The frequency characteristics of excitationsignals from the newgeneration weather radar at Urumchi before and after equipped with a bandpass filter are discussed, and the constituent structure and impedance transformation functions of the band pass filter are analyzed. Fourier transform is conducted on the excitationsignal function and responsesignal function, respectively, to gain the corresponding frequency function, which is then compared with the measurements. It is found out that that the installation of the bandpass filter brought about a satisfactory result, which can avoid radar microwave signal disturbance to other local microwave equipments due to the frequency band width of the radar.