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Ku band pattern reconfigurable substrate integrated waveguide leaky wave horn antenna
Accepted Manuscript Short communication Ku Band Pattern Reconfigurable Substrate Integrated Waveguide Leaky Wave Horn Antenna Tanvi Agrawal, Shweta Srivastava PII: DOI: Reference:
S1434-8411(17)32088-5 https://doi.org/10.1016/j.aeue.2018.01.022 AEUE 52211
To appear in:
International Journal of Electronics and Communications
Received Date: Accepted Date:
31 August 2017 22 January 2018
Please cite this article as: T. Agrawal, S. Srivastava, Ku Band Pattern Reconfigurable Substrate Integrated Waveguide Leaky Wave Horn Antenna, International Journal of Electronics and Communications (2018), doi: https://doi.org/10.1016/j.aeue.2018.01.022
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Ku Band Pattern Reconfigurable Substrate Integrated Waveguide Leaky Wave Horn Antenna Tanvi Agrawal, Shweta Srivastava Department of Electronics and Communication Engineering, Jaypee Institute of Information Technology, Noida, India [email protected], [email protected]
Abstract: A dual band substrate integrated waveguide H plane sectoral horn antenna with reconfigurable radiation characteristics has been proposed in this paper. Designed antenna acts as a perfect broadside radiator at 16.1 GHz and perfect endfire radiator at 14.4 GHz frequency. Broadside radiation has been achieved by etching rectangular slots in the flared section of horn exhibiting a gain of 8.87 dBi. To achieve perfect endfire radiation, dielectric loading is done at the edge of horn and at this frequency antenna shows a gain of 11.3 dBi. The horn and the loaded dielectric are integrated by using the same single substrate resulting in easy fabrication and low cost. The proposed design has been fabricated and measured results are in good agreement with the simulated results. Index terms: Substrate integrated waveguide antenna, leaky wave antenna, pattern reconfigurable antenna, horn antenna, Ku band antenna. I-Introduction: Substrate integrated waveguide (SIW) technology maintains most benefits of conventional waveguide and
this is the reason why SIW has been a favourable prospect for high frequency components and circuits. The main advantages of SIW technology is its compact size, light weight, low profile, and easy fabrication. The SIW technology has been widely used to design leaky-wave antennas [1-6]. The SIW based leaky wave antennas have an easy structure that produces a narrow beam [7-8]. Leaky wave antennas scan its radiation pattern with change in frequency. In [2], a leaky wave antenna based on SIW technology with H shaped slots has been investigated. By using these slots the beam scans for all broadside angles with a maximum simulated gain of 16 dBi at some frequencies. Juhua Liu et. al. in [7] presented a SIW leaky wave antenna with transverse slots which scans from near endfire to complete broadside direction with frequency. The antenna is a slow wave structure near endfire. In [8], non uniform slots have been used on SIW to achieve leaky wave structure. Again the scanning angle with frequency is in the broadside direction. Souad Doucha in [9] used axial slots to design a leaky wave antenna at millimeter wave applications with scanning angles in broadside directions.
1
The leaky wave antenna so far provides an end fire radiation that has a partial end fire characteristics and it scans to broadside till far. With the growing need for communication among multiple devices connected to each other there is stringent requirement of antenna that can radiate or receive in both endfire and broadside direction. While endfire radiation is helpful in direction finding for different navigating devices, broadside radiation is also necessary for GPS applications and other transceiver applications . Yashika Sharma et. al. in [10], presented an antenna that radiates in both far endfire and broadside direction. But, to achieve this dual pattern a three element MIMO antenna has been used in which two elements radiate in endfire direction and one radiates in broadside direction. Also this antenna is designed using microstrip technology which has its own drawback of spurious radiations and low power handling capability. This letter demonstrates a SIW technology based H plane horn antenna that provides both endfire and broadside radiation at two different frequencies. This antenna has a gain of 11.3 dBi in endfire direction and 8.87 dBi in broadside direction which make this antenna suitable for above discussed applications. The antenna has been designed on RT Duroid 8550 having thickness 3.2 mm, dielectric constant of 2.2 and a loss tangent of 0.0009. The results have been verified through measurements. II-Antenna Design: (a) SIW Horn antenna design The proposed configuration of the H-plane substrate integrated waveguide based antenna is given in Fig.1. Substrate integrated waveguide is a planar technology that is easy to fabricate. The horn antenna has been designed on the same substrate as the waveguide using SIW technology. Hence, structure of the antenna becomes compact.
