Aperture Coupling Between Dielectric Image Lines

Aperture coupling between dielectric image lines is used develop a design technique for directional couplers at millimeter-wave frequencies. Expressions for coupling coefficients and directivity, employing coupling between image lines through apertures in the common ground plane are developed. The design procedure is illustrated by application 10-, 20-, and 30-dB directional couplers in rectangular image lines with circular aperture coupling.