Design of Compact Dual-mode Dual-band Microstrip Bandpass Filter Using Stepped-impedance Resonator for Wireless Communication Applications

A compact dual-mode dual-band microstrip bandpass filter (BPF) based on stepped impedance resonator (SIR) for wireless communication applications is introduced in this paper. By choosing a proper impedance ratio, a BPF operating at 2.4 and 5.2 GHz is designed and analyzed. By adjusting the perturbation size, two degenerate modes are excited and coupling within the first passband. Two transmission zeros which further improve the performance of the BPF locate on both sides of the first passband. To verify the proposed concept, a dual-band BPF example is designed, fabricated and measured. The center frequencies (CFs) of the two passbands are 2.4 GHz and 5.2 GHz, respectively. The measured insertion losses (ILs) in the two passbands are less than 1.3 dB and 1.72 dB, and their associated return losses (RLs) are greater than -27.8 dB and 20.3 dB, respectively. The area of fabricated filter is about 16.3 x 16.3 mm(2).