Aperture Couplings in Multilayer Filtering Structures

In multilayer structures apertures in metallic sheets can be used as coupling elements between resonators located on different layers, allowing very compact filter designs. In this paper, some novel types of planar microwave bandpass filters, using aperture couplings, in structures with three metallic layers, are considered. Couplings between two miniaturized resonators are investigated, by full electromagnetic field simulation. Based on the results of this study, several models of planar microwave bandpass filters, with a single or with two apertures, are designed, verified by simulation, fabricated and measured. Compared to the classical filters, these novel structures show a good compactness and can offer some technological advantages.