Design of Microwave Patch Hybrid Couplers with Arbitrary Power Ratio and Impedance Transformation

Xianshi JING  Sheng SUN  Lei ZHU  

Publication
IEICE TRANSACTIONS on Electronics   Vol.E98-C   No.7   pp.644-650
Publication Date: 2015/07/01
Online ISSN: 1745-1353
DOI: 10.1587/transele.E98.C.644
Type of Manuscript: Special Section PAPER (Special Section on Microwave and Millimeter-Wave Technology)
Category: Passive Circuits/Components
Keyword: 
branch-line couplers,  cross slots,  impedance transformer,  patch hybrid coupler,  power ratio,  

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Summary: 
A miniaturized patch hybrid coupler with arbitrary power ratio and impedance transformation is proposed and designed by loading a pair of asymmetric cross slots on a squared patch resonator. To obtain the arbitrary power ratio and impedance transformation, the rectangular size of stepped slot ends should be well designed to be asymmetry and thus to obtain the different inductive loadings along two current paths. Theoretically, the equivalent transmission line model is first developed to understand the physical relationship between the patch and traditional branch-line hybrids. The matching/isolation and power ratio conditions are then derived at center frequency. By following a detailed design guideline, a prototype of the hybrid with 1:2 power ratio and 1:1.3 impedance transformation is designed and fabricated at 4.2 GHz. The measured results show a good agreement with simulated results, where the measured -10 dB impedance bandwidth achieves 18% and the bandwidth of 90°±6° phase difference is about 35% in a frequency range from 3.5 GHz to 5 GHz.