Proximity Fed Broadband 1200 Sectoral Microstrip Antenna

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Available online at www.sciencedirect.com Procedia Computer Science 00 (2017) 000–000

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Procedia Computer Science 115 (2017) 101–107

7th International Conference on Advances in Computing & Communications, ICACC-2017, 2224 August 2017, Cochin, India

Proximity Fed Broadband 1200 Sectoral Microstrip Antenna Amit A. Deshmukha*, Pritish Kamblea, Akshay Doshia, Disha Issrania, and K. P. Rayb a

EXTC Department, DJSCE, Vile – Parle (W), Mumbai, India b Electronics Department, DIAT, Pune, India

Abstract Novel configuration of 1200 Sectoral Microstrip antenna is proposed. Compared with equivalent circular patch, 120 0 Sectoral patch has higher resonance frequency for the fundamental mode and it gives bandwidth of 1200 MHz (~59%). Resonant length formulation at fundamental mode in 1200 Sectoral patch is proposed. Using the same, design of 1200 Sectoral patch at resonance frequency of 1000 MHz is presented which yields more than 575 MHz (~ 50%) of bandwidth. This bandwidth is more than that obtained in circular patch operating in the same frequency range. Proposed 1200 Sectoral patch gives broadside radiation pattern with peak co-polar gain of more than 9 dBi. © 2017 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the scientific committee of the 7th International Conference on Advances in Computing & Communications. Keywords: Broadband microstrip antenna; Circular microstrip antenna; Sectoral microstrip antenna; Resonant length; Proximity feeding

1. Introduction Wider bandwidth (BW) in microstrip antenna (MSA) is realized by using multi-resonator configurations in which additional resonant mode with respect to fundamental patch mode is either introduced by using parasitic patch or it is introduced by cutting the slot inside the patch [1 – 6]. Addition of parasitic patch increases antenna size whereas the

* Corresponding author. Tel.: +91 22 2610 7010; fax: +91 22 2619 4988. E-mail address: [email protected]

1877-0509 © 2017 The Authors. Published by Elsevier B.V.

Peer-review under responsibility of the scientific committee of the 7th International Conference on Advances in Computing & Communications.

1877-0509 © 2017 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the scientific committee of the 7th International Conference on Advances in Computing & Communications 10.1016/j.procs.2017.09.082

