Abstract: A method for determining target echo detection efficacy of a signal processing algorithm of a radar system involves generating a simulated noise complex envelope sequence, generating a simulated radar target echo signal complex envelope pulse sequence and adding the simulated noise complex envelope sequence to the simulated radar target echo signal complex envelope pulse sequence, thereby producing simulated noisy radar target echo signal complex envelope sequence. The simulated noisy radar target echo signal complex envelope sequence is inputted into the signal processing algorithm and the output of the signal processing algorithm is analyzed to determine target echo detection efficacy of the signal processing algorithm.

Abstract: Modern tactical radars frequently use phase shifters to electronically specify or steer the spatial position of the antenna beam without requiring mechanical motion of the antenna. These phase shifters can only be set correctly for a specific frequency. If a waveform is transmitted through the antenna which consists of multiple segments which differ in frequency or modulation from that frequency used to steer the position of the beam, errors are introduced into the monopulse measurement. These monopulse errors are reduced or eliminated by correction factors. The monopulse errors are corrected by pre-computed factors or terms which result from the differences in frequency and modulation used in the waveform from the frequency used to steer or position the beam. Correction is also provided for radar altitude. These correction factors are easily pre-computed and applied only when needed to minimize the computational requirements.

Abstract: A method for displaying information relating to the range and Doppler of a remote target includes transmitting electromagnetic energy toward the target, and receiving reflected signals defining a two-dimensional (range-Doppler) radar image. The reflected signals are matched-filtered, which tends to blur the image. The image is deblurred while the features of thermal noise enhancement and irregularity of the deconvolved output are constrained to produce a single point deblurring output.

Abstract: The proper timing or alignment for coherent or noncoherent integration of radar pulses returned from a potentially moving target is determined by determining the entropy associated with sets of range samples based on a plurality of different velocity hypotheses. That set associated with the minimum entropy is deemed to be the correct velocity hypothesis, and integration is then performed using the velocity hypothesis so determined.

Abstract: A polarimetric radar system transmits a signal which is nominally the desired polarization, but which may deviate therefrom. A calibration operation is performed using a symmetrical radar reflector, to determine the gains and phases of reception of two mutually orthogonal components of the received reflected signal which result in nulling of the two polarization components of the reflected signal. These gains and phases represent receive corrections which result in a simulation of perfect polarization purity on both transmission and reception. The corrections established during calibration are applied to the receive signals during normal (non-calibration) operation, to improve the effective polarization of the transmission and reception.

Abstract: An apparatus and method for radar detection of spectral moments and other spectral characteristics of echoes includes an agile antenna which directs an antenna beam in a direction for a dwell interval. A clutter filter reduces clutter. In order to eliminate the need for fill pulses to stabilize the clutter filter, the clutter filtering is accomplished by matrix multiplication of the echo signal in each range bin by the inverse of the covariance matrix for that range. This reduces the dwell at each range interval, and provides a stream of pulse-to-pulse information at each range interval. The pulse-to-pulse data in each range interval is spectrum analyzed to extract the desired spectral information, which is displayed.

Abstract: A method and apparatus for identifying a remote target includes a transmitter for transmitting pulses of energy toward the target for generating echo signals, and a receiver for receiving the echo signals, and for generating received signals representing the target, noise and clutter. The received signals are applied through a plurality of cascaded channels, each including a Doppler filter cascaded with a multiplier, each also including range sidelobe suppression, for, in each of the cascaded channels, narrowband filtering the signals passing therethrough about a controllable center frequency, and for, if necessary, converting the signals passing therethrough to baseband, for thereby applying one of a plurality of Doppler filtered baseband signals to the input of each of the range sidelobe suppressors of each of the cascaded channels. The power of the Doppler filtered baseband signals in each range bin is evaluated for determining the frequency at which the spectral density is greatest.

Abstract: A radar transmits dispersed pulses in which the subpulses are modulated by first and second mutually complementary code sequences, the autocorrelation functions of which are selected so that, in the sum of their autocorrelation functions, the main range lobes add, and the range sidelobes cancel. The received pulses with their Doppler sidebands are applied to a plurality of channels, each of which (except one) contains a mixer-oscillator combination that removes a specific Doppler phase shift along the range dimension at a different channel frequency. One channel has no mixer-oscillator because it is centered at a zero channel frequency. Within each channel, the received signals modulated by the first and second codes are matched-filtered by filters matched to the first and second codes, respectively, to produce first and second time-compressed pulses, each including (a) a main lobe representing the target range, and (b) undesirable range sidelobes.

Abstract: A radar system transmits dispersed pulses, and receives echoes from targets. The echo signals are digitized and applied over a number of signal paths. In each signal path except one, the digitized signal is multiplied by one of a plurality of differential exponential signals, for converting the echo signal of different exponential signals, for converting the echo signal in each path to baseband, with the baseband frequency representing a particular Doppler which depends upon the exponential signal. In the one remaining signal path, no multiplier is used, and the echo signal is deemed to be at baseband. The signals in each path are applied through a cascade of a pulse compressor and a range sidelobe suppressor. Since Doppler filtering has not yet taken place, full compression and range sidelobe reduction is not achieved, because of extraneous pulse-to-pulse phase shifts.

