A compact frequency-selective surface (FSS) having a quasi-elliptic bandpass response is presented in this paper. This was realized by vertically cascading substrate integrated waveguide (SIW) cavities. A single SIW cavity FSS has been fully studied and approximate analytical formulas are introduced to calculate its resonant frequencies. Two different resonances can be excited by a plane wave in the single SIW cavity FSS. According to theories of the cascading cavity filter and dual-mode filter, cross coupling can be realized in cascading SIW cavity FSSs, thus a compact FSS with a quasi-elliptic bandpass response is implemented. A Ka-band sample was fabricated by a printed circuit board (PCB) process. Experiments were carried out to validate this design method. Measured results are in agreement with predicted ones. The proposed quasi-elliptic FSS presents a number of advantages, namely, high selectivity, stable performance, and much reduced volume.
Luo, G. Q., Hong, W., Lai, Q. H., Wu, K., & Sun, L. L. (2007). Design and Experimental Verification of Compact Frequency-Selective Surface with Quasi-Elliptic Bandpass Response. IEEE Transactions on Microwave Theory and Techniques, 55(12), 2481–2487. https://doi.org/10.1109/TMTT.2007.910085