Analysis on Transmission Zeros in Cross-Coupled Microstrip Filters

ABSTRACTThe reason of a pair of transmission zeros located near the passband of a cross-coupled microstrip filter is discussed. Moreover, with the use of tapped transmission line, another two transmission zeros are generated. To verify the analysis, a two-layer cross-coupled microstrip filter with tapped-line technique is developed, where four transmission zeros are found close to the passband, thus, realizing an enhanced filter selectivity. The two-layer cross-coupled microstrip filter is fabricated and examined experimentally. Measurements agree with the simulations.