Abstract: A radar system simultaneously transmits first and second signals toward a target at higher and lower carrier frequencies, respectively. Each carrier is phase-modulated by a set of pulses. The first set of pulses is dispersed in time, and the second set of pulses is mutually complementary thereto. The transmitted pulses are reflected by the target and received simultaneously. The received signals are processed separately by Doppler filtering. Each Doppler-filtered return is code-matched filtered, and the filtered signals in each Doppler channel are summed with the corresponding Doppler-and-code-matched-filtered signals originating from the other transmitted frequency, to form range signals. Each range signal has its main lobe enhanced and its sidelobes suppressed by the summing of the code-matched-filtered mutually complementary echoes.

Abstract: A radar system includes a doppler/pulse compressor/range sidelobe suppressor filter bank (40), which separates received echo signals according to their frequency spectrum into doppler channels, and within each doppler channel performs pulse compression for reducing the duration of the received signals, and also performs range sidelobe suppression, for improving range resolution. It may be advantageous to perform certain types of processing in the time domain, such as determination of spectral moments for estimating velocity spread, mean closing velocity, and reflectivity of a diffuse target such as a weather phenomenon. An inverse (frequency-to-time) transform (50) is performed on the signals produced by the doppler/pulse compressor/range sidelobe suppressor filter bank (40), to produce a reconstructed version of the received signals. In these reconstructed signals, the pulses are compressed, and range sidelobes are reduced. The time-domain processing (62) is performed on the reconstructed signals.

Abstract: A multipurpose system provides radar surveillance for air traffic control purposes. The system includes four separate active phased-array antennas, each with .+-.45.degree. coverage in azimuth, from 0.degree. to 60.degree. in elevation. Each antenna element of each phased-array antenna is coupled by a low-loss path to the solid-state amplifier associated with a transmit-receive (TR) module. Each antenna produces a sequenc of pencil beams, which requires less transmitted power from the TR modules than a fan beam, but requires more time beacuse the pencil beam must be sequenced to cover the same volume as the fan beam. In order to scan the volume in a short time, the PRF is responsive to the elevation angle of the beam, so higher elevation angles use a higher PRF. Low elevation angle beams receive long transmitter pulses for high power, and pulse compression is used to restore range resolution, but the long pulse results in a large minimum range within which targets cannot be detected.

Abstract: A ranging system such as a radar system transmits signal pulses toward a diffuse target, such as an atmospheric disturbance. The echoes are processed by quantizing and by doppler filtering to produce a plurality of frequency components representing the radial velocities of various parts of the disturbance, which components are expected to be contaminated by an unknown amount of noise. The noise value is established by squaring the echo signals to produce power-representative signals. The signal samples are ranked according to amplitude, and one or more of the largest-value samples are discarded to reduce the order of the sample set. A Kolmogorov-Smirnov test statistic is generated and compared with a threshold established by the desired confidence level. If the test statistic exceeds the threshold, the order of the sample set is again reduced, and the test statistic again compared with the threshold.

Abstract: A radar generates first and second mutually complementary binary code sequences. The autocorrelation functions of the first and second pulse sequences are selected so that, in the sum of their autocorrelation functions, the main lobes add, and the sidelobes are of equal amplitude and opposite polarity, and therefore cancel. The radar sequentially transmits dispersed pulses in which the chips are phase modulated with the two codes. The received pulses are applied uncompressed to the input of a Doppler filter bank, which filters them into various Doppler channels, each representative of a particular radial velocity of the target. Within each channel, the received signals modulated by the first code are matched-filtered by a filter matched to the first code, to produce a first time-compressed pulse, and those modulated by the second code are matched-filtered by a filter matched to the second code, to produce a second time compressed pulse.

Abstract: Conventionally, a shift register receives radar video return signals and es them into a signal processing and detecting means. Since continuous, large cross-section echoes such as those derived from land masses may saturate the processor, the present apparatus is set to blank such land masses. For this purpose, the shift register capacity is made coextensive with the continuous land mass echo and further, the register is provided with a series of taps spaced one from the other a distance representing selected increments of the range extent being tested. Each tap output is applied to an amplitude-thresholder to pass only higher strength echoes to a counter. Count-responsive means operating as a counter threshold control the radar signal processor to the extent that when the total count exceeds a certain number a processor "shut-off" signal is generated. When the count goes below the certain number a "turn-on" signal is generated.

Abstract: CFAR systems may become ineffective when extraneous targets present in thhold control cells raise the threshold detection level to such a point that the target in the cell being tested becomes obscured. The present circuitry locates the particular threshold control cell or cells having the extraneous target and eliminates it from the threshold detection level computation.

Abstract: A digital processor for discretely sampled information signals, of the type such as radar return signals and communication signals. Means are disclosed for determining the positions and values of extrema and the positions of the leading and trailing edges of extended pulses occurring between sampling instants. Means are also disclosed for determining the duration of such extended pulses.