Optimization design of UWB passive bandpass filter's standing wave ratio

The filter's voltage standing-wave ratio (VSWR) cannot be designed by network synthesis method, so the optimal design method of a filter's VSWR with termination capacitance is proposed in this paper. Based on the circuit designed by network synthesis method, parallel inductance was transformed to series inductance and parallel capacitances in the input and output ports of the circuit. Then optimize the circuit by unconstrained optimization method so that the filter's amplitude-frequency can be arithmetic symmetrical and VSWR is close to 1. The simulation result indicates that the optimal method can make not only the filter amplitude-frequency arithmetic symmetrical, but also the max value of VSWR just 1.0399, the max value of group delay ripple is 2.1374 ns and the max passband ripple is 0.001626 dB, furthermore relative bandwidth exceeds 83%.