Pole-zero analysis window using prototype lowpass filter approximation approach can be used for any type (bandpass, bandstop, lowpass or highpass) of the designed filter to obtain the filter’s frequency responses to determine the stage, bandwidth, passband ripple and number of transmission zeros of the filter that meets all the requirements. For bandpass type filters, pairs of the equalization zeros can be added to improve the group delay response of the filter. Exact pole and zero locations of the desired filter can be obtained automatically or manually. In stead of checking the passband insertion loss and gain flatness of the filter with finite unloaded Q of the resonator or capacitor/inductor after the synthesis process, FilSynth can computer the effect of the finite Qu analytically at pole-zero stage so that the frequency responses of the filter can be determined precisely at beginning.

At pole-zero window or response window, the frequency responses of the lowpass prototype filter can be saved into memory for use during the optimization process.