Design of Dual-band Cavity Filter Using Frequency Transformation Method

This paper presents two different dual-band cavity filters based on the frequency transformation. The cavity filters have two different configurations. The one is presented by directed coupling between adjacent resonators, and the other one is presented by introduced cross coupling between nonadjacent resonators to generate a pair of transmission zeros. At first, according to the filter specification the coupling coefficients between resonators and the external quality factors are calculated and obtained. Then the model of the dual-band cavity filters are established with Ansoft HFSS, the simulation result agrees well with the result of equal circuit in ADS, indicating that this method is correct and feasible. Finally, the comparison between the cascade type structure and cross coupling type structure shows that the later has more excellent stopband performance.