Frequency-spreading coupler

A wide band travelling wave amplifier is describes which includes an input waveguide coaxially disposed about an interaction waveguide. Both waveguides are tapered with the same direction of increasing cross-section. The interaction waveguide is a high-pass filter while the input waveguide is a low pass filter. The input waveguide is positioned relative to the interaction waveguide so that each cutoff plane in the input waveguide corresponding to a given frequency, omega(c), is displaced in the direction of increasing cross-section from a cutoff plane in the interaction waveguide corresponding to omega(c) where omega(c) is any frequency in the frequency band of the amplifier. A slot, disposed between the cutoff planes corresponding to omega(c) couples the omega(c) frequency component of an input wave from the input waveguide to the interaction waveguide.