A novel compact microstrip dual-mode bandpass filter

In this article, a novel microstrip dual-mode bandpass filter is presented. The characteristics and the field patterns of the dual-mode resonator are investigated using full-wave electromagnetic simulations firstly. It is found that the response of this filter exhibits a desirable stopband response that the first spurious passband naturally occurs at 4f₀. Then the feed lines are designed in the structure of direct coupling, and this structure can reduce the radiation loss of the filter. Finally, a dual-mode filter is optimally designed, fabricated and measured. Both simulated and measured results are given and compared.