Triple‐band parallel coupled microstrip bandpass filter with dual coupled length input/output

Abstract

Abstract A three‐order triple‐band bandpass filter is proposed to operate at 1.8/3.5/5.2 GHz for DCS, WIMAX, and WLAN applications. Three 1/2λ open‐loop resonators and two novel modified input/output structures parallel coupled are used as the bases. The cascaded resonators are designed for wide bandwidth and high out‐of‐band rejection. The modified input/output structure is used to tune the suppression/improvement of each spurious resonance. The filter is printed on Al 2 O 3 ceramic substrate with 0.635 mm in thickness and has the relative dielectric constant 9.4. Because of the high dielectric constant substrate and novel feed in/out structure, the proposed filter with optimized parameters exhibits low insertion loss, high out‐of‐band rejection, wide bandwidth, and simple structure. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 995–997, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24257