Abstract: A method and apparatus for hybrid analog-digital pulse compression, as well as, a method of use and manufacture includes an analog intermediate frequency filter, a converter, and a digital correlator. The analog intermediate frequency filter filters and weights returned echo signals, and the digital correlator compresses the filtered and weighted echo signals. The frequency or impulse response of the digital correlator is set based on the frequency or impulse response of the analog intermediate frequency filter to obtain a pulse compressor with minimal mismatch loss and improved sidelobe suppression. The invention provides for the lowest possible sampling rate of analog-to-digital convertors used with the apparatus; thus, minimizing the cost of this device and all subsequent digital processing.

Abstract: Sea clutter can be removed from radar signals by accurately determining sea velocity in a coverage area of a radar scan, updating a median value for the coverage area, and selecting a clutter rejection filter for the coverage area biased on the median value for the coverage area. Preferably, a median sea velocity is stored for each coverage area, as the median value. When processing begins for a coverage area, a previously stored median sea velocity is retrieved and updated. The median sea velocity is updated by converting the median sea velocity into a median phase difference between two echo signals, based upon carrier frequency and the time between receipt of two echo signals, which is preferably more than one interpulse period. The difference in phase between the two echo signals is compared with the median phase difference and the median sea velocity is increased if the median phase difference is smaller and decreased if the median phase difference is larger.

Abstract: A method and apparatus are disclosed for providing optimum radar beam patterns to provide complete radar coverage at both short ranges and long ranges in a radar system using solid state transmitters. Long pulses for covering long ranges are generated and split into a pair of signals with a specific amplitude and phase relationship. These signals are provided to a transmit beam forming matrix of an array antenna to generate an optimum pattern for long range coverage. Short pulses are generated for providing short range coverage and are split into a pair of signals which are phase shifted differently from the long pulses. These signals are then provided to the transmit beam forming matrix to generate a different beam pattern for providing short range detection. The short range beam pattern has a sufficient amount of energy to provide coverage to maximum desired altitude over a range extending to where echoes from the long pulses may be received undistorted.

Abstract: A unitary surface acoustic wave device for continuous quadraphase coding of a high amplitude video impulse with provisions for controlling the rise and fall times of such impulse.

Abstract: A phase detector receives two input digital signals representing Cartesian coordinates of a vector and outputs a digital signal indicative of the phase angle of the vector. The input digital signals are logarithms of the square of, for example, in-phase and quadrature components of a radar signal and are subtracted in the phase detector to produce a difference signal having a magnitude and a polarity. The polarities of the difference signal and the two information signals are used to determine the octant of the phase angle by addressing a read only memory. The magnitude of the difference signal is used as an address of a read only memory storing digital values corresponding to angles within an octant. The octant output by the first read only memory and the angle output by the second read only memory together indicate the phase angle of the vector.

Abstract: A high-power high-isolation switch for high-power devices which switch power to one of several alternative output ports. Unwanted leakage is attenuated and high-isolation between the output ports is obtained. In addition, protection against burn-out during abnormally high leakage conditions is provided where the devices employed are not self protecting.

Abstract: A single-scan editor of bird echoes uses range rate to aid in identifying bird echoes. The range rate is preferably calculated from change in phase between one interpulse period to the next interpulse period and both unfiltered and MTI filtered signals are used for the calculation of change in phase. The unfiltered phase difference is used if the logarithm of the total power of the phase difference exceeds a predetermined threshold during at least one of the interpulse periods and if not, the MTI filtered phase difference is used if the total power of the MTI filtered signal exceeds a corresponding predetermined threshold. If neither threshold exceeds the corresponding threshold, no calculation is made. Due to the relationship between phase difference and range rate, several possible range rates correspond to most phase differences. Therefore, an occurrence of each of the possible range rates is counted over the course of a cycle.

Abstract: A dual stacked beam radar in which, after listening to low stack beams, and waiting for their echoes to return, a transmitter signal is transmitted on high, the high stack beams being listened to during the longer dead times during variable interpulse periods of the low stack beams.

Abstract: A two-parameter clutter map for storing two variables for every spatial location in order to define both the intensity of the interference and the fluctuation characteristics of the interference from scan-to-scan. The two variables are obtained by processing input data from an integrator in two n-pole integrators having different orders. The ratio of the two variables or their difference in logarithmic form is employed as a measure of the scan-to-scan fluctuation characteristics. An option to control alarms and the leading edge of moving rain storms is also provided.

Abstract: A radar stability measurement system uses a microwave delay line that may be coupled between a standby transmitter and a standby receiver to test the stability of the standby channel in a radar system having at least two channels. A pulse output by the standby receiver is sampled in portions. Several samples of each portion are taken, samples are analyzed to produce a sum of residue power (P.sub.rm) and a sum of zero Doppler power (P.sub.om) for the m-th portion. After all samples of all portions have been taken, a single indicator of stability is calculated as ten times the log of the ratio ##EQU1## The measurement system can also be applied to single channel systems, although a short interruption of system operation may be necessary.

Abstract: Method for determining and using clutter estimates in a radar clutter map. The method does not require synchronization of the transmitted radar pulses with the azimuth coordinates of the map cells. Data inputs close to each map azimuth location are used to estimate the echo amplitude in the map cell which would result if the antenna beam was pointing directly at the clutter when one data sample occurred. A burst of pulses are transmitted and return echoes are processed to produce clutter signals at least twice within the time it takes for the antenna to scan one beamwidth. Clutter echoes received adjacent in azimuth to the map cell for which the value is being calculated are converted by a formula into a value for adjusting the present map cell value. The formula takes into consideration the magnitude of the values, the difference between the values, the antenna beam width, and the azimuth spacing of the samples.

