Tunable bandpass filter with wide tuning range of center frequency and bandwidth based on circular SIW

Abstract

This paper presents a circular substrate integrated waveguide (SIW) bandpass filter (BPF) with wide tuning range of center frequency and bandwidth (BW). For designing such a filter, lumped varactors loaded at two metal posts are utilized to adjust the center frequency, and the bandwidth is tuned by varactors mounted between two SIW cavities. One transmission zero (TZ) can be located at the lower or upper stopband by controlling the mixed coupling between two resonators. The external coupling is changed by using two lumped varactors mounted between feedlines and resonators. Eventually, the BPF with tunable center frequency and bandwidth is designed, fabricated and measured. Measured results indicate the center frequency is tuned from 1.48 to 2.61 GHz (up to 55.3%) while maintaining a 3-dB absolute BW of 31 ± 2 MHz, and the 3-dB bandwidth is tuned from 29 to 250 MHz (up to 8.6). Insertion loss from 1.8 to 4.8 dB is observed within the wide tuning range.