Compact tunable bandpass filter with wide tuning range using ring resonator and short-ended coupled lines

A tunable bandpass filter with wide tuning ranges for both the centre frequency and bandwidth is presented. The filter is based on using a ring resonator connected to a short-ended coupled-line structure. Two transmission zeros are generated in the upper stopband resulting in a sharp cutoff and harmonic suppression across a wide stopband. A thorough procedure is used to analyse the proposed filter. A prototype is fabricated and tested. The achieved results indicate a wide centre frequency and bandwidth tuning ranges of 0.52-1.42 GHz and 90-320 MHz, respectively.