A compact millimeter-wave stripline diplexer with two modified hairpin filters

A very compact low-loss stripline diplexer for millimeter-wave applications is presented. For the most compact configuration, a parallel-coupled half-wavelength resonator filter, a folded staggered resonant array filter and a hairpin filter are compared to determine which filter is proper for the diplexer. Two configurations of T junctions are analyzed. A diplexer of 2.73 mm by 3.06 mm and consisting of one hairpin filter with a pair of lines folded inside and another hairpin filter with tapped lines close to the other end of the resonators is developed. The total size of the diplexer is smaller than the one-half guided wavelength at center frequency of 26.5 GHz.