A design solution for compact slotted waveguide array antennas based on SIW technology

[3]. The SIW, together with other types 
of synthesized waveguide such as SINRD, can be generalized by a new concept 
called “substrate integrated circuits (SICs)” that allow the integration of planar and 
non-planar structures within the same substrate [7]. 
 This paper presents a design method for an SWA using SIW technology, called 
compact SIW slot array antenna, which is fed by a combination of microstrip 
power dividers. The array and feeding network can be manufactured on a substrate. 
As a result, not only the size, weight, and cost of the slotted waveguide array 
antennas are reduced, but also the side and back lobe levels are reduced, 
manufacturing repeatability and reliability are enhanced. 
 2. DESIGN METHOD 
2.1. Slotted Waveguide Array Antenna (SWA) 
 The design SWA is often based on the procedure described by Stevenson, and 
22 D. T. Viet, T. T. Tram, “A design solution for compact  based on SIW technology.” 
Research 
Elliot [8-12], in which the waveguide is short circuit at a ¼ of wavelength from the 
center of the last slot. The slot spacing is ½ of wavelength. For rectangular slots, 
the slot length is about ¼ of 0. The resulting sidelobe level of the array antennas is 
related to the excitation of each element. In SWA, the excitation of each slot is 
proportional to its conductivity. In vertical slots on the waveguide’s wide wall, the 
slot’s conductivity changes following its displacement from the centerline to the 
wide wall [9]. Therefore, for each desired sidelobe level, the appropriate positioner 
displacement needs to be calculated carefully. 
 Elliott proposed two main equations that need to be solved simultaneously to 
determine the displacement and length values for each slot [8]. These two 
equations are based on Stevenson’s equations [9], Babinet’s principles, and also on 
the Taylor formula [13] and the length adjustment coefficient [14] of Oliner, in 
addition to Stegen’s assumption on the generality of the resonant slot length. 
 In summary, the existing resonant SWA design process is fairly complex. It 
mainly relies on several equations to derive both the displacement and the length of 
each slot. In this paper, the authors will present a simple design process. All the 
slots have the same length and use sample equations to determine the slot’s 
heterogeneous positions to achieve the desired sidelobe level. Other parameters 
such as distance between slots and their distance from both the feed port and the 
terminal will be taken from the instructions set by Elliott and Stevenson. 
 Fig. 1. Configuration of a metal waveguide slot array antenna. 
 For a rectangular metal waveguide of dimensions (a x b), as shown in fig.1, the 
general rules and functions for the vertical positions of the slots on the wide wall 
are as follows [12, 13]: 
 • The center of the first slot, slot 1, is located at a distance of ¼ guided 
wavelength or 3λg/4, from the feed point of the waveguide, 
 • The center of the final slot, located at g/4 or 3λg/4, from the waveguide 
terminal. 
 • The distance between the center of two slots is λg/2. 
 • Where cut = 2a, λg is the guided wavelength calculated by the following: 
 
  (1) 
 
 √ 
  
Journal of Military Science and Technology, Special Issue, No.72A, 5 - 2021 23 
 Electronics & Automation 
where λ0 is the wavelength in free space and λcut is the wavelength in the 
waveguide. 
 • Slot width: (2) 
 • Slot length:  (3) 
2.2. SIW slot array antenna 
 Compact SIW slot array antenna structure is based on the SWA principle, which 
replaces the metallic waveguide with an equivalent dielectric substrate. A 
schematic view of the SIW slot array is shown in fig.2. Such waveguide is 
composed of two parallel arrays of holes, which define the waveguide’s TE wave 
propagation. The propagation coefficient and the radiation loss are determined by 
parameters “w”, “p” and “d”, denoted the SIW’s width, the period, and the 
diameter of vias, respectively. Using SIW technology, a non-planar metal 
waveguide can imitate a SIW, resulting in intrinsical planarity, and it can be 
manufactured in practice and more easily integrated into inputs/outputs. 
 Khe dọc
 p
 d w
 h
 Lỗ kim loại 
Fig. 2. Configuration of SIW slots. Fig. 3. SIW and equivalent rectangular 
 waveguide. 
 As shown in fig.2, the SIW is equivalent to a typical rectangular waveguide 
filled with dielectric, and therefore, it can be analyzed using only the width of an 
equivalent waveguide [15]. 
 Calculations for the normalized width of the equivalent SIW are given in (4) 
and (5). 
 If Wcon is the width of the normal metal waveguide and εcon = 1, the width of the 
equivalent dielectric-filled waveguide is: 
 (4) 
 √ 
 From (4), dimensions of SIW are calculated as follows: 
 d 2 d 2
 ww and ll (5) 
 eff 0.95s eff 0.95s
where weff, leff are the effective width and length of SIW, and w, l are the width and 
length of the SIW. 
