New parallel /spl lambda//2-microstrip line filters with transmission zeros at finite frequencies

The paper presents a new class of /spl lambda//2-microstrip line filters with transmission zeros at finite frequencies. The filters take advantage of the difference between the propagation constants of the even and odd modes of two symmetric coupled microstrip lines to generate the transmission zeros in addition to the reflection zeros of the passband. A simple model is used to show that the transmission zeros are not due to cross-coupling of nonadjacent resonators but rather to internal anti-resonances in the structure. The results obtained from a full-wave solution using a commercial software package are in good agreement with those of the model. Examples of filters with transmission zeros in the lower or upper stop-bands are presented.