Modeling and performance improvement of folded coupled lines in miniaturized Quasi‐lumped directional couplers

An efficient modeling method for folded coupled inductors for application in quasi-lumped directional couplers designed in both symmetric and asymmetric structures has been proposed. The presented model takes into account the deteriorative effects which occur when coupled inductors realized as electrically short coupled-lines matched to the high impedance standard are folded into, for example, meander or spiral pattern. The deteriorative influence of coupled-lines' folding on the performance of the resulting directional coupler has been modeled as additional lumped inductors and capacitors on the schematic diagram of a quasi-lumped directional coupler's subsection. Moreover, it has been shown that this deteriorative influence can be substantially minimized when values of lumped elements constituting the directional coupler are appropriately changed. The proposed design procedure has been experimentally verified by measurements of two 3-dB single-section directional couplers designed in symmetric and asymmetric structures as quasi-lumped couplers with folded coupled inductors. The measurement results show a good agreement with both circuit and electromagnetic analysis which proves the correctness and usefulness of the presented methods. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:1–9, 2015.

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