Received: 25 April 2017
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Revised: 24 July 2017
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Accepted: 28 July 2017
DOI: 10.1002/mmce.21155
RESEARCH ARTICLE
Compact substrate integrated waveguide mono-pulse antenna array Javad Soleiman Meiguni Faculty of Electrical and Computer Engineering, Semnan University, Semnan, 3513119111, Iran Correspondence Javad Soleiman Meiguni, Faculty of Electrical and Computer Engineering, Semnan University, Semnan, 3513119111, Iran. Email:
[email protected]
| Seyed Amin Khatami | Ali Amn-e-Elahi Abstract A compact monopulse antenna array based on substrate integrated waveguide technology is presented through this article. The design is fabricated on Printed Circuit Board (PCB) technology consisting of a double-layered 8-cell array antenna with a slot in the middle-ground metal used for aperture-coupling excitation and reducing unwanted spurious emissions from feed network. The Impedance bandwidth and AR bandwidth are enhanced due to optimal feed network, including Rat-Race coupler to generate sum and difference patterns for mono-pulse applications operating at 10 GHz. The prototype of the proposed antenna with the size of 124*25 mm2 is fabricated and tested. Measured results compared very well to simulation results obtained by CST microwave studio and show 210-dB impedance bandwidth of 4% and 222 dB null-depth in difference mode. KEYWORDS antenna array, difference pattern, mono-pulse antenna, SIW, sum pattern
1 | INTRODUCTION Monopulse antennas are widely used in radar applications. With the trend of high-speed data rate in radar, requirements for circular polarized (CP) antennas with wide impedance bandwidth and wide AR-bandwidth are necessary. Monopulse antenna with CP capability would be a key component in modern tracking radar, range-finder and control systems. Large impedance bandwidths and AR bandwidths are prime characteristics of UWB monopulse antennas. An UWB crescent-shaped radiating element is reported in Ref. [1] which sum and difference patterns achieved by in-phase and out-of-phase excitations of the two coaxial ports. A cavity backed slot antenna for automotive mono-pulse radar has been reported in Ref. [2] operating in 2.613.44 GHz. A dual band cavity backed circular polarized antenna operating in 12 GHz, and 14 GHz has been studied in Ref. [3]. A high resistivity silicon wafer based millimeter wave microstrip Rotman lens has been proposed in Ref. [4–6] for phased array radar and RFID applications. In order to optimize the complete RF system integration, substrate integrated waveguide (SIW) has been put forward due to its ease of Int J RF Microw Comput Aided Eng. 2017;e21155. https://doi.org/10.1002/mmce.21155
integration and low-loss and high-quality factor characteristics. It can be simply fabricated by printed circuit board (PCB) and low temperature co-fired ceramic (LTCC) processes. In this way, nonplanar rectangular waveguide can be fabricated in planar form, compatible with common available processing techniques. They have been made by using two rows of metallic cylinders or via embedded in a dielectric substrate which electrically connects two parallel metal plate in both sides. For thin layer substrates, there is no longitudinal current through the side walls like the classical rectangular waveguides. This yields that the SIW structure could only support TEm0 modes in the lack of any guided TMmn modes.7,8 A high gain 94 GHz SIW mono-pulse antenna array is introduced in Ref. [9]. The proposed W-band antenna has low radiation efficiency compared with metallic waveguide based structure. An SIW feed network is employed to waveguide-fed microstrip antenna array using standard PCB process.10 A single-layer right hand circular polarized (RHCP) SIW antenna with square ring slot and shorting pin has been investigated in Ref. [11]. Side-lobe level improvement is an important issue for large type of array antenna structure. In the directive beam antenna, the
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Design parameters of the proposed 4-cell array antenna
(Unit 5 mm) Param. Value Param. Value Param. Value Param. Value
FIGURE 1
Structural layout of the proposed 4-cell array antenna
radiation pattern will be sharpened at higher frequencies which cause some limitations in operating bandwidth selection. The coupling between the radiators is another drawback for compact mono-pulse antennas. Several approaches have been reported in literature to overcome this problem.12–14 Low-profile and good specifications in pattern and polarization are some challenges of the previous researches. There is also a trend to achieve a low side lobe level (SLL) characteristic in combination with maximum null-depth in difference mode of the mono-pulse antennas. In this article, we first propose a 4-cell SIW antenna in section 2 with circular polarization capability, which is applicable, in sum, and difference pattern generation. Then, we propose an 8-cell array antenna based on an improved 1808 Rat-Race hybrid and four slots in the middle layer used for aperturecoupling excitation with detailed simulations presented in section 2. The prototypes of the designed antennas have been fabricated, and its scattering matrix and radiation patterns have been measured and compared with those of the simulated results in section 3. Good agreement between the simulation and measurement results shows the validity of the proposed array antenna. Finally, section 4 concludes the article.
