A novel double-layer microstrip bandpass filter

This paper presents a new type of microstrip bandpass filter. It is realized in a double-layer configuration, as shown in fig. 1. This design makes use of the vertical dimension to achieve a size reduction over conventional microstrip parallel coupled bandpass filters [1]. These conventional filters have significant overall widths because the widths depend on the number of coupling sections. Also, they require very small spacings between the parallel coupled resonators which may be difficult to achieve in a fabrication process. The proposed new filter, with the overlaid resonators, is much narrower in overall width and does not require close spacings between resonators. An earlier study [2] investigated a modified parallel coupled microstrip bandpass filter with its topology somewhat similar to the one here. However, it is still a single layer structure and therefore the tight spacings between resonators are still essential.