Research on the Parasitic Passband Suppression of Microstrip Stepped Impedance Resonator Filters

In this paper, the stepped impedance resonator filter is introduced whose parasitic passband, one of the key characteristics of stepped impedance resonator filter, is analyzed. Then, the methods to improve the parasitic passband suppression are proposed. The research shows that three different components: the lambda/4 open stub, the VIA and the resistance attached to the center of the stepped impedance resonator, can be used to suppress parasitic passband to some extent. After the comparison among these three methods, the conclusion is drawn that the stepped impedance resonator filter with a 10 Omega resistance loaded at the center of the resonator is the suitable choice for best frequency response.