Showing papers on "Moving target indication published in 1973"

Moving target indicator system

Abstract: An improved moving target indicator system operable with antenna side lobe blanking, that substantially eliminates false target reports at the output of the moving target indicator so as to overcome a problem associated with radar systems using moving target indicator and side lobe blanking arrangements. The system provides one additional bit or an action bit in memory for each range bin in each canceller stage of the moving target indicator system. When side lobe blanking occurs, an associated bit is applied to the system and this bit is allowed to propagate through the second canceller as well as any subsequent cancellers. Thus, during each pulse repetition interval that would be affected by side lobe blanking action, a blanking gate is energized to inhibit the generation of false targets. For a radar system utilizing step transmission, a variable recirculating delay is provided to insure that regardless of the time of occurrence of the side lobe blanking condition, the output of the moving target indicator unit will be blanked the required number of periods.

The Effect of Staggered PRF's on MTI Signal Detection

Abstract: Long-range surveillance radars use MTI techniques to detect moving targets in a clutter background. The transmitter PRF is usually staggered to eliminate the blind speeds due to aliasing of the target and clutter spectra. A spectral analysis of the target and clutter signals is performed for the case of nonuniform sampling, and it is shown that the clutter spectral density continues to fold over at the basic PRF, but the signal spectrum becomes dispersed in frequency, which means that an MTI rader will never be completely blind to moving targets.

Moving target indicator with minimum clutter interference

Abstract: A radar moving target indicator system employs a cancellation filter having the width of its cancellation notch controlled in accordance with the angle of the radar scan. As the antenna scans at wide angles (30* to 50* from the line of movement of the radar platform) the frequency response of the filter is switched so that the cancellation notch is wide. The notch is narrowed for smaller scan angles. AC switching transients in the radar output display are eliminated by keeping the circuit parameters constant for those portions of the filter which see D.C. components of the input signal.

Platform motion compensating for airborne radars

Abstract: Platform motion of an airborne radar system of the moving target indicator type is compensated for by an adaptive displaced phase center antenna arrangement. The signals detected by the two receiving beams are combined to form sum and difference signals. Thereafter, the sum signals have subtracted therefrom delayed sum, difference and delay difference signals which are weighted by coefficients determined by cross-correlating these signals and the output signal obtained from the above subtraction. The system thus combines the DPCA and the side lobe cancellation concept to eliminate signals received from stationary targets. The receiving beams may be squinted to compensate for antenna rotation.

Target tracker having target recognition means

Abstract: A monopulse radar system having automated target identification capability. first target recognizer, which can recognize a desired target by its radar signature, is used to improve direction finding performance by accurate placement and reduction in size of a receiver range gate. An additional target recognizing means is provided and allows integration of the return signal only if the signature of that return has been recognized as characteristic of the desired target.

Hybrid filter employing digital techniques and analog components and amti radar employing same

Abstract: A filter employing the principles of digital filters representative of Z-transform solution of mth-order difference equations is implemented using analog components; arithmetic units are realized by resistive networks employed with operational amplifiers, and memory elements are realized by the use of switched capacitors. A particular embodiment comprises a cascade implementation of a Cauer or elliptic filter applied to range-gated clutter attenuation in an airborne moving target indicator (AMTI) radar; time sharing of arithmetic units among range bins, multiplexing of slow filters for achievement of faster overall system response, and electronically variable filter characteristics (through electronic component selection) are disclosed.

Moving-target-indicator recursive radar filter using bucket-brigade circuits

Abstract: A prototype clutter-rejection filter for radar is described. It uses analogue shift registers of the bucket-brigade type, which, in common with charge-coupled devices, can combine the flexibility of digital processing with the simplicity of analogue operation. Certain imperfections in the devices are shown to be particularly important for moving-target-indicator filtering.

Sequential automatic gain control circuit

Abstract: The sequential automatic gain control circuit is an improved AGC circuit that can be used in search and track radars which receive a series of pulse returns from each target. The sequential AGC is well suited for monopulse radars and moving target indication (MTI) processing where gain stability and gain match between channels are required. The maximum input signal levels are sensed by a pair of AGC circuits which alternately provide output levels for a predetermined time. The output signal levels are proportional to the maximum input signal received during the previous pulse return period.

Design of a staggered-p.r.f. moving target indication filter

Abstract: To avoid blind speed phenomena, staggered-p.r.f. m.t.i. systems are used in modern radars for detection of high-speed targets. In this paper a procedure is presented which considers both the effect of filter weights and the interpulse durations. The goal of this procedure is to yield an m.t.i. response with minimum variations in the pass-band and maximum attenuation in the stop-band.

Performance of Cascaded MTI and Coherent Integration Filters in a Clutter Environment

Abstract: : The combination of moving target indicator (MTI) and coherent integration filters can provided velocity filtering with advantages that neither technique can provide alone. These techniques are evaluated as a special case of a transversal filter which lends itself to analysis using matrix algebra. This approach gives a simple, easily understood insight into the effects of weighting the input radar data. The resulting matrix equations are evaluated and the results are plotted for some special configurations. The computer programs which were written as a part of this research are not restricted to these configurations nor to the type of clutter spectrum that is assumed. It is shown that the performance of coherent integrators in a coherent noise (clutter) environment cannot be predicted with a concise analytical expression. In particular, the weighing of the input data and the covariance matrix of the interference determine the integrator performance.

Clutter Spectra of Low PRF AMTI Pulse-Doppler Radar

Abstract: Approximate expressions are derived for the video clutter spectra in the receiver of a low pulse repetition frequency (PRF), airborne moving target indicator (AMTI), pulse-Doppler radar for both step-scanning and continuous-scanning antennas. The receiver is assumed to process the received waveform with a clutter-tracking oscillator and a window function is employed to obtain short-term spectra. Except for the broadening effects of the window function, it is shown that the clutter spectrum can be simply related to the antenna voltage-gain pattern. It is further shown, in the scanning antenna case, that the combined spectral broadening due to platform motion and antenna scanning cannot be assumed to be the result of the convolution of the separate effects unless the antenna gain pattern has a Gaussian shape. The approximate clutter expressions are illustrated by examples and are shown to agree well with the results of computer calculations.

Improved Moving-Target-Indicator Filtering for Phased Array Radars

Abstract: : A technique is described for using recursive digital filters in the moving target indicator of phased array radars. This technique, called initialization, is effective in reducing the severe transient effects normally exhibited by these filters for large clutter input signals. Consequently, the superior frequency characteristic of recursive filters can be realized. The problem is addressed from the state variable point of view and a general initialization expression is derived. This procedure is illustrated for example filters, and typical moving target indicator output sequences are shown. The concept of 'dynamic' frequency response is introduced and used to demonstrate the effectiveness of initialization for moving target indicator input sequences of varying length.