Abstract: A radiometer (100) uses the fringe pattern of an interferometer (110) to scan a scene to produce a time record from which a high-resolution radio frequency, or other radiation, distribution of the scene can be reconstructed. A matched filter (120), or other means, transforms the time record according to a function of a signature of the determinable scanning motion relative to the fringe pattern.For many applications, the modulation transfer function (123) of an included matched filter is the complex conjugate of the Fourier transform of the signature that would be produced by a constant point emitter scanned by the lobes of the interferometer fringe pattern.Two-dimensional reconstructions may be provided for by multiple scans at different orientations. Alternatively, frequency scanning or another scanning technique can provide resolution orthogonal to the fringe pattern scanning motion.

Abstract: A phased array antenna system (20; 120) having an array (22; 122) of radiating elements (24-30; H1-H32), such as pyramidal horns, and a distribution network (32; 124) connected thereto, has a dual mode of operation where each mode produces a composite beam which can and preferably does produce an identical far-field electromagnetic radiation pattern. The first composite beam is made up of a plurality of individual beams, forming a linear combination of excitation coefficients (a.sub.1 -a.sub.4) that are mathematically orthogonal to the linear combination of excitation coefficients (b.sub.1 -b.sub.4) of the individual beams of the other composite beam. A plurality of input ports (42-44; 176-178) are provided, and each composite beam is associated with an information-bearing input signal applied to one of the input ports.

Abstract: A satellite communication system employing a satellite in a geostationary orbit about the earth for communicating with ground stations disposed along a region of the earth positioned along an arc of a great circle of the earth. The satellite carries a frequency-scanning antenna array oriented for scanning a beam of electromagnetic radiation in one plane aligned with the arc of the great circle. Each position of the beam is formed with a different frequency of the radiation. The operating frequency of each ground station is selected to match the frequency of a beam directed from the satellite to the ground station. An antenna assembly formed of two confocal parabolic reflectors provides for a multiplication of the effective aperture of an array of radiating elements of the antenna, and also for a demagnification of a scan angle of radiation emanating from the array of radiating elements.

Abstract: Apparatus is provided for simultaneously rotating a plurality of parallel shafts connected, for example, to an array of rf switches that feed energy to or from an array of antenna feed horns. Each shaft is connected by a separate crank to a planar drive plate that is controllable moved relative to the switches in an orbiting fashion, to rotate the shafts in unison. The drive plate is controllably moved by a motor drive system that includes an orbiting motor secured to the plate and a base motor secured to a fixed substrate that houses the switches. The output shafts of the two motors are coupled together such that operation of either motor moves the orbiting motor, and thus the drive plate, in an orbiting motion about the base motor and substrate.

Abstract: A satellite communication system is disclosed that would allow for communication between mobile and fixed terminals. The communications system includes a plurality of mobile users, a satellite in geosynchronous orbit for providing frequency addressable uplink and downlink signals to the mobile terminals, a base station for receiving siganls from and transmitting signals to the satellite and a plurality of fixed users coupled to the base station. The system provides the advantage of frequency reusability and frequency addressability in the uplink and downlink transmissions of the mobile users.

Abstract: A receiver is disclosed for acquiring and tracking a data signal in a highly stressed environment. The receiver comprises first and second I.F. sections, a mixer for translation from the first I.F. frequency to the second I.F. frequency, a 2 kHz bandpass filter at the second I.F. frequency, signal translator for synchronous translation of the signal at the second I.F. frequency to baseband, a digitizer for complex sampling operation on the baseband signal, a microprocessor for processing the digital samples, and a numerically controlled oscillator coupled to the mixer and controlled by the microprocessor. The microprocessor formulates matched digital discrete Fourier transform filters which drive frequency, phase and symbol lock loops at the symbol rate. Each of the loop filters is formed by symbol-rate recursive, first-order equations.

Abstract: A spacecraft (100) such as a satellite, is shaped roughly in the form of a cup with a hollow inner cavity (106) such that a plurality of such spacecraft may be stowed for launch in a nested stack (204), thereby enabling a greater number of satellites to be launched simultaneously with a single launch vehicle (201). The cup-shaped configuration results from the satellite having a base member (105) with panels or side walls (101a, 101b, 101c) extending from portions of the perimeter of the base member at a non-zero angle thereto.

Abstract: A solar cell assembly wherein a solar cell is provided with electrical layer contacts for both the p-type semiconductor layer and the n-type semiconductor layer which are exposed on a top side of the solar cell, so that electrical contact to both layers can be made from the top side of the cell, and a glass cover overlying the solar cell includes a pair of U-shaped electrical cell contacts extending over the sides of the glass cover so that one leg of each U makes contact with one of the layer contacts and the other leg is accessible from the top of the cover glass. External electrical contact to the cell is easily and conveniently made, and cells can be electrically joined to adjacent cells in an array using a connector bar. The glass cover also supports the solar cell so that excess material on the substrate of the solar cell can be etched away to reduce the weight of the solar cell assembly.

Abstract: A system located on board a geosynchronous satellite for detecting spin axis precession and developing thruster control signals for restoring the spin axis to the desired attitude. Fuel economy is enhanced by performing the major attitude correction at a time when the fuel expended contributes to that required for orbit inclination control.

Abstract: A nutation sensor and nutation control system using a relative spin phase sensor in a dual-spin stabilized satellite is disclosed. The relative spin phase sensor provides index pulses indicative of the relative spin phase and rate between the satellite rotor and platform. Nutation of the satellite perturbs the relative spin position of the rotor and platform and means are provided for analyzing index pulse arrive times to calculate nutation of the satellite. In the nutation control system, means are provided to apply a nutation damping torque to the satellite.

