A novel microstrip bandpass filter with an elliptic-function response using improved dual-stub resonator

Abstract

In this article, a new microstrip bandpass filter (BPF) with multiple transmission zeros is designed, simulated and measured. The presented filter is based on a composite dual-stub resonator. The modified resonator with dual-bandgap resonant characteristic is composed of the parallel open-and short-circuited stubs, and cascaded by an additional stub line. The location of transmission zeros can be adjusted independently by varying the physical lengths of shunt resonant stub or cascaded stub line, so as to improve the filter selectivity. The proposed filter consists of two identical main transmission lines and three equal-length combined resonators with different length ratios between the cascaded section and open-/short-circuited stubs. Finally, a planar BPF with minimum insertion loss 0.65 dB, centred at 2.08 GHz with a 3-dB fraction bandwidth of 26.8% and six transmission zeros is implemented and verified by experiment.

A Novel Wideband Bandpass Filter Using Coupled Lines and T-Shaped Transmission Lines With Wide Stopband on Low-Cost Substrate

“…However, RF filters present several problems of spurious responses mainly due to the presence of the second harmonic if such conventional designs are used. Various filters are designed with different methods, in order to obtain wide bandwidth, wide upper stopband, and high selectivity [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21]. Methods using the three-line microstrip coupled structure, split ring resonators (SRRs), multimode resonators, open-ended stubs, transversal signal interaction concepts and defected ground surface have been introduced for the WBPF designs with good wideband responses.…”