Wide-band distributed rf coupler

An rf traveling-wave amplifier including:

• a tapered interaction waveguide wherein the cross-section thereof gradually increases from a small first end thereof to a larger second end for propagating electromagnetic energy in a broad frequency band therein;
• an input waveguide disposed external to said interaction waveguide for providing electromagnetic waves to be amplified;
• a multiplexer distributed coupler circuit disposed external to said interaction waveguide for coupling electromagnetic energy from said input waveguide to said interaction waveguide comprising a plurality of channel frequency filters disposed outside said interaction waveguide, with each filter tuned to a different frequency passband, with each filter coupled to said interaction waveguide at a different appropriate cross-sectional position along the tapered length thereof such that the interaction waveguide cutoff frequency at that position approximately matches the wave frequency propagated by said filter so that electromagnetic energy propagated by the given filter will excite the desired mode of electromagnetic energy to propagate toward said larger second end of said interaction waveguide.