L1
4.5
L8
1.27
W6
1.7
Lp
7.93
L2
4.4
L9
1
W7
1.15
Wg
0.15
L3
14
W1
1.7
W8
0.72
P
1.7
L4
4
W2
3
R1
3.88
Lx
6.85
L5
7
W3
4.5
La
22.47 Ws
10.17
L6
3.74
W4
3
Wa
31
Ls
10.2
L7
9.4
W5
1.7
Wp
8.3
Wd
5.5
in Table 1. It consists of two adjacent modules, including a square ring slot antenna11 separated by SIW channels. The working mechanism of the array SIW antenna is investigated by combining signals in order to generate sum and difference patterns. The antenna bottom is covered by a large ground plane. The multiple via holes connect the bottom side on the ground plane and the top metal. A 1808 Rat-Race coupler with enhanced microstrip to SIW transitions is applied for feed network as an equal power divider. The scattering characteristics of the Rat-Race coupler are improved by using a stepped impedance configuration, which is shown in Figure 2A. The loading stubs act as an impedance transformer and thus effectively enhanced the impedance matching of the planar antenna array. The maximum gain of this array at the bore-sight direction occurs if the incident voltages of the radiators are in-phase for sum mode and out-phase for
2 | ANTENNA DESIGN AND PARAMETRIC DISCUSSION In mono-pulse array antennas, the sum pattern will be generated for the case of in-phase excitation of the radiators, while the difference mode operates by out-phase excitation of the radiators under specific conditions. The circular polarization capability gives higher robustness to the radar system and makes the recognition of targets with complex surface feasible. The design procedures for array antennas are discussed throughout this section.
2.1 | Design of 4-cell CP antenna array The structural layout of the designed 4-cell antenna array is shown in Figure 1 and the designed parameters are illustrated
FIGURE 2
Simulated scattering parameters for (A) the Rat-Race coupler. (B) the proposed 4-cell array antenna
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results of the proposed array. More than 30 dB isolation depicted in the Figure 2 shows the effective isolation between two ports of the array.
2.2 | Design of compact 8-cell monopulse antenna array
F I G U R E 3 Compact 8-Cell monopulse antenna array discussed. (A) Block diagram. (B) Disassembled top view. (C) Disassembled bottom view
difference mode, respectively. The incident wave must have circular polarization (CP), due to existence of shorted pins inside the radiators. The electromagnetic fields perturb simply near the shorting via lead to circular polarization capability. The SMA connectors were connected to the top and bottom of the antenna making a better placement of the mono-pulse functionality. Figure 2B gives the scattering
FIGURE 4
The motivation behind this article is to extend the previous modular antenna sections into a compact 8-cell monopulse antenna array as shown in Figure 3A. According to the block diagram, the sum and difference patterns are obtained from the terminals of the coupler via the illustrated formulations. The presented antenna consists of four SIW power dividers, two microstrip power dividers and a 1808 microstrip RatRace coupler. It is composed of three metal layers printed on low-loss dielectric substrates. To have a preferable impedance matching condition, two 50 X input impedance lines are designed to feed the antenna.15 Rigorous checks have been applied for 1808 Rat-Race coupler design in conjunction with two T-match branch-line power divider. It is interesting to say that each branch of the T-match branch-line’s arm, acts as a so-called k/4 impedance transformer to match the input 50 X microstrip line and output microstrip to SIW transition sectors. The results are acceptable and will be discussed in the next section. Four rectangular slots are etched on the middle grounded layer, for the aperture coupling mechanism. Although the element phase is controlled to maximize the array gain, the existence of the ground plane minimizes couplings among radiators. The radiating elements are the same as the previous design for a 4-cell array. However, thanks to the aperture-coupling mechanism in 8-cell array, undesirable spurious harmonic response does
Geometrical configuration of the proposed 8-cell antenna. (A) Top view. (B) Bottom view
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T A BL E 2 Design parameters of the compact 8-cell monopulse antenna array discussed (Unit 5 mm) Param. Value Param. Value Param. Value Param. Value R1
3.88
L10
1
W6
7.4
Lx
17
Wr
6.21
L11
5.75
W7
1
Wx
2.6
L1
0.93
L12
18.9
W8
7.27
Li
14
L2
1.7
L13
7.2
W9
11.51 Ws
10.4
L3
2.66
L14
1.7
W10
1.8
Ls
10.4
L4
3.83
L15
1.7
W11
1.7
Wp
8.1
L5
1.06
W1
1.3
W12
2
Lp
8.54
L6
7.43
W2
2.1
Ld
5.5
La
31
L7
2.16
W3
4.42
Wc
10.44 Wa
22.84
L8
1.62
W4
4.71
Lc
17
0.25
L9
1.67
W5
1.7
P
1.7
Lg
