Harmonic-suppressing bandpass filter based on coupled triangular open-loop stepped-impedance resonators

This work develops two harmonic‐suppressing bandpass filters. One has a direct‐coupled‐resonator structure and the other has a cross‐coupled‐resonator structure. The triangular open‐loop stepped‐impedance resonator is used to synthesize filters because it can create two tunable transmission zeros to suppress multi‐spurious responses in the upper stopband. The coupling coefficients of typical coupled pairs of resonators and the external quality factors of two basic feeding configurations are exploited in filter synthesis. A three‐pole Chebyshev filter and a four‐pole selective‐response filter are designed and fabricated herein. The first spurious peaks of these two experimental filters occur at five times and four times the operating frequency, respectively. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 187–191, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24866