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In this work, a step-by-step development of a compact microstrip rat-race coupler (RRC) has been presented and discussed. A high degree of miniaturization has been obtained by substituting six quarter-wavelength uniform atomic building blocks of a RRC by their nonuniform counterparts. The miniaturization procedure has been realized in three progressive steps: (i) the first layout solution of a miniaturized RRC has been acquired using an accurate mathematical model of a nonuniform transmission line (NUTL); (ii) the second layout solution has been obtained by a manual refinement and electro-magnetic (EM) fine-tuning of the NUTL geometry aimed at the utilization of the interior of the RRC in a highly efficient manner; (iii) the final layout, occupying only 8.5% estate area in comparison to a conventional RRC, is the result of the EM optimization. The experimental results confirm the theoretical predictions, proving the vital usefulness of the approach.
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Bekasiewicz et al. (2014) studied this question.
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