not cause problem, and the feed region is isolated from the radiating region of the antenna due to the existence of a ground plane.16 On this occasion, a compact 8-cell array design is feasible instead of 4-cell array antenna. In the case of port one excitation, the phase of wave transmitted through each square ring slot antenna in top layer, is in-phase, which yields to the sum pattern production. In the case of port two excitation, 1808 phase difference in the incident wave will be achieved at the input terminals of both four adjacent array square antennas. For each mode of the antenna, the unused port should be terminated with a 50 X match load. The proposed antenna shown in Figure 4 occupies an overall area of 124*25 mm2 and the designed parameters explained in Table 2. The electric field gradations under the radiators’ metal as well as simulated radiation patterns at
FIGURE 5
F I G U R E 6 Simulated radiation pattern at 10 GHz. (A) Sum pattern excitation. (B) Difference pattern excitation
10 GHz are plotted in Figure 5 and Figure 6, respectively. The field distribution for the case of port one excitation exhibits a similar field pattern for eight square ring antennas, while a strong opposite field distribution can be observed for port two excitation in difference mode. The simulated group delay of the antenna is relatively flat in the pass band and varies between 0.5 ns and 1.5 ns. It means variation in the
Electric field gradation under top metal at 10 GHz. (A) Sum pattern excitation. (B) Difference pattern excitation
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F I G U R E 8 Simulated and measured reflection coefficients of the proposed antennas. (A) 4-cell antenna. (B) 8-cell antenna
reported in Figure 9 for 4-cell array and compared with9 in sum mode excitation. The measured SLL is below 212.5 dB in E-Plane with a little discrepancy by its simulated one (215 dB) due to fabrication tolerances and measurement errors. The existing differences between the simulated and measurement results are due to ignoring the coaxial cable, and the antenna holders used during the simulation procedure. F I G U R E 7 Photographs of the fabricated antennas. (A) Top view of 4-cell antenna. (B) Top view of the 8-cell antenna. (C) Bottom view of the 8-cell antenna
phase is negligible for this UWB antenna to transmit/receive high data rate pulse without distortion.
3 | COMPARISON WITH EXPERIMENTAL RESULTS The prototypes of the proposed antennas have been fabricated accurately based on a low-loss Ro 4003 substrate with the relative permittivity and height of 3.38 and 31 mil, respectively. The metal thickness of the PCB is considered as 18 mm. The Figure 7 shows photos of the fabricated antennas. The Agilent-E8361C PNA microwave network analyzer is used to measure the antenna reflection coefficients which are shown in Figure 8. The radiation patterns of the proposed antennas were measured in an anechoic chamber. The simulated and measured radiation patterns at 10 GHz, in sum, and difference-mode excitation has been
F I G U R E 9 (A) Comparison of E-plane radiation patterns for the 4-cell antenna and 11 in sum mode excitation. (B) E-plane radiation patterns in difference mode excitation for the 4-cell antenna
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results were approved by measured results showing 4% return loss bandwidth, 2% 3-dB AR bandwidth and 222 dB null-depth in difference mode excitation. ORCID Javad Soleiman Meiguni 1900-7520
http://orcid.org/0000-0003-
R EFE RE NC ES [1] Rezazadeh N, Shafai L. Ultrawideband monopulse antenna with application as a reflector feed. IET Microwav Antennas Propag. 2016;10:393–400. [2] Vikram VM, Sha S, Bredow JW, Lu M. Wideband cavity backed slot antenna for automotive monopulse radars. Electron Lett. 2010;46:675–677. [3] Zhang QC, Wu W. Compact dual-band circularly-polarised cavity-backed slot antenna. Electron Lett. 2011;47:947–948.
FIGURE 10
E-plane radiation patterns of the 8-cell antenna. (A) Sum mode excitation. (B) Difference mode excitation
The simulated and measured radiation patterns, in sum, and difference-mode excitation has been depicted in Figure 10 for 8-cell antenna array. It is noticed that more directive patterns are feasible by array configuration. The measured main lobe positions have a good correspondence with those of the simulation results. A 213.45 dB and 222 dB nulldepth has been achieved in difference-mode excitation for 4cell and 8-cell array antenna, respectively. The measured 222 dB null-depth for 8-cell array antenna showing its effectiveness in mono-pulse applications. The asymmetrical radiation pattern does not occur for array antennas because of appropriate placement of SMA connectors. However, low radiation-efficiency is a common drawback for many types of SIW antennas due to their large microstrip to SIW transitions, and matched-line feed networks. The double-layered 8-cell antenna design leads to overcome this drawback.
