal (Soltani et al., 2008, 2011). The hall sensor can be used to control speed of the BLDC motor. Due to errors in the measurements of angle, however, it is not appropriate for precision positioning (Kim et al., 2013). The motion sensors (tilt, gyro and compass) are relatively low price, low bandwidth and include frequency drift in the output (Hilton et al., 1989). 5.2. Signal detection Signal detection plays an important role in closed loop tracking system. Number of developed systems use the AGC signal of the digital receiver tuner to measure the signal strength (Cho et al., 20 03; Dybdal & Pidhayny, 20 02; Kim et al., 2013; Min et al., 20 0 0; Van Hoi et al., 2015a,2015b). The AGC signal, an analog output voltage of a tuner is useful for indicating strength of the satellite signal (Kim et al., 2013). The signal detection is also achieved by sensing/detecting RF signal (Bolandhemmat et al., 2009; Brain et al., 1989; Gawronski, 2001). The output commanding signal from the control unit is dependent on the strength of the detected signal. 5.3. Control unit It is the main part of the system. It reads analog data from sensors or signal detector, converts it into digital form, processes and generates the commands. The output commands from this unit are decided by the control algorithm (software). The controllers used in control unit are Personal Computers (PC) (Densmore & Jamnejad, 1993; Edgar et al., 2007; Holleboom, 1987; Ming et al., 2005; Papaioannou & Langley, 1985; Pirhadi et al., 2005), microcontrollers (Edgar et al., 2007; Gawronski, 2001; Van Hoi et al., 2015a,2015b), microprocessors (Cho et al., 2003), DSPs (Bolandhemmat et al., 2009; Kim et al., 2006; Zhai et al., 2009) and PLCs (Yalcin & Kurtulan, 2009). The PC is easy to program and has high speed processing. Also the capability of modification in program and its implementation is the added advantage of PC. The PC uses the modified and improved algorithms without changing the hardware (Pirhadi et al., 2005). The costs of microcontrollers and microprocessors, compared to PC based systems are very low. 5.4. Motors The motors used to control antenna axes are the stepper motors (Alhasan & Alzubaidi 2015; Gawronski, 2001; Holleboom, 1987; Min et al., 20 0 0; Nikolic et al., 2010; Papaioannou & Langley, 1985), DC motors (Bolandhemmat et al., 2009; Garcia-Sanz et al., 2011; Gawronski, 2001; Isa & Basher, 2005; Zhai et al., 2009), geared DC motors (Cho et al., 2003), Brushless DC (BLDC) motors (Kim et al., 2006, 2013), Brushless AC (BLAC) motors (Taheri et al., 2014) and DC servo motors (Singh et al., 2012; Ming et al., 2005; Van Hoi et al., 2015a,2015b; Yalcin & Kurtulan, 2009). The stepper motor is more effective in steering the antenna (Holleboom, 1987). The synchronous motors are fairly expensive and make the system complicated (Papaioannou & Langley, 1985). The linear behavior of DC motors leads to the easier control and made them to

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use traditionally in tracking systems. The low life span and overheating of armature winding in DC motors limits the high-speed repetitive applications (Bolandhemmat et al., 2009). BLDC motors have advantages of high torque characteristics for high speed dynamic response, high efficiency, long operating life, low noise and higher speed suitable for antenna tracking applications. However, the higher cost and difficulties in repair are the disadvantages of these motors (Kim et al., 2013). A driver for motor depends on type of a motor used in the system. 5.5. Gear system The gear system is one of the key factors in antenna tracking system. The accuracy, size and motor torque of the system depend on the gear system. Generally gears are classified as spur, helical, herringbone, warm and bevel. The spur gear is cheaper but it produces noise in the system at high speed than helical gears. Helical cut gears minimize the system backlash. The use of antibacklash reduction gearing reduces the size and required torque from each motor and increases the positioning accuracy (Papaioannou & Langley, 1985). The use of dual drive technique reduces backlash effect (Taheri et al., 2014). The cost of gearing depends on size of the gear wheel, gearbox and material. The dual drive chains with torque biasing mechanism reduce backlash angle (Garcia-Sanz et al., 2011). For stepper motor with stepping angle of 1.8º per step and gear ratio of 10:1, the positioning accuracy is 0.18º in full step mode and 0.09º in half step mode of the motor (Min et al., 20 0 0; Papaioannou & Langley, 1985). 5.6. Antenna The control system for an antenna depends on its application. Antenna parameters also affect design of system (Hao & Yao, 2011). The antenna systems have been developed for tracking DSN antennas, satellite antenna like parabolic (Cesar et al., 2012; Kim et al., 2013; Min et al., 20 0 0), corrugated horn, microstrip patch array (Hilton et al., 1989), phased array antenna (Bolandhemmat et al., 2009; Tanaka et al., 1992), active integrated patch array antenna (Basari et al., 2010), etc.. The hung and bulky antenna system is heavy. It requires high power and has low tracking speed (Basari et al., 2010). Antenna weight and mass are the important design factors for mobile antenna system (Kuramoto et al., 1988). The cost of an antenna is also an important parameter (Hao & Yao, 2011). 6. System parameters/performance Antenna control system parameters needs to be viewed as electrical, mechanical and environmental. Some important parameters of the system under these categories are listed below. (a) Antenna Positioning Coordinates: There are three main positioning coordinates of the antenna control system: azimuth, elevation and polarization. Generally, the elevation angle is controlled between 0° and 90° and the azimuth over complete circle (Alhasan & Alzubaidi, 2015; Nikolic et al., 2010; Van Hoi et al., 2015a,2015b; Yalcin & Kurtulan, 2009). (b) Positioning Accuracy: It is a minimum pointing angle at which positioning system receives a strongest signal from the source. It is measured in degree or arcsec. It depends on mechanical and electronic design of the system (Gawronski, 2001; Papaioannou & Langley, 1985). (c) Speed: It is the speed of rotation of antenna in azimuth, elevation and polarization. It is measured in degree/second (º/s). (d) Acceleration: It is a rate of change in velocity of antenna rotation. It is measured in degree/second² (º/s²).

