Abstract
A novel backward microstrip coupled-line coupler which has been designed based on the metamaterial and composite right/left handed (CRLH) transmission line (TL) concepts is proposed. Coupling coefficient, bandwidth and size of proposed microstrip coupler are improved by coupled interdigital TLs which have been realized only by one interdigital capacitor. The design procedure to reach the coupler with predefined coupling coefficient and characteristic impedance of its ports is clearly presented. The designed and fabricated prototype is a 3-dB microstrip coupler with 0.2 mm spacing between its coupled lines over a wide bandwidth of 60% from 2. 3∼ 4 GHz centered at 3.2 GHz. The coupled-line length and the width of the proposed structure are approximately λg/4 and λg/36, respectively, which makes it more compact than the conventional cascaded CRLH microstrip coupledline couplers.
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