Highly Selective Microstrip Bandpass Filters in Ka-Band

Highly selective microstrip bandpass filters in Ka-band are developed by suitably inserting the attenuation poles in an edge-coupled structure. The attenuation poles at the high and low passband edges are introduced by adding a capacitively coupled gap and tapped open stubs in the conventional microstrip edge-coupled filter. In this study, the improved filters with center frequencies at 28 GHz and 38 GHz are fabricated on Teflon and Al2O3 substrates. Both filters have better selectivity and occupy the same area when compared with the conventional edge-coupled filter.