Six-port Microstrip Ring Coupler

Model

The symmetrical six-port junction has been designed for use as a five-way equal power divider and utilized in a six-port reflectometer setup. The six-port coupler can be implemented in different forms such as a ring structure, double-ring structure or ring-with-star structure. The thickness of the substrate is 2.30 mm and the relative dielectric constant is 2.5. Edge sources are used to feed the microstrip line at all ports.

Simulation

A template broadband simulation is prepared by using six edge sources and six ports. The conformal FDTD solver is employed. Then, the S-parameter Simulation Setup tool is applied to build six simulations to extract the six-port S-parameters of the ring coupler. The maximum grid step is 1.7 mm and the minimum grid step is 0.05 mm in the frequency region of interest. The UPML absorbing boundary conditions are used to truncate the domain.

Results

The six-port S-parameters of the ring coupler is obtained by using the S-parameter Evaluation tool. The second figure shows simulated frequency response of the coupler. The structure is matched and its bandwidth can be further broadened by implementing, for example, double-ring-with-star structure. The couplings to the other ports are symmetrical, i.e., S21 = S61 , S31 = S51.

Ref. S. P. Yeo, et. al., First-Order Model of Symmetrical Six-Port Microstrip Ring Coupler, IEEE Tran. Microwave Theory and Tech., vol. 39, no. 9, Sept. 1991.