MTI Optimization in a Multiple-Clutter Environment

A means of optimizing a moving target indicator (MTI) filter for rejecting several types of clutter, which are generated by different mechanisms such as by rain or the ground, is formulated. lt is found that the optimal performance of such a filter depends on the spectral density functions, average radar cross sections, and the relative mean Doppler frequencies of each type of clutter. lt is shown that the optimal improvement factor of such a filter is bounded by the weighted average (weighted in accordance with the radar cross sections of the clutter types) of the improvement factor for the individual clutter type. lt is also shown that the improvement factor of such a filter is a function of the relative mean Doppler frequency f0 between the clutter types. As f0 increases, the performance of the MTI system degrades. The worst improvement factor occurs when f0 is equal to half of the radar pulse-repetition frequency (PRF).     

On the Optimization of MTI Clutter Rejection

In this paper is formulated the problem of optimization of the improvement factor of a nonrecursive MTI by minimization of a quadratic form. The minimum normalized clutter output (a reciprocal of the average improvement factor) is the minimum eigenvalue of this quadratic form, and the corresponding eigenvector is the optimal weight to be used in this filter. By use of classic matrix theory, some properties of this MTI improvement factor are shown, namely, that it is bounded and is a monotonic function of the clutter spectrum variance. Also discussed is the limit of an MTI system having a large number of cancellers. Finally, the problem of a staggered-PRF MTI filter is examined, for which it is shown that its improvement factor is bounded by two equivalent constant-PRF MTI systems. One of these systems has a PRF equal to the lowest PRF of the staggered-PRF system, while the other has a PRF equal to the highest PRF of the staggered system.     

Clutter Covariance Matrix Form Effect on Adaptive MTI Performance

The performance of an adaptive moving target indicator (MTI), which employs a Wiener predictor by means of a transversal filter, is discussed, taking into consideration the effect of the form of the clutter covariance matrix on the MTI performance. It is emphasized that the main tap position in the transversal filter is an important factor which provides degrees of freedom in the clutter covariance matrix to improve the MTI performance. Calculation results show that by exploiting these degrees of freedom, excellent performance is feasible, in particular shorter transient response.     

On Increasing Usable MTI Filter Bandwidth by Removing Linear-Phase Constraint

It has been shown in the literature that the linear-phase constraint of finite-duration impulse-response (FIR) digital filters can, under certain circumstances, be effectively traded either for a better filter amplitude response or a reduction in the number of filter coeficients. It is shown that such a tradeoff can be exploited for moving target indicator (MTI) radar signal processors to increase the usable bandwidth for target detection. Although it is demonstrated that the increase is significant for narrowband (ground) clutter, it is negligible for wideband (weather) clutter.     

Effect of timing jitter on performance of MTI filters

The effect of transmitting timing jitter and sampling jitter on a multipulse clutter cancellation