Compact Broadband High-Directivity Microstrip Directional Coupler

B. M. Fabiani, E. S. Sakomura, T. A. B. Gripp, D. C. Nascimento


The difference between phase velocities of the odd and even modes in inhomogeneous microstrip coupled lines makes the microstrip directional coupler a poor device regarding directivity. In this work, this issue is successfully compensated by the addition of a matching network at the ports of coupled lines. Furthermore, the proposed matching network, composed of a single segment of microstrip line, was extensively studied providing significant insights for the design of a compact and broadband device. As result, simple design equations based on coupled lines S-parameters are obtained, as well as the achievable operation limits of the proposed matching network. Finally, in order to validate the proposed design methodology, a compact microstrip directional coupler is constructed to operate with directivity higher than 30 dB over a 4-GHz bandwidth.



Broadband, directional coupler, high-directivity, matching network, microstrip line

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