Abstract: An automatically adjustable equalizer for modifying the spectral contour of digital, analog, and magnetically recorded signals. A temperature sensor-controlled switching circuit automatically adjusts the delay and forward gain parameters of the equalizer so as to optimize the equalization contour, in discrete ranges, over a wide range of temperatures, pressures or other physical processes or conditions.

Abstract: The 2.times.2 bypass switch utilizes a single polarizing beam splitter and a 90.degree. polarization twist layer of liquid crystal held between two right angle prisms. The outer surfaces of the prisms provide a series of total internal reflections to direct light about the switch so that a single polarizing beam splitter may be employed to divide an incident beam into two counter-rotating orthogonally polarized beams and to recombine the beam at the switch selective output port. A compound switch is realized by double folding the optical path in two parallel planes in one embodiment and along parallel paths in the incident plane in another embodiment.

Abstract: In a stabilized gyrocompass having meridian seeking gyroscopic means and slaved horizontal gryoscopic means disposed upon a common platform, a signal representative of the angle which develops between the meridian seeking gyro and the platform in response to the dynamic effects of the vehicle is generated. The generated angle is proportional to the northerly inertial velocity term and is used to control the platform in azimuth, thereby providing a dynamically correct stabilized gyrocompass without the use of accelerometers or gravity sensors which are conventional in the art.

Abstract: The Controlled Return to A.C. (CRA) magnetic recording and reproducing system applies a high frequency erase signal continuously to the write head except at the detents. At the detents polarity controlled interruptions of the high frequency erase signal are embedded therein. A positive interruption, a negative interruption and the absence of an interruption provides a ternary recording capability at the detent. The high frequency erase signal is controlled in phase to provide polarity coherent interruptions. A CRA cell includes two controlled interruptions providing a mapping of three binary digits into two CRA digits. The controlled interruption results in an opposite polarity pulse pair upon readback.

Abstract: A range profile classifier wherein targets are identified based on the sequences of their received range profiles. Individual looks at a target are taken and it is assumed that the aspect angle of observation changes by no more than a predetermined amount. Correlations are made with reference data, which correlations are then summed recursively according to preselected restrictive criteria to obtain the most likely sequence corresponding to the target for which reference data is stored in the range profile target classifier.

Abstract: A method of fabricating semiconductor devices on semi-insulating GaAs substrates is provided. Pre-etched holes in the substrate are covered with a dielectric which is etched to expose the substrate only at the bottom of the holes. Epitaxial growth of active GaAs in the holes may then proceed with a single crystallographic orientation. The dielectric covering the sidewalls of the holes prevents unwanted random growth and poor surface morphology of the active area.

Abstract: A color purity adjustment assembly for color cathode ray tube indicators of the shadow mask type wherein the two ring magnets surrounding the tube neck for determining the magnitude and direction of the resultant magnetic field across the neck are manually angularly adjustable about the tube neck in the same or opposite directions by means of a differential gearing arrangement coupled therebetween.

Abstract: A flat panel display in which a matrix array of electro-sensitive pixel elements organized in rows and columns are coupled to photosensitive devices such as photoresistors. The photoresistors are in turn coupled to X and Y addressing leads which contain X and Y alphanumeric or graphic information to be displayed in the matrix array. The photoresistors are illuminated with light sources substantially in synchronism with signals present on the X or Y addressing leads. Upon illumination by a scanning light source such as a self-scanning gas discharge device, the photoresistor's resistance drops and permits the information on the X and Y addressing leads to be coupled to the appropriate pixel. Addressing of large flat panel displays using as few as two driver circuits for the X and Y leads and as few as four driver circuits for the self-scanning gas discharge device is thus possible.

Abstract: A compressor parses the input data stream into segments where each segment comprises a prefix and the next symbol in the data stream following the prefix. The prefix of a segment is the longest match with a previously parsed segment of the data stream. The compressor constructs a search tree data base to effect the parsing and to generate a pointer for each segment pointing to the previous segment matching the prefix. The search tree comprises internal nodes including a root and external nodes denoted as leaves. The nodes are interconnected by branches representative of symbols of the alphabet. Each parsed segment of the input data is represented by a path from the root to a leaf. The tree is adaptively constructed from the input data such that as each new segment is parsed, one new internal node of the tree is created from a leaf and new leaves are defined, one for each symbol already encountered by the encoder plus an additional branch to represent all potential but unseen symbols.

Abstract: A miniature coaxial transmission line to waveguide transition particularly useful for frequencies beyond 40 GHz utilizes a projecting center conductor of a miniature coaxial line inserted directly into a waveguide. A metallic cylindrical sleeve is affixed to the end of the projecting center conductor to form a probe. The coaxial line is housed in the waveguide flange, and a plate is affixed across the cross section of the waveguide to provide a short circuit.