2.3. Design of SIW slot array antenna 
 To design a vertical slot array, an iterative technique has been developed by 
Elliott [10]. This procedure requires knowing the scattering property of a single 
slot as a slot length and offset function since such information is used to “detune” 
24 D. T. Viet, T. T. Tram, “A design solution for compact  based on SIW technology.” 
Research 
the slot to compensate for mutual coupling. A SIW slot array can be designed 
using a modified Elliott’s procedure [11], including the internal high order mode 
coupling, which cannot be ignored since the substrate’s thickness is always much 
smaller than the width of the equivalent waveguide. 
 The feed network is composed of microstrip power dividers. As shown in fig.4, 
it can be manufactured on the same substrate. 
 The transition from microstrip to SIW has been investigated in [3]. After a 
careful tuning procedure, its in-band insertion loss can be better than 0.3 dB. All 
the SIW slots are excited with the same amplitude and phase in the design 
procedure. 
 SIW slot array antenna designed with 2 x 8 slots with the specifications shown 
in table 1 below: 
 Table 1. Technical parameters of the SIW slot array antenna system. 
TT Specifications Unit Value 
1 Frequency GHz 9,8 ÷ 10,2 
2 Standing wave ratio 2 
3 Return loss dB < -10 
4 Gain dBi 16 
5 Azimuth Half Power Beam Width (-3 dB level) Degree 15.4 ÷ 17.5 
6 Azimuth side sidelobe level dB - 18 
7 Elevator Half Power Beam Width (-3 dB level) Degree 33 ÷ 36 
8 Polarization Horizontal 
 Following the specifications in table 1, based on the theory given in section 2.1, 
the SIW slot antenna array is designed on Roggers 5880 substrate with dielectric 
constant εr = 2.2, substrate thickness h = 0.508 mm, copper layer thickness t = 
0.017 mm. The dimensions of the X-band SIW slot array antenna are shown in 
table 2. 
 Table 2. Dimensions of the SIW slot array antenna. 
TT Specifications Unit Value 
 1 Number of slots slots 2x8 
 2 Length of SIW mm 156,35 
 3 Width of SIW mm 2x21 
 4 Slot spacing mm 13,3 
 5 Slot length mm 9,4 
 6 Slot width mm 0,9 
 7 Hole diameter mm 0,5 
 8 Hole spacing mm 1 
 Length of short circuit (from the center of the mm 
 9 6,4 
 8th slot) 
10 Length of feed (from the center of the 1st slot) mm 52,1 
Journal of Military Science and Technology, Special Issue, No.72A, 5 - 2021 25 
 Electronics & Automation 
 3. SIMULATION AND EXPERIMENTAL RESULTS 
 The simulation and manufacturing results of a SIW array antenna consisting of 
2 x 8 slots at a frequency of 10 GHz are shown in fig.4 to fig.9. 
 Fig. 4. Simulation on CST software of Fig. 5. Fabricated SIW slot array 
 SIW slot array antenna. antenna. 
 Fig. 6. Three-Dimensional Radiation Pattern of SIW slot array antenna. 
 a. Simulation result b. Measured result 
 Fig. 7. Standing wave ratio VSWR. 
 a. Simulation result b. Measured result 
 Fig. 8. Radiation patterns in the azimuth angle at a frequency of 10 GHz. 
26 D. T. Viet, T. T. Tram, “A design solution for compact  based on SIW technology.” 
Research 
 a. Simulation result b. Measured result 
 Fig. 9. Radiation patterns in the elevation angle at a frequency of 10 GHz. 
 Table 3 presents the simulation results and actual measurement results of the 
SIW slot array antenna. 
 Table 3. Comparison of simulation results 
 and measurement results of SIW slot array antennas. 
TT Unit Simulation Measurement 
 Technical parameters 
 results results 
1 Frequency GHz 9,8 ÷ 10,2 9,8 ÷ 10,2 
2 Voltage standing wave ratio 2 2 
3 Return Loss dB < -10 < -10 
4 Gain dBi 16 16 
5 Azimuth Half Power Beam 13.5 ÷ 17.4 12.9 ÷ 16.9 
 Degree 
 Width (-3 dB level) 
6 Azimuth side sidelobe level dB - 18 - 17.0 
7 Elevator Half Power Beam 33.9 ÷ 36 33.0 ÷ 35.3 
 Degree 
 Width (-3 dB level) 
8 Polarization Horizontal Horizontal 
 The calculated and measured results show good agreements, which implies that 
such a type of antennas can be constructed without any tuning. The obtained 
results also demonstrate the advantage of a SIW slot array antenna: the low 
sidelobe levels. This parameter can also be improved by adjusting the simulation 
parameters and increasing the number of arrays antenna. 
 Dimension wise, the SIW antenna 2x8 elements (156,35x42x0,508) mm in X 
band is more compact than the traditional metal ODS 2x8 elements (about 
400x30x60) mm. In addition, studying the power level of Roggers 5880 substrate 
on MVI software showed that the substrate could sustain pulsed peak power of 
more than 100 W. This demonstrates that the small SIW slot array antenna can be 
applied in practice in radar stations’ antenna systems. 
