Planar type square shaped ceramic resonator filter for millimeter-wave integrated circuits

TE_0nδ mode circular ceramic resonators are usually used at centimeter frequencies due to their low loss natures. However, their employment in a planar type wide-band band-pass filter in the millimeter-wave region is problematic because of the poor coupling factors between the resonators and the input/output waveguides. With this in mind, we applied square ceramic resonators to millimeter-wave band-pass filters. From theoretical and experimental investigations, it was confirmed that the coupling factor of the EH_12δ mode square ceramic resonator is larger than that of circular ceramic resonators. Low-loss band-pass filters with relative bandwidths from 2.5% to 10% were designed and successfully fabricated by using the square ceramic resonators.