Reflectionless Ultra-Wideband bandpass filter based on suspended coplanar waveguide-microstrip broadside coupling

In this paper, a reflectionless ultra-wideband (UWB) bandpass filter (BPF) is proposed based on complementary diplexer, which is composed of a BPF and two bandstop filters (BSFs). BSFs are added to the two ports of the BPF as the auxiliary channels. At the same time, resistors are connected to the terminals of the BSFs to absorb stopband signals of the BPF reflected back to the source. Among them, the BPF consists of four broadside coupled lines of suspended coplanar waveguide-microstrip (SCPW-MS), and the BSF consists of a coupled line and an open-circuited stub. The two complement each other to form the reflectionless UWB BPF. As an example, a reflectionless UWB BPF with center frequency of 5.3 GHz, fractional bandwidth (FBW) of 113 %, and minimum insertion loss of 0.5 dB has been successfully developed. The fabricated device has the advantages of low loss, UWB and self-packaging.