Broadband transition between substrate integrated waveguide and rectangular waveguide based on ridged steps

Transcription

1 This article has been accepted and published on J-STAGE in advance of copyediting. Content is final as presented. IEICE Electronics Express, Vol.* No.*,*-* Broadband transition between substrate integrated waveguide and rectangular waveguide based on ridged steps Teng Li a), Hongfu Meng, and Wenbin Dou b) State Key Laboratory of Millimeter Waves, Southeast University, Nanjing , China a) b) Abstract: A broadband transition between substrate integrated waveguide (SIW) and rectangular waveguide (RWG) is proposed. Five ridged steps in the RWG and a multi-section SIW are designed to expand the bandwidth. The measured results agree well with the simulations, a return loss better than 15 db and an insertion loss less than 2.45 db are obtained at the wide band from GHz to 40 GHz for a back-to-back structure. Keywords: Broadband, Transition, SIW, Waveguide Classification: Microwave and millimeter wave devices, circuits, and systems References IEICE 2014 DOI: /elex Received May 7, 2014 Accepted May 23, 2014 Publicized June 12, 2014 [1] D. Deslandes, and K. Wu. IEEE Trans. Microw. Theory Tech. 51 [2] (2003) 593. [2] M. Bozzi, A. Georgiadis, and K. Wu. IET Microwaves, Antenna and Propagation. 5 [8] (2011) 909. [3] T. Kai, J. Hirokawa, and M. Ando. Antennas and Propagation Society International Symposium. 4 (2002) 436. [4] Yong Huang, and Ke-Li Wu. IEEE Trans. Microw. Theory Tech. 51 [5] (2003) 1613 [5] L. JungAun, J. Hirokawa, and M. Ando. Antennas and Propagation Society International Symposium. (2006) [6] Lin Li, Xiaoping Chen, Roni Khazaka, and Ke Wu. Asia Pacific Microwave Conference. (2009) [7] Xiaobo Huang, and Ke-Li Wu. IEEE Microw. Wireless Compon. Lett. 22 [10] (2012) 515. [8] R.Głogowski, J.-F. Zürcher, C. Peixeiro, and J.R. Mosig. Electronics Letters. 49 [9] (2013) 602. [9] L. Xia, R. Xu, B. Yan, J. Li, Y. Guo, and J. Wang. Electronics Letters. 42 [24] (2006)

2 [10] J. Li, G. Wen, and F. Xiao. Electronics Letters. 46 [3] (2010) 223. [11] D. Dousset, K. Wu, and S. Claude. Electronics Letters. 46 [24] (2010) [12] Haiyan Jin, Weijian Chen, and Guangjun Wen. Electronics Letters. 48 [7] (2012) 355. [13] Florian D. L. Peters, Tayeb A. Denidni, and Serioja O. Tatu. Microwave and Optical Technology Letters. 0 [0] (2012) [14] Zamzam Kordiboroujeni, and Jens Bornemann. IEEE Microw. Wireless Compon. Lett. 23 [10] (2013) 518. [15] D. Deslandes, and K. Wu. IEEE Trans. Microw. Theory Tech. 54 [6] (2006) Introduction In recent years, Substrate integrated waveguides (SIWs) have received much attention and been widely used in microwave and millimeter waves application [1]. SIWs are integrated waveguide-like structures and can be fabricated in planar form by using two rows of conducting cylinders or slots embedded in a dielectric substrate that electrically connect two parallel metal plates. SIW structures preserve most of the advantages of conventional rectangular waveguides (RWGs), such as high Q-factor, cut-off frequency characteristic and high power capacity; furthermore, they have still more advantages like those of a microstrip line, for example, low-profile, low-cost, light weight and easy integrated with other circuit components. Therefore, many components such as antennas, power dividers, filters and oscillators, have been studied based on SIW technology [2]. As frequency increases to the millimeter wave band and taking into account the need of low-loss, the interface port of the current measurement devices is RWG, such as network analyzers. Consequently, an effective transition between SIW and WR-28 standard waveguide is required. There were two types of configurations have been developed, a right-angle where the axes of both waveguides are perpendicular [3-8] and an in-line configuration where the both waveguides are collinear [9-12]. The right-angle transitions employed a coupling aperture cut in the broad wall of SIW to ensure the matching between both waveguides. Although some improvement have been done [7, 8], the bandwidths are still narrow and not satisfying the requirements of many broadband systems. The in-line transitions were realized by probes, such as radial probe [9], fin line probe [10], substrate taper [11], and antipodal quasi-yagi antenna probe [12], inserting into smooth height-tapered waveguide or normal waveguide. In [13], two-step architecture was designed in RWG with a probe inserting into waveguide cylindrical hole. In this paper, a broadband transition realized by a RWG with five ridged steps and a multi-section SIW is presented. Three transitions are discussed and the ridged steps with bulged shape in the middle can improve the performance and compress the size. A back-to-back transition has been fabricated and the measured results agree well with simulations. 2

