Practical design of microstrip directional couplers

A practical method to have a complete design of symmetrical two-line microstrip directional couplers is given analytically without prior knowledge of the physical geometry for the first time. The design method requires only the information of the port impedances, coupling and operational frequency. The analytical results are verified experimentally. The error between the measured and analytical results is found to be within 3%. The design tables and the measured results are presented for Teflon, and FR4, which are widely used in microwave applications