Dual-Band Dual-Mode Compact Multilayer Quasi-Elliptical SIW Filter

This paper proposes a novel dual-band filter by vertically stacking three dual-mode substrate integrated wave-guide (SIW) cavities. With a fully enclosed cavity, by using the TE101 and $\text{TE}_{201}$ modes, a compact dual-band filter with a controllable frequency ratio is achieved. To improve the selectivity, the filter is configured with four transmission zeros (TZs) nearby the passband with good symmetry through cross coupling. The filter's size is only 0.61 $\lambda_{d}\times 1.15\lambda_{d}$ , and the measured in-band minimum insertion loss is 0.92 and 1.45 dB for the first and second bands, respectively. The proposed filter shows the merits of a miniaturized size, low insertion loss, high selectivity, and good out-of-band suppression.