Tapered Velocity Couplers

S. E. Miller, Coupled Wave Theory and Waveguide Applications, B.S.T.J., 33, pp. 677-692, May, 1954. 1 Iii waveguide and transmission line networks, it is often desired to transfer power from one line to another. To this end, various hybrid junctions and ordinary directional couplers were developed some years ago. More recently, S. E. Miller has made use of the fact that when two transmission lines with equal phac? velocities are continuously coupled over some length, a signal introduced into one line will be completely transferred periodically back and forth between the lines. (Fig. 1.) This principle is employed in power-"splitting" devices where power is, for instance, equally divided between two lines. Half of the signal power is permitted to transfer from one line to the other and at this point the coupling is discontinued. (Fig. 2(a).) Another obvious application of this coupling principle is a means to effect complete transfer of a signal from one line to another. (Fig. 2(b).) Now the trend is toward systems which are capable of handling even greater bandwidths. Miller's approach to the problem of coupled waves has led to waveguide couplers which are useful over bandwidths of 25 per cent and better. However, with the advent of traveling-wave tube amplifiers and similar devices, useful bandwidths of two-to-one and more have become desirable. The bandwidth of the Miller scheme is limited because the strength of coupling and the electrical length of the coupling 1