Design of a Reflectionless Bandpass Filter by Using Self-Packaged Suspended Coplanar Waveguide-Microstrip Hybrid

In this brief, a suspended coplanar waveguide-microstrip hybrid reflectionless bandpass filter (BPF) is proposed. Based on the two-port reflectionless low-pass prototype, the lumped-element parameter reflectionless bandpass filter is derived by using the frequency transformation and equal attenuation conditions between the lowpass and bandpass filters. Then the reflectionless bandpass filter is implemented by using parallel coupled line, short-circuit stub, and a T-shaped resonator which is used for improving the out-of-band performance. The reflectionless BPF has been fabricated and measured, which has a fractional bandwidth of 40.2%, a dual-port return loss attenuation of greater than 9.1dB from DC to 4.7GHz, and an insertion loss of 0.65 dB at center frequency of 2.76 GHz. The experiment results approach to the prediction, and the advantages of high frequency selectivity, self-packaging and favorable electromagnetic shielding have also been verified.