Fig.1. Proposed Configuration of SIW based H-plane horn antenna with a=10mm, L1=14mm, L2= 27mm, a1= 40mm, Ls= 7mm, Ws= 1.3mm, p=2mm, h=3.2mm, R= 0.8mm
2
SIW is a compact form of waveguide consists a dielectric material having metallic conductors at top and bottom. Two metallic layers of substrate act as top and bottom walls of waveguide. To realize side walls of waveguide, metallic vias are placed at a distance smaller than the wavelength of the operation. The separation of adjacent vias and radius of vias are denoted by ‘p’ and ‘R’. There values are computed by using the design rules of SIW [11-13]. The SIW is designed for a cutoff frequency of 10 GHz with the parameters such as width ‘a’= 10 mm, center-to-center distance between the metallic vias ‘p’ = 2 mm and diameter of the metallic vias‘d’= 0.5 mm using the following equations: (1) where weff is the width of the waveguide (see Fig. 1). Width ‘a’ of the SIW is designed to work SIW horn antenna at 14.4 GHz. The quadrature phase error of the horn antenna is decided by aperture length ‘a1’ and ‘L2’. The higher order mode excitation can also be governed by these values i.e. ‘a1’ and ‘L2’. The value of the L2 has been optimized to get dual band behavior. The shortened length ‘L1’ causes quadratic phase error in the H plane antenna. It can be corrected by using dielectric loading which serves as phase corrector. The radiation pattern of the antenna without dielectric loading is given in Fig. 2. It is clear that phase error caused by shortened length L2 distorts the radiation pattern of the sectoral horn antenna. The distortion is higher at 16.1 GHz due to higher phase error.
Fig.2 Radiation Pattern for SIW Horn antenna without using dielectric (a) at 14.4 GHz with max gain of 7.45 dBi (b) at 16.1 GHz with max gain of 4.24 dBi ( it is clear from figures that radiation pattern is not properly end fire at both frequencies) To correct this phase error a dielectric slab of length L3 has been used as shown in Fig. 1. The length ‘L3’
3
of the dielectric slab decides the beamwidth both in the H plane and E- plane of the horn antenna [14-15]. By selecting proper value of the length ‘L3’ the beamwidth in both the plane will be narrowed and hence the gain will be high in the end fire direction. The radiation pattern of the horn antenna with dielectric loading has been shown in Fig. 3. It is clear from this figure that the dielectric loading increases the gain of the antenna and after loading the antenna radiates perfectly in the endfire direction.
(a)
(b)
Fig.3. 2D Radiation patterns for the H plane sectional based horn antenna without slots at frequency (a) 14.4 GHz (b) 16.1 GHz (both are endfire) (b) SIW Horn antenna with slots: To obtain radiation along broad side direction three rectangular slots of size Ls x Ws have been etched out on one side of the flared section as shown in Fig. 1. These slots act as leaky wave antenna and enable antenna to radiate in broadside direction [9, 16-17]. The position of the slots has been decided based on electric field distribution inside the SIW horn antenna. Selected dimensions of the slots make it resonate at 16.1 GHz. (c) Parametric study (i). Flaring angle of the horn antenna Horn antenna has maximum gain at a flaring angle ‘θ’ (Fig. 4) where the impedance of line matches with the impedance of free space [18]. At this flaring angle maximum field propagate in the antenna. In this design, the field distribution is observed at different flaring angles and it has been found that maximum field is propagating for a flaring angle of 26.5 degrees (Fig. 7). The field is not propagating properly at other flaring angles due to poor impedance matching. The maximum field is propagating in the case of
4
26.5 degrees. Hence, gain is high at this flaring angle. The gain of the antenna also depends on the aperture of antenna. For higher aperture area gain will be more. For higher flaring angles of the horn antenna the aperture will be high but due to impedance mismatch the radiation pattern will not be proper and gain will be less at endfire direction. The length of the flaring section also affects the gain of the antenna. Table 1 summarizes the gain of the antenna at different flaring angles.
