WIDE BANDWIDTH COPLANAR WAVEGUIDE DIRECTIONAL COUPLER

Abstract

In this thesis, various types of directional couplers using coplanar waveguide technology have been investigated on the basis of quasi-static assumptions and some full-wave numerical results. The theoretical assumptions have been validated by experimental results and some practical designs have been presented. The interdigitated coplanar directional couplers based on conformal mapping technique introduced in this thesis have a more general structure with either even or odd number of coupled strips, finite substrate thickness and unequal strip or gap width. The ease and fast calculation makes it attractive to be used in CAD-oriented design tools. The application of equivalent line concept to the design of multiple-section broadband coplanar directional couplers has been verified by theoretical simulation and experimental measurement. The full-wave spectral-domain technique has been developed to analyse periodically nonuniform coplanar waveguide and the numerical results are verified by experimental measurements. Some practical designs of coplanar coupler and power divider have also been presented. From the theoretical studies and experimental results, the uniform coplanar directional couplers have better directivities and wider bandwidths than their microstrip counterparts. The additional parameter in coplanar structure makes the design more convenient and a large range of couplings with high directivity and wide bandwidth can be achieved using coplanar waveguides. Some future work is also suggested in this thesis.