Compact and highly selective dual/tri‐band BPFs using folded T‐shaped stub‐loaded resonators for WLAN and WiMAX applications

Abstract

ABSTRACTIn this article, a series of dual‐/tri‐band bandpass filters (BPFs) using folded T‐shaped stub‐loaded resonators (TSSLRs) are presented for WLAN and WiMAX applications. The proposed TSSLR is constructed using two λ/4 resonators and a T‐shaped folded stub. A controllable transmission zero will be generated at the desired transition band leading to sharp roll‐off skirts and excellent out‐of‐band suppression by adjusting the length of the folded stub. After combining two or three TSSLRs with flexible feed‐lines, very compact overall sizes of 0.29 λg × 0.16 λg, 0.30 λg × 0.22 λg for dual‐band BPFs and 0.28 λg × 0.19 λg, 0.30 λg × 0.22 λg for tri‐band BPFs can be obtained. The measured results of the two dual‐band BPFs (I and II) show excellent characteristics of low insertion loss of 1.2/0.87 and 0.7/0.77 dB and wide fractional bandwidth (FBW) of 15.3%/24.2% and 28.7%/16.3%, respectively. Insertion losses of the tri‐band BPFs (III and IV) based on simulation results are approximately 0.2 dB and FBWs range from 10.34% to 15.02%, which prove excellent performance and further verify the design method. Furthermore, ultra‐high roll‐off factors of 54 dB and 67.5 dB per 100 MHz have been achieved in simulation results of the tri‐band BPF IV's 1st and 2nd up transition bands, respectively. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:312–319, 2016