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slot cut MSAs are relatively complex to design [1 – 12]. Radiating patch in MSA can take any arbitrary shape but from analysis and modelling point of view regular shapes like, rectangular, circular are preferred [1]. Circular shape in MSA offers nearly same antenna characteristics to that given by rectangular/square radiating patch but it offers better harmonic rejection for signal generated from RF source at given transmitting frequency [1]. This is because in circular MSA (CMSA) fundamental and higher order modes are function of roots of Bessel function of k th type that do not follow harmonic progression [1]. Variation of circular MSA (CMSA), a 270 0 Sectoral MSA (S-MSA) is reported [13]. Compared to CMSA, it has additional resonant mode whose frequency lies below the fundamental TM11 mode frequency of CMSA. Wide band configurations of 2700 S-MSA by embedding rectangular slot is reported, which yields BW of 500 MHz (>45%) [13]. However over VSWR BW it shows high cross polar radiation pattern. By tuning Sectoral angle in S-MSA, wideband response has been achieved [14]. In 3400 S-MSA, maximum BW of more than 700 MHz is reported [14]. However in these varying angle S-MSAs, variation in co-polar antenna gain by 3 to 4 dBi is noticed over the BW. In this paper, a novel design of 120 0 S-MSA using proximity feed for wide band response is proposed. Due to smaller patch area as compared to equivalent CMSA, 120 0 Sectoral patch as derived from the same, has higher fundamental mode resonance frequency. The 120 0 Sectoral patch yields simulated and measured BW’s of 1200 MHz (~59%) with broadside radiation pattern and peak gain of more than 9 dBi. The resonant length formulation at fundamental patch mode in 1200 S-MSA is proposed. The frequency calculated using the same agrees closely with the simulated results for changing substrate thickness. Further using proposed formulation, design of 120 0 S-MSA at the fundamental mode frequency of 1000 MHz, is presented. This configuration gives simulated and measured BW of more than 575 MHz (~50%) with broadside radiation pattern and with peak gain of more than 9 dBi. Thus to compare, proposed 1200 S-MSA offers nearly two times the BW to that given by equivalent CMSA, and higher BW as compared to the slot cut variations of CMSA. The formulation in resonant length at fundamental patch mode can be used to design similar antennas at different resonance frequency. The proposed antenna was fabricated using copper plate and was suspended in air using foam spacers. Since foam has dielectric constant (re) of 1.06, it does not largely affect the antenna characteristics. Antenna is fed using 50  N-type connector of 0.32 cm inner wire diameter. Square ground plane of 30 cm side length is used in simulations and measurements. For experiments, ‘ZVH – 8’ vector network analyzer, RF source ‘SMB 100A’ and spectrum analyzer ‘FSC – 6’ were used. The measurements were carried out inside the Antenna Lab. 2. 1200 S-MSA Proximity fed design of CMSA, equivalent 270 0 S-MSA and 1200 S-MSA is shown in Fig. 1(a – c). For h = 3.0 cm, circular patch radius is calculated for its TM11 mode frequency to be around 950 MHz [1]. The radius (r) is found to be 7 cm. The simulated plot showing variations in real and imaginary part of input impedance for this circular patch obtained using IE3D software is given in Fig. 1(d). Resonant peaks due to fundamental TM11 (945 MHz) and higher order TM21, TM02 and TM31 modes are observed. In equivalent 2700 S-MSA, additional resonant mode whose frequency lies below the TM11 mode of CMSA is seen, as shown in Fig. 1(d) [13, 14]. In 2700 S-MSA, across fundamental and higher order resonant modes, bi-directional variations in surface currents exist. Due to this BW realized with respect to these modes, shows higher cross polar level radiation pattern [13, 14]. To realize 1200 SMSA, first complementary of 2700 Sectoral patch is realized (900 S-MSA) and further its angle is increased from 900 to 1200, as shown in Fig. 1(c). The 1200 S-MSA is simulated for xf = 3.5 cm, and its impedance plots showing variations in real and imaginary part of input impedance, is shown in Fig. 1(d). A resonant peak at a frequency equal to 1187 MHz is observed. Surface current distribution at the same is shown in Fig. 2(b). One half wavelength variations in surface currents that is directed along  = 1350, is observed. This is the fundamental mode in Sectoral patch. An effect of variation in proximity feed location in 1200 S-MSA on the excited resonant modes is studied and the same is shown in Fig. 2(a). When feed is placed towards the patch vertex point (i.e. ‘xf’ is decreased), frequency of observed resonant mode increases. The surface current distribution for 120 0 S-MSA, for ‘xf’ = 1.0 cm is shown in Fig. 2(c). At this feed location, current now shows half wavelength variation along orthogonal diagonal patch axis, i.e. along  = 450. Due to current variation along patch radius here, fundamental resonant mode frequency has



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increased. Thus in 1200 S-MSA, an appropriate selection of proximity feed position will give dual polarized response, i.e. E-plane is either directed along  = 1350 or along  = 450.

Fig. 1. (a) Top; and (b) side views of proximity fed CMSA and 2700 S-MSA; (c) proximity fed 1200 S-MSA and their resonance curve plots showing impedance variations against frequency

Fig. 2. (a) Resonance curve plots for varying feed point locations, h = 3.0 cm; h1 = 2.8 cm, and their surface current distribution for xf = (b) 3.5; and (c) 1.0 cm for proximity fed 1200 S-MSA

In the present work, proximity feed location below the vertex point of 1200 S-MSA is chosen. For h = 3.0 cm, and h1 = 2.8 cm, by optimizing strip dimensions, broadband response in 1200 S-MSA is realized. The input impedance plots obtained using simulations is shown in Fig. 3(a). The simulated BW is 1090 MHz (57.3%). Using VNA ‘ZVH8’ experiment was carried out, and the measured BW is 1124 MHz (60%) as shown in Fig. 3(a). The air substrate thickness in 1200 S-MSA is 3.0 cm. With respect to fundamental mode frequency of 1200 S-MSA, here air substrate thickness is 0.160. This substrate thickness is higher. Therefore, an effect of reduction in substrate thickness on fundamental mode frequency of 1200 S-MSA is studied. Resonance curve plots showing variations in real and imaginary part of input impedance for the same are explained in Fig. 3(b). It is observed that frequency increases with decrease in thickness. This increment is attributed to variation in fringing field length with the thickness. By optimizing coupling strip dimension wide band response in 1200 S-MSA is obtained for h = 2.0 cm. Here, in optimum design, strip parameters are, Ls = 1.4 cm, xf = 0.9 cm and h1 = 1.6 cm. Input impedance plots for the same are shown in Fig. 3(c). Here the simulated and measured BW’s are 1261 MHz (58.2%) and 1289 MHz (62%). Due to optimum placing of loop inside VSWR = 2 circle in smith chart, wider BW is obtained for h = 2.0 cm than in 3.0 cm. The fabricated prototype of Sectoral antenna is shown in Fig. 3(d). For Sectoral MSA with ‘h’ = 2 cm, radiation pattern is measured over the BW and at center frequency it is shown in Fig. 4(a, b). As observed from the current

