Abstract: A method for allowing a correlation function to be applied to binary codes f length 3 to length 128. A user may specify the desired length of the binary codes for correlation processing; whether the binary code is to use a phase sidelobe level as the threshold or a sidelobe amplitude as the threshold. The user will also be asked to specify the threshold as well as an in phase coefficient referred to as alpha and an out of phase coefficient referred to as a beta. The user may also specify that the codes be expanded which results in correlated compounds having a length twice that of the specified length being displayed to the user. When the user has specified the parameters for correlation processing of the binary code length selected by the user, the program of the present invention will process the binary codes eliminating allomorphic and symmetrical forms of the codes from correlation and then display the results to the user.

Abstract: A method for allowing a correlation function to be applied to binary codes of length 3 to length 255. A user may specify the desired length of the binary codes for correlation processing; whether the binary code is to use a phase sidelobe level as the threshold or a sidelobe amplitude as the threshold. The user will also be asked to specify the threshold as well as an in phase coefficient referred to as beta and an out of phase coefficient referred to as a alpha. When the user has specified the parameters for correlation processing of the binary code length selected by the user, the program of the present invention will process the binary codes eliminating allomorphic forms of the codes from correlation and then display the results to the user.

Abstract: A beamformer for a main antenna and a plurality of auxiliary antennas converts the main and each of the auxiliary signals to digital form. Each of the real and auxiliary digital signals is applied to a pair of real multipliers, in which multiplication by beamforming weights is performed, to produce one weighted real main signal, one weighted imaginary main signal, and a plurality of weighted real and weighted imaginary auxiliary signals. The weighted real main and auxiliary signals are summed together by a cascade of summers, and the weighted imaginary main and auxiliary signals are likewise summed together by another summed cascade. A digital product detector is connected to the output of each summer cascade. The first digital product detector produces in-phase and quadrature components of real detected signals, and the second digital product detector produces in-phase and quadrature components of imaginary detected signals.

Abstract: An antenna distribution network for an antenna array which provides independent sum and difference aperture excitations and enables a reduction in the difference channel radiation sidelobe levels. The circuit operates to smooth out the step discontinuity in the complex signal excitation of the radiating aperture in the difference mode by reducing considerably the amplitude of at least two corresponding elements located on opposite sides of the array center. A circuit of four four-port hybrid devices is employed, and introduces no effect when in the sum mode.

Abstract: An AWTSS is shown to be made up of an improved synthetic aperture radar (SAR) for generating radar maps with various degrees or resolution required for navigation of an aircraft and detection of ground targets in the presence of electronic countermeasures and clutter. The SAR consists, in effect, of four frequency-agile radars sharing quadrants of a single array antenna mounted within a radome on a "four axis" gimbal with a sidelobe cancelling subarray mounted at the phase center of each quadrant. Motion sensors are also mounted on the single array antenna to provide signals for compensating for vibration and stored compensating signals are used to compensate for radome-induced errors. In addition, a single processor is shown which is selectively operable to generate radar maps of any one of a number of desired degrees of resolution, such processor being adapted to operate in the presence of clutter or jamming signals.

Abstract: An AWTSS is shown to be made up of an improved synthetic aperture radar (SAR) for generating radar maps with various degrees of resolution required for navigation of an aircraft and detection of ground targets in the presence of electronic counter measures and clutter. The SAR consists, in effect, of four frequency-agile radars sharing quadrants of a single array antenna mounted within a radome on a "four axis" gimbal with a sidelobe cancelling subarray mounted at the phase center of each quadrant. Motion sensors are also mounted on the single array antenna to provide signals for compensating for vibration and stored compensating signals are used to compensate for radome-induced errors. In addition, a signal processor is shown which is selectively operable to generate radar maps of any one of a number of desired degrees of resolution, such processor being adapted to operate in the presence of clutter or jamming signals.

Abstract: A new system and technique for cancelling interference in frequency agile ceiving systems. Main and auxiliary signals are supplied to a pair of multiple loop side-lobe cancellers which are capable of being tuned to different frequencies. At the same time, under the control of a timing clock, plural frequencies are selected and multiplexed between two channels at the time of a radar pulse transmission. The side-lobe cancellers and radar are coupled to the channels such that each caneller operates at a given frequency for two consecutive pulse periods, with the radar transmitting at said given frequency during the second pulse period. By continuously cycling between the two channels, each canceller is operating at the proper frequency to cancel interference even though the radar is changeing frequency on a pulse to pulse basis.

Abstract: An adaptive antenna array system steers a plurality of antennas to direct e null toward an undesired source of interference to reduce noise and enhance detection of desired signals. A null indication processing system adjusts the phase and amplitude of the antenna branches to steer the null and provide a null angle indication and display. Digital controller and memory circuits provide automatic operation.

