Microstrip bandpass filter design using triangular open loop resonators with improved cross‐coupled structure

Abstract

Abstract In this letter, a highly selective microstrip bandpass filter using triangular open‐loop resonators with improved cross‐coupled structure is designed, fabricated, and measured. The new cross coupling structure is implemented by inserting two L‐shaped stubs into the triangular open‐loop resonators. A good agreement is achieved between simulated and measured results. Measurements are given to verify that a passband from 5.1 to 5.5 GHz with the insertion loss less than 1.0 dB and return loss more than 20 dB is obtained. There are two transmission zeros on both sides of the passband which lead to higher selectivity for the passband. In addition, two extra transmission zeros are observed obviously and located at about 7.0 GHz and 9.0 GHz, respectively, for high out‐of‐band rejection. The filter has a compact size of 10 mm × 6 mm which amounts to about 0.3 λ g × 0.2 λ g . © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 2346–2348, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24599