Customizable Design of Multiport Reflectometers Targeting Arbitrary Smith Chart Regions

This article presents a novel design approach for a multiport reflectometer that enables region-specific optimization over arbitrary regions of interest (ROIs) on the Smith chart. The proposed algorithm constructs four statistical objective functions that capture average error, error uniformity, worst case deviation, and high-risk outlier performance. These competing objectives are jointly optimized using a Pareto-based approach to yield nondominated center distributions. The proposed method is first validated on two geometrically symmetric ROIs, where it generates optimized center distributions that match or outperform prior heuristic-based designs. It is then applied to a highly asymmetric ROI, for which conventional geometric strategies fail. A customized five-port reflectometer implementing the customized center distribution is fabricated using microstrip weakly coupled-line couplers. For comparison, a referenced reflectometer with a globally optimal center distribution layout is also realized. Both prototypes are calibrated and tested at 1GHz. Results show that the customized design significantly improves measurement accuracy within the target ROI, reducing both the average magnitude error from 0.62 to 0.08dB and phase error from 5.67° to 0.86°. The approach offers a flexible and scalable framework for the customized designs of multiport reflectometers tailored to specific measurement requirements and serves as a practical reference for integrated reflectometry systems in emerging low-cost applications.