Abstract: A radiometric imager for providing a series of registered images of a scene, each image corresponding to the radiation pattern for a unique, narrow frequency band. One embodiment includes a single frequency-dispersive linear antenna providing an output signal based on a series of conical fanbeams, with the antenna being controllably rocked about one axis and rotated about a perpendicular axis such that each fanbeam intersects each segment of the scene a plurality of times. In alternative embodiments, the imager includes a second frequency-dispersive linear antenna arranged in parallel with the first antenna to produce a fanbeam interferometer. Rocking movement of the two antennas coupled with either translation of the two antennas, rotation of the two antennas about an axis parallel with the antenna axes, or movement of the two antennas toward and away from each other, provides sufficient data to permit creation of the registered images.

Abstract: A method for estimating vehicle reference speed and acceleration utilizing an adaptive filter for providing periodically updated reference values given by a currently extrapolated value plus a correction term which is a function of current wheel slip, wheel acceleration and wheel velocity. The method may be successfully employed over a wide range of road friction coefficients and may be used for traction control as well as anti-skid braking, since the approach does not assure a fixed limiting wheel acceleration. The method avoids the necessity of maintaining low slip values on preselected wheels in order to obtain suitable reference speed values.

Abstract: A short slot waveguide hybrid coupler is disclosed wherein the coupling factor is switchable over a predetermined range of discrete coupling factors. A coupling slot formed in the common dividing wall between the contiguous first and second waveguides of the coupler allows coupling of electromagnetic energy between the two waveguides in accordance with a first coupling factor. A plurality of conductive pins are arranged for selective insertion into the coupling slot to effectively shorten the slot and thereby progressively reduce the coupling factor as more pins are inserted into the coupling slot.

Abstract: A method and apparatus for precisely determining the relative velocity of an interferometer and a scene being scanned. The apparatus uses a matched filter technique in which reference signals based on high and low relative velocity estimates are correlated with an incoming interferometer signal and controllably adjusted until the correlation is maximized. The controllably adjusted reference signals are then used to produce an extremely accurate and precise measurement of relative velocity.

Abstract: A direct digital frequency synthesizer including a counter circuit for receiving input signal pulses and for providing a corresponding output signal after receiving a number of input signal pulses, the number being selected based on the state of a control signal. The invention includes a circuit for generating a substantially random sequence of numbers and a comparator circuit for comparing a respective number of the substantially random numbers to a predetermined number and for providing the control signal in response thereto.

Abstract: An image processing system 10 includes an array (12) of detectors 14, each of which is designed to produce a current proportional to incident radiation. This system provides image processing at a viable sampling rate even for very large arrays and permits very efficient determination of single element detections.The modulation functions supplied from a weighted summer (18). The weighted summer applies an invertible matrix of weights to a series of orthonormal Walsh functions defined over a predetermined sampling interval, the Walsh functions being generated by a function generator (16).The modulated outputs of the array are combined by a summer (20) and distributed among parallel channels by a divider (22). Correlators (24) correlate the signal in each channel with a respective one of the original Walsh functions. The correlated outputs are digitized by analog-to-digital converters for transmission and processing by a digital processor (28).

Abstract: An optical nutation sensing method and apparatus is provided which is functional at low spin rates and during thruster firings while being relatively insensitive to spacecraft flexures. The advantageous operation of the present invention is afforded by provision of first and second beams of coherent light energy in opposite directions into a coil of optic fiber or other suitable means for restraining the path thereof. The coil lies in a plane normal to the transverse angular momentum vector. The beams are combined at the output ends of the coil in such a way as to create an interference pattern which varies as the satellite nutates. The variation in the interference pattern is detected by photodetector circuitry to provide an output signal representative of the nutation.

Abstract: A method of fabricating hollow square inner conductors having precise outer dimensions is disclosed. A first "u" shaped slot (10) is machined in a base plate (12) and a cover plate (16) is then brazed to the sloted surface (18). The cover plate (16) is machined to provide a first wall (20) of desired thickness. Second and third slots (22, 24) are machined in the base plate (12) parallel to the first slot (10) on opposite sides thereof to provide second and third walls (26, 28) of the hollow conductor (38). A sacrificial metal (30) having a melting point below that of the base plate metal is cast into the second and third slots (22, 24). A fourth wall (36) is formed by machining material from the base plate face (32) opposite the slotted surface (18). The sacrificial metal (30) is then removed to provide the hollow inner conductor (38) having precise outer dimensions (A, B).

Abstract: A microwave oscillator in a loop configuration comprises three substantially identical amplifier stages each having its own phase shift at a selected oscillating frequency. A transmission delay element having a phase shift at the selected oscillating frequency, is also in the loop configuration, so that the oscillator has zero phase shift around the loop at the oscillating frequency. Each amplifier stage has at least one active component with resistive feedback, which is connected to DC blocking and filtering capacitors. Capacitor values between 2.2 and 5.1 pf are used making the oscillator design amenable to cost effective conventional hybrid and semiconductor processes.

Abstract: A reconfigurable beam antenna system (12) comprises focusing means, a plurality of antenna elements (A, B, C, and D), a feed network (14), and a variable beam controlling means (16). The focusing means has a reflecting surface (18) which is adapted to reflect a plurality of electromagnetic energy signals. The feed network (14) comprises a plurality of feed ports (I1, I2, I3, and I4), a first plurality of hybrid couplers (30 and 32) connected to the feed ports, a plurality of phase shifters (34 and 36) connected to the first plurality of hybrid couplers, a second plurality of hybrid couplers 38 and 40 connected to both the first plurality of hybrid couplers and the phase shifters, and a plurality of antenna ports (01, 02, 03 and 04) connected to both the second plurality of hybrid couplers and the antenna elements (A, B, C, and D).