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distribution as shown in Fig. 2(c), since effective current contribution is directed along diagonal axis, E-plane is directed along  = 450. Due to uni-directional current variation present over most of the patch, pattern is in the broadside direction with cross polar levels less than 10 dB. Similar pattern characteristics are observed over the complete BW. The 1200 S-MSA shows co-polar gain of more than 7 dBi over complete BW with peak gain of above 9 dBi as shown in Fig. 4(c). In pattern and gain measurements, reference Horn antenna operating in the same frequency range was used.

Fig. 3. (a) Input impedance plots for h = 3.0 cm; (b) resonance curve plots for variations in ‘h’ and ‘h 1’; (c) input impedance plots for h = 2.0 cm; and (d) fabricated prototype; for proximity fed 1200 S-MSA

Further to design 1200 S-MSA, resonant length formulation at its fundamental mode is proposed. As seen from current distribution in Fig. 2(c), maximum contribution of surface currents are varying along the radial length and also it is the shortest length in Sectoral patch. Therefore resonant length formulation at fundamental mode (re) for proximity feed position nearer the vertex point in 120 0 S-MSA is obtained by using equation (1). The second term on right hand side of equation (1) accounts for fringing field extension length. On air substrate, resonance frequency (fr) is calculated by using equation (2). For the given 1200 S-MSA and for substrate thickness (h) of 3.0, 2.6 and 2.2 cm, the calculated frequencies are, 1595, 1651 and 1712 MHz, respectively. These frequencies are in close agreement with simulated values, as given in Fig. 3(b). Further using proposed formulation 120 0 S-MSA is designed for fundamental mode frequency of 1000 and 2000 MHz, as discussed below.

re  r  0.8h

(1)

fr  30/2re

(2)



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Fig. 4. (a, b) Polar radiation pattern plot at centre frequency of BW; and (c) gain variation over the same for proximity fed 120 0 S-MSA

3. Design of Proximity fed 1200 S-MSA A 1200 S-MSA is designed using above formulation for fundamental mode frequency of 1000 and 2000 MHz. Since proximity feed is used, at each frequency design is presented for substrate thickness of 0.10. At 1000 MHz frequency, for substrate thickness of 3.0 cm (0.10), using equation (1) and (2), radius of Sectoral patch is calculated to be 12.6 cm. This Sectoral patch when simulated shows frequency of 1037 MHz, which is closer to the desired value. Further by optimizing strip parameters, wide band response is realized. For Ls = 2.2 cm, xf = 0.4 cm and h1 = 2.5 cm simulated BW is 603 MHz (51%) as shown in Fig. 5(a). The experiment was carried out and measured BW is 615 MHz (52.7%). Similarly using equation (1) and (2), for fundamental mode frequency of 2000 MHz, and for substrate thickness of 0.10, patch radius of 1200 S-MSA is calculated to be 6.3 cm. This when simulated gives frequency of 2060 MHz which is closer to the desired frequency. The antenna is optimized for wider BW by tuning strip dimensions, its position below the patch and the substrate thickness. A simulated BW of 1150 MHz (48.8%) for Ls = 1.1 cm, xf = 0.5 cm and h1 = 1.2 cm is obtained as shown in Fig. 5(b). In this case measured BW is 1175 MHz (49.9%). For 1200 S-MSA at 1000 MHz, radiation pattern at center frequency of BW and gain variation over the same are shown in Fig. 6(a – c). The pattern remains in the broadside direction across entire BW with co-polar peak gain of more than 9 dBi. Similar pattern and gain response is obtained for Sectoral MSA at 2000 MHz. Thus proposed formulations can be used to realize broadband proximity fed 1200 S-MSA at given resonance frequency on thicker air substrate.

