Modified coupled line trans-directional coupler with arbitrary power divisions and its application to a 180° hybrid

Abstract

A modified trans-directional (TRD) coupler for designing compact coupled line 180° hybrid with non-interspersed input/output ports is proposed. The modified TRD coupler which is composed of a coupled line and three different shunt capacitors features the characteristic of arbitrary power division and dc blocking. Design equations for the modified TRD coupler are derived using the ABCD matrix. Based on the modified TRD coupler and combined with the coupled line contra-directional (CTD) coupler, a novel coupled line 180° hybrid is constructed. It inherits the characteristics of the modified TRD coupler including arbitrary power division and dc blocking. Moreover, the input and output ports of the 180° hybrid are non-interspersed. In the topology of the proposed 180° hybrid, no bond wires, via holes or multilayer structures are required. The configuration of the 180° hybrid is analysed and the design equations are derived. Using the design equations, the coupling coefficients of the CTD and the modified TRD coupler can be flexibly chosen according to different fabrication conditions. As an example to validate the feature of the proposed 180° hybrids, two prototypes with 3 and 6 dB coupling coefficients are devised. The measured results are in good agreement with the simulated ones.