Fig.4. Proposed Configuration of SIW H-plane horn antenna with flaring angle as θ. Table1. Parametric study on the angle of the flaring of horn antenna without slots Frequency F= 14.4 GHz Angle ‘θ’ (in degree)
Frequency F= 16.2 GHz
Gain (dB)
Remarks
Gain (dB) Gain is less compared
25
8.98
7.58
26
1.031
1.887
26.5
10.3
10.4
to optimized antenna Gain is low The optimized antenna dimensions
27
4.542
2.675
27.5
4.019
3.567
Size of the horn antenna is increased
28
4.061
4.259
Gain is low
The end fire
5
pattern is not in 29
-0.5977
3.331
proper shape and consists of
30
1.1.43
minor lobes.
1.858
(ii). Rectangular Slots: Investigations have been carried out by varying the number of slots from 1 to 4 along the flared section of the SIW horn antenna. Radiation patterns for these multiple slots have been given in fig.5. From this figure, it is clear that for slots other than three the radiation pattern is not perfectly endfire and has some back radiation at 14.4 GHz. Also at 16.1 GHz the radiation is not perfectly broadside. The optimum result was obtained for three slots, wherein the radiation pattern of the antenna was perfectly end fire and broadside at the respective frequencies (see fig. 9).
(a)
(b)
Fig.5. Radiation pattern of etching different slot on the antenna with 1, 2, 4 slot at (a) 14.4 GHz (b) 16.1 GHz III-Discussion of the result (a). SIW antenna without slots The S11 parameter of this structure is given in Fig.6 which shows two operating frequencies of the antenna. The points of resonance remain the same on etching out the slots and matching improves at 14.4 GHz. The measured results of the horn antenna are in accordance with the simulated one. Antenna is excited by a SMA probe connector at a port ‘X’ shown in Fig.1.
6
Fig.6. Measured and simulated return loss S11 (dB) of H plane SIW horn antenna without and with slots. The current distribution inside the SIW antenna without slots for the two operating frequency bands is given in Fig.7. It shows that the field travels in the substrate of SIW antenna like it travels in a waveguide and radiates through the flared section of horn. The simulated and measured radiation pattern of the SIW based horn antenna without slots at both resonant frequencies are given in Fig.3. The pattern exhibits that the antenna is radiating in end fire direction with a gain of 10.3 dBi and 10.4 dBi at 14.4 GHz and 16.1 GHz frequencies.
(a) (b) Fig.7. Current distribution of H plane sectional based horn antenna without slots at frequency (a) 14.4 GHz (b) 16.1 GHz
7
From the Fig.3, it is observed that the measured results of the radiation pattern of the antenna match with the simulated one. (b ). SIW antenna with slots The current distribution of SIW H plane sectoral horn antenna with rectangular slots is given in Fig.8. The dimensions of the slots have been optimized to make them resonate at 16.1 GHz. It is clear from this figure that the current at 14.4 GHz does not excite the slots and the antenna radiates in the end fire direction. At 16.1 GHz the slots gets excited and the fields radiate through slots in the broad side direction. Hence at 16.1 GHz, it acts as a broadside radiator.
(a) (b) Fig.8. Current distribution of H plane sectional based horn antenna with slots at frequency (a) 14.4 GHz (b) 16.1 GHz. The fabricated prototype of the H plane horn antenna with and without rectangular slots is given in Fig. 9. Measured and simulated radiation patterns given in Fig.10, show that the antenna has a gain of 11.3 dBi in end fire direction and 8.87 dBi in broadside direction. The gain of the antenna increases on adding the slots at 14.4 GHz but reduces slightly at 16.1 GHz with a complete transition in the direction of radiation. Considering that the antenna is acting as a leaky wave antenna at 16.1 GHz, the gain achieved is quite high. The measured results are very near to the simulated results.
