Wave Coupling by Warped Normal Modes

It is now well known that complete transfer of power can be effected from one to another of two waveguides provided there is distributed coupling between the waveguides and provided the phase velocities are equal. 1 ' 2 A good illustrative analog is a pair of coupled pendulums having the same period. The periods correspond to the wavelengths in the waveguides; passage of time for the pendulums corresponds to distance along the waveguides; the energies in the pendulums at a particular time correspond to the wave powers in the two waveguides at a particularly point along the waveguides. As energy is interchanged between pendulums with increasing time, power is interchanged between waveguides with distance. To obtain a complete interchange of power for the waveguides requires a particular length which is determined by the coupling. As long as the 1 S. E. Miller, Coupled Wave T h e o r y a n d Waveguide Applications, B . S . T . J . , 33, p. 661, M a y , 1954. See this p a p e r for a d d i t i o n a l bibliography on wave coupling. 2 B. M. Oliver, Directional E l e c t r o m a g n e t i c Couplers, Proc. I . I i . E . , 42, p. 1686, N o v . , 1954.