Dual-Band Filter Synthesis with Frequency-Variant Couplings Based on Two Low-Pass Prototypes

In this paper, the frequency-variant coupling structure is applied for the first time to a two-passband filter based on two low-pass prototype functions, which allows for a simpler topology in addition to the different order, return loss and bandwidth of the different passbands. In this work, matrix synthesis method are given to implement asymmetric double passband filters with frequency-variant coupling. By using this method, the frequency-variant coupling matrix of the dual-passband filter can be obtained. The paper gives an example of a fifth-order, three-zero-point dual passband filter designed with two passband return losses less than 15 dB and 20 dB respectively.