Frequency-Reconfigurable Input-Reflectionless Bandpass Filter and Filtering Power Divider With Constant Absolute Bandwidth

An RF input-quasi-reflectionless bandpass filter (BPF) with reconfigurable center frequency and constant absolute bandwidth (ABW) is presented. The proposed BPF is based on a tunable complementary-diplexer architecture, which is made up of a main bandpass-type channel and an auxiliary channel with nearly-complementary bandstop-type filtering response that are synchronously reconfigured in frequency. The auxiliary channel is terminated by a resistor to absorb the RF power reflected by the main channel within its out-of-band region. In this manner, input-quasi-reflectionless capability is obtained. As an original technique, the constant ABW is attained in this overall BPF across the tuning range by means of the compensation of the bandwidth variations between its two channels. Subsequently, as a further application of this filter design concept, an RF frequency-adaptive Wilkinson-type power divider (PD) with constant-ABW filtering response and input-quasi-reflectionless behavior is reported. A single resistively-terminated bandstop-type branch is connected at the input port of the filtering PD to absorb the non-transmitted RF-input-signal energy. For validation purposes, a varactor-tuned frequency-reconfigurable input-quasi-absorptive BPF and a 3-dB filtering PD with constant-ABW are built and measured.