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Fig. 5. Input impedance plots for proximity fed 1200 S-MSA for fundamental mode frequency of (a) 1000; and (b) 2000 MHz

Fig. 6. (a, b) Polar radiation pattern plot at center frequency; and (c) gain variation over BW for proximity fed 1200 S-MSA at 1000 MHz



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The proximity fed CMSA for r = 7 cm, gives simulated and measured BW of 382 MHz (36.7%) whereas U-slot cut CMSA of same patch radius yields BW of 454 MHz (43.5%). Here the patch area is 154 cm2. The simulated gain plots for CMSA and U-slot cut CMSA are also given in Fig. 6(c). The patch area for 120 0 S-MSA at 1000 MHz is 166 cm2. Thus in comparison proposed Sectoral patch with only 7.2% increase in patch area, yields higher BW with better gain characteristics (larger peak gain) as compared to the CMSA and its U-slot cut variation. 4. Conclusions Proximity fed design of 1200 S-MSA derived from equivalent CMSA, is proposed. It yields simulated and measured BW of more than 1200 MHz (~60%) with broadside radiation pattern and peak gain of more than 9 dBi. Resonant length formulation for fundamental patch mode in 1200 Sectoral patch is proposed. The frequency calculated using the same closely agrees with simulated result for varying substrate thickness. Using proposed formulation, design of 1200 S-MSA in 1000 MHz frequency band is presented. It yields more than 600 MHz (~50%) of BW with peak antenna gain of higher than 9 dBi. At same resonant frequency, proposed 120 0 Sectoral patch gives higher BW with better gain characteristics, for only 7.2% increase in the patch area. References [1] G. Kumar, K. P. Ray. Broadband Microstrip Antennas. Artech House. USA. 2003. [2] K. L. Wong. Compact and Broadband Microstrip Antennas. John Wiley & sons Inc. New York. USA. 2002. [3] T. Huynh, K. F. Lee. Single-Layer Single-Patch Wideband Microstrip Antenna. Electronics Letters 1995; 31 (16): 1310 - 1312. [4] Abdelnasser A. Eldek. Miniaturized Patch Antenna for RFID Tags on Metallic Surfaces. Microwave and Optical Technology Letters 2011; 53 (9): 2170 – 2174. [5] Y. J. Wang, C. K. Lee et al. A Novel Microstrip Patch Antenna for 3G IMT-2000 Mobile Handsets. Microwave and Optical Technology Letters 2001; 31 (6): 488 – 491. [6] Y. J. Wang, Y. B. Gan et al. A Broadband and Compact Microstrip Antenna for IMT-2000, Dect, and Bluetooth Integrated Handsets. Microwave and Optical Technology Letters 2002; 32 (3): 204 – 207. [7] S. Bhardwaj, Y. R. Samii. A Comparative Study of C-shaped, E-shaped, and U-slotted Patch Antennas. Microwave and Optical Technology Letters 2012, 54 (7): 1746 – 1756. [8] S. G. Weigand, H. Huff et al. Analysis and Design of Broadband Single Layer Rectangular U-slot Microstrip Patch Antenna. IEEE Transactions on Antennas & Propagation 2003; 51 (3): 457 – 468. [9] E. S. Neves, M. V. T. Heckler et al. Single Layer Rectangular Patch Antenna With Two Pair of Parallel Slits. Microwave & Optical Technology Letters 2003; 37 (5): 355 – 359. [10] B. L. Ooi, Q. Shen. A Novel E-shaped Broadband Microstrip Patch Antenna. Microwave & Optical Technology letters 2005; 27 (5): 348 – 352. [11] G. Kumar, R. K. Kotapati. Aperture Coupled Microstrip Antennas. IETE Technical Review 1999; 16 (1): 85 - 88. [12] K. P. Ray, G. Kumar. Hybrid Coupled Planar Microstrip Antennas. IETE Technical Review 1999; 16 (1): 81 - 84. [13] Amit A. Deshmukh, Ankita R. Jain et al. Broadband 2700 Sectoral Microstrip Antenna. Microwave and Optical Technology Letters 2014; 56 (6): 1447 – 1449. [14] Amit A. Deshmukh, Neelam V. Phatak. Broadband Sectoral Microstrip Antennas. IEEE Antennas and Wireless Propagation Letters 2015; 14: 727 – 730.