8
(a)
(b)
Fig.9. Fabricated antenna prototype (a) without slot (b) with 3 rectangular slots
(a)
(c)
(b)
(d)
9
Fig.10. Radiation patterns for the H plane sectional based horn antenna with slots at frequency (a) 2D at 14.4) GHz (b) 2D at 16.1 GHz (c) 3D at 14.4 GHz (d) 3D at 16.1 GHz
IV-Conclusion An H- plane sectional horn antenna using substrate integrated waveguide technology is being presented in this letter for reconfigurable radiation characteristics. The antenna is working as an end fire radiator at 14.4 GHz and at 16.1 GHz it is acting as broadside radiator. Broadside radiation of the antenna has been achieved by etching slots on one side of flared section. Antenna has been fabricated and the measured results of the antenna match with the simulated ones. The presented antenna is first of its kind which is having complete endfire and complete broadside radiation characteristics at two frequencies. References:
[1] Feng X., Wu K., “Guided-wave and leakage characteristics of substrate integrated waveguide”, IEEE Trans. Microwave Theory Tech., Jan 2005; 53: 66-73. [2] Khalichi B., Nikmehr S., Pourziad A., “Development of novel wideband H-plane horn antennas by employing asymmetrical slots based on SIW technology”, Inter. Journal of Electronics and Comm. (AEÜ)., Sep. 2015; 69: 1374-1380. [3] Oliaei M., Abrishamian M. S., “Corrugated SIW K Band Horn Antenna”, Inter. Journal of Electronics and Comm. (AEÜ)., Dec. 2014; 68: 1199-1204. [4] Ramesh S., Rao T. R., “High gain dielectric loaded exponentially tapered slot antenna array based on substrate integrated waveguide for V-band wireless communications”, Inter. Journal of Electronics and Comm. (AEÜ)., Jan. 2015; 69: 48-55. [5] Liu J., Jackson D. R., Long Y., “Substrate Integrated Waveguide (SIW) Leaky-Wave Antenna With Transverse Slots”, IEEE Trans. Antennas Propag., Sep 2011; 60: 20-29.
10
[6] Zhang C., Wang J., Chen Meie., Zhang Z., and Li Z., “A New Kind of Circular Polarization LeakyWave Antenna Based on Substrate Integrated Waveguide” ”, Inter. Journal Antennas Propag., 2015; 2015: 1-7. [7] Liu J. H., Tang X. H., Li Y. X., and Long Y. L., “Substrate integrated waveguide leaky-wave
antenna with H-shaped slots”, IEEE Trans. Antennas Propag., 2012; 60: 3962-3967. [8] Yan L., Hong W., Hua G., Chen J., Wu K., Cui T. J., “Simulation and experiment on SIW slot array antenna”, IEEE Microw. Wireless Compon. Lett., Aug 2004; 14: 446-448. [9] Doucha S., Abri M., Badaoui H. A., “Leaky Wave Antenna Design based on SIW Technology for Millimeter Wave Applications”, WSEAS Trans. Comm., 2015; 14: 108-112. [10]
Sharma Y., Sarkar D., Saurav K., Srivastava K.V., “Three-Element MIMO Antenna System With
Pattern and Polarization Diversity for WLAN Applications”, IEEE Antennas Wireless Propag. Lett., Nov 2016; 16: 1163-1166. [11]
Deslandes D., Wu K., “Substrate integrated waveguide leaky-wave antenna: Concept and design
considerations”, in Proc. Asia–Pacific Microw. Conf., Dec. 2005; 346–349. [12]
Deslandes D., Wu K., “Accurate modeling, wave mechanisms, and design considerations of a
substrate integrated waveguide”, IEEE Trans. Microw. Theory Tech., Jun. 2006; 54: 2516–2526. [13]
Bozzi M., Georgiadis A., Wu K., “Review of substrate- integrated waveguide circuits and
antennas”, IET Microw. Antennas Propag., 2010; 5: 909-920. [14]
Xu J., Hong W., Tang H., Kuai Z., Wu K., “Half-mode substrate integrated waveguide (HMSIW)
leaky-wave antenna for millimetre wave applications”, IEEE Antenna Wireless Propag. Lett., 2008; 7: 85–88. [15]
Wang H., Zhang B., Che W.Q., “Dielectric Loaded Substrate Integrated Waveguide (SIW) H-
Plane Horn Antennas”, IEEE Trans. Antennas Propag., 2009; 58: 640-647.
11
[16]
Zhao Y., Shen Z., Wu W., “Conformal SIW H-plane horn antenna on a conducting cylinder”, IEEE
Antennas Wireless Propag. Lett., 2015; 14: 1271–1274. [17]
Mallahzadeh A. R., Esfandiarpour S., “Wideband H-plane horn antenna based on ridge substrate
integrated waveguide (RSIW)”, IEEE Antennas Wireless Propag. Lett., 2012; 11: 85–88. [18]
Wang L., Vigueras M. G., Folgueiras. M. A., Juan R. M., “Wideband H-plane dielectric horn
antenna” IET Microw. Antennas Propag., 2017; 11: 1695-1701.
