Phase shifter based tunable bandpass filters

A tunable bandpass filter with a phase shifter as the tuning component is presented. The filter is based on a half wavelength transmission line and two small capacitors where the half wavelength transmission line is replaced by a phase shifter to realize a tunable filter. The tuning range of the fabricated filter is 30% and the core size is 11×5 mm². To improve the performance of the filter, a fixed and a tunable transmission zero are added at the input and the output of the filter and the series capacitors are replaced by varactor diodes. A tuning range from 721 MHz to 1110 MHz (42.5%) for a constant bandwidth of 188 MHz is achieved.