Synthesis of Tri-Band Bandpass Filter Based on Frequency Transformation Using Tangent Function

In this paper, a tri-band bandpass filter design method was proposed. It is a coupling matrix synthesis method which provides a high freedom for setting zeros, order and bandwidth of each pass band for the first time. By mapping the single-band low pass prototype to the tri-band bandpass prototype using tangent function and then mapping the tri-band bandpass prototype to its practical frequency domain, a tri-band bandpass filter design can be realized finally. To validate the proposed method, a design in MATLAB was given at the end.