Abstract: The invention concerns an application of linear system parameter estimation techniques to finite amplitude sonar devices, to extract fine grained angular position information about echo sources. The invention makes use of the fact that the waveform return by a reflecting object within the sonar's beam varies according to its relative angular position from the receiver, and a discovery that this variation may be fit to a linear system model using autoregressive estimation theory to extract the nature of the variation. In all cases, the information is extracted without the mechanical or electrical steering of the sonar transmitting beam.

Abstract: A decimation-in-frequency fast-Fourier-transform butterfly circuit for performing a radix-four butterfly operation includes a first group of adders (86, 88, 90, and 92), a second group of adders (70, 72, 74, and 76), and a group of twiddle-factor multipliers (78, 80, and 82) that are interconnected in such a way as to perform the radix-four fast-Fourier-transform algorithm. Additionally, bypass lines (102, 104, 106, and 108) bypass the first group of adders, and switches (94, 96, 98, and 100) switch between the signals on the bypass lines and those from the first group of adders. As a result, the circuit performs a radix-four FFT operation when the switches are in one state, and it performs two radix-two FFT butterfly operations simultaneously when the switches are in the other state.

Abstract: A pilot valve suited for use as the first stage of a large hydraulic valve system. The pilot valve virtually eliminates the steady state fluid leakage associated with orifice-based prior art systems. A pair of low noise and long life fluid restrictors are employed having flat openings thereto over which a flexible metal strip is disposed. The ends of the strip adjacent each opening are attached to one edge of rolling members whereby they can be rolled progressively off of and over the openings by an electrically driven actuator. In this manner, fluid flow through the two restrictor paths are controlled simultaneously to change the amount of fluid passing therethrough. Taps are provided in each restrictor for taking out the control fluid flow and pressure which are applied to the main valve as the driving means thereto.

Abstract: In a spread-spectrum direction-finding system, the outputs of the several antenna elements (10a-d) are progressively translated in frequency by a chirped local oscillator (14) and mixers (12a-d) and applied to a two-dimensional dispersive filter (18), which time compresses the results of single-frequency components in the antenna-element outputs to narrow pulses. Limiters (24a-d) remove any strong narrow-band components that are compressed by the dispersive delay line (18) so that further processing to detect a spread-spectrum signal is not degraded by the presence of narrow-band signals. The use of a common two-dimensional delay line (18) to provide the time compression avoids the need to maintain phase tracking among a plurality of separate parallel one-dimensional dispersive delay lines.

Abstract: A signal-acquisition system (10) for a circular antenna array (12) includes a two-dimensional compressive receiver (18) that performs a two-dimensional Fourier transformation in time and position on the outputs of the array. Each of the outputs of the compressive receiver (18) is fed to input ports of several processing units (24), which multiply them by an appropriate time-dependent function. The resultant modified signals are then processed by Butler matrices (30) that together have a matrix of output ports (32). Each output port is associated with a different combination of azimuth and elevation angles. A signal source at given azimuth and elevation angles with respect to the array (12) causes its greatest response in the output port (32) associated with those angles.

Abstract: Signals from antenna elements (14) of a rectangular array (12) are translated in frequency by mixers (16) fed from a chirped local oscillator (19). The resultant signals are fed to the first of two groups (20 and 36) of two-dimensional delay lines connected in series at right angles to each other. The two-dimensional delay lines are dispersive, having a linear relationship of delay to frequency, and the sweep rate of the local oscillator (19) is such that the signals caused by a given frequency component at the mixer input ports are completely compressed in time when they reach the output ports (46) of the delay lines of the second group (36). As a consequence, the device performs a three-dimensional Fourier transformation from time and two spatial dimensions to temporal frequency and two dimensions of spatial frequency. When fed by a two-dimensional antenna array, the output of the device can readily be interpreted as indicating the direction of the source and the frequency at which it is radiating.

