COMPACT, ULTRA-BROADBAND COPLANAR-WAVEGUIDE BANDPASS FILTER WITH EXCELLENT STOPBAND REJECTION

A compact, ultra-broadband coplanar-waveguide (CPW) bandpass fllter (BPF) is demonstrated. The proposed CPW-BPF is essentially designed by exploiting CPW short-stub and open-stub structures. Technically, the proposed fllter comprises shunt short- stub and series open-stub structures that are connected in a cascade topology. The higher and lower cutofi frequencies are mainly related to the electrical length of the shunt short stub and the series open stub, respectively. In addition, the stopband rejection is enhanced through an incorporation of CPW bandstop structures. The proposed fllter design is verifled through experimental demonstration. The corresponding lumped equivalent and transmission-line equivalent circuits are provided for circuit design purpose. Compared with the classical CPW-BPFs, the proposed fllter is of a relatively simple and compact conflguration. The demonstrated CPW-BPF has about 110% 3-dB fractional bandwidth, sharp selectivity, and great stopband rejection.