High-Selectivity Filtering Phase Shifter With Multiple Transmission Zeros

A four-port microstrip filtering phase shifter including two stub-loaded resonators and two phase delay lines is presented. Bandpass filtering responses and transmission zeros (TZs) can be determined by stub-loaded resonators with source-load coupling, while arbitrary phase shift can be designed by adjusting the length of phase delay lines. The phase difference changes gradually as the frequency changes and then wide bandwidth of the filtering phase shifter can be realized. The measured minimum passband insertion loss is 0.5 dB. With the phase difference of 90° ± 10°, the simulated and measured passbands are from 7.61 to 9.49 GHz and from 8.01 to 9.37 GHz, respectively. A measured TZ at 4.72 GHz and another measured TZ at 13.31 GHz are created to realize high selectivity.