A quad‐band defected microstrip structure loaded bandpass filter for standard GPS , WiFi , WLAN , and WiMAX applications

Abstract

A quad-band bandpass filter is proposed using a defected microstrip structure (DMS) for GPS, WiFi, WLAN, and WiMAX applications. This filter uses a stub-loaded stepped-impedance resonator (SL-SIR). The proposed filter is fabricated on an RT/Duroid5880 substrate (εr = 2.2, h = 0.787 mm, tanδ = 0.0009). Then, the LC equivalent circuit of the proposed filter is presented. A 28th-order transfer function is obtained and approximated by 8th-order transfer functions. The results of simulation, measurements and the LC equivalent circuit are in good agreement. The proposed filter operates at 1.6, 2.48, 3.76, and 5.44 GHz. The measured insertion losses are 0.32, 027, 0.51, and 0.41 dB in the four bands, while the return losses are better than 10 dB in all frequency bands. Finally, the proposed filter is compared with other bandpass filters.