Compact 60 GHz low-temperature cofired ceramic filter with quasi-elliptic bandpass response

This study presents a 60 GHz quasi-elliptic bandpass filter with a compact and planar structure. The proposed filter was constructed by stacking substrate integrated waveguide (SIW) cavities on the central transverse plane of a shielding SIW cavity. Jerusalem cross (JC) apertures and circular apertures were etched on the metal layers of the stacked SIW cavities to enable dual-mode operation and energy coupling. In the dual-mode cavities, the TM110 cavity mode and JC aperture mode can be excited simultaneously. Cross-mutual couplings exist among the resonant modes, resulting in two finite transmission zeros with each at either side of the passband. Multilayer low-temperature cofired ceramic technology was adopted to manufacture the experimental filter. The measured centre frequency was 60 GHz at a fractional bandwidth of 4.5% with two finite transmission zeros located at 53.7 and 65 GHz, thereby achieving highfrequency selectivity.