Two branch-line couplers are introduced that utilize a combination of regular microstrip (MS) and negative-refractive-index (NRI) lines. Interesting phase compensation (0/spl deg/ phase shift) at the output port and a choice of /spl plusmn/90/spl deg/ phase shift at the through port, with respect to the input, are possible. On the other hand, one of the dimensions of the coupler is significantly reduced, compared to a corresponding conventional branch-line coupler, but without any bandwidth degradation.
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Islam et al. (2004) studied this question.
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