 4. CONCLUSIONS 
 This paper has presented theoretical foundations for designing compact SIW 
slot array antennas. The integration on a dielectric substrate makes the size and 
Journal of Military Science and Technology, Special Issue, No.72A, 5 - 2021 27 
 Electronics & Automation 
weight of the SIW slot array antenna much smaller than the conventional metal 
waveguide, with the benefit of low sidelobe level. This new structure is suited for 
planar array antenna designs at the centimeter and millimeter ranges. 
 The simulation and measured results of the 2x8 elements SIW slot antenna array 
show a good agreement between theory and practice, proving that such a SIW slot 
array antenna structure can replace the metal waveguide in slot array antenna 
systems without any adjustment. 
 With the development of simulation techniques and computation tools, we can 
develop compact SIW slot array antennas with a more significant number of slots 
and rows to meet the smaller azimuth plane’s requirements (less than 10) for X 
band antenna systems. 
 This article was presented at the National Conference: Application of High Technologies in 
Practice - 60 years of development in the Academy of Military Science and Technology. 
 REFERENCES 
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[2]. Rueggeberg, W., “A multi-slotted waveguide antenna for high-powered 
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[3]. D. Deslandes and K. Wu, “Integrated microstrip and rectangular waveguide 
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[4]. J. Hirokawa and M. Ando, “Single-layer feed waveguide consisting of posts 
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 Propagat., vol. AP-46, pp. 625–630, May 1998. 
[5]. H. Li,W. Hong, T. J. Cui, K.Wu, Y. L. Zhang, and L. Yan, “Propagation 
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[6]. D. Deslandes and K. Wu, “Single substrate integration technique of planar 
 circuits and waveguide filters,” IEEE Trans. Microwave Theory Tech., vol. 
 51, pp. 593–596, Feb. 2003. 
[7]. K.Wu, “Integration and interconnect techniques of planar and non-planar 
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 411–416. 
[8]. Elliott, R. S. and L. A. Kurtz, “The design of small slot arrays,” IEEE Trans. 
 Antennas Propagat., Vol. 26, 214–219, March 1978. 
[9]. Stevenson, A. F., “Theory of slots in rectangular waveguides,” Journal of 
 Applied Physics, Vol. 19, 24–38, 1948. 
[10]. Elliott, R. S., “An improved design procedure for small arrays of shunt 
 slots,” IEEE Trans. Antennas Propagat., Vol. 31, 48–53, January 1983. 
[11]. Elliott, R. S. and W. R. O’Loughlin, “The design of slot arrays including internal 
 mutual coupling,” IEEE Trans. Antennas Propagat., Vol. 34, 1149–1154, 
 September 1986. 
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[12]. Elliott, R. S., “Longitudinal Shunt Slots in Rectangular Waveguide: Part I, 
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 CA, USA. 
[13]. Oliner, A. A., “The impedance properties of narrow radiating slots in the broad 
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[15]. D. Deslandes, L. Perregrini, P. Arcioni, M. Bressan, K. Wu, and G. 
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 TÓM TẮT 
 NGHIÊN CỨU GIẢI PHÁP THIẾT KẾ ĂNG TEN MẢNG KHE 
 ỐNG DẪN SÓNG GỌN NHẸ SỬ DỤNG CÔNG NGHỆ SIW 
 Ăng ten mảng khe ống dẫn sóng (ODS) là cấu trúc quan trọng của ăng ten 
 siêu cao tần với nhiều ứng dụng trong hệ thống ra đa và thông tin liên lạc. 
 Các hệ thống ăng ten mảng khe ODS trước đây chủ yếu được gia công trên 
 các ống dẫn sóng bằng kim loại, các nghiên cứu thiết kế ăng ten mảng khe 
 ODS sử dụng vật liệu chất nền điện môi là một vấn đề mới. Bài báo này đưa 
 ra những kết quả trong nghiên cứu, thiết kế và chế tạo ăng ten mảng khe ODS 
 sử dụng công nghệ SIW (Substrate Intergrated Waveguide) trong dải tần băng 
 X. Kết quả nghiên cứu sẽ là nguồn dữ liệu quan trọng trong việc lựa chọn các 
 giải pháp thiết kế ăng ten mảng khe ODS sử dụng công nghệ SIW gọn nhẹ thay 
 thế cho ăng ten mảng khe sử dụng ODS kim loại truyền thống trong các ứng 
 dụng thực tế cho các hệ thống anten của đài ra đa băng X. 
Từ khóa: Ăng ten mảng khe; ODS; SIW; Siêu cao tần. 
 Received Jul 30th 2020 
 Revised Mar 31th 2021 
 Published May 10th 2021 
Author affiliations: 
 Viện Ra đa, Viện KHCNQS. 
 *Corresponding author: vietroc04@gmail.com. 
Journal of Military Science and Technology, Special Issue, No.72A, 5 - 2021 29