(e) System Torque: It is a force required to rotate antenna in given direction. It depends on antenna weight, friction, gear ratio, motor drives, speed, wind pressure and environmental conditions. (f) Power: It is total power required for the system. It is measured in watt. The power required for the system depends on weight of the antenna, speed, gearbox, maximum wind torque acting on the drives etc..(Basari et al., 2010; Yalcin & Kurtulan, 2009). (g) Temperature and Humidity: The change in temperature and humidity also affects the performance of antenna control system. The holding torque and accuracy also depend on temperature. Additionally, gear ratio, gearing backlash, system weight, system height, drive type, etc. also need to be considered (Payne & Haider, 1993). 7. Systems for antenna tracking Wodek Gawronski discussed performance criteria to design the antenna control system. He addressed three control algorithms Proportional-Integral (PI), Linear Quadratic Gaussian (LQG) and H∞ with their properties, tracking precision and the limitations. The PI is simple and reliable. It is not suitable in stringent pointing requirements. It is not useful in control of large antennas. It is useful to control the sub-reflector. The bandwidth, speed and ability to reduce disturbances in the system can be improved by increasing proportional gain of PI controller. However, it produces unstable structural vibrations. These parameters are improved by using LQG and H∞ controller. LQG controller has shorter response time, disturbance rejection properties, small margins compared to PI controller. Therefore it is better than PI. The performance of LQG is further improved in H∞ controller. The H∞ controller has acceleration limits because of the existing motor drives and gear systems. This limits the benefits of H∞ controller. To overcome this limit Wodek Gawronski suggested the use of command pre-processor in software that modifies antenna commands. This avoids the excessive rate and acceleration (Gawronski, 2001). Dybdal and Pidhayny presented rate corrected step tracking open loop method. This method is extension of commonly used method of relatively stationary signal sources such as geostationary satellites. It is useful for dynamic signal source (low altitude orbit satellite). There are two phases; initial acquisition and trajectory tracking in rate corrected step tracking procedure. In the initial acquisition phase, satellite signal coming into view is pointed. The second phase is used for validation of the satellite. In this phase sampling rate for the validation is also varied according to azimuth and elevation rates. It is more frequent for higher angle. This technique improves accuracy and response of the system. The technique avoids the cost and complexity over closed loop (Dybdal & Pidhayny, 2002). Pirhadi et al. implemented geostationary satellite step tracking subsystem with MATLAB® using Simulink and Data Acquisition toolbox, Real Time Workshop and Real Time Windows Target features. Its GUI (Graphical User Interface) capability is suitable to interface user and tracking hardware. The GUI has manual and auto tracking modes. The manual tracking mode is useful for choosing satellite by selecting proper azimuth and elevation angles. The autotracking is implemented with gradient step tracking technique. The simulated results show that the developed method is easy to implement the desired algorithm for autotracking geostationary satellite (Pirhadi et al., 2005). Zhai et al. simplified turntable based complicated and costly system using semi-physical simulation. The system consists of antenna and its drive systems, MATLAB/Simulink/xPC real time

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simulator platform, compound controller (DSP), image processing computer, sub-satellite point display computer and tracking and data relay satellite (TDRS) simulator. In addition to slewing, scanning and auto tracking modes of antenna the system introduced various other modes such as the ‘none instruction mode’ – for no execution of any operation, ‘origin position mode’ – to define origin position, ‘ceasing motor mode’ - to stop antenna movement and ‘reversion antenna mode’ – to put antenna back into the original position. In ‘whole process mode’ the antenna slews and scans until it catches the target. The system verifies the antenna acquiring and tracking processes beneficial in designing satellite antenna pointing control (Zhai et al., 2009). Yalcin and Kurtulan designed antenna tracking system for 15 kg, 45 cm diameter rooftop dish. The antenna steers in azimuth and elevation angles for given directions. The tracking system is operated in manual mode and auto mode. In the manual mode the azimuth and elevation angles are set by using up-down keys. They considered wind deviation effect and assumed the wind speed of the order of 150 km/h. They also discussed the power budgeting by proper selection of motors and corresponding drives. A complete system is implemented by designing Proportional-Derivative (PD) and Proportional-Integral-Derivative (PID) type digital control algorithm with Programmable Logic Controller (PLC) (Siemens S7222). The PD controller is used in inner loop to prevent the integration of the disturbance by system dynamics. The PID controller used in outer loop controls the angular position. A TD200 (with human machine interface) text display is used to enter user data, monitor current antenna position and to manually steer the antenna. The zero angle positions are determined by the limit switches for each axis. The antenna tracking system is simulated by using MATLAB simulink (Yalcin & Kurtulan, 2009). Garcia-Sanz Mario et al. designed an advanced novel nonlinear/robust controller with high-performance servo-system for large radar antennas, by combining robust QFT (Quantitative Feedback Theory) technique with nonlinear switching strategies. The developed system is demonstrated by using simple model of radar antenna consisting of DC motor coupled to gearbox and antenna load. The servo system consists of three cascaded loops: current, velocity and position. The current loop is much faster than other loops. The velocity loop is lead lag controller. The position loop is designed for performance testing. The system is designed and compared with linear, fast and slow controller. The system showed high performance robust tracking, disturbance rejection and guaranteeing performance even for system parameter uncertainty (Garcia-Sanz et al., 2011). Singh et al. designed, developed and implemented X-band ground station antenna control drive system for remote sensing satellite considering orbit prediction tracking mode with elevation over azimuth mount. The authors discussed various steps of the antenna drive control system design: estimation of total mechanical load, deciding optimum gear ratio, selection of motor with its drive amplifier, selection of encoder, with better resolution and modeling of drive control system. Due to efficiency, counter torque worm planetary gear box was chosen. The developed servo control drive system consists of PID controller, power amplifier, BLDC or BLAC motor, feedback control loop and load (reflector). It is cost effective. The simulated results are very close to the ideal performances of system (Singh et al., 2012). Taheri et al. presented dual drive axis control system for LEO satellite tracking. A feedback error learning (FEL) controller with neural network is implemented for X-Y pedestal. The system mainly consists of two AC servo motors, encoder, computer with DI/O card and two gear boxes (90:1). The angle of rotation is calculated by using encoder. The system control algorithm is implemented using C++ visual studio. The authors also discussed X-Y pedestal kinematic, backlash compensation with dual drive