4 | CONCLUSION A compact double-layer 8-cell array SIW antenna has been designed and measured for circular polarization mono-pulse applications. The design procedure for optimum feed networks presented in this article. A Rat-Race based feed network with enhanced microstrip to SIW transitions is developed showing the high isolation between input terminals as well as efficient placement of sum and difference ports. The antenna is low-profile and compact with acceptable radiation patterns, in sum, and difference modes. The prototype of antenna was fabricated and tested. Simulation
[4] Attaran A, Chowdhury S. Fabrication of a 77 GHz Rotman lens on a high resistivity silicon wafer using lift-off process. Int J Antennas Propag. 2014;2014:1–9. [5] Attaran A, Rashidzadeh R, Kouki A. 60 GHz low phase error rotman lens combined with wideband microstrip antenna array using LTCC technology. IEEE Trans Antennas Propag. 2016;64:5172–5180. [6] Attaran A, Rashidzadeh R, Muscedere R. Rotman lens combined with wide bandwidth antenna array for 60 GHz RFID applications. Int J Microw Wirel Technol. 2017;9:219–225. [7] Chien HY, Shen TM, Huang TY, Wang WH, Wu RB. Miniaturized bandpass filters with double-folded substrate integrated waveguide resonators in LTCC. IEEE Trans Microw Theory Tech. 2009;57:1774–1782. [8] Deslandes D, Wu K. Accurate modeling, wave mechanisms, and design considerations of substrate integrated waveguide. IEEE Trans Microw Theory Tech. 2006;54:2516–2526. [9] Cheng YJ, Hong W, Wu K. 94 GHz substrate integrated monopulse antenna array. IEEE Trans Antennas Propag. 2012;60:121–129. [10] Busuioc D, Safavi-Naeini S, Shahabadi M. High frequency integrated feed for front end circuitry and antenna arrays. Int J RF Microw Comput-Aided Eng. 2008;19:380–388. [11] Lacik J. Circularly polarized SIW square ring-slot antenna for Xband applications. Microw Opt Technol Lett. 2012;54:2590–2594. [12] See TSP, Chen ZN. An ultra-wideband diversity antenna. IEEE Trans Antennas Propag. 2009;57:1597–1605. [13] Zhang S, Ying Z, Xiong J, and, et al. Ultra-wideband MIMO/ diversity antennas with a tree-like structure to enhance wideband isolation. IEEE Antennas Wirel Propag Lett. 2009;8:1279–1282., [14] Locatelli A, Modotto D, Pigozzo FM, and, et al. A planar differential and directive ultrawideband antenna. IEEE Trans Antennas Propag. 2010;58:2439–2442., [15] Amani N, Kamyab M, Jafargholi A, Hosseinbeig A, Meiguni JS. Compact tri-band metamaterial-inspired antenna based on CRLH resonant structures. Electron Lett. 2014;50:847–848. [16] Meiguni JS, Kamyab M, Hosseinbeig A. Theory and experiment of spherical aperture-coupled antennas. IEEE Trans Antennas Propag. 2013;61:2397–2403.
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A U T HO R B IO G R A P H I E S JAVAD SOLEIMAN MEIGUNI was born in Tehran, Iran, on June 16, 1982. He received his M.Sc. and Ph.D. in electrical engineering from K. N. Toosi University of Technology, Tehran, Iran, in 2008 and 2013, respectively. In 2013, he joined the Faculty of Electrical and Computer Engineering, Semnan University, as an assistant professor. He has been involved in department and group level service activities with several undergraduate and postgraduate students. He has authored or co-authored of several papers in peer-reviewed journals and conference proceedings. His researches are mainly focused in the areas of computational EM modeling, EMC, millimeter-wave, and THz technology for different range of applications. SEYED AMIN KHATAMI was born in Semnan, Iran, on March 2, 1992. He received his B.Sc. and M.Sc. in telecommunications from Semnan University, Semnan, Iran in 2015 and 2017,
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respectively. He is currently a design engineer in the areas of RF, microwave, microstrip antennas, and planar filters. ALI AMN-E-ELAHI was born in Tehran, Iran, on November 27, 1990. He received the B.Sc. degree in telecommunications from Islamic Azad University of Shahr-e-Rey, Tehran, Iran, in 2014. Currently, he is working toward the M. Sc. degree in telecommunications from Semnan University. His research interests include different types of antenna design and measurement such as SIW antennas, and planar multilayer antennas.
How to cite this article: Soleiman Meiguni J, Khatami SA, Amn-e-Elahi A. Compact substrate integrated waveguide mono-pulse antenna array. Int J RF Microw Comput Aided Eng. 2017;e21155. https://doi.org/10. 1002/mmce.21155
