A tunable bandpass filter with constant absolute bandwidth using folded slotline uniform‐impedance resonators

Abstract

A simple tunable bandpass filter (BPF) with constant 3-dB absolute bandwidth using folded slotline uniform impedance resonators (UIRs) is proposed. The tunable BPF consists of a pair of coupled folded slotline UIR, where the varactor diode elements are loaded to control its center frequency. Measured results show that a wide tuning range from 1.76 to 2.35 GHz with constant 3-dB absolute bandwidth (ABW) of 310 ± 10 MHz is realized. Meanwhile, a pair of transmission zeros (TZs) are generated aside both sides of the passband due to the coupling between source and load, which improves the selectivity of the passband.