Abstract: A frequency-and-direction-finding system (10) employing a circular array (12) performs a two-dimensional Fourier transformation in space and time on the signals from the individual elements. The results of the transformation are fed to multipliers (22) that multiply them by correction factors that are derived from antenna patterns of the array but do not include the bearing-dependent factors in those systems. The result is an ensemble of values whose relative phases represent a spatial frequency proportional to the bearing angle of the source. Accordingly, a second fast-Fourier-transform circuit (26) operating on this ensemble of values produces an output only on an output port corresponding to the bearing angle of the source.

Abstract: A receiver employs fast-Fourier-transform modules to process the received signals in the frequency domain. It samples the input signal at a high sampling rate to cover a broad input bandwidth, but it transforms the sampled input signals in short segments, segments that cover time durations considerably shorter than the duration of the impulse response of the receiver's tuner filter. The transform of the sampled input signal is multiplied by a Gaussian transfer function to reduce the amount of information contained in the signal, and the values of the resultant frequency-domain sequence are reordered in such a manner as to correspond to resampling in the time domain at a slower rate. This results in coverage of the time duration of an input segment by a relatively small number of samples.

Abstract: In a digital communications system, one of two tones is selected for each bit, a first tone for a "0" and a second tone for a "1"; the tones are unique for each bit. The tones for all of the bits of a byte are sent simultaneously, in a burst or pulse. At the receiver, a parametric model-based spectrum analysis is performed to find the constituent frequencies which produced the composite spectrum. This spectrum analysis uses autoregressive parameter estimation techniques to determine the most likely combination of frequency components which would have generated the composite spectrum. The combination of frequency components so found is then decoded to yield the corresponding bit values represented by those frequencies. The use of autoregressive spectral analysis techniques to recover the frequency components in the composite signal provides both bandwidth compression (by virtue of increased resolution) and faster signalling rates in transmitting just such signals.

Abstract: A system for indicating the direction of a source of radio waves received by a circular antenna array (12) includes a Butler matrix (18) that receives the array outputs and feeds the resultant matrix outputs to correction circuits (22) whose transfer functions are the inverses of the direction-independent factors of antenna patterns generated by antenna elements driven at relative phases that advance around the array at rates that complete an integral number of cycles in one circuit of the array. The resultant corrected signals are fed to a compressive receiver (26), which accordingly generates an output on an output port whose position indicates the direction of the source of the signal.

Abstract: A microwave antenna (10) is excited by two independently driven feed lines (30 and 32) so that the plane of polarization of the resultant microwave radiation depends on the relative amplitudes of the signals on the two feed lines. The feed lines are disposed between two parallel ground planes (12 and 14), in one of which is etched an aperture (18). The periphery of the aperture forms ridges (20, 22, 24, and 26) in registration with the feed lines (30 and 32). Conductive eyelets (27) extend between the ground-plane conductors (12 and 14) to act as shorting elements that surround the aperture to form a cavity defined by the shorting elements and the ground-plane conductors. The resultant antenna, which may, for instance, have a thickness of only one-tenth of a wavelength, achieves a 2:1 VSWR bandwidth on the order of 30%.

Abstract: A data word (bits ID.0.-ID15) is supplied to the address inputs of a memory arrangement U1, U2, U3 whose outputs S0-S3 supply to a parallel shifter SN a control word specifying the number of shifts required. As described, two read-only memories receive respective halves of the data word and feed a multiplexer U3 which selects the outputs of U1 unless the latter indicating that all its inputs are zero (or one, for negative numbers) in which case control is passed to U2. The sign bit (ID15) is supplied to both memories.

Abstract: A waveguide-to-stripline transition includes a stripline portion (14) that fits over an opening in one end of waveguide (12). The stripline portion has a cavity defined by an upper ground-plane conductor (20), a lower ground-plane conductor (22), and a rectangular arrangement of plated-through holes (28) that electrically connect the upper ground-plane conductor (20) to the lower ground-plane conductor (22). The upper ground-plane conductor (20) is etched to provide an aperture (32) with a conductive crosspiece (34) extending longitudinally across it. A plated-through hole (36) connects the crosspiece (34) to the center conductor (26) to provide a T-shaped feed element in the cavity. As compared with prior-art waveguide-to-stripline transitions, this transition is mechanically stronger and has higher power-handling capability.

