Symmetrical Four-Port Reflectionless Network And Its Application For Wideband Filter/Diplexer Design

In this paper, a symmetrical four-port reflectionless network is proposed. Based on the proposed network, two pairs of bandpass filter (BPF) and bandstop filter (BSF) with complementary response are used for circuit implementation. The proposed circuit can not only achieve bandpass/bandstop function between arbitrary two adjacent ports, but also exhibit reflectionless characteristic at all ports. Meanwhile, the BPF consists of two T-junctions with defected ground structure (DGS), while the BSF is composed of stepped-impedance resonator (SIR) and DGS. To verify the mechanisms, an all-port reflectionless filter/diplexer (i.e., four-port circuit) operating at center frequency
$f_{0}$
of 4.34 GHz with 58.0% fractional bandwidth (FBW) is implemented and fabricated. The measured reflectionless range is from 0.01 to 9 GHz with the reflectionless level below 10 dB.