3 Fig. 1. SIW structure 2 SIW design An SIW structure, as shown in Fig. 1, is equivalent to a conventional dielectric-filled metallic rectangular waveguide and the cut-off frequency f c of main mode TE 10 is designed in accordance with WR-28 standard waveguide (7.112 mm mm) which is GHz. The substrate used here is RT/Duroid 5880 with following specifications: ε r = 2.2, tanδ = , and a thickness of mm. The ground plane is formed by a 17 μm-thick layer of copper.the equivalent width of SIW a eff can be obtained from a eff c. (1) 2 f c Therefore, the equivalent width is 4.8 mm. The width of SIW a SIW can be calculated from [14] SIW eff r a a p e e (2) d / p d / p ( ) where p is the pitch between adjacent metallic vias and d represents the diameter of metallic vias. The applicable range of Eq. (2) covers all practical SIW applications in condition of 0.5 < d/p < 0.8 [15]. To take account of manufacture process, the parameters are chosen as follows: d = 0.5 mm, p = 0.72 mm, d/p = And from Eq. (2), a SIW = 5.2 mm is calculated. 3 Transition analysis and design In order to obtain a wideband impedance matching and transform waveguide from the higher RWG to the lower SIW, a multi-section matching transformer with steps structure is considered to be a competitive candidate. Therefore, a transition consisting of stepped RWG and multi-section SIW is introduced, as depicted in Fig. 2(a). Five steps numbered from 1 to 5 are used for height transforming from the RWG to the SIW and the last four steps are designed in the same height for simplicity. The insert section of SIW with the upper copper etched is widened to the WR-28 width and inserted to the RWG. The followed adjusting section with width W t and length L t is used for matching between the insert section and SIW. Another structure with six steps, as shown in Fig. 2(b), is considered to improve performance. The multiple resonance behavior can be realized by optimization and the simulated results carried out by HFSS are depicted in Fig. 3. It can be seen that the 5-stepped structure and 6-stepped structure have the bandwidth of GHz and GHz respectively, with reflection coefficient better than 20 db. However, the larger dimensions and the slight improvement 3

4 Fig. 2. Configurations of (a) the 5-stepped transition, (b) the 6-stepped structure, and (c) the ridged 5-stepped structure. Fig. 3. Simulated results of the three structures. indicate that applying more steps is not an effective suggestion. The RWG part of the stepped transitions can be seen as a partly dielectric-filled waveguide and the steps are used to guide electromagnetic wave to the substrate. Inspired by ridged waveguide where the electric field is concentrated on the ridge, a novel 5-stepped structure is invented as shown in Fig. 2(c). Four steps are bulged out at the center with different widths and lengths. They are acting as ridges concentrating power in the middle. Therefore, the energy can be transited mostly from the wide inserted section or RWG to the narrow adjusting section. Based on the optimized 5-stepped transition, the initial value of parameters in ridged 5-stepped transition can be determined. The lengths and widths of ridges are limited by the corresponding steps. All parameters are optimized slightly by genetic algorithm and HFSS so that optimal result is achieved. The result is also shown in Fig. 3 and the corresponding parameters are summarized in Table I. It is found that the obtained bandwidth is GHz ( GHz) and most of 4

5 Table I. Parameters of the developed transition (unit: mm). Symbol L 1 L 2 L 3 L 4 h h g L in L t W t Value Symbol L s1 L s2 L s3 L s4 W s1 W s2 W s3 W s4 r Value Fig. 4. Photograph of the proposed back-to-back transitions. the reflection coefficients are below 25 db. In addition, the inserted length L in is compressed. Compared with the normal stepped structures, the overall matching improvement of the transition is feasible with the developed steps introduced. 4 Simulated and measured results The proposed transitions were cascaded back-to-back for experiment and the photograph is shown in Fig. 4. Two SIW sections are fabricated in different lengths to estimate the attenuation. Several alignment pin holes and screws were mounted in the SIW and RWG and the interface ports of RWGs are matched with WR-28. The measurements were made by an Agilent E8363C vector network Fig. 5. Simulated and measured results for back-to-back transition. 5

6 Fig. 6. Simulated results for a single transition with different gap. analyzer. Fig. 5 shows the measured S-parameters of shorter prototype in comparison with simulated results. Simulations for the back-to-back prototype show insertion loss lower than 0.5 db and return loss better than 20 db in the GHz frequency range. Experimental results show insertion losses are between 1.35 and 2.2 db and the return loss is better than 15 db in the frequency band GHz. Comparing with the longer prototype, the attenuation of the SIW is about 0.01 db/mm at 30 GHz. The length of the shorter one is 25 mm and the introduced transmission loss is around 0.25dB. Therefore, the insertion loss of a single transition is below 1 db. The difference between simulated and measured results around 23 GHz is also analyzed. Considering of the thickness of substrate and errors of mechanical process, there is a gap between SIW and RWG along x-axis, as depicted in Fig. 6. It is observed that as the gap growing, the return loss becomes worse around 23 GHz which is similar to the measured result. 5 Conclusions In this paper, a novel broadband transition between SIW and RWG is presented. Three stepped structures have been discussed. By introducing ridged steps in the RWG, a compact size and much improvement have been obtained. The good agreement between the measured results and simulations verifies the design procedure. Due to compact size, wide bandwidth and convenience integration, the proposed transition is very suitable for millimeter-wave communication, radar and measuring applications. Acknowledgments This work was supported by the National Natural Science Foundation of China under grant