COMPACT TRIPLE-BAND BANDPASS FILTER USING MULTI-MODE RESONATOR (MMR) WITH MULTIPLE TRANSMISSION ZEROS

Abstract

In this article, compact triple-band microstrip bandpass filter (BPF) with tunable centre frequencies andbandwidths as well as multiple transmission zeros (TZs) is presented. The proposedfilter is designed based on novelmulti—mode resonator (MMR), and the even-/odd-mode analysis method is employed to investigate its resonantcharacteristics. By changing the lengths of two loaded coupled open stubs and coupling space between them, tworesonant modes can be tuned and the bandwidth can be controlled. Also, two additional TZs are generated due to thedual-fingerfeed structure. Moreover, these two 725‘ can be controlled by the lengths of two fingers, and high passbandselectivity and band-to-band isolation level are achieved with ten TZs. The three centre frequencies of the proposedtriple-band BPF are located at 1.9, 3.55, and 7.33 GHz, respectively. In addition, the overall circuit size of thefabricatedfilter is much smaller in comparison with previous works. For demonstration, prototype filter is fabricatedand measured, and good agreements are obtained between the measured results and electromagnetic (EA!) simulatedones.