Abstract: Multi-beam antenna feed networks employ more aperture ports (e.g., ports I, II, III, IV and V) than beam ports (e.g., ports A, B, C and D) to achieve low sidelobe lossless operation, particularly for cellular communications. With five aperture ports, signal value outputs at the aperture ports represent orthogonal outputs having phase gradients effective to provide a four beam radiation pattern. The feed arrangement includes directional couplers (e.g., C11, C21) and phase shifters (e.g., P22, P23) intercoupled between the beam ports and aperture ports to provide the desired orthogonal aperture excitation. An example of specific directional coupler and phase shifter circuit values for a matrix network for a four beam port to five aperture port feed network configuration is provided.

Abstract: Systems are provided to derive a value of barometric pressure at a defined location in the atmosphere at a computed geometric height. By using the geometric height in a look-up table of pressure/height values representing a standard atmospheric profile, atmospheric deviation data indicative of the difference between measured and reference pressures at that atmospheric location (C) is derived. Ground-based interrogators (10,20) located at spaced positions are used to initiate response signals from airborne transponders commonly installed in transient aircraft (C). Using resulting range data based on round-trip timing differences in signals sent to (12,16) and received from (16,14) the airborne transponder (C), geometric analysis and computation is used (18) to determine the geometric height of the transponder representing a specific atmospheric location.

Abstract: Mutual coupling effects, which would tend to degrade operation of a two-element end-fire array over a frequency band, are overcome by provision of an inter-element coupling impedance which is effective to equalize the Q at the inputs to the quadrature-excited elements. A quarter-wave transmission line section is coupled between the inputs to provide such impedance, which has a value selected to offset the effect of mutual coupling on Q. For a pair of monopoles, the inter-element coupling line is connected to the respective monopoles by quarter-wave sections having impedances selected in order to provide desired input impedances. The performance of dual-element end-fire slot or dipole array antennas may similarly be improved. Linear array antennas of four or more elements are provided by forced feeding of the additional elements from the basic dual-element configuration in accordance with the invention.

Abstract: The need to widely separate antennas (e.g., transmit and receive antennas) for VHF radio and other applications is avoided by high-isolation antenna systems with collocated antennas and cancellation of intercoupled signals. A transmit antenna in the form of a vertical dipole can be mounted atop a mast with a receive antenna comprising a multi-element array of vertical dipoles supported on the same mast below the transmit antenna. Opposing pairs of the dipole receiving elements are located in 180.degree. positions on opposite sides of the mast so as to be symmetrically located in the omnidirectional antenna pattern of the transmit antenna. Resulting intercoupling to the receive dipoles is equal and in-phase and is cancelled out by the antiphase combining of signals from the dipoles of each pair of the receive dipoles. Reciprocally, cancellation of coupled signals is achieved with reversal of the receive and transmit functions of the respective collocated antennas.

Abstract: Array antennas for aircraft use have a shiftable center of radiation. The antenna beam of a group of laterally spaced array antennas is steered and the beam shape is controlled by relative shifting of the centers of radiation of the arrays. Beam tilting in a fuselage mounted system of array antennas uses controlled selection of active antennas.

Abstract: A switched capacitor integrator is used within the feedback loop of an automatic gain control (AGC) circuit to provide a very long time constant (5 minutes or more) when the amplitude of the gain-controlled signal is within predetermined limits. The time constant is automatically and quickly changed to a much shorter value when the gain-controlled signal is outside the predetermined limits, thereby allowing the AGC circuit to rapidly bring the gain-controlled signal amplitude within the desired range between the predetermined limits. Time constants of orders of magnitude longer than those readily realized with prior art methods of long time-constant filtering are achieved.

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 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.