An ultra compact quad-band bandpass filter with high harmonic suppression using SL-TSSIR

Abstract

This paper presents a highly compact quadband bandpass filter architecture, based on a new modified tri-section stepped impedance resonator TSSIR, serving multi-standard wireless communications systems. The proposed filter is composed of a second order tri-section SIRs loaded with a short stub resulting in four arbitrary frequency modes, three of them created by the TSSIR while the fourth is dependent on the TSSIR and the short stubs. The inclusion of the short stubs allows for creation of a much lower frequency band without sacrificing the filter size or insertion loss. As proof of concept, a quadband filter operating in the 0.75, 2.1, 3.5, and 5.2 GHz frequency bands is designed and implemented with 60% reduction in filter size. The fabricated filter achieves 3-dB fractional bandwidths of 38.6, 4.6, 10.14, and 5.3% while presenting an insertion loss of 0.65, 1.3, 1, and 1.8 dB, in the four bands, respectively. Out-of-band rejection better than 20dB is achieved up to a frequency 10.5 times the lowest operating frequency; this is attributed to the use of simple T-shaped feed lines both at the filter input and output. The measured results show good agreement with the predicted ones.