1. Continuously variable directional couplers in rectangular waveguide;Brodwin;IEEE Trans. Microwave Theory and Tech.,1963
2. Yamawaki and Sugiyama, Japan Patent S41-20378.
3. Tanaka, Hirooka and Ohshita: Variable-coupling InSb directional coupler, Nat'l Conv. Record of I.E.C.E., Japan, p. 824 (1974).
4. A variable directional coupler using InSb thin films;Tanaka;IEEE Trans. Microwave Theory and Tech.,1976