Bandwidth-size design trade-offs for compact spline-parameterised patch couplers by means of electromagnetic-driven multi-objective optimisation

摘要

Broad bandwidth and small size are the key performance figures for contemporary microwave couplers. These requirements are conflicting, i. e. improvement of one generally leads to degradation of the other assuming fixed topology of the circuit at hand. From a designer's perspective, the knowledge about available design trade-offs is indispensable as it permits for tailoring the circuit for particular applications as well as comparing alternative coupler topologies in a conclusive manner. In this work, investigations of design trade-offs for a miniaturised spline-parameterised patch coupler (PC) are carried out. By means of rigorous surrogate-assisted multi-objective optimisation, a set of designs that represent the best possible compromises between the coupler bandwidth and miniaturisation rates are obtained and analysed. To maintain the computational cost of the design process at acceptable levels, despite a large number of geometry parameters, sequential domain patching is utilised as the optimisation engine. A re-tuning process that involves local approximation surrogates supplements identification of the initial design set. For the sake of illustration, a hybrid PC operating at 5.6 GHz is considered. The set of designs found for this circuit represent trade-offs spanning from 0.9 GHz to over 1.8 GHz (bandwidth) and from 360 to 517 mm2 (footprint area).