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technique and neural network controller. The dual drive technique is useful for minimizing backlash effect. The FEL system presents modification of traditional controller and does not require plant Jacobian calculation. It shows better performance compared to traditional PID and PD controllers in satellite tracking (Taheri et al., 2014). Van Hoi et al. designed and manufactured auto-tracking system for searching the satellite. The system is designed around PIC16F628, computer, 12-bit ADC, GPS receiver and sensor. It uses both the traditional PID and Fuzzy-PID controllers. The PID controller parameters are obtained by using Ziegler-Nichols method. The PID controller is tuned by fuzzy controller based on current parameter of the classical error and rate of change of error. The step tracking control process is implemented with fuzzy PID controller. After receiving sensor signal from microcontroller the system calculates the azimuth and elevation angles. The simulation on SIMULINK shows that the fuzzy PID controller is better. This is because the PID controller is oscillatory and has long setting time (Van Hoi et al., 2015a). Van Hoi et al. proposed an improved step tracking system for receiving continuous signal from satellite. The step tracking algorithm is improved by combining it with open loop control. At first when system turns ON the antenna is controlled by the open loop method. The GPS receiver and angle sensors are used to calculate the positioning parameter (azimuth and elevation angle) to track desired satellite. The system then turns to the step tracking mode. This tracking mode continues until signal is more than threshold. When the signal is below threshold level, the system automatically switches to the open loop tracking mode. This reduces searching and tracking time. Both, the traditional and fuzzy controllers are implemented in the system. The fuzzy controller results better response and tracking time of the order of 0.4 s and 0.5–0.7 s respectively. For traditional controller these periods are 0.6 s and 0.6 s respectively. (Van Hoi et al., 2015b). Kalliomaki and Tiuri developed electronic tracking antenna system for satellite signal reception in VHF range. Here the antennas are directed in different directions to cover whole sky. The satellite receiver controls the switch which further connects to the antenna for desired signal. For the feeble signal, a new antenna is automatically searched and switched in. In this system the receiver receives good signal but not the strongest always. It is lost during search of a new antenna. The system is suitable for weather satellite (Kalliomaki & Tiuri, 1970). 8. Systems for antenna positioning Dimitrijevic and Antic designed satellite antenna positioning system. It is developed by using two inputs and single output (TISO) robust fuzzy controller. The fuzzification is performed with triangular membership functions. Based on fuzzy inference the control signal is calculated. The center of gravity method (sum of gravity) is used for defuzzification. It converts the control signal fuzzy value to analog control signal. The system is verified by digital simulation. It is seen that the robust TISO fuzzy controller is useful to control satellite antenna position in bounded external disturbances. The system reduces the oscillations typical for variable structure systems around the steady state (Dimitrijevic & Antic, 1999). Nikolic et al. developed antenna positioning system based on orthogonal Legendre type filter for detection of electromagnetic field gradient. The system was designed so as to turn antenna towards the transmitter. The control algorithm of the system consists of gradient detection and movement organization towards extremum. The azimuth and elevation axes are separately adjusted via two stepper motors. In the experiments elevation angle is controlled between 0° and 90° and azimuth for full circle. Here PID,

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fuzzy and orthogonal controllers are employed and adjusted without knowing transfer function. A PID controller is adjusted by using Ziegler–Nichols method and fuzzy controller using PD error. The Fuzzy controller is much slower. The PID controller produces overshoots during rapid changes of the target position. The merit of the system is the easy determination of electromagnetic field. The realization of the filter is very simple, fast, robust and precise. The antenna control system in terms of efficiency, speed and tracking accuracy is validated by laboratory experiments and comparative study (Nikolic et al., 2010). Okumus et al. studied antenna azimuth positioning control system using fuzzy controller and traditional PID controller. The system modeling is done with MATLAB/SIMULINK. It consists mainly potentiometer, power amplifier, pre-amplifier, motor and load. The designed FLC is tested by defining various rules and using different membership functions. It is seen that the triangular membership function results more sensitive, fastest and sharp response without steady state error. Compared to classical PID the FLC is more convenient form for the desired system (Okumus et al., 2012). Rafael et al. developed an automatic system for maneuvering parabolic dish antenna for satellite signal reception. A system was developed around GPS for monitoring spatial location and digital receiver to provide the Carrier to Noise ratio (C/N) of the signal. A Java based S3A user friendly software with graphical user interface was developed. It processes information about database and satellite. After choosing satellite it produces reference position of the antenna. Accordingly servo mechanical signals are generated and signal reception is improved. When the antenna reaches reference position it monitors the quality of the received signal by checking C/N ratio. For good reception it was found to be ≥ 8 dB. For reception of good quality signal, continuous fine tuning is done. The authors also developed fuzzy controller consisting of 63 rules. With the system developed, antenna alignment is done within 3 minutes with good C/N ratio of 8.44 dB (Cesar et al., 2012). Okumus et al. proposed self-tuning fuzzy logic controller (STFLC). They designed PID, FLC and STFLC by using MATLAB/SIMULINK and tested for various membership functions and rules for FLC and STFLC. The PID controller is tested for various gains. The self-tuning FLC is used to tune scaling factor, fuzzy gains of controller input error and its change. It is observed that STFLC gives better performance than FLC and PID (Okumus et al., 2013). Alhasan and Alzubaidi designed full remote controlled positioning system for the satellite dish antenna. The system is developed by using stepper motors for positioning three axes (azimuth, elevation and polarization) of an antenna. Here, a user enters the satellite coordinates in the form of longitudes and latitudes. The system software calculates the azimuth, elevation and polarization angles. Accordingly the stepper motors steer the antenna towards selected satellite. The system requires less time for antenna alignment. It is useful for automatic and precise positioning antenna for desired satellite (Alhasan & Alzubaidi, 2015).

