Wide Stopband Planar Microwave Bandpass Filter Design

Muhammad Riaz, Bal S Virdee


This paper describes a high selectivity microstrip bandpass filter fabricated using microstrip integrated technology with a wide stopband. The proposed filter consists of electromagnetically coupled 50Ω input and output feedlines that are strategically loaded with spiral inductors in order to introduce transmission zeros in the filter’s stopband response. Simulation results reveal that the proposed design enables the upper and lower transmission zeros to be adjustable independently by (±16.5%) prior to fabrication. Moreover, the coupling scheme employed allows the filter’s centre frequency to be adjusted by 8.69% and 3dB fractional bandwidth by 7.1% with insignificant effect on the stopband characteristics. The measured result confirms the filter exhibits a relatively sharp roll-off skirt with a passband insertion-loss of 1.51 dB and return-loss that is better than 15 dB. The proposed filter is suitable for applications in high interference environments and cognitive radio systems.


Planar filters, microstrip integrated technology, microwave filters, high selectivity filters, wide out-of-band rejection

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DOI: http://dx.doi.org/10.22385/jctecs.v31i0.313