Kwo R Chu

US Patent:

45338752, Aug 6, 1985

Filed:

Jun 16, 1982

Appl. No.:

6/389133

Inventors:

Yue-Ying Lau - Silver Spring MD
Kwo R. Chu - Annandale VA
Victor L. Granatstein - Silver Spring MD
Larry R. Barnett - Manassas VA

International Classification:

H01S 100
H01J 2308

US Classification:

330 4

Abstract:

A high power amplifier for amplifying millimeter-wave radiation comprising: a length of metallic waveguide tapered from a small cross-sectional end to a larger cross-sectional end; a magnetron-type electron injection gun for injecting a spiral beam of relativistic electrons at the small end of the waveguide for propagation axially therein so that the wall radius of the tapered waveguide increases in the downstream direction of the electron beam; an input coupler for launching electromagnetic waves to be amplified into the waveguide at the large waveguide end thereof such that the individual frequencies in the input waves are reflected at various points along the constriction of the waveguide taper so that they copropagate with and are amplified by the electron beam; and a magnetic circuit for generating an axial magnetic field within the tapered waveguide with a unique profile approximately in accordance with the following equation to maintain synchronism: ##EQU1## where the z subscript is the waveguide axial direction, the. perp. subscript designates the direction perpendicular to this axial direction, and the o subscript represents those quantities at the entrance point for the electron beam into the waveguide. This device has been found experimentally to have negligible launching loss and low sensitivity to electron velocity spread.

US Patent:

45674019, Jan 28, 1986

Filed:

Jun 12, 1982

Appl. No.:

6/389132

Inventors:

Larry R. Barnett - Manassas VA
Yue-Ying Lau - Silver Spring MD
Kwo R. Chu - Annandale VA
Victor L. Granatstein - Silver Spring MD

Assignee:

The United States of America as represented by the Secretary of the Navy - Washington DC

International Classification:

H01J 2538
H01J 2534

US Classification:

315 5

Abstract:

A wide-band distributed coupler for coupling rf energy from an input waveguide into a tapered interaction waveguide in a traveling-wave amplifier comprising a plurality of channel filters connecting between the input and interaction waveguides, with each filter coupled to the interaction waveguide at the appropriate cross-sectional position along its tapered length where the interaction waveguide cutoff frequency approximately matches the wave frequency propagated by the filter. Each filter comprises, in one embodiment, a main coaxial cavity tuned to a distinct center frequency, a first simple isolation cavity for coupling rf energy between the input waveguide and the main cavity, and at least one second simple isolation cavity for coupling energy between the main cavity and the tapered interaction waveguide. This coupler is compatible both in bandwidth and geometry with the tapered interaction waveguide.

US Patent:

43629687, Dec 7, 1982

Filed:

Jun 24, 1980

Appl. No.:

6/162702

Inventors:

Kwo R. Chu - Annandale VA
Phillip A. Sprangle - Silver Spring MD
Victor L. Granatstein - Silver Spring MD

Assignee:

The United States of America as represented by the Secretary of the Navy - Washington DC

International Classification:

H01J 2534

US Classification:

315 35

Abstract:

A slow-wave, cyclotron-type, travelling-wave-tube amplifier in which the m-wave interaction is the result of a Weibel-type instability. The travelling wave is slowed down in its propagation through the waveguide by a dielectric liner located on the inner wall of the waveguide. The bunching mechanism is the result of the V. sub. perp. . times. B. sub. perp. Lorentz force.

US Patent:

43769179, Mar 15, 1983

Filed:

Jun 25, 1980

Appl. No.:

6/163003

Inventors:

Achintya K. Ganguly - Alexandria VA
Kenneth L. Davis - Alexandria VA
Kwo R. Chu - Annandale VA

Assignee:

The United States of America as represented by the Secretary of the Navy - Washington DC

International Classification:

H01S 102

US Classification:

331 941

Abstract:

A solid-state cyclotron maser for generating low power (1 watt or less) signals in the submillimeter frequency range (300 GHz-30,000 GHz) includes an accelerating region, a drift region, and a metal grid therebetween. Both regions are formed from semiconductor material, such as indium antimonide, having non-parabolic energy bands. The drift region is a thin disc having metallized outer surfaces, but includes an annular opening in the metal on the front side and a circular opening in the metal on the back side, and is grounded. A grid of metal rings is placed on the annular opening of the drift region. The accelerating region is a hollow cylinder having a metallized front surface. It couples to the drift region for covering the annular opening and the grid. A negative bias voltage is applied to the accelerating region and a magnetic field is applied to the maser at an angle to the axis of the maser. Electrons propagate in spiral trajectories through the accelerating region, grid and drift region.

