A Varactor and FMR-Tuned Wideband Band-Pass Filter Module With Versatile Frequency Tunability

A varactor and FMR-tuned wideband band-pass filter (BPF) module with versatile frequency tunability has been devised and realized on RT/Duroid substrate. By connecting four variable capacitance diodes (varactors) to the four open-circuited stubs of an X-band passive composite-BPF and adjusting the reverse bias voltage from 2 to 22 V, the 3 dB passband of the passive composite-BPF was continuously tuned from 7.7-12.4 GHz to 11.4-17.5 GHz. The corresponding bandwidth (BW) was enlarged from 4.7 to 6.1 GHz and the upper frequency of the passband was extended from 12.4 to 17.5 GHz, namely, a total frequency span of 9.8 GHz. The BW of the passive composite-BPF was further FMR-tuned using a pair of Band-Stop Filter (BSF). By setting the reverse bias voltage at 22 V together with the bias magnetic fields at 3250 and 4200 Oe, respectively, to the two BSFs, the 6.1 GHz BW and 9.8 GHz frequency span were compressed to 1.4 GHz toward the high-end frequency. The 4.7 GHz BW and 9.8 GHz frequency span were also compressed to 1.0 GHz toward the low-end frequency with 2650 and 3500 Oe bias magnetic fields and 2 V reverse bias voltage. Thus, the combination of the varactor and FMR-tuning has facilitated versatile passband and its BW tuning covering the X-and Ku-bands with both large frequency tunability and greatly improved frequency selectivity.