Abstract: The method of repeatably making an antenna coupler for holding a test antenna in a repeatable fixed position on the exterior surface of an aircraft or the like relative to a working antenna disposed within the aircraft. A positive mold is made of the area adjacent the antenna within the aircraft. A temporary RF shielding box is placed over the positive mold and the mold is modified to support the box repeatably in a fixed position. Pins are provided to interact with mounting holes for an antenna. A permanent box to be used as part of the coupler is mounted on the positive mold. A ribbon gasket comprising a plurality of tubular, compressible members of an RF shielding material and having mounting tabs along the length thereof is disposed against the surface of the mold about the peripheral edge. The gasket and the box are interconnected by an epoxy material, including RF shielding means. The coupler is removed from the mold and the antenna is mounted to the mounting holes.

Abstract: A DC motor particularly adapted to operate in the presence of translational movement between the armature (rotor) and the field (stator) magnets. The field magnets comprise a plurality of magnets formed into a pair of concentric, closed-spaced, parallel rings mounted to rings of soft, magnetic material. The armature is a planar armature wound in a serpentine pattern so as to cross back and form between the rings only on radial lines from a center point on the armature. The radial conductor lines are sized with respect to the width of the magnetic ring such that even in the presence of translational motion, only the radial conductors cross between the rings and the motor can continue to operate.

Abstract: An improvement to a baseband system having a plurality of down converters feeding a single baseband receiver for assuring the same mean time to intercept while maximizing the probability of intercept as a multi-band, autonomous receiver. All channels of the converter unit are operated simultaneously and a unique tag is added to the output signal from each of the down converters whereby the signal can be identified by the balance of the system as to its associated converter. In one embodiment, the tag comprises an amplitude notch appearing on the output signal at a different time following the receiver threshold being exceeded. In a second embodiment, the tag comprises a frequency step added to and/or subtracted from each output signal at the same time following the exceeding of the receiver threshold. In a third embodiment, the tag comprises a phase shift applied to the output signal.

Abstract: A directional antenna system having a passive arrangement for reducing the amplitude of signals received in the direction of one of the side lobes of the antenna pattern. The system includes a main directional antenna and two or more auxiliary antennas, each of which has less directivity than the main antenna. The auxiliary antennas are aimed in the direction of a selected side lobe of the main antenna whose effect is to be diminished. The outputs of all the antennas are combined in a network having appropriate amplitude and phasing adjustments to cause the combined outputs of the auxiliary antennas to interfere destructively with the energy received by the main antenna in the direction of the selected side lobe.

Abstract: A microwave antenna is made of a pair of parallel ground-plane conductors (12 and 14), one of which forms a generally cruciform aperture (18). A pair of T-shaped feedlines are disposed with their cross pieces (22 and 34) in registration with the respective arms (20 and 36) of the aperture 18 and are independently driven from stems (26 and 32) disposed between the ground-plane conductors.

Abstract: A mechanical and electrical connection for a piezoelectric member of polyic material such as polyvinylidene fluoride, and method for forming such a connection. To form the connection, the piezoelectric member is first masked to prevent a preselected portion of its surface from being coated during subsequent coating operations. An electrically conductive member such as a lead wire or a solderable terminal is then attached to the nonmasked area of the piezoelectric member with adhesive such as epoxy. The masked piezoelectric member, the electrically conductive member, and (incidentally) the mask are then coated with a conductive coating such as sputtered gold to electrically connect the conductive member to the piezoelectric member. The mask can now be removed from the piezoelectric member if desired, although it can be left in place as a convenient vise.

Abstract: A hand held paper pager is disclosed in which a transmitted message is displayed in alpha/numeric form by a precessing display which moves the received message across the display in a continuous fashion so that the display need be only large enough to present a relatively small portion of the total message at any given time. In one embodiment a dot matrix LED display is used and is driven by a recirculating shift register memory to provide the precession of the message as a result of the recirculation. In another embodiment the pager may also include a message entry section in which the precessing display is used to present and edit the message prior to transmission either via an acoustic telephone link to a remote transmitter, or directly from a transmitter carried in the pager/encoder package.