New Types of Very Compact 90° ACPS Branchline Couplers using CPW Shunt Stubs

A very compact 90° ACPS branchline coupler for Ka/K-band, advanced SATCOM terminal systems is reported. The proposed method takes advantage of the integration of coplanar waveguide (CPW) shunt stubs and asymmetric coplanar stripline (ACPS) lines. The coupler does not use lumped inductors or capacitors and, consequently, has the advantages of excellent design accuracy even at high frequencies. In comparison to conventional hybrid couplers, this coupler offers lower insertion loss, higher compactness (a significant 55% reduction in circuit area) and does not require a CPW quarter wavelength transformer in order to overcome the input and output port characteristic impedances. Additional degrees of design freedom can be obtained by the inclusion of shunt CPW stubs and these are the reason for the major reduction in size. The reduced size couplers are potential building blocks for the growing wireless communications market.