Abstract: An array antenna system and a method of exciting an array antenna wherein antenna elements are arranged on a curved surface. A desired radiation pattern with an undesirable sidelobe being suppressed is provided by compensating for the irregular density of antenna elements and by matching the null positions of the actual radiation pattern and an ideal Taylor radiation pattern.

Abstract: An apparatus and method for identifying sidelobe transmitted and/or received radar signals. The apparatus is utilized in a radar system having a transmitter for generating at least one detection signal, an antenna system defining a mainbeam and sidelobe radiation pattern for transmitting each detection signal and for receiving electromagnetic signals including echo signals each corresponding to a reflection from an object of a transmitted detection signal, and a receiver system for processing each received echo signal. The apparatus is embodied as a system for identifying each echo signal received upon the antenna system sidelobe and each received echo signal having a corresponding detection signal transmitted on the antenna system sidelobe.

Abstract: A system for discriminating between signals received on the mainbeam of an antenna system and signals received on the sidelobe of the antenna system. The system utilizes a main antenna and multiple auxiliary antennas. The signals received on the main antenna are coincident on one or more of the auxiliary antennas. The auxillary antenna signals are multiplexed separated for single channel processing. The main antenna signal is compared with each of the multiplexed auxiliary antenna signals. The result of these comparisons are used to determine whether the signal received on the main antenna was received on a mainbeam or a sidelobe.

Abstract: A system for reducing sidelobes of phased array antenna systems is performed by tapering the current amplitide of edge elements in the array while maintaining a full uniform current to the center elements in the array. Tapering may be adjusted with variable impedance devices until optimum sidelobe reduction is achieved.

Abstract: An adaptive sidelobe blanker uses the covariance matrix used to form an adaptively nulled main channel to generate an adaptively nulled version of an omnidirectional antenna pattern. Individual antenna control includes sampling, digitizing, and storage of an antenna signal. Complex antenna weights manipulate the antenna signals in both the main channel and the blanker channel to provide desired steering of the antenna nulls. The adaptively nulled blanker channel is compared to the adaptively mulled main channel to determine if a received target return is a main beam target or a sidelobe target.

Abstract: Anti-jamming apparatus and method for a radar system having a main antenna utilizes a single electronic-scan auxiliary antenna having a plurality of radiating elements each coupled to appropriate phase shift means. The auxiliary antenna is successively sighted in directions of each of a plurality of jammers. First and second receiving chains respectively coupled to the main and auxiliary antennas supplies a processor with components of the signals received by the antennas. The computer supplies control signals to control the sighting of the auxiliary antenna so that it radiates in the direction of each jammer maximum radiation values, the components of which are those of the field radiated by the main antenna in the direction of the sighted jammer. The processor also provides an output signal comprising a vectorial combination of the signals received by the main and auxiliary antennas. The auxiliary antenna is thus successively used as an auxiliary adjusting antenna, and then used as an anti-jamming antenna.

Abstract: Sidelobe jamming in dual diversity troposcatter link receivers is effectively suppressed by providing an auxilliary low power antenna, the output of which is differenced from the high power main antenna signals prior to processing in the receivers's dual diversity demodulator. The auxilliary antenna power is substantially equal to the sidelobe power of the main antennas. The auxilliary antenna receives jamming power that is comparable to the jamming power received by the main antennas. However, it receives much lower desired signal power. Differencing of the signals therefore, cancels jamming power with minimal effect on the desired signals.

Abstract: A method and a device for reducing the power of jamming signals received by the secondary lobes of the main antenna AP of a radar transmitting at a random frequency f.sub.E (n), with which is associated a number of secondary antennas ASl, . . . ASN. The signals used for the calculation in circuit (10) of the weighting coefficients (Wl to WN) to be applied to obtain a signal resulting from the weighted linear combination of the secondary signals Dl, . . . DN to be subtracted from the signal Do in the main channel (VPD) relative to the transmission frequency f.sub.E (N+1) are those (V.sub.0, V.sub.1, . . . V.sub.N) processed in the main and secondary auxiliary channels (VPA, AsAl, . . . ASAN) relative to the transmission frequency f.sub.E (n+1) of the next recurrence train during the period of radar reception of the recurrence train corresponding to the transmission frequency f.sub.E (n) for the jammed range slots selected by circuit (15).

Abstract: A moving target indication (MTI) radar which includes TACCAR circuitry or similar means for shifting the frequency of the transmitter/local oscillator, includes a main directional antenna, and subordinate antenna elements for detecting returns from sidelobe directions. The signals from the subordinate antenna elements are modulated, and modulated return pulses are identified and employed to eliminate false pseudo moving target signals which would otherwise be received from the side lobes of the main antenna.