12
S1434-8411(17)32088-5 https://doi.org/10.1016/j.aeue.2018.01.022 AEUE 52211
To appear in:
International Journal of Electronics and Communications
Received Date: Accepted Date:
31 August 2017 22 January 2018
Please cite this article as: T. Agrawal, S. Srivastava, Ku Band Pattern Reconfigurable Substrate Integrated Waveguide Leaky Wave Horn Antenna, International Journal of Electronics and Communications (2018), doi: https://doi.org/10.1016/j.aeue.2018.01.022
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Ku Band Pattern Reconfigurable Substrate Integrated Waveguide Leaky Wave Horn Antenna Tanvi Agrawal, Shweta Srivastava Department of Electronics and Communication Engineering, Jaypee Institute of Information Technology, Noida, India [email protected], [email protected]
Abstract: A dual band substrate integrated waveguide H plane sectoral horn antenna with reconfigurable radiation characteristics has been proposed in this paper. Designed antenna acts as a perfect broadside radiator at 16.1 GHz and perfect endfire radiator at 14.4 GHz frequency. Broadside radiation has been achieved by etching rectangular slots in the flared section of horn exhibiting a gain of 8.87 dBi. To achieve perfect endfire radiation, dielectric loading is done at the edge of horn and at this frequency antenna shows a gain of 11.3 dBi. The horn and the loaded dielectric are integrated by using the same single substrate resulting in easy fabrication and low cost. The proposed design has been fabricated and measured results are in good agreement with the simulated results. Index terms: Substrate integrated waveguide antenna, leaky wave antenna, pattern reconfigurable antenna, horn antenna, Ku band antenna. I-Introduction: Substrate integrated waveguide (SIW) technology maintains most benefits of conventional waveguide and
this is the reason why SIW has been a favourable prospect for high frequency components and circuits. The main advantages of SIW technology is its compact size, light weight, low profile, and easy fabrication. The SIW technology has been widely used to design leaky-wave antennas [1-6]. The SIW based leaky wave antennas have an easy structure that produces a narrow beam [7-8]. Leaky wave antennas scan its radiation pattern with change in frequency. In [2], a leaky wave antenna based on SIW technology with H shaped slots has been investigated. By using these slots the beam scans for all broadside angles with a maximum simulated gain of 16 dBi at some frequencies. Juhua Liu et. al. in [7] presented a SIW leaky wave antenna with transverse slots which scans from near endfire to complete broadside direction with frequency. The antenna is a slow wave structure near endfire. In [8], non uniform slots have been used on SIW to achieve leaky wave structure. Again the scanning angle with frequency is in the broadside direction. Souad Doucha in [9] used axial slots to design a leaky wave antenna at millimeter wave applications with scanning angles in broadside directions.
1
The leaky wave antenna so far provides an end fire radiation that has a partial end fire characteristics and it scans to broadside till far. With the growing need for communication among multiple devices connected to each other there is stringent requirement of antenna that can radiate or receive in both endfire and broadside direction. While endfire radiation is helpful in direction finding for different navigating devices, broadside radiation is also necessary for GPS applications and other transceiver applications . Yashika Sharma et. al. in [10], presented an antenna that radiates in both far endfire and broadside direction. But, to achieve this dual pattern a three element MIMO antenna has been used in which two elements radiate in endfire direction and one radiates in broadside direction. Also this antenna is designed using microstrip technology which has its own drawback of spurious radiations and low power handling capability. This letter demonstrates a SIW technology based H plane horn antenna that provides both endfire and broadside radiation at two different frequencies. This antenna has a gain of 11.3 dBi in endfire direction and 8.87 dBi in broadside direction which make this antenna suitable for above discussed applications. The antenna has been designed on RT Duroid 8550 having thickness 3.2 mm, dielectric constant of 2.2 and a loss tangent of 0.0009. The results have been verified through measurements. II-Antenna Design: (a) SIW Horn antenna design The proposed configuration of the H-plane substrate integrated waveguide based antenna is given in Fig.1. Substrate integrated waveguide is a planar technology that is easy to fabricate. The horn antenna has been designed on the same substrate as the waveguide using SIW technology. Hence, structure of the antenna becomes compact.
