Abstract: A field effect transistor (FET) structure suitable for use at microwave frequencies is fabricated on a planar surface of a semi-insulating single crystal GaAs substrate which has been cut and polished to present the (110) surface. This orientation is selected because of its non-polar and other unique surface and interface properties. The (110) crystal axis is tilted from the normal of the planar surface in the direction to expose more of the (111) Ga face about 5.degree. to facilitate molecular beam epitaxial (MBE) growth of smooth, defect-free thin films. An elongate gate electrode is formed along the bottom of an anisotropically etched trench having a pair of longitudinal sidewalls, one vertical and the other tilted outwardly. The trench is selectively oriented on the substrate to facilitate such anisotropic etching.

Abstract: An image intensifier tube comprising an input screen assembly which includes a photosensitive semiconductor wafer having a substrate of one conductivity type material forming a plurality of P-N junctions with a planar array of mutually isolated islands of opposite conductivity type material, the islands protruding substantially equal distances from a common surface of the substrate, an opaque film of resistive material overlying the exposed areas of the islands and the common surface of the substrate, a layer of electroluminescent material disposed in abutting relationship with the distal ends of the islands and a layer of photoemissive material disposed in axially aligned relationship with the electroluminescent layer.

Abstract: An RF-AM transmitter of the type including a power pulse amplifier driving an RF amplifier with a modulating voltage via a low pass filter includes a pulse width modulator for deriving variable frequency pulses having a frequency that is a direct function of an RMS like function of the amplitude and frequency of an information source; the width of the pulses is determined by the instantaneous amplitude of the information signal source. The pulse width modulator includes a constant amplitude, variable frequency triangular wave voltage controlled oscillator responsive to a DC signal representing the frequency and amplitude of the information source. In response to amplitude crossovers between the variable frequency triangular wave and the information source, transitions in the pulse width modulated wave are derived.

Abstract: A size sensing X-ray cassette tray having a pair of longitudinally spaced opposing front and back cassette clamps linked together by a center pivoted arm and link members for unison movement. A side sensing arm is connected by an elongatable link member to a pivoted leg which is actuated by a probe of an X-ray system. Arcuate potentiometers are coupled to the pivoted arm and the side sensing arm so as to provide electric signals corresponding to the x and y dimensions of a mounted cassette. The potentiometers are nonlinear so as to provide respective cosine and sine correction and thereby make the output signals substantially linear with the dimensions of sensed cassettes.

Abstract: An x-ray rotor structure wherein a target support stem has an externally threaded end portion brazed to an internally threaded surface of an encircling bushing which is provided with a barrier layer of oxidation restricting material. The stem is made of predominantly molybdenum material and the bushing is made of iron cobalt nickel alloy material having therein a small percentage by weight of titanium. The barrier layer comprises a layer of substantially pure nickel material which coats the entire inner surface of the bushing including the internally threaded portion thereof. Thus, the titanium is restricted from leaching to the surface during brazing and forming oxides which prevent the surface from being completely wetted by the brazing material. As a result, during brazing, the liquified brazing material alloys with the nickel material of the barrier layer to wet the inner surface of the bushing completely.

Abstract: A counterflow helium mass spectrometer leak detector in which a helium sample passes in a reverse direction through a diffusion pump to a mass spectrometer for measurement. The diffusion pump includes a conventional foreline and a second foreline provided with an ejector stage. A test sample is coupled from a test port through a bypass valve to the conventional foreline in a high sensitivity mode and is coupled to the second foreline in a low sensitivity mode. In the low sensitivity mode, the bypass valve is closed. An apertured control plate in the diffusion pump controls the relative reverse rates of duffusion from each foreline to the diffusion pump inlet by controlling the rates of vapor flow an annular pumping stages and to the ejector stage. The ejector stage includes a nozzle for directing a stream of vapor into the second foreline so as to inhibit flow of helium into the diffusion pump and establish a lower reverse diffusion rate at the second foreline.

Abstract: A loop directional RF coupler between a waveguide and coaxial line maintains a high degree of directivity while providing substantially improved coupling values. A conductive loop assembly terminating the coaxial line is accepted into an aperture means defining an aperture in one wall of the waveguide section of the coupler. The aperture is greater in diameter than the largest transverse dimension of the loop, or of the loop assembly. A capacitive or inductive conductive obstacle is affixed to an interior wall of the waveguide section adjacent the aperture. A second conductive obstacle is positioned downstream of the first obstacle to compensate any mismatch.

Abstract: A two-stage cryosorption pump has a first stage at a higher temperature and a second stage at a lower temperature. Sorption surfaces of reticulated vitreous carbon formed on the second stage have high rigidity and exceptionally high void volume.

Abstract: A millimeter wave wideband circulator which employs a triangular ferrite prism with symmetrically grooved sides. The prism is configured to support a pair of closely-spaced higher order resonance mode sets which function to enlarge the bandwidth of the circulator and to suppress spurious mode resonances in the center and roll-off portions of the bandpass. The simplicity of the junction design combined with the non-critical alignment requirement of the ferrite prism makes practical the fabrication of a multi-junction millimeter wave circulator in a single integrated housing.

Abstract: An RF-AM transmitter includes a pulse amplifier responsive to a pulse width modulated (PWM) signal derived in response to an information signal. A low pass filter converts pulses derived by the power amplifier into a variable amplitude signal that is DC coupled to a power supply for an RF amplifier. An amplifier system including the pulse and RF amplifiers has stray capacitance coupled to a modulator which derives the PWM signal; the stray capacitance lengthens narrow modulator output pulses so they are excessively long. The amplitude of only the narrow pulses is reduced by a resistor-capacitor timing circuit in series with a switch to substantially preserve the narrow pulse area. The switch provides a low impedance path from the timing circuit to a reference potential terminal when current initially flows in the circuit during pulse transitions and throughout the length of each of the short duration pulses.

Abstract: A sputter coating source has separate annular targets spaced outwardly from each other around a central axis. Magnetic field generating means are provided to establish magnetic field lines over each target around an annular path. Each target has its own separate magnetic field generating means including an electromagnet having a separately controllable power supply whereby the strength of the magnetic field over each target may be separately controlled. The targets are electrically separated from each other, and each target has a separately controllable power supply whereby the plasma power for each target may be separately controlled. More than two separate targets may be employed, and the various targets may be positioned at different distances from the substrate. The targets may be made of magnetic material.

Abstract: A pressure sealed waveguide to coaxial line connection formed with a low cost, non-pressurizable waveguide to coaxial line adapter, an elastomeric sealing boot, and a specially configured mounting seat on a housing which contains a pressurizable waveguide cavity. The connection provides a low cost alternative to hermetically sealed waveguide to coaxial line adapters.

Abstract: A helium mass spectrometer leak detector includes a spectrometer tube connected to the inlet of a high vacuum pump. Helium tracer gas passes in reverse direction through the high vacuum pump from the foreline to the spectrometer tube. Relatively high pressure gross leak tests are performed, while maintaining the foreline of the high vacuum pump at the required operating pressure of about 100 millitorr, by passing the tracer gas in reverse direction through one or two stages of a mechanical vacuum pump. Test port pressures up to about atmosphere can be accommodated, with only a single mechanical vacuum pump required. According to another feature, high test port pressures are accommodated using a variable flow restrictor and reverse-connected mechanical vacuum pump in combination.