Design of a two-port reflectionless waveguide bandpass filter with high power handling capability

This paper proposed a two-port reflectionless bandpass filter (BPF) based on the waveguide implementation, which is required in high power-handling and low-loss applications. The two-port reflectionless waveguide BPF working mechanism is first addressed, where a four-port scheme is constructed by combining a pair of wideband 3-dB quadrature couplers and two identical reflective BPFs. The undesired reflected signals at the stopband of the reflective BPF are absorbed by the loads applied to the isolation ports of the couplers. In this manner, the proposed BPF allows for achieving a two-port reflectionless behavior. For verification, a reflectionless waveguide BPF prototype centered at 3.8 GHz with a 3-dB fractional bandwidth of about 4 % is fabricated and measured, showing good agreement between the measured and simulated results. The experimental results illustrate that over the operating range of 3.16–4.36 GHz, a good two-port reflectionless performance is attained, with a minimum insertion loss of 0.71 dB.