Novel compact bandpass filters based on anisotropic artificial dielectrics

A contribution to development of compact and cost-effective bandpass filters in a multilayer substrate is presented. Miniaturization of the filters is achieved by a three-dimensional (3-D) design approach and an anisotropic artificial dielectric of a high permittivity. The 3-D approach is provided by the use of both a planar transmission line and a vertical interconnection formed by signal and ground vias. The artificial dielectric, occupying the vertical interconnection, is formed by a conductive plate connected to the signal via. Improvement of the electrical performance and controlling bandwidth in the filter is made by specific anisotropy of the artificial dielectric which is provided by corrugations of the conductive plates. Bandpass filters based on two types of corrugations have been presented. In the first type, the corrugations are oriented in parallel to the microstrip line connecting two signal vias, while in the second one they are perpendicular to the microstrip line. Simulation and measurement data, which are in a good agreement, show characteristic features of proposed components.