Directional coupler with high directional attenuation - has parallel strips on substrate with such thickness and permittivity as to equalise phase velocities of transverse electromagnetic waves

摘要

The coupler is in the form of planar, parallel coupled strip lines (1, 2) and has a slot in the metall coating (3) on the substrate underside (4), and a recess (5) in the supporting plate (6) below the substrate (7). Its cross-section geometry, while retaining advantages of simple micro-strip directional couplers, has such thickness and permittivity of the substrate, and required directional attenuation and frequency, that at a certain frequency (e. g. 3 GHz) the phase velocity of both TEM wave types taking part in the coupling are equal.