feedback information is given by shaft encoder. A stepper motor is used to steer the antenna. The developed system and computer program determine the correct orbit. With step tracking method the reliability of receiving antenna system is improved under adverse weather condition (Holleboom, 1987). Kuramoto et al. developed mechanically steered antenna tracking system for land mobile satellite communication. The system consists of eight element spiral printer array antenna and antenna drive mechanism with the single channel tracking. The method used for tracking is similar to the conical scanning. The antenna beam direction is changed mechanically by rotating the antenna feed horn or sub-reflector. By switching the PIN diode phase shifter beam direction is changed electrically. If the antenna is offset from the satellite direction, received signal levels is the difference between the two switched beams. From this difference antenna position is referred and the motor is driven to direct antenna towards the satellite. When the received signal becomes lower than the threshold level, due to obstacles like buildings, the antenna tracking mode is changed to the search mode. The antenna is rotated until it receives the optimum signal strength, which is higher than the threshold level. The single channel tracking system is simple as compared to dual channel tracking system. It requires less number of equipments. It is suitable for land mobile applications. The system is easy to extend for two axes (azimuth and elevation) (Kuramoto et al., 1988). Rama Rao et al. described, design and measurement of a prototype of the cassegrain antenna system. The system is controlled by using PIN diode with electronic beam squinting. It is useful for achieving fast, closed loop tracking of the satellite by sampling beacon signal. Designed antenna works on the 7.25–7.75 GHz downlink and 7.9–8.4 GHz uplink frequency. To locate the satellite position, four symmetrical positions squinted lobes are placed at 90 degree intervals on the antenna boresight axis. The intensity of the satellite beacon signal at each squinted beam position is detected through sequential comparison of the four squinted beam signals. Based on the position of the satellite both the elevation and azimuth planes are determined. The four squinted beam positions are generated very rapidly through fast acting PIN diode switches. In fraction of seconds the amplitude comparison of the beam position is completed. Therefore the system allows for ‘near real time’ tracking of the satellite to count scintillations and multipath fading from roadside obstacle or signals received from an antenna mounted on fast moving vehicle. The ‘Track while receive’ tracking system mode is used. The electronic beam squint system is less expensive than electronically scanned phased array or four channel monopulse system, as it needs a single receiver. It is also several times faster than mechanical tracking system like conical scanning or step tracking. The system is modified for applications such as small size, low profile, electrically shaped reflector antenna. Therefore it is more suitable for deployment of military vehicle (Rama Rao et al., 1994).

9. Systems for adverse weather condition

10. Systems for mobile vehicles

Holleboom developed step tracking antenna system using PC. The system helps to receive maximum signal strength from the satellite. The system consists of three modes of antenna control: step track, programtrack and orbital data. In step tracking, hill climbing technique is used for the maximum signal strength reception from the satellite. The programtrack mode helps to calculate a next hour position of the satellite by using some coefficients. These coefficients are calculated by using orbital data from predicted az/el data from other sources like EUTELSAT. The van switch and shaft encoder are used in feedback signals. The van switch indicates number of revolutions and directive movement of the screw. The absolute and accurate position of

Ito and Yamazaki described a practical mobile 12 GHz television receiving system for vehicle mounted satellite antenna receiver. The elevation and azimuth pointing mechanism is performed by using a gyroscope and potentiometer. The authors explained three tracking methods: step tracking, conical scanning and monopulse. The system is developed around phase comparison monopulse tracking. It consists of four flat panel antenna units (A, B, C and D). Each unit consists a Base Station (BS) converter and tuner. The converted signal consists two types of signals which are used for antenna tracking and signal reception. The received output signals from ABCD in pair are sent to azimuthal in-phase combined circuit. The signals A+B and C+D are sent to elevation in-phase combiner

