The present invention relates generally to millimeter and submillimeter wave amplifiers, and more particularly, to a traveling wave amplifier with a special wide-band distributed coupler therefor for wide-band operation at high power levels.
Information carrying systems such as radar and communications devices require an amplifier mechanism with substantial instantaneous bandwidth rather than simply an oscillation mechanism. In order to provide wide-band high power operation in traveling wave amplifiers, the use of a tapered interaction waveguide in conjunction with a specially profiled magnetic field has been proposed in Application Ser. No. 389,133, filed June 16, 1984, entitled "Wide-Band Gyrotron Traveling-Wave Amplifier" by Y. Y. Lau, L. R. Barnett, K. R. Chu, and V. H. Granatstein. The gyrotron traveling-wave amplifier disclosed therein comprises a tapered waveguide wherein the cross-section thereof gradually increases from a small first end to a larger second end for propagating electromagnetic energy therein, a magnetron device for generating a beam of relativistic electrons with helical electron motion for application to the small first end of the tapered waveguide to propagate in the axial direction therein, a magnetic circuit for generating a tapered magnetic field within the waveguide in a direction approximately parallel to the axis of the waveguide, and an input coupler for launching an input electromagnetic wave so that it co-propagates with the electron beam in the waveguide.
The above-mentioned waveguide is tapered such that its cutoff frequency varies over a predetermined bandwidth. This device then utilizes a reverse rf injection scheme wherein the electromagnetic wave to be amplified is applied at the large end of the tapered waveguide so that it propagates in the waveguide until its individual frequencies are reflected when they reach the point in the waveguide taper where they approximately match the cutoff frequency of the waveguide. These reflected frequencies then co-propagate with and are amplified by the electron beam. It can be seen that this type of coupling scheme will yield a good rf coupling efficiency into the tapered interaction waveguide.
However, in order to take full advantage of the very broad-band nature of this traveling wave amplifier, improved broad-band input couplers are required with a geometry compatible with the tapered interaction waveguide.