New Types of 3-dB Directional Couplers of Microstrip Transmission Lines

In this paper the author has brought forward three new types of 3-dB directional couplers suitable to microstrip circuit. The originality of these couplers is that by using these couplers extraordinary close coupling which is less than 1-d/sup B/ can easily be achieved. An analysis is given to the electric field distribution and the characteristic impedance of the coupling circuit. The designing curves and the design of the 3-dB coupler with experimental data are provided in the paper.