Triple-Passband Channelized Passive Filter With Infinite Input-Quasi-Reflectionless Range

A transmission-line-based sharp-rejection channelized passive bandpass filter (BPF) with 1.87/2.5/3.21-GHz triple-band response and infinite input-quasi-reflectionless (IQR) range is reported. Two RF power input absorption mechanisms are combined into it, as follows: 1) a balanced-type/two-branch circuit with a 90° at 2.5-GHz transmission line input phase-delay stage in one channel to attain a 1.6–3.4-GHz 10-dB-referred IQR range and 2) an input lossy circuit that dissipates the RF power echoes in the 0–1.6-GHz and 3.4–5-GHz bands, respectively. In this manner, as the overall transfer function is frequency quasi-periodic with the 5-GHz spectral period, a theoretically infinite IQR bandwidth is attained. Moreover, by exploiting transversal signal-interference principles owing to the transmission-line-based phase-delay stages that are inserted at the outputs of its two channels, an increased selectivity triple-band BPF response with multiple transmission zeros (TZs) is obtained. The basic RF operational foundations of the engineered triple-passband IQR channelized filter are presented, along with the measured results of a manufactured proof-of-concept microstrip prototype.