Abstract: A method and apparatus is disclosed for selectively modulating r.f. signals received/transmitted via the radiation pattern side lobes of an r.f. antenna structure. Such modulation permits discrimination between desired r.f. signal energy received via the primary radiation pattern lobe and unwanted r.f. radiation (e.g. noise, jamming or other interference signals) received/transmitted via the secondary or side lobe(s) of the radiation pattern.

Abstract: A sequential decorrelator arrangement for an adaptive antenna array comprising a plurality of antenna elements the outputs of which feed a cascaded beamforming network having a succession of stages, each stage having one less decorrelation cell than the preceding stage and the first stage having one less cell than the number of antenna elements.The network includes means for applying weighting to the signals applied as inputs to the cells of at least the first stage. The decorrelation cells in each stage comprise means for applying simple rotational transforms to the input data in accordance with a weighting factor common to all the cells in a stage, each stage further including means for deriving said weighting factor from the weighting factor deriving means of the previous stage and the output of one cell of the preceding stage. Each stage includes means for scaling the output of each cell in the stage by a scaling factor calculated from the weighting factor deriving means of the stage.

Abstract: Secondary lobe cancellation (SLC) is used to reduce the power of jamming signals received by the sidelobes of a main radar antenna. The signal from the radiation pattern of the main antenna is summed with signals from auxiliary radiation patterns. Each auxiliary pattern is chosen to be directional, to have a null or at least a gain minimum in the direction of maximum radiation in the main antenna pattern, to have its phase center close to that of the main antenna pattern, and to have gain minimums in those directions for which the sidelobes of the main antenna pattern are low enough to be insensitive to jamming signals. The various patterns may all be derived from an array antenna, e.g. a multibeam antenna, an aplanatic lens antenna, or a chandelier fed antenna.

Abstract: Disclosed is an antenna system having a first antenna directed to receive a desired signal wave and a second antenna directed to receive only an interference signal wave superposed on the desired signal wave. Both signals received by the first and second antennas are combined and the amplitude and phase shift necessary for the second antenna signal to cancel the interference signal component existing in the first antenna signal is calculated from the combined signal. By combining the controlled second antenna signal with the first antenna signal, the desired reception signal having an improved S/N ratio can be obtained.

Abstract: Subarray amplitude tapering is a simple, lower cost method of generating low sidelobes in an antenna's far field pattern. Unfortunately, this simple technique also generates unwanted grating lobes. Placing the exact amplitude taper at the element outputs produces the desired far field pattern, but the architecture is complicated and expensive. An alternative to these two techniques is a design process that entails placing amplitude tapering at subarray outputs and element amplitude tapers that are identical between corresponding elements in groups of identical subarrays. In this way, the amplitude taper approximates the desired taper much better than subarray tapering alone, yet groups of subarrays are identical so that the design remains very simple.

Abstract: Improved gain control in a multiplexed adaptive array processor having main and a reference channel receiver is achieved by means of an AGC circuit controlling the gain of the reference channel receiver over its dynamic range, an AGC circuit slaved to the reference channel receiver AGC circuit controlling the main channel receiver, and a separate AGC circuit controlling the output of the main channel receiver.

Abstract: In side-lobe cancelling equipment direct jammer signals appearing in an auxiliary antenna channel are better correlated with reflected jammer signals in a main antenna channel by splitting the signal in the auxiliary channel into two parts, one of which is directly correlated with direct jammer signals in the main channel and the other is passed through a delay line to alter its timing to match the timing of the reflected jammer signals in the main channel.

Abstract: An aperture transformation sidelobe canceller includes a plurality of auxiliary feed elements disposed in the vicinity of, but critically offset from, a main feed horn. The signal paths for the auxiliary feed horns are coupled through a low loss cascade RF variable direction coupler network to be combined with the RF signal path for the main antenna feed. The combined signal path is coupled to a performance monitoring processor which, in turn, adjusts the coupling action of each variable directional coupler to achieve the necessary weighting and combining of the auxiliary feed signal paths. The critically offset auxiliary feed elements provide the capability of achieving very broadband and deep nulls from the simple variable directional coupler network. The null availability makes it possible to null the entirety of the main elements sidelobe region, including backlobe and even the first sidelobe region of the antenna pattern, as the offset auxiliary feed horns provide substantial coverage in this region.

Abstract: A pulse radar apparatus is provided with a first receiver (4) connected to a directional antenna (3) and a second receiver (13) connected to an omnidirectional antenna (12). The receivers (4, 13) are suitable for reception and processing of long-duration and short-duration radar signals respectively, whereby at least the long-duration signals are frequency-modulated and subjected to pulse compression. The radar apparatus is further provided with a side-lobe blanking circuit (20) and switching means (25, 26).