Novel compact dual-mode tri-band bandpass filter for WiMAX & GSM applications

This paper presents a novel, compact size planar microstrip tri-band BPF designed to produce three passbands for WiMAX and GSM applications. The tri-band BPF center frequencies are 900 MHz, 2.45 GHz and 3.5 GHz. A design methodology as well as design guidelines are proposed based on cross-coupled resonators to produce tri-section stepped-impedance resonators for the second and third passbands and dual-mode resonators for the first and second passbands. This novel tri-band BPF is simulated, optimized, fabricated and measured. Filter measurements are in very good agreement with simulations which verifies this novel idea as well as the proposed design procedure. The fabricated filter provides better size reduction and at the same time performs superior enhancement in insertion losses and keeps adequate passbands compared to other published tri-band microstrip filters.