Development of a compact microstrip resonant cell aimed at efficient microwave component size reduction

A comprehensive comparison of a wide collection of compact microstrip resonant cells (CMRCs) found in the extensive body of literature has been presented. The evaluation of different CMRC designs has led to the selection of the most promising CMRC geometry for the efficient miniaturisation of modern microwave components. To showcase the vital effectiveness of the approach, the initially selected CMRC has been notably improved and applied to an exemplary microwave component, that is, a branch-line coupler, to obtain its size reduction without degradation in its performance. Exemplary prototype circuits have been designed to mimic the frequency characteristics of a classic coupler, simultaneously presenting a substantial 75, 80 and 85% surface area reduction. The best solution obtained has been experimentally validated. The measured in-band results are in excellent accordance with the theoretical characteristics, whereas the broadband performance depicts an additional effect, that is, the strong suppression of unwanted signals in 2.6-7 GHz frequency band. The multi-step CMRC evaluation and improvement procedure proposed presents an efficient design methodology for novel compact circuit topologies developed in microstrip technology.