Rapid Dimension Scaling of Miniaturized Microstrip Couplers with Respect to Operating Conditions and Substrate Parameters

A simple, reliable methodology for geometry parameter scaling of compact microstrip couplers is presented. Our approach allows for rapid re-design of the structure with respect to the operating conditions (operating frequency and power split ratio) as well as material parameters of the dielectric substrate (permittivity and thickness). The scaling process involves an inverse surrogate model constructed from a set of optimized reference designs obtained at the level of the equivalent circuit representation of the coupler, as well as an iterative correction procedure for fine tuning of the design. A demonstration example of a compact rat-race coupler indicates that accurate dimension scaling can be achieved at a low cost of up to three EM simulations of the structure, for a wide range of operating conditions (1 GHz to 2 GHz for the operating frequency, -3 dB to 0 dB for power split) and substrate parameters (0.7 mm to 1.5 mm for the thickness, and 2.5 to 3.5 for dielectric permittivity).