Moment method of computing equivalent circuit of coplanar waveguide T-junction

Abstract

For some of its advantages, the coplanar waveguide (CPW) is preferred to the microstrip line in developing monolithic microwave integrated circuits (MMICs). However, due to lack of powerful design software, the potentials of this line have not been fully exploited. This paper introduces a computer technique for the determination of the equivalent circuit of the CPW T-junction. It can be extended to find the equivalent circuits of CPW bends, terminations, steps etc. The technique is based on the assumption of the quasi-TEM wave propagation in the CPW structure. The electric and magnetic fields around the junction are derived from electric and magnetic potentials which are the solutions of the Laplace equation. These solutions are achieved using the spectral domain formulation in conjunction with the moment method. Results presented include the equivalent circuit of a T-junction which was evaluated in order to find its scattering parameters when the junction is shorted at one of its ports. These parameters are compared with those obtained by an electromagnetic simulator, and with those measured.