Abstract
The theme of this work has been multilayer microwave circuits, and has focused on two aspects, namely multilayer interconnects and multilayer antennas. The report provides a detailed analysis of unwanted coupling in multilayer interconnections. New data are presented on the effects of coupling between conductors in highly integrated, multilayer circuits working at frequencies up to 100 GHz. Whilst multilayer circuits greatly reduce the circuit size, they introduce unwanted coupling between transmission lines at different levels of the multilayer structure. The unwanted coupling due to high packing density may detract from the electrical performance of the multilayer package, and this is becoming a critical design consideration. To achieve signal transmission with minimal interference, the coupling between adjacent lines should be minimized. Using a combination of electromagnetic simulation and practical measurement criteria for the optimum spacing of conductors in multilayer ceramic packages has been established. The work was based around the use of photoimageable thick-film conductors and dielectrics; the dielectric had a relative permittivity of 3.9 - 8 and the conductors were silver. Three situations were considered; a cross-over structure, a parallel coupled line structure and a right angle bend structure, all in a multilayer configuration. All of these geometries were modelled using an electromagnetic simulator (ADS - Momentum), and the results of simulation were confirmed by practical measurement. The practical circuits were fabricated on alumina, with the crossover and coupled lines built up with successive layers of photoimageable thick-film paste. Using the experimental data, general design rules have been developed to summarize the results and provide guidance to the circuit designer on the minimum spacing between conductors in a multilayer package. These design guidelines were then exploited to produce some novel antenna structures using multilayer techniques. The antenna designs were fabricated using polymer and RT/Duroid materials with frequencies ranging from 10-20GHz. Data are presented on the practical performance of the novel antennas, which are five novel variations of an antenna based on a travelling wave feed system namely: radiation enhanced travelling wave feed circular polarized antenna; dual-ring multilayer circular polarized antenna; split-ring triplate antenna; multilayer circular polarized active beam steering antenna; compact quadruple polarized concentric ring array.