Compact and Low Cost Substrate Integrated Waveguide Cavity and Bandpass Filter Using Surface Mount Shorting Stubs Ali Doghri, Anthony Ghiotto, Tarek Djerafi, Ke Wu Poly-Grames Research Center, Département of génie électrique, Ecole Polytechnique de Montreal, C. P. 6079, Succ. Centre-ville, Montréal, QC, Canada H3C 3A7 Abstract — A compact and low cost substrate integrated waveguide (SIW) cavity and bandpass filter using Surface Mount (SM) shorting stubs is proposed in this paper. These cavity and filter allows a drastically reduction in Printed Circuit Board (PCB) footprint. They are compact and also low cost as there fabrication involves standard PCB process and SM technologies. For demonstration purpose, one cavity and one 7 th order bandpass filter were designed and fabricated over Ka-band. The cavity is designed at the center frequency of 34 GHz. It achieves an unloaded Q u factor of 201 with a footprint of only 1.9 x 6.3 mm 2 compared to 5.38 x 6.3 mm for a planar cavity. Then, a 7th order filter is designed at the center frequency of 34.5 GHz. It provides a sharp frequency selectivity using arranged transmission-zeros and achieves a bandwidth of 1 GHz with an insertion loss of better than 2.9 dB with a footprint of only 11.2 x 6.3 mm 2 . The experimental prototypes achieve good performances. They potentially have many applications in microwave and millimeter wave devices, circuits and systems. Index Terms — Bandpass filter, cavity, double-loaded SIW cavity, surface mountable, substrate integrated waveguides (SIW). I. INTRODUCTION The ever-expanding demand for compact and low cost microwave and millimeter wave components is among the most critical issues for wireless systems. As one basic component, the need for compact, low loss and low cost cavities and filters has been growing. This work addresses this issue as it proposes a novel type of compact and low cost cavity and filter whose fabrication is based on standard Printed Circuit Board (PCB) process and Surface Mounting (SM) technologies. There is huge number of publications related to cavities and filters including waveguide filters with shorting stubs [1]. This type of filter has the advantage of allowing multiple transmission zeros in the stop band by adding shorting stubs in the E and/or H-planes [2]. This is important as the use of shorting stub building blocks offers the freedom to introduce Transmission Zeros (TZs) in any pre-specified frequencies that improves the filter selectivity and stop band attenuation. However, one factor that might have limited their use is their sized and fabrication complexity using three dimensional (3D) waveguide technologies. This work presents their implementation using low cost planar Substrate Integrated Waveguide (SIW) technology. On thesis of this technology, planar H-plane cavities and filters showing good performances were reported in the literature [4]. Nevertheless, the PCB footprint of those components is still relatively large. This work introduces the use of SM shorting stubs as building blocks in designing cavities and filters that allows a significant PCB footprint reduction. The proposed compact SIW cavity using SM shorting stubs as building elements is reported in section II. In section III, a 7 th order SIW filter also based on SM shorting stubs is demonstrated. Those devices are simulated using ANSYS’s HFSS EM software. II. SURFACE MOUNTABLE (SM) SIW CAVITY The conventional SIW cavity design consists of a rectangle arranged in the main coupling path. This generally makes the overall structure wider in one or more directions. On the other hand, a cavity disposed transversally to the direction of propagation would ensure high integrability and compactness. In this way, the third dimension generally not used in SIW design can be effectively exploited [3]. The top view and the 3D view of the proposed cavity are shown in Fig. 1. The cavity is constructed using two SM shorting stubs, one on each side of the main substrate. A. Design Procedure The proposed transversal cavity operates in the TE 201 mode. It is designed by the use of classical analytical equations of the rectangular waveguide counterparts. The resonant frequencies in SIW cavity can be calculated represented by the following relationship: (1) where W and L are the width and length of the cavity, respectively, m and q are the indices of mode, ߤ ௥ and ߝ ௥ are Fig. 1. Geometry of the cavity, a) main SIW, b) cavity 3D view. W 1 = 1.43 mm, l 1 = 0.38 mm, a = 4.77 mm, S 1 = 2.31 mm. ( ) ( ) 2 2 0 ( ) / / , 2 r r r c f mW q L με = + ⋅ m0q TE 978-1-4673-1088-8/12/$31.00 ©2012 IEEE