Abstract: An apparatus for control of ground clutter breakthrough in MTI radar which remove hard limited clutter signals while allowing increased detection sensitivity to moving targets when such strong clutter returns are not present. Logic is provided to prevent the removal of strong moving target return even in the presence of hard limited clutter.

Abstract: An optical switch utilizes a birefringent device to cause orthogonally polarized components of an arbitrarily polarized incident light beam to propagate along separate paths. A polarization rotator is positioned in one path to rotate the polarization of the light beam propagating therealong to that of the light beam in the other path. The two paths are simultaneously deflected to selected parallel paths in accordance with the switching desired. A second polarization rotator reestablishes the initial polarization and the beams are recombined by a second birefringent device to emerge from the selected output terminal as an arbitrarily polarized light.

Abstract: A hybrid analog/digital autopilot utilizing analog inner loops in each control axis of the aircraft and a digital processor for providing outer loop commands and inner loop gain augmentation commands to the inner loops. The command from the processor to each inner loop is buffered by an adaptive rate limit circuit that initially transmits high frequency commands and over a predetermined time interval limits the command rate to a safe low value. Alternatively, the adaptive rate limit buffer transmits the high frequency command up to a predetermined attitude limit and thereafter transmits a command limited to a low safe rate.

Abstract: A dome antenna with cross polarization compensation for reducing cross polarization induced monopulse tracking errors controls the polarization at the elements of the feed array to reduce the cross-polarization component in a far field radiation pattern of the antenna. Cross-polarization components at each element in the feed array for a linearly polarized plane wave incident at a predetermined direction to the dome are determined and each element is oriented to be polarized orthogonally to the cross-polarized component at that element.

Abstract: In a Global Positioning System type of navigation system, a biphase modulated radio frequency input signal is applied to the "front end" of a double heterodyne receiver having a second intermediate frequency stage which operates in the audio frequency range. The audio output signal is phase locked to a 1 KHz reference signal and is applied to a microprocessor for processing via an interface circuit which includes a relatively simple amplitude detector and a novel biphase detector. The microprocessor also controls the phase shifting of a pseudorandom noise code generator whose output is modulated with the output of the first intermediate frequency stage of the receiver.

Abstract: A low self-capacitance inductor is described for use as an output inductor in high frequency inverter power supplies. A pair of channel-shaped ferrite core members are assembled with a gap of material approximating the permeability of air. The core members are arranged to provide an axial aperture therebetween. A plurality of conductor segments are disposed in the aperture and are electrically interconnected to plated through holes in a supporting printed circuit board assembly. The conductor turns for the inductor are selected by the pattern of printed circuit interconnections between selected ones of the plated through holes, whereby the same current densities in the inductor are achieved for different conductor turns arrangements.

Abstract: A receiver accurately measures the Doppler shift of a radio signal from a transmitter having a known frequency and moving with respect to the receiver by using the signal from another transmitter of known frequency as a reference. The signals from the two transmitters are received by a single antenna, separated, and processed in separate channels. In a typical application using Global Positioning System satellite signals, each signal is discretely extracted by auto-correlation with its own pseudorandum noise signal, filtered, amplified, and applied to second mixers in phase locked loops in the respective channels. The two resulting second IF signals are applied to an output mixer whereupon the resulting difference output signal represents the difference in frequency between the two Doppler signals.

Abstract: In a gyroscopic reference system of the type having force rebalanced or flexure suspended gyroscope rate sensors and pulse width modulated torquer signals, undesirable transformer like coupling between the torquer coils and the pick-off coils and transformer like coupling between the torquer coils themselves causes a bias drift error. The transformer coupling and the bias drift error are alleviated or substantially eliminated by selecting the pick-off excitation frequency to be a non-integer multiple of the torquer coil frequency and by delaying the trailing edges of the pulses of the pulse width modulated torquer signals.

Abstract: An apparatus and method for scanning a circular array through 360.degree. with tapered aperture illumination function to achieve radiated beams with desired sidelobe levels. A switching matrix selects a predetermined number of active elements from the total number of elements disposed about the circle to form a sub-array. To this sub-array a variable amplitude distribution network is coupled to establish excitations at each active element in accordance with a desired amplitude distribution function.

Abstract: A compact apparatus for transmitting and receiving multiple sonar beams utilizes an acoustic lens to direct plane waves incident in desired directions to electroacoustic transducers positioned on spherical shell segments centered in the focal regions of the lens associated with the incident beams. The electroacoustic transducers transmit spherical waves that are transformed by the acoustic lens to plane waves emergent in the desired directions.