US Patent:

42245761, Sep 23, 1980

Filed:

Sep 19, 1978

Appl. No.:

5/943894

Inventors:

Victor L. Granatstein - Silver Spring MD
Phillip Sprangle - Silver Spring MD
Adam T. Drobot - Annandale VA
Kwo R. Chu - Annandale VA
J. Laurence Safter - Alexandria VA

Assignee:

The United States of America as represented by the Secretary of the Navy - Washington DC

International Classification:

H01S 100
H01J 2316

US Classification:

330 4

Abstract:

An apparatus for amplifying coherent radiation at millimeter and submillimeter wavelengths includes the combination of a travelling-wave-tube cyclotron-maser-amplifier structure and a magnetron-injection electron gun. The amplifier structure includes a fast-wave drift tube and an electromagnetic wave launcher within the bore of a superconducting magnet. The magnetron-injection electron gun is also within the bore of the magnet and is coupled to the drift tube. As a travelling wave is launched in a preferred mode in the drift tube, the electron gun injects an annular beam of relativistic electrons having both large energy transverse to the axis of the device and small energy spread into the drift tube so that the electrons gyrate at their cyclotron frequency in orbits about the lines of the axial magnetic field produced by the magnet. The travelling wave is amplified by extracting energy from the relativistic electron beam. Efficiency of this energy transfer is optimized by tapering the magnetic field near the output end of the wave-beam interaction region.

US Patent:

45544840, Nov 19, 1985

Filed:

Aug 29, 1983

Appl. No.:

6/527626

Inventors:

Michael E. Read - Oakton VA
Yuval Carmel - Haifa, IL
Kwo R. Chu - Annandale VA
Achintya K. Ganguly - Alexandria VA

Assignee:

The United States of America as represented by the Secretary of the Navy - Washington DC

International Classification:

H01J 2500

US Classification:

315 4

Abstract:

A complex cavity gyrotron designed for stable operation at high order modes. The device comprises circuitry for generating an annular electron beam, a coupled cavity disposed coaxially with the electron beam and having a first and second adjacent coaxial sections with the dimensions of these coaxial sections adjusted so that different modes with the same azimuthal eigen number but different radial eigen numbers are simultaneously resonant at approximately the same frequency in the two sections, and circuitry for generating an axial magnetic field within the cavity. Few, if any, combinations of modes other than the combination chosen will simultaneously resonate in the cavity thereby effecting higher order mode suppression. The present design has a low susceptibility to beam velocity spread and is effective for any combination of modes with identical azimuthal eigen numbers.

US Patent:

43706215, Jan 25, 1983

Filed:

Mar 11, 1980

Appl. No.:

6/129294

Inventors:

Phillip A. Sprangle - Silver Spring MD
Robert A. Smith - Washington DC
Kwo R. Chu - Annandale VA

Assignee:

The United States of America as represented by the Secretary of the Navy - Washington DC

International Classification:

H01S 400

US Classification:

330 4

Abstract:

An electron cyclotron maser high-frequency generator/amplifier having a cavity resonator positioned in an axial magnetic field. A spiralling beam of relativistic electrons is injected into the cavity and stimulated emission of radiation by the electrons takes place at the frequency of a wave mode supported by the cavity resonator. The transverse efficiency, defined as the average electron energy loss divided by its initial transverse energy, is maximized by disposing a shaped iron collar about the cavity resonator to provide an axial magnetic field in the cavity resonator whose amplitude increases in the beam direction-of-travel. In an alternative embodiment, the transverse efficiency is maximized by tapering the inner wall of the cavity in the axial direction to provide a wave-mode in the cavity resonator whose electric-field amplitude increases in the beam direction-of-travel.