Harmonic suppressed single groove PCML bandpass filter

This paper presents the design of single grooved parallel-coupled microstrip bandpass filter with improved passband response and first harmonic suppression. The undesired first harmonic spurious response is suppressed through transmission zero frequency realignment method. A single groove is located at the center of the parallel-coupled line. It is employed for the realignment of the transmission zero and first harmonic frequencies. Two three-stage bandpass filters of different operating bandwidths were designed and implemented with optimized groove. The measured results validate real harmonics suppression performance with controllable single groove dimensions.