Abstract: First and second aluminum members are joined by the steps of(a) dissolving and removing completely the aluminum oxide layer from the surface of each of said first and second members to be joined and replacing each of the aluminum oxide layers with a layer consisting essentially of zinc;(b) plating at least one of the zinc layers with a non-alloy cadmium;(c) assembling and retaining together said first and second aluminum members so that the surfaces to be joined are held in contact with one another and placing said aluminum members in a vacuum; and(d) heating the members while in the vacuum thereby forming a bond between said first and second aluminum members.

Abstract: A preamplifier for beamforming hydrophone signals of a sonar array. The invention uses an amplifier that provides a current-source type of output for driving the beamforming network, thus avoiding the substantial signal loss inherent in using voltage-source amplification. To obtain the stability of gain required in this type of operation, the invention employs a negative feedback system that can be easily adjusted by choice of resistors to accommodate desired levels of shading and signal equalization. The advantages provided are savings in cost, reduction in size and power requirements and improved in signal-to-noise ratio.

Abstract: In a system having plural signal-carrying channels, a phase shift is introduced between a signal in one of the channels and a reference signal for calibrating the individual channels. The reference signal is obtained by adding samples of signals in other ones of the channels. The phase shift is introduced by phase-shift apparatus responsive to a command signal directing a continuous monotonic increment of phase. The phase incrementing introduces a frequency shift (a serrodyne), which produces a beat-frequency signal for mixing a channel signal with the reference signal. The beat-frequency signal is phase locked to a modulation patern of a command signal, whereby a measurement of phase (or delay) can be made between the two signals for calibration of each channel within the system.

Abstract: An antenna comprising a linear array of active elements positioned in one or more rows. The back portion of the array is partially enveloped by a reflector. The reflector includes a backwall and at least one sidewall perpendicular to the backwall and extending forward of the backwall. In one embodiment of the invention, a single row of dipole radiators form the linear array. In a second embodiment of the invention, a row of folded monopoles mounted on an imaging ground plane form the linear array. The radiation pattern is directed forward of the reflector, the back radiation in the E-plane being suppressed by the sidewall of the reflector.

Abstract: A flat panel display system is provided in which the pixels thereof are illuminated by optical fibers. Economy and compactness are achieved by using micromechanical light modulators to demultiplex light from a limited number of LED's to a large number of pixels. By using micromechanical light modulators incorporated in an integrated circuit, the flat panel display system is relatively economical, has low power consumption, and produces a display of very high resolution. The display also may be provided in full color.

Abstract: A sonobuoy system and method for deploying an array of transducers in a substantially horizontal line at a desired depth below the surface of a body of water. The trailing end of the array is deployed first, allowed to descend, and suspended at the desired operating depth. The leading end of the array is then released, allowed to descend slowly, and suspended at the desired operating depth. A drag device attached to the trailing end of the array causes the trailing end of the array to be stretched out away from the leading end, thereby maintaining the array in a substantially horizontal line at the desired depth. The system and method make it possible to deploy horizontal line arrays in a minimum of time and at shallow depths.

Abstract: Stereo decoders for use in AM stereo receivers are disclosed which have two different modes of operation, one of which suffers adverse effects from the presence of co-channel interference and employs envelope detection to develope an (L+R) representative signal. When such interference is detected the decoder switches to a second mode of operation, which is less affected by the interference, and also switches to synchronous detection to develop the (L+R) representative signal.

Abstract: An antenna radome, suitable for use with high precision, environmentally sensitive array antennas, includes a dielectric sheet formed to protect the antenna from environmental conditions and a series of conductors fixed on the sheet in a certain pattern so that the sheet with the conductors provides a lower reflection coefficient to electromagnetic waves at the antenna's operating wavelength than in the absence of the conductors. Current is caused to flow through the conductors, thus generating heat in areas of the dielectric sheet where the conductors are fixed. Accordingly, ice formation on the protective dielectric sheet can be prevented while the antenna array is operational, and accurate antenna performance is ensured. Further, the dielectric sheet presents a significantly lower reflection coefficient at the operating wavelength than radomes in which a conventional grid of heater wires is provided for melting ice.

Abstract: An amplitude control system particularly suitable for an active antenna array includes a power detector for generating a power level signal representative of a level of radio frequency (RF) energy radiated by an antenna element, or groups of elements, in a phased antenna array. A reference signal corresponding to a desired value for the radiated level of RF energy is set by a control device, and the power level signal and the reference signal are compared with one another. Depending on the comparison result, an attenuator associated with an RF amplifier than drives the antenna elements, is adjusted to maintain the radiated RF energy at the desired value set at the control device.

Abstract: In the ground-based equipment of a microwave landing system (MLS), a linear array antenna is employed to generate both a scanning guidance beam, which provides azimuthal position data to an incoming aircraft, and a pair of out-of-coverage indication (OCI) beams, which are disposed outside of the sector covered by the scanning guidance beam. For sweeping the guide beam, phase shifts are updated in a linear phase gradient to scan the beam to the right and to the left of the centerline of the antenna. To form the pair of OCI beams, the main lobe of the antenna radiation pattern is directed to one side of the antenna's centerline, outside the normal scanning range, thereby producing a grating lobe on the opposite side of the centerline. Furthermore, a quadratic phase shift function is superimposed upon the linear phase gradient to defocus the OCI beams so as to fill a sufficient sector of space, on both sides of the scanned region, for OCI coverage.

