Microwave Bandpass Filters Using Couplings With Defected Ground Structures

In this paper some novel types of microwave bandpass filters using defected ground structures are investigated. In the microstrip technology the use of defected ground structures (DGS) allows designs of filters with tight couplings, without the necessity of using very narrow coupling gaps. In multilayer filters DGS can be used as coupling elements between resonators, allowing very compact filter designs. A study of the couplings between two planar microstrip resonators in the presence of a DGS, and between two planar resonators located on different layers and separated through a DGS in a multilayer structure, is presented. Based on the results of the study some models of planar microwave bandpass filters were designed and simulated, with a single or with two slots etched in the ground plane. These novel filter structures show a good compactness and can offer some technological advantages, compared to the classical. Key-Words: microwave filters, defected ground structures, multilayer filters, extended coupling matrix, attenuation poles.