A compact tri-band bandpass filter using asymmetrical stub-loaded resonator

Abstract

ABSTRACT This paper proposes a novel compact tri-band bandpass filter based on two coupled asymmetrical stub-loaded resonators (ASLR). The proposed filter can achieve three resonant frequencies by tuning uniform impedance line, short-circuit stub, and open-circuit stub, respectively. In addition, the asymmetrical stub can be loaded at any position of the main branch, which will facilitate the circuit design for no impedance of special ratio is needed, and the design bound can be alleviated. Meanwhile, thanks to its simple structure, the whole filter occupies an area of 0.021 λg 2 based on RO4350B substrate, much smaller than other similar tri-band filters. Measurement results show that the filter achieves fractional bandwidths (FBW) of 7.5%, 6.4% and 4.2%, respectively for three bands. The proposed filter is small and can achieve a high-frequency selectivity at 2.45 GHz, 3.5 GHz and 5.25 GHz, corresponding to Bluetooth, World Interoperability for Microwave Access (WiMAX) and Wireless Local Area Network (WLAN), respectively. The proposed filter will find a wide application in wireless communications thanks to its attractive advantages.