Abstract: An azimuthal scanning antenna for an aircraft landing system is formed of a set of vertically disposed columnar radiators arranged side-by-side in a horizontal array. The columnar radiators are tilted back in pitch 7.5.degree.. Individual ones of the radiators are formed of waveguide sections terminated by reflecting end walls. The terminating walls provide for a standing wave of electromagnetic field in response to microwave electromagnetic energy applied to the waveguide section by a feed disposed at or near the bottom of the waveguide section. Slot apertures are disposed along a front wall of each waveguide section, and are oriented at a selected angle relative to a perpendicular relationship to the sidewalls. The orientation of the slots introduces a variation in coupling for illumination of the radiation aperture of the radiator wherein the phase center is offset from a central point towards an upper end of each of the waveguide sections.

Abstract: A synchronous transmission system that improves reception in areas where the main and the satellite signal create significant self interference. At least one of the synchronous transmitters is phase modulated in accordance with a selected modulation function which varies at a sub sonic rate.

Abstract: The present invention achieves the above objects, among others, by providing apparatus for converting a supplied AC input signal into an AC output signal having a selected lower frequency than the frequency of the AC input signal, which apparatus translates individual half cycles of the supplied AC input signal to an intermediate output signal with selected amplitude and polarity such that during successive pairs of first and second periods, each such period corresponding to a predetermined number of half cycles of the AC input signal, the translated half cycles of the AC input signal all have the same first selected polarity during each first period and have the same second selected polarity during each second period, with the first and second polarities being opposite. The apparatus filters the intermediate output signal to develop the AC output signal having the selected lower frequency.

Abstract: Multi-system or "universal" AM stereo receivers are provided which require no switching of the receiver's stereo decoder circuitry regardless of which AM stereo system signal is being received. In accordance with one aspect of the invention, acceptable stereo sound is achieved for all AM stereo systems by introducing a selected amount of distortion correction in the L-R channel of the universal receiver and a selected phase difference between the L+R and L-R channels. In addition, perceived stereo separation in AM stereo and other stereo receivers is enhanced by also properly selecting the gain in the L-R channel in relation to the L+R channel.

Abstract: In a superheterodyne receiver which employs a frequency synthesizer to generate local oscillator (LO) frequencies, there is provided apparatus which determines when an undesirable frequency relation exists, which may produce a condition known as a "tweet", and which adjusts the frequency of the LO signal so as to prevent, reduce or eliminate the tweet.

Abstract: A lossless spatial filter having N input ports and N output ports and printed on a single substrate. The filer is used in combination with an antenna system which radiates wave energy signals into a selected angular region of space and into a desired radiation pattern. The aperture of the system includes a plurality of N antenna elements. The antenna elements are arranged along a predetermined path and each element is connected to only one output port of the spatial filter. A beam steering unit controls the direction of radiation. A signal generator supplies a power divider having N output signal ports each connected to a phase shifter controlled by the beam steering unit.

Abstract: A noise trap circuit particularly suitable for use in an electro-acoustic system, operates to suppress low level signals or noise while allowing a relatively large signal to pass unattenuated between input and output terminals of the circuit. Blocking elements between the input and output terminals establish a high impedance path to the noise but switch to a conductive state when the large signals are present at the input terminals. Shunt elements across the output terminals provide a low resistance path or "crowbar" when only the noise is present at the input terminals, but switch to a non-conductive state when the large signals are sensed at the circuit input.

Abstract: An apparatus for supporting a large volumetric array of acoustic sensors in water is packaged in a standard configuration sonobuoy envelope and utilizes conventional sonobuoy deployment components. A housing within the envelope contains a plurality of tubular extendable members stored on drums and extendable to form array support booms upon deployment of the apparatus. A plurality of releasable array modules are releasably attached to the housing, each module containing an array cable and a plurality of acoustic sensors secured to and along the cable. As the apparatus enters and descends through the water, the tubular members extend to form array support booms. The array modules are synchronously released to the extension of the tubular members and as the modules descend, the array cables and acoustic sensors deploy, the array cables forming catenaries between points on array support boom pairs or between the housing and points on the various booms.

Abstract: Asymmetrical sideband amplitude modulation (AM) stereo transmission apparatus which transmits left (L) plus right (R) stereo information (L+R) in one stereo channel and a signal including L-R stereo information in a second stereo channel. Benefits include significant reduction of modulation envelope distortion in null regions of the transmitter's antenna radiation pattern and improved quality of reception in the presence of adjacent channel and co-channel interference, easing of the difficulty in tuning continuously tuned receivers and improvement of the fidelity of such receivers when side tuned, while at the same time providing a signal which, when received and decoded by an independent sideband AM stereo receiver, provides pleasing stereo effects.

Abstract: The fault monitoring function of an executive monitor contained in a microwave landing system is verified by evaluating a history of the parametric information sampled by an executive monitor and storing in memory the number of out of tolerance parametric signals received from an antenna means over a predetermined time period, replacing the stored number of out-of-tolerance parametric signals with a predetermined number that will be beyond a second predetermined limit if another out-of-tolerance parametric signal is added to said number, adding one such internally generated out-of-tolerance parametric signal to said predetermined number, generating an alarm if said sum is beyond the second predetermined limit, and restoring the previously stored number of out-of-tolerance parametric signals received from the antenna means if the alarm was generated, and shutting the system down if an alarm was not generated.