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circuit. The signal A+B+C+D is sent to the vehicle via rotary coupling transformer for demodulation. The control signal at the same time is sent to azimuthal monopulse circuit, elevation monopulse circuit and elevation rotary drive. The signals from azimuthal, elevation, gyroscope and potentiometer are sent to the CPU. The output of the CPU is used to drive and control the antenna azimuth and elevation axis unit. The drive system is rotated at maximum speeds of 15 rpm in azimuth direction and 12 rpm in elevation direction. The system has an elevation range of 25–90º and azimuth of 0–360º. The CPU completes one session within 5 ms (Ito & Yamazaki, 1989). Brain et al. developed KA-band antenna tracking system for inter-orbit communications (IOC). A novel lightweight tracking antenna is employed for electronically generated higher order waveguide mode (TE21 ). A tracking system is developed by using MSS (Mobile Satellite Services) unit consists of tracking antenna, receiver, the data handling unit (DHU) and PIN switch driver (PSD). The DHU is controlled by beam switching sequence via PSD. A single pulse train output from DHU causes PSD to switch one of the four PIN diodes in antenna to ON state. This causes the main beam to scan into the corresponding quadrant. The received RF signal is synchronously sampled with receiver ALC loop. After averaging it over a number of samples the results are stored. It is repeated for all four beams. The signal levels obtained from the opposite beams are subtracted and transformed from the tracking planes into the fixed X and Y rotational planes required for antenna pointing mechanism controller. The resultant system is successfully implemented in flight hardware with extremely short time scale. The system is rapid, accurate (accuracy better than 0.5°) with reliable RF sensing capability (Brain et al., 1989). Tanaka et al. describes antenna tracking system for L-band mobile satellite communication. The system is developed by Communications Research Laboratory (CRL) antenna system using geomagnetic sensor and optical fiber gyroscope (OFG). It consists of phased array antenna and open loop tracking method. The benefits of the open loop tracking system are, (i) Satellite can be found in shadowing and blocking. (ii) Tracking does not depend on signal level. (iii) Complicated movements of land vehicles affect less In tracking, before vehicle starts the initial absolute direction of the vehicle is detected by using geomagnetic sensor. The angular velocity is calculated by using OFG. When vehicle starts, the data from OFG and geomagnetic sensor are sent to the computer at the rate 10 data/S. The standard deviation (SD) for 20 data of the geomagnetic sensor is calculated. Using this value the antenna is controlled. When deviation is greater than 1°, the antenna is controlled by using OFG. The OFG is also calibrated by using the geomagnetic sensor. The system is tested in the field for the ETS-V satellite. It is seen that the antenna tracking algorithm given shows good performance. This antenna system is useful for land vehicle satellite communications (Tanaka et al., 1992). Densmore and Jamnejad described the K and Ka-band mobile vehicle satellite tracking system. The system is successfully developed by Jet Propulsion Laboratory for NASA’s Advanced Communication Technology Satellite (ACTS) mobile terminal project. The system describes antenna assembly consisting of RF and mechanical characteristics. The motor steers the reflector and feed horn antenna and optical encoder verifies commanding angle of the motor. The antenna controller also describes, inertial yaw rate sensor, tracking control system and mechanical dithering. The mechanical dithering is used to measure antenna azimuth pointing error and thus enabling closed loop tracking. The RF losses in monopulse tracking are overcome in mechanical dithering. In antenna tracking system, satellite pointing information is provided by a yaw rate sensor. The internal sensor bias drift are compensated by using

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closed loop feedback. In some cases system is locked for reflected signal when the satellite is shadowed by obstacle (satellite direct signal are blocked). The test results show that the performance is very good and proved all requirements. The system shows fractional pointing error. The system is able to complete full azimuth scan within 5 s (Densmore & Jamnejad, 1993). Tseng and Teo designed fuzzy logic controller for a ship mounted robust satellite antenna tracking system. The system copes with sensor imprecision and noisy sea environment. The fuzzy logic controller designed with 22 fuzzy rules is found to achieve goal target. The authors also described kinetics of antenna, ship and motor dynamics. The simulation is achieved for a set goal of 45° for both azimuth and elevation. The performance is compared with PID controller. The fuzzy logic controller gave precise tracking and exhibited more superior performance than the PID controller. The PID controller constant (gain) values are extracted by using fuzzy logic controller process. The authors also discussed spiral search method valuable for finding a true orientation of satellite location (Tseng & Teo, 1995). Watanabe et al. developed small antenna receiving system for a passenger car. The system mainly consists of planer array antenna, antenna assembly, motor assembly, receiver assembly, signal detector, gyroscope and controller. The use of pattern synthesis technique in the system allows to dispense the elevation tracking by widening beamwidth. The controller used both received and gyroscope signals during tracking. The field test experimentally proved that the tracking is more faster than 40º/s. The simple structure of the system results in low manufacturing cost (Watanabe et al., 1996). Min et al. developed antenna azimuth tracking system for mobile vehicle by measuring the AGC signal strength. They used active stabilization method for mechanical steering. The tracking algorithm consisted differential and left-right tracking methods. In differential case, the difference of present and past AGC signal is considered. This is not fast tracking method. In left–right rotation method, the antenna is alternatively rotated in the left and right directions by the constant angle. The tracking system has ’reset’, ’searching’, ’tracking’ and ’idle’ states. The system is developed with μPD70322, MAX197 ADC and Direct-broadcast Satellite (DBS) tuner. A stepper motor is used to rotate the antenna. To avoid signal drop, long time high speed tracking techniques is used. The system tracks the satellite within 0.2–0.6 s (Min et al., 20 0 0). Won and Kim developed three axes marine satellite antenna system using 3D CAD technique. The control system was developed by using a sensor fusion and PIDA (Proportional, Integral, Derivative and Acceleration) algorithm. The sensor signal, signal processing and digital pre-filter algorithms are developed to improve sensor performance and overcome sensors effect. All algorithms are tested by PC with antenna base excitation simulator. Test results show that, sensor fusion algorithm rejects lateral acceleration limit of a tilt sensor and also gyro sensor drift. The PID with acceleration (PIDA) algorithm stabilized each axis of the antenna. For step input, system has no steady state error and rise time less than 0.4 s. The system shows pointing error less than 0.2° (Won & Kim, 2005). Ming et al. developed conventional ship mounted antenna tracking system for improved accuracy. The system is developed by using H∞ controller around a ship mounted INMARSAT antenna. The hardware consists of computer, control circuit unit and driving axes of the antenna. For driving each axis a DC servo motor is used. The outputs from potentiometer, rate gyro and inclinometer are connected to the computer. The roll and pitch angles of antenna are calculated by computer using rate gyro and inclinometer output. According to calculated angles the motors are rotated by varying PWM duty ratio. The duty ratio for the PWM of each motor is derived by the control algorithm. An H∞ controller was designed and implemented in the antenna tracking system. The use