Abstract: An adaptive detection threshold system for moving target detector and moving target indicator radar systems. The threshold system uses data from the echo input signal to reconstruct a threshold level closely resembling the output clutter residue in doppler filters due to point clutter sources. At least three azimuth data values are used, with the values being from adjacent coherent processing intervals and separated in azimuth a distance approximately equal to the beamwidth of the antenna system. The data at the same range from the three azimuths is combined to form an estimate of the residue at the output of a doppler filter, assuming that the echo is caused by point clutter. Compensation for radar instability and changes in scan rate or interpulse period is included. Data from conventional constant false alarm rate processing designed to control alarms from distributed interference, such as weather echoes, is also used to compensate the residue estimate.

Abstract: An arrangement for selecting between different doppler filter pairs having response characteristics optimized for ground clutter or moving rain clutter rejection. The selecting process detects the amplitude and mean doppler of the received radar echoes. The filter which is optimized for rain clutter rejection is normally used until clutter amplitude is detected above a predetermined value and the mean doppler is detected as being equal to or near zero. When such a detection is made, the filter optimized for ground clutter rejection is selected. Portions of the selecting device allow for the selection to be determined over several samples rather than switching the filters in each sample or coherent processing interval. Another portion of the circuitry changes the predetermined values which must be exceeded for a selection of the ground clutter filter, thereby preventing another filter change with only a small change in detected amplitude or mean doppler.

Abstract: A radar having a multiplicity of receive beams stacked in elevation and a target height extractor especially for use therein are disclosed. In operation, a set of range sweeps corresponding to an azimuth scan of the stacked receive beams across a detected target is established. A range cell interval corresponding to the detected target is estimated for each range sweep of the set. A target range measurement is computed from a set of estimated range intervals. Only the radar receive beam echo information corresponding to the estimated range cell interval for each range sweep of the established set is used by the height extractor to compute a corresponding set of elevation angles. A target elevation angle is formed as the weighted average of this computed set. Only one height computation is performed for each established set of range sweeps based on a function of factors including the computed target elevation angle and computed range measurement of the corresponding established set of range sweeps.

Abstract: A system and method of compensating a digital doppler processor for unbalance in in-phase I and quadrature Q signal inputs thereof is disclosed. The method includes the steps of measuring the unbalance in the I and Q signal inputs to the digital doppler processor, determining a desired set of weighting coefficients based on the measured unbalance, and performing doppler filter calculations in the digital doppler processor with the desired set of weighting coefficients. The system comprises a sensor for measuring the unbalance in the I and Q signal inputs to the digital doppler processor, and apparatus for determining a desired set of weighting coefficients for the doppler filter calculations of the doppler processor based on the measured unbalance of the sensor.

Abstract: In a radar which transmits a phase-coded train of sub-pulses and which derives the in-phase (I) and quadrature (Q) components of the received echo signals with respect to a local reference oscillator is embodied a phase discrimination constant false alarm rate (CFAR) system partially comprising a phase angle sensor for measuring the phase angle of the echo signal as one of at least eight predetermined phase angle representations, which are characterized preferably by binary numbers in Gray format, based on the relative magnitudes and polarities of the I and Q components of the echo signal. The phase angle representations may correspond exclusively to phase angle increments in the phase angle interval of 0.degree. to 360.degree. with respect to the local reference oscillator. Preferably, the phase angle increments are evenly partitioned within the 360.degree. interval.

Abstract: This invention discloses pulse radar apparatus for the transmission of radar pulses having a pair of frequencies in each rf pulse. One of the frequencies transmitted in each pulse is repeated in the succeeding pulse while the other frequency is changed to a new frequency. Moreover, the repeated frequency appears in the same relative position in the pulse pair as in its original occurrence.

Abstract: An MTI radar system having a four pulse canceller where the interpulse periods vary preferably according to a double or triple sawtooth pattern is disclosed. The four pulse canceller is comprised of a two pulse canceller cascaded with a three pulse canceller. The three pulse canceller is arranged to accomplish summations of three weighted pulses in two operations, one involving fixed binomial weights (1, -2, 1) and the other variable components (a', b', c'). The interpulse period choices and sequence of use permit the variable weights to be defined by polarity and binary fractions implemented by the use of controllable scalers and polarity reversers.

Abstract: A low PRF pulse doppler radar system utilizing a VIP digital filter bank signal processor to suppress echoes from terrain, rain, and chaff, and pass echoes from aircraft moving at higher speeds is disclosed.Each of a plurality of VIP filters individually provides high attenuation to undesired signals over designated frequency bands, the width of which are a large fraction of 1/T.sub.av where T.sub.av is the average interpulse period. Little or no attenuation of desired signals having doppler frequencies greater than 1/T.sub.av occurs. The outputs of the plurality of filters are desensitized to prevent false alarm from clutter, and the presence of a desired radar pulse echo is determined by a comparison with a threshold level.

Abstract: A pulse radar system transmits a pulse containing an upper and a lower sideband frequency signal. The upper and lower sideband signals are formed by a stable local oscillator signal and a coherent oscillator signal which are mixed in a mixer. The frequency separation between the upper and lower sidebands is sufficient to cause fluctuations in the desired target radar cross section to be statistically independent with respect to the upper and lower sideband frequency components in the transmitted pulse. Target reflected pulses are separately processed for each transmitted frequency component. The probability of detection is improved by mathematically combining the separately-processed output signals of each frequency component.