Fig.1. Proposed Configuration of SIW based H-plane horn antenna with a=10mm, L1=14mm, L2= 27mm, a1= 40mm, Ls= 7mm, Ws= 1.3mm, p=2mm, h=3.2mm, R= 0.8mm
2
SIW is a compact form of waveguide consists a dielectric material having metallic conductors at top and bottom. Two metallic layers of substrate act as top and bottom walls of waveguide. To realize side walls of waveguide, metallic vias are placed at a distance smaller than the wavelength of the operation. The separation of adjacent vias and radius of vias are denoted by ‘p’ and ‘R’. There values are computed by using the design rules of SIW [11-13]. The SIW is designed for a cutoff frequency of 10 GHz with the parameters such as width ‘a’= 10 mm, center-to-center distance between the metallic vias ‘p’ = 2 mm and diameter of the metallic vias‘d’= 0.5 mm using the following equations: (1) where weff is the width of the waveguide (see Fig. 1). Width ‘a’ of the SIW is designed to work SIW horn antenna at 14.4 GHz. The quadrature phase error of the horn antenna is decided by aperture length ‘a1’ and ‘L2’. The higher order mode excitation can also be governed by these values i.e. ‘a1’ and ‘L2’. The value of the L2 has been optimized to get dual band behavior. The shortened length ‘L1’ causes quadratic phase error in the H plane antenna. It can be corrected by using dielectric loading which serves as phase corrector. The radiation pattern of the antenna without dielectric loading is given in Fig. 2. It is clear that phase error caused by shortened length L2 distorts the radiation pattern of the sectoral horn antenna. The distortion is higher at 16.1 GHz due to higher phase error.
Fig.2 Radiation Pattern for SIW Horn antenna without using dielectric (a) at 14.4 GHz with max gain of 7.45 dBi (b) at 16.1 GHz with max gain of 4.24 dBi ( it is clear from figures that radiation pattern is not properly end fire at both frequencies) To correct this phase error a dielectric slab of length L3 has been used as shown in Fig. 1. The length ‘L3’
3
of the dielectric slab decides the beamwidth both in the H plane and E- plane of the horn antenna [14-15]. By selecting proper value of the length ‘L3’ the beamwidth in both the plane will be narrowed and hence the gain will be high in the end fire direction. The radiation pattern of the horn antenna with dielectric loading has been shown in Fig. 3. It is clear from this figure that the dielectric loading increases the gain of the antenna and after loading the antenna radiates perfectly in the endfire direction.
(a)
(b)
Fig.3. 2D Radiation patterns for the H plane sectional based horn antenna without slots at frequency (a) 14.4 GHz (b) 16.1 GHz (both are endfire) (b) SIW Horn antenna with slots: To obtain radiation along broad side direction three rectangular slots of size Ls x Ws have been etched out on one side of the flared section as shown in Fig. 1. These slots act as leaky wave antenna and enable antenna to radiate in broadside direction [9, 16-17]. The position of the slots has been decided based on electric field distribution inside the SIW horn antenna. Selected dimensions of the slots make it resonate at 16.1 GHz. (c) Parametric study (i). Flaring angle of the horn antenna Horn antenna has maximum gain at a flaring angle ‘θ’ (Fig. 4) where the impedance of line matches with the impedance of free space [18]. At this flaring angle maximum field propagate in the antenna. In this design, the field distribution is observed at different flaring angles and it has been found that maximum field is propagating for a flaring angle of 26.5 degrees (Fig. 7). The field is not propagating properly at other flaring angles due to poor impedance matching. The maximum field is propagating in the case of
4
26.5 degrees. Hence, gain is high at this flaring angle. The gain of the antenna also depends on the aperture of antenna. For higher aperture area gain will be more. For higher flaring angles of the horn antenna the aperture will be high but due to impedance mismatch the radiation pattern will not be proper and gain will be less at endfire direction. The length of the flaring section also affects the gain of the antenna. Table 1 summarizes the gain of the antenna at different flaring angles.
Fig.4. Proposed Configuration of SIW H-plane horn antenna with flaring angle as θ. Table1. Parametric study on the angle of the flaring of horn antenna without slots Frequency F= 14.4 GHz Angle ‘θ’ (in degree)
Frequency F= 16.2 GHz
Gain (dB)
Remarks
Gain (dB) Gain is less compared
25
8.98
7.58
26
1.031
1.887
26.5
10.3
10.4
to optimized antenna Gain is low The optimized antenna dimensions
27
4.542
2.675
27.5
4.019
3.567
Size of the horn antenna is increased
28
4.061
4.259
Gain is low
The end fire
5
pattern is not in 29
-0.5977
3.331
proper shape and consists of
30
1.1.43
minor lobes.