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of H∞ controller in the system resulted five times improvement in the accuracy. The tracking improves with accuracy upto ± 0.03º, short settling time and steady state deviation less than 2º (Ming et al., 2005). Kim et al. designed two axes stabilized antenna tracking system for mobile vehicles using fuzzy-PID controller. The system consists of flat antenna, BLDC, DSP (TMS320F2812) and a tuner. It tracks moving object-unmanned helicopter by sensing AGC signal. The designed controller is verified by simulation using MATLAB. The performance of both Fuzzy-PID and PID controllers are compared for simulations and real field experiments. The result shows that the fuzzy-PID controller is superior in performance, robust and simpler than conventional PID. It gives better tracking and robust performance in different environmental conditions. Also it is better in overshoot and settling time. The PID controller produced greater vibration (Kim et al., 2006). Edgar et al. developed AVR microcontroller (AVR ATMEGA8535) based antenna positioning system for geostationary satellite and mobile applications. The system software is developed by using the Visual Basic 6.0. In the hardware part GPS is used to find the location of the antenna position. It gives upgraded information every second related to antenna positioning in the form of latitude, longitude and altitude. By polling digital compass the antenna orientation position is obtained through microcontroller. The system is cost effective and has low power consumption (Edgar et al., 2007). Chang and Lin designed mobile satellite antenna tracking system using intelligent controller. Using traditional, fuzzy logic control or by combining both methods antenna tracking and stabilization loops are designed and effects on parameters (Phase and Gain margin) are studied. The tracking performances are degraded due to the parameter variation and reducing tracking loop gain. A PD type fuzzy controller is also applied for lower tracking loop gain. It resulted better performance than traditional controller. Thus, the intelligent controller is better for the lower antenna gain and the system parameter variation effects are reduced (Chang & Lin, 2008). Soltani et al. proposed a robust FDI for a ship mounted satellite antenna tracking system. The optimization is based on fault diagnosis. The system is useful in nonlinear model Satellite Tracking Antenna (STA). The suggested method is able to estimate the fault for a class of nonlinear system acting under the external disturbances. The FDI algorithm is verified through implementation of the antenna system on ship. It fulfills desired fault diagnosis specifications (Soltani et al., 2008). Noordin et al. discussed the antenna positioner for moving vehicle. The system is useful for C-band environment, geostationary satellite applications. The system consists of horn antenna (3 kg), antenna positioner developed with azimuth and elevation plane with precision of 1º. For system development, moving vehicle speed of ∼60 km/h is considered. The antenna positioning platforms use three servo motors. The two servo motors are used for azimuth and elevation axes control and one to enable antenna dish rotation. During rapid changes of the tracker angle movement, a steady state error is occurred in the system. It is reduced by using FGA (Fast Genetic Algorithm) as an optimizer for PID controller. It needs to select a suitable processor. For implementation of Artificial Intelligence (AI) in control system, a large memory and fast speed is required (Noordin, et al., 2008). Bolandhemmat et al. developed hybrid tracking algorithm method for mobile active phased array antenna system. It is developed around a mechanical stabilization loop and a directionof-arrival (DOA) estimation algorithm. The irregularities of sensors are compensated by utilizing electronic feedback from the phased array antenna. The system hardware is developed by using LNB, DVB, RF detector, motors and DSP (Digital Signal Processing). The satellite ID is extracted from the DVB. The system worked in

