Effect of I/O Capacitor on Properties of Coaxial Filter Coupled with a Hole

In order to improve properties of filter,the method of adjusting two-pole dielectric coaxial filter coupled with a hole had been developed.The relationships between frequency and loaded Q value of coupled dielectric resonator and I/O coupling capacitors were theoretically analyzed.Two-pole dielectric filter coupled with a hole was made of microwave dielectric ceramics with er=74.The method of adjusting filter was discussed specifically by observing the S11 wave pattern.The results showed that S11 wave pattern and amplitude could reflect if I/O coupling capacitors were appropriate or not.Finally,the filter with the following characteristics was made: center frequency 902 MHz,pass-band width 13.2 MHz,stop-band attenuation at f0±40 MHz higher than 24.9 dB.The adjusting technique was proved useful for more than two-pole dielectric filters.