A high stability fully tunable filter with frequency, bandwidth and transmission zero tuning

Abstract

Based on the double folded 1/4 mode substrate integrated waveguide (DFQMSIW) resonator, a two-pole DFQMSIW tunable filter with frequency, bandwidth and transmission zeros tuning is proposed in this paper. In order to increase the stability of the filter, the constant bandwidth can be maintained by changing the coupling coefficient by two varactor diodes when tuning frequency and transmission zeros. The center frequency can be tuned in the range of 1.1 GHz–1.9 GHz, transmission zeros can be tuned from 1.41 GHz to 1.5 GHz with bandwidth unchanged, and bandwidth can be tuned from 120 MHz to 200 MHz. The insertion loss is about −1.3 dB to −3 dB.