Combline filter with tunable bandwidth and centre frequency

A new method for the design of tunable bandpass filters is presented. It is based on a dual-band combline structure. One of the passband responses centre frequency and bandwidth can be tuned without the need for coupling adjustment, while the other passband can be shifted up in frequency or filtered out. A prototype design has been constructed, and measured results shows wide tuning range and over 300% bandwidth adjustment range, clearly demonstrate the principle.