A Compact Very Narrow Band Coaxial Cavity Resonator Filter at X-band with SMA Connector Feed

A practical compact narrowband coaxial cavity filter with capacitively coupled feed at X-band has been presented here. The filter has about 1dB-bandwidth of 1.6% and very good rejection bandwidth. More than 30dB rejection is achieved at 220MHz offset from the centre frequency. Good harmonic rejection of more than 50dB is also achieved. A very simple feeding technique has been implemented.