1.858
(ii). Rectangular Slots: Investigations have been carried out by varying the number of slots from 1 to 4 along the flared section of the SIW horn antenna. Radiation patterns for these multiple slots have been given in fig.5. From this figure, it is clear that for slots other than three the radiation pattern is not perfectly endfire and has some back radiation at 14.4 GHz. Also at 16.1 GHz the radiation is not perfectly broadside. The optimum result was obtained for three slots, wherein the radiation pattern of the antenna was perfectly end fire and broadside at the respective frequencies (see fig. 9).
(a)
(b)
Fig.5. Radiation pattern of etching different slot on the antenna with 1, 2, 4 slot at (a) 14.4 GHz (b) 16.1 GHz III-Discussion of the result (a). SIW antenna without slots The S11 parameter of this structure is given in Fig.6 which shows two operating frequencies of the antenna. The points of resonance remain the same on etching out the slots and matching improves at 14.4 GHz. The measured results of the horn antenna are in accordance with the simulated one. Antenna is excited by a SMA probe connector at a port ‘X’ shown in Fig.1.
6
Fig.6. Measured and simulated return loss S11 (dB) of H plane SIW horn antenna without and with slots. The current distribution inside the SIW antenna without slots for the two operating frequency bands is given in Fig.7. It shows that the field travels in the substrate of SIW antenna like it travels in a waveguide and radiates through the flared section of horn. The simulated and measured radiation pattern of the SIW based horn antenna without slots at both resonant frequencies are given in Fig.3. The pattern exhibits that the antenna is radiating in end fire direction with a gain of 10.3 dBi and 10.4 dBi at 14.4 GHz and 16.1 GHz frequencies.
(a) (b) Fig.7. Current distribution of H plane sectional based horn antenna without slots at frequency (a) 14.4 GHz (b) 16.1 GHz
7
From the Fig.3, it is observed that the measured results of the radiation pattern of the antenna match with the simulated one. (b ). SIW antenna with slots The current distribution of SIW H plane sectoral horn antenna with rectangular slots is given in Fig.8. The dimensions of the slots have been optimized to make them resonate at 16.1 GHz. It is clear from this figure that the current at 14.4 GHz does not excite the slots and the antenna radiates in the end fire direction. At 16.1 GHz the slots gets excited and the fields radiate through slots in the broad side direction. Hence at 16.1 GHz, it acts as a broadside radiator.
(a) (b) Fig.8. Current distribution of H plane sectional based horn antenna with slots at frequency (a) 14.4 GHz (b) 16.1 GHz. The fabricated prototype of the H plane horn antenna with and without rectangular slots is given in Fig. 9. Measured and simulated radiation patterns given in Fig.10, show that the antenna has a gain of 11.3 dBi in end fire direction and 8.87 dBi in broadside direction. The gain of the antenna increases on adding the slots at 14.4 GHz but reduces slightly at 16.1 GHz with a complete transition in the direction of radiation. Considering that the antenna is acting as a leaky wave antenna at 16.1 GHz, the gain achieved is quite high. The measured results are very near to the simulated results.
8
(a)
(b)
Fig.9. Fabricated antenna prototype (a) without slot (b) with 3 rectangular slots
(a)
(c)
(b)
(d)
9
Fig.10. Radiation patterns for the H plane sectional based horn antenna with slots at frequency (a) 2D at 14.4) GHz (b) 2D at 16.1 GHz (c) 3D at 14.4 GHz (d) 3D at 16.1 GHz
IV-Conclusion An H- plane sectional horn antenna using substrate integrated waveguide technology is being presented in this letter for reconfigurable radiation characteristics. The antenna is working as an end fire radiator at 14.4 GHz and at 16.1 GHz it is acting as broadside radiator. Broadside radiation of the antenna has been achieved by etching slots on one side of flared section. Antenna has been fabricated and the measured results of the antenna match with the simulated ones. The presented antenna is first of its kind which is having complete endfire and complete broadside radiation characteristics at two frequencies. References:
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