http://orcid.org/0000-0003-3276-8463
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Abstract
The relation between load impedances and the characteristic impedance of the rat-race ring has been derived. To minimize the circuit size, the 270°-long section has been replaced by a shorted coupled-line section. Moreover, to achieve appropriate coupling coefficient in the required coupled-line section, a modified Lange structure consisting of five-coupled lines has been applied. Furthermore, the second structure has been proposed having improved operational bandwidth, in which coupled-line matching sections are added. The theoretical analysis has been verified by measurements of the fabricated rat-race couplers operating at the center frequency 1 GHz. The designed couplers transforms 50 Ω input impedance into 10 Ω, which proves their practical applications.