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Abstract
Trans-directional (TRD) couplers with capacitor-shunted ground-defected coupled coplanar waveguides (CPWs) and inductor-loaded asymmetric coplanar waveguides are proposed for weak coupling applications. To achieve weak coupling as well as perfect impedance match, unequal shunt capacitors and same series inductors are loaded on the coupled CPWs. In addition, a defected-ground structure is etched under the coupled CPWs for realizing high-impedance coupled lines with the printed circuit board technology. Two TRD couplers with coupling values of 10 and 20 dB are investigated theoretically and experimentally. The measured results show that the directivity of the proposed TRD coupler is better than that of conventional parallel-coupled microstrip-line coupler.
Acknowledgments
This work was supported jointly by the National Natural Science Foundation of China (No. 61071044), the Traffic Applied Basic Research Project of the Ministry of Transport of China (No. 2010-329-225-030), the Fundamental Research Funds for the Central Universities (No. 2012TD007), and the National Key Technologies R&D Program of China (No. 2012BAH36B01).