Approach to the design of slot-coupled-line directional couplers

A novel approach to realization of slot-coupled-line directional couplers providing greater design flexibility, especially for higher frequency ranges, has been proposed. It has been shown that isolation and coupling level of the directional coupler can be improved by insertion of two uncoupled transmission lines of appropriate electrical lengths and impedance in-between two slot-coupled-line sections. The presented approach has been verified by EM simulations and measurements of 3-dB coupler operating at the center frequency f₀ = 24 GHz.