This article has been accepted for inclusion in a future issue of this journal. Content is final as presented, with the exception of pagination. IEEE MICROWAVE AND WIRELESS COMPONENTS LETTERS 1 Study of Bend Discontinuities in Substrate Integrated Gap Waveguide Jing Zhang, Student Member, IEEE, Xiupu Zhang, and Ahmed A. Kishk Abstract—This letter presents a study of bend discontinuities in the substrate integrated gap waveguide (SIGW), and proposes a simple solution to minimize the discontinuity effects. Both curved and chamfered right-angle bends are studied. It is found that with a proper ratio of the chamfered length and the bend via diameter, the possible cavity resonances can be suppressed and the desired performance is achieved. The curved bend, however, allows the bend via to have a larger diameter, which could be required due to the fabrication issue. This letter will be of great help to realize future feeding networks for SIGW antenna arrays or other types of cost-effective SIGW passive components, where many discontinuities are naturally present. The proposed discontinuity solution is validated experimentally by a fabricated SIGW prototype of two 90° bends. Index Terms—Discontinuity, gap waveguide (GW), plated via, strip bend, substrate integrated gap waveguide (SIGW). I. I NTRODUCTION S UBSTRATE integrated gap waveguide (SIGW) was newly proposed in [1], as a substitute for the bulky standard metal ridge GW or the microstrip-ridge GW [2], [3]. Based on the low-cost printed circuit board (PCB) process, the SIGW significantly reduces the size and weight of the stan- dard metallic GW and enhances the compatibility/integration to other planar circuits. As seen in Fig. 1, the SIGW is comprised of two layer substrates: a gap layer in which the waves propagate, and an upper layer to realize the perfect magnetic conductor (PMC) surface with periodic plated vias. The required conducting ridge using two contacted printed metal strips efficiently removes the effects of the plated vias drilled in the strip, which exists in the microstrip-ridge GW and heavily perturbs the current flowing on the strip [3]. In the SIGW, the fields are concentrated below the lower surface of the lower strip and thus will no longer meet the plated vias in the upper strip. This also helps the waves avoid the high-loss electroless nickel immersion gold (ENIG) coating on the copper strip top, which even causes a frequency shift in addition. The ENIG coating is not avoidable in the microstrip- ridge GW, since its waves are propagating in the air gap Manuscript received October 15, 2016; accepted December 1, 2016. This work was supported by the Quebec FQRNT Project in Broadband Photonic Devices. J. Zhang and X. Zhang are with iPhotoincs Laboratories, Depart- ment of Electrical and Computer Engineering, Concordia University, Montreal, QC H3G1M8, Canada (e-mail: z_jin25@encs.concordia.ca; xzhang@ece.concordia.ca). A. A. Kishk is with the Department of Electrical and Computer Engi- neering, Concordia University, Montreal, QC H3G1M8, Canada (e-mail: kishk@encs.concordia.ca). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/LMWC.2017.2661707 Fig. 1. SIGW with a double 90° bend. (a) Distributed 3-D view. (b) Zoomed- in-view unmodified bend. (c) Zoomed-in-view chamfered bend without via. All the via holes are copper plated. on the strip top, i.e., the ENIG-plated side of the copper, instead of the strip lower surface containing no ENIG plating in the SIGW. Furthermore, a gap of a constant height is guaranteed in the SIGW with the gap layer substrate, instead of the unstable air gap in the microstrip-ridge GW [4]. The radiation or surface waves in the substrate do not appear in the SIGW, a GW-based structure, compared with the microstrip line [1], [2]. Also, the advantages of the SIGW over the stripline are evident. Any vertical asymmetry in the stripline can generate unwanted higher order waveguide modes and the conductor loss due to its used two ground planes will be much higher [5]. Moreover, as proved in [1], the SIGW is able to have a much wider fundamental-mode band than the substrate integrated waveguide and has no mode conversion loss if integrated to other TEM/quasi-TEM lines. One simple straight-through SIGW, i.e., without bends, was realized in [1]. While, many discontinuities are naturally present in any actual microwave circuits, such as power dividers and a feeding network for antenna arrays. Thus, it is of great interest and necessary to study the discontinuity of the strip-ridge bend, thus providing good guidelines for design, which is not covered in [1]. This letter is very different from the discontinuity in the classic microstrip line, in which no plated via is connected to the metal strip. Moreover, it will be seen that the proposed bend configuration is much easier and more practical than the method presented in [3] for the microstrip-ridge GW, which has to fine tune up to three sets of vias at the bend and even each set has at least three vias. In addition, much better return loss, S 11 , over a wider band is obtained with the proposed method. II. CHAMFERED RIGHT-ANGLE BEND An SIGW with two 90° bends is shown in Fig. 1. The PMC is built by periodic plated vias, which are about 0.762 mm 1531-1309 © 2017 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. 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