Some Theory and Applications of Periodically Coupled Waves

In a previous paper it was shown that two parallel-traveling coupled waves can interact with complete power interchange even though they have different phase constants. 1 This is accomplished by introducing a variation in coupling in the direction of wave propagation. The ideal coupling variation is a pure phase variation whose period exactly matches the beat period between the uncoupled waves, however, it was also shown in that paper that a simple periodic magnitude variation of the coupling can also yield complete power interchange between waves having different phase constants. In this paper we outline some of the possible applications of periodic coupling. Complete power exchange between two modes of a single hollow metallic waveguide is illustrated. In two dielectric or hollow metallic waveguides, or in a combination of them, complete power exchange (or a desired fractional exchange) can be arranged. Frequency selective filters in the above structures can be obtained or broadband interactions can be chosen by suitable design. The periodic coupling phenomenon can be applied in lumped element parametric devices by modulating the pump waveform periodically; we give the 2189