A New Class of High Performance Broadband 3 db Directional Couplers in Thin Film Technique

It is the purpose of this paper to show that planar broad-band 3 db directional couplers can be constructed in micro-strip-slot and thin film technique, etching both sides of a ceramic substrate. No overlapping or bonding wires are needed and the dimensions of the layout are by no means critical. An accurate, straightforward and closed form theory, which has been developed for this type of coupler, allows 3 db couplers to be constructed whose measured performance is within a few tenths of db of the predicted performance. The measured insertion loss of these couplers, including the connector losses, is as low as 0.3 db in C-band and 0.6 db in X-band. The ±0.5 db bandwidth is approximately one octave and the isolation of the coupler is better than 30 db over this band.