Bibliography on Directional Couplers, 1935-1953

Active DC directional couplers

“…The literature is extensive; four bibliographies [1]- [4] list approximately 400 references, almost all of which deal with transmission line or waveguide directional couplers. In addition, there are numerous references on telephone hybrid circuits, which are one-half of a directional coupler located at the end of a transmission line.…”