First‐order reflectionless filter topology with symmetrical responses

In this work, we present a bilateral reflectionless filter topology. A low‐pass filter prototype and its theoretical frequency responses are given. The frequency responses are obtained by means of ABCD matrices, thereby showing that the proposed prototype is reciprocal, symmetrical, and reflectionless at both ports. A first‐order bandpass filter with the reflectionless characteristic has been designed by applying the conventional low‐pass‐to‐bandpass transformation to the proposed low‐pass filter topology. It is verified by measurement results that the proposed bandpass filter can have less than −20 dB reflection coefficient over the passband and stopband at both ports with the same transmission response of a conventional first‐order bandpass filter.