Design of Dual Band and Tri-band Bandpass Filter (BPF) with Improved Inter-band Isolation Using DGS Integrated Coupled Microstrip Lines Structures

Abstract

A novel approach to design dual-band as well as a triple-band BPF with improved isolation is ventured in this paper. In dual-band filter, dual mode property of coupled line filters is utilized to obtain resonant frequencies at 2.4 GHz and 7.4 GHz suitable for WLAN and WiMAX application respectively. Additionally a rectangular-ring DGS element is introduced within the coupled line filter to obtain a separate mid-band resonance at 5.2 GHz. The frequency shifting property of the pass bands due to cross-coupling between the microstrip line resonators and the DGS element is mostly eliminated by implementing stepped impedance open stub (SIOS) technique. All filter configurations are fabricated, measured and compared with the simulated models to validate the practical effectiveness. Stop band isolation > 40 dB and insertion loss (IL) < 0.8 dB is attained in all the filter configurations.