environmental changes such as temperature, humidity and aging as well. It reduces the vertical yaw disturbances up to 60 º/s and 85 º/s2 . It also keeps the azimuth angle error in the permissible range of [−1º, +1º] (Bolandhemmat et al., 2009). Basari et al. presents simple, compact, light-weight and low cost electronic-tracking antenna system using open loop tracking method with GPS-gyro module and data acquisition program for field measurement. It is tested in various environments to track Engineering Test Satellite VIII(ETS-VIII). The measurements are carried out in circular path (vehicle travelling in circular path at 10 km/h). The antenna beam is steered electronically. The measurements are carried in the open field area and under the blockage area to evaluate propagation characteristics C/No, BER (Bit Error Rate) and fade characteristics. The parameters are affected by some obstacles like utility poles, pedestrian overpasses and roadside trees (Basari et al., 2010). Hao and Yao developed step tracking system for mobile DBS reception system. The gradient algorithm, curve fitting algorithm and 2D model based step tracking methods require valid model between received signal strength and the antenna beam direction. The authors proposed improved step tracking method based on Simultaneous Perturbation Stochastic Algorithm (SPSA). The proposed algorithm is designed and verified through simulation. It is found to be more efficient, easy to implement, simplifies the architecture and gives fast tracking compared to traditional step tracking (Hao & Yao, 2011). Soltani et al. proposed a Fault Tolerant Control (FTC) system for ship mounted satellite antenna. The system is useful to control certain faults like communication system malfunction and signal blocking. These faults loose the tracking functionality and make the system instable. The robust FDI is designed to supervise FLC system. The system is modeled and implemented for real time. Its effectiveness is tested on ship simulator (Soltani et al., 2011). Lin and Chang designed and simulated mobile antenna tracking system using both traditional and fuzzy control methods. Antenna tracking and stabilization loops are designed with traditional controller for bandwidth and phase margin requirement. Time and frequency domain analysis are studied to obtain two key parameters of the antenna tracking and stabilization loop. The stabilization loop is designed by proportion and PI compensator method. The PI compensator method is better than proportion. For both these cases, the tracking becomes worst for the lower tracking loop gain. By using PD type fuzzy controller with simplified triangular distribution function, parameter variation effect is found to be reduced. The antenna performance is analyzed by simulation. The performance obtained with fuzzy controller is better for lower and higher antenna tracking loop gains (Lin & Chang, 2011). Tiezzi et al. designed S-band antenna positioning system by electronic switching for geostationary satellite. The system is designed for electronic beam steering with simultaneous reception and transmission. The tracking system is designed by using a position and attitude sensors integrated on the antenna. The system consists of a low-profile, easily installable vehicle antenna. The microprocessor collects data from electronic compass, GPS and gyroscope sensors. It processes data and determines the vehicle position and orientation with respect to satellite and selects respective beam for automatic pointing the satellite during the vehicle motion. The integration of the sensors on the antenna package and completion of tracking without external input are the advantages of the system. Additionally, the directivity is found to be improved by 2 dB with respect to omni directional pattern. The improvement in the directivity gives the improved system performance (Tiezzi et al., 2012). Cho et al. designed antenna control system using step tracking algorithm along with H∞ controller. The step tracking procedure is divided into three modes: scan, tracking and stop. The scan mode

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is useful to capture antenna beacon signal. It finds locations at which full step tracking is possible. It is used to sharpen directionality of the satellite antenna. A tracking mode is one-step towards the satellite to obtain higher receiving signal strength. When signal is fully received the tracking mode executes stop drive mode. The stop drive mode is beneficial to avoid mechanical damage when desired received signal levels are obtained. During the antenna stop mode, the processor continually checks the levels of the received signal. When this level goes below the threshold level due to the disturbances or unexpected movement of the antenna, the scan mode begins again. The strength of the signal is measured by AGC output voltage of the tuner. The antenna position system consists of two geared DC motors (connected to elevation and azimuth axes), servo drivers and power amplifier. The selected gear ratios in the system are 1800:1 for elevation and 3600:1 for azimuth. The real time controller is implemented using the CEMTOOL software and the DSP/IO board (RG-DSPIO) supplied by REALGAIN Company. The H∞ control algorithm is designed with simplified real constant weight functions. It is useful to enhance time response characteristics and reduce steady state error. It has robust performance and it is superior to PID controller for the longer sampling period. The designed system does not require additional sensors. The tracking is done by using AGC signal. The system worked satisfactorily for ship vehicle (Cho et al., 2003). Kim et al. designed precise satellite parabolic antenna tracking system controlling two axes (elevation and azimuth) using BLDC motors, encoders, gyro sensor and digital tuner. It is developed for exact positioning and rapid movement of satellite antenna. It is developed around six degrees of freedom. The encoder is useful for precise positioning. The satellite signal strength is found from AGC signal of the digital tuner. The BLDC motion position control is obtained by PI algorithm. The gyro sensor determines antenna initial position during tracking. The AGC signal for antenna rotation of 360º is recorded and stored in memory. The tracking loop continues for peak AGC. When the AGC goes below threshold the loop is repeated. The system is useful for precise tracking on the moving ship or car (Kim et al., 2013). Kocadag and Demirkol described the real time satellite tracking system using Kalman filter for parabolic dish antenna mounted on mobile vehicle. The system uses on board sensors of the android device, GPS for detection of the moving vehicle in the form of latitude and altitude, electronic compass for detecting the orientation of mobile vehicle, accelerometer and magnetometer sensors for finding position of the antenna. The steps in the developed system are to, read look angles (azimuth and elevation) of the android device and filter by low pass filter, read the GPS position of the android device, calculate satellite look angles, calculate difference between look angles of android device and satellite, filter difference by real time Kalman filter to calculate change in satellite look angles for moving vehicle, store all measured and calculated values in the text file form on the device. The system uses open source library for Kalman filter calculations (Kocadag & Demirkol, 2015). 11. Systems for antenna parameter measurement Papaioannou and Langley described microcomputer based automatic antenna control system for radiation pattern measurements. The system mainly consists of ITT2020 computer, horn antenna, three stepper motors for azimuth, elevation and polarization positioning. The check on angle of positioning and movement is kept with the help of opto-switches. The system software is designed in Applesoft BASIC. Starting with initially azimuth angle 0º (boresight), referencing first opto-switch, maximum azimuth angle θ m and stepping angle are read from the memory. The positioner is rotated by –θ m degree with reference to boresight. The signal amplitude is measured and processed. The azimuth angle is incremented

