Stub-tuned microstrip bandpass filters for millimeter-wave diplexer design

This letter presents a new design for microstrip bandpass filters and its application to a millimeter-wave diplexer. Basically, parallel-coupled microstrip lines are utilized for bandpass response and non-uniform open-circuited stubs are added to tune the bandwidth of the passband and improve out-of-band rejection. The designed filters are connected to make a diplexer, which can be used in a phased-array transceiver system operating in millimeter-wave range. The diplexer is designed to separate an input signal containing both 32GHz and 35GHz into two signals of 32GHz and 35GHz, respectively or to combine two signals at 32GHz and 35GHz into one signal.