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by θ . These steps are repeated up to +θ m. The provision is made to store or print the radiation pattern. The elevation and polarization angles are also controlled in similar way to azimuth positioner. The radiation pattern of the horn antenna is measured at 22 GHz with the system. The system is relatively simple and versatile for measurement of radiation pattern (Papaioannou & Langley, 1985). Anderson et al. developed simple, user friendly and cost effective Antenna Measurement System (AMS) consisting of antenna under test, transmitting antenna, antenna positioners, network analyzer, anechoic chamber, PC and ethernet. It measured two important parameters: radiation pattern and input impedance. The antenna positioner is developed by using two servo motors. The motor placed at the bottom rotates between 0° and 180º and top between 0° and 90º. The steps of the motors and time delay are user defined. The information from network analyzer and antenna positioner is managed in a PC. The user friendly control system software is developed by using LabView (Anderson et al., 2010). 12. Remote location monitoring systems Payne and Haider developed a high performance remotely controllable, receiving antenna tracking system for telemetry. It is designed by using Electronically Scanned (ESCAN) Tracking Feed of Scientific-Atlanta Inc. It constitutes eight feet reflector, PWM power amplifiers and microprocessor based servo controller. The remote operations are performed by using IEEE-488 remote interface. All servo drive components were placed on single diaphragm using modular pedestal model 13,211.The azimuth and elevation systems are identical. Each axis is driven by spur gear reducer, combination brake, tachometer and high torque servo motor. The joystick, operated through serial input port, connected externally to the system allows rapid repositioning of the axes. The operator is facilitated for control/change all system parameters remotely using basic control logic. The system is functional in verity of flight regimes as well as low elevation angle tracking situations (Payne & Haider, 1993). Isa and Basher demonstrated the radio-telescope antenna accurate positioning system. They used DC motors for positioning of azimuth and elevation axes. A motor control unit is designed by using DC relays with H-bridge circuit. To initialize the motor positions two limit switches are used. The drive system is developed with LabView and data acquisition board. The current position of the motor is sensed by virtual instrument (VI) and pulse generator circuit designed with IC555. Accurate positioning of the telescope is controlled by using VI LabView. Built-in internet developer toolkit is also used for remote access and control (Isa & Basher, 2005). 13. Conclusion In present communication state-of-the-art antenna control systems are reviewed. These systems are useful in antenna tracking, positioning, adverse weather, mobile vehicles, antenna parameter measurement and remote location monitoring. The architecture, computation, control, application, advantages and disadvantages of various methods are discussed. Various algorithms used for the antenna control are PI, PD, PID, fuzzy, PD-fuzzy, PID-Fuzzy, Self-tuned fuzzy, LQG, H∞ , genetic, neural network. The tracking methods for signal tracking are manual, monopulse, electronic, left-right, differential, auto-tracking, conical, step tracking. The advances in algorithms have reduced major issues and increased performance of the systems. The implementation of advanced algorithm requires a high speed and large memory size processors. Most of the systems are developed or simulated by using MATLAB and LabView.

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The system performance depends on mechanical, electronic design and environmental conditions. The advances and the technology of this field need robust, precise, high speed, low cost, accurate, low power, light weight as well as environment effect free antenna control system. This can be achieved by selection of proper electronic and mechanical components with proper algorithm for the desired application. 14. Future scope For major issues in the antenna control system, appropriate selection of the antenna, signal detectors, sensors, control unit, motor, motor driver and gears in system design will give better solution. The use of light weight low profile antenna can reduce the motor torque and hence power and the system cost will be reduced and the system speed will be increased. As the antenna systems are on the top of building or vehicle, the use solar power can be better alternative for power. The new algorithms need to be developed by combing present algorithms to improve system performance in the form of speed, bandwidth, gain margin, phase margin, stability of the system. The speed is one the most important parameter when antenna is mounted on vehicles. The accuracy in signal detection can be improved by using advanced RF detector chips. The use of high precision gears, sensors, and motors with microstepping technique can improve positioning accuracy of the antenna. The use of high precision gearing technique can increase the positioning accuracy but may result in increased system cost. The use of microstepping driver for motor may dilute this issue requiring increased system power. As the software tools are costly it is essential to develop a low cost computer simulator for testing antenna control system/algorithm. The low cost antenna control systems can be developed for antenna positioning, tracking and parameter measurement using modern low cost, low power, small size microcontrollers with Graphical User Interface (GUI) designed by using visual computer languages.

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Yalcin, Y., & Kurtulan, S. (2009). A rooftop antenna tracking system: design, simulation, and implementation. IEEE Antennas and Propagation Magazine, 51(2), 214–224. Zhai, K., et al. (2009). Semi-physical simulation research of the antenna acquiring and tracking system without turn tables. In IEEE international conference on computer modeling and simulation, ICCMS ’09 (pp. 28–32). Asif A. Mulla was born on August 15, 1984 in Shalgaon, India. He received the B.Sc. degree in Electronics and M.Sc. in Electronics with specialization in Embedded Systems from Shivaji University, Kolhapur in 2005 and 2007 respectively with distinction. He is the recipient of Shivaji University, Merit Scholarship (2006– 07). He qualified the Maharashtra State Eligibility Test for Lectureship (SET) in 2007. He joined the Yashwantrao Chavan College of Science, Karad in 2009 as Assistant Professor. His areas of research interest include system automation, control systems, computer/microcontroller applications in communication and smart antennas. Pramod N. Vasambekar was born in Hingangaon, BK, India in 1963. He received the B.Sc., M.Sc. and Ph.D. degrees in Physics from Shivaji University, Kolhapur in 1984, 1986 and 1995 respectively. Starting his career as a lecturer in electronics in 1986, he joined the Shivaji University in 1989. He is teaching the courses on microwave and communication electronics. He worked as a co-ordinator of Department of Computer Science. Currently he is working as a professor and head of the Department of Electronics. His research interests include ferrite sensors, microwave communication, antennas and computerized automation. He contributed many papers in international journals and conferences. He is also a co-author of two books on computer programming. He is life member of MRSI, NIAR, CSI and fellow of IETE.

Please cite this article as: A.A. Mulla, P.N. Vasambekar, Overview on the development and applications of antenna control systems, Annual Reviews in Control (2016), http://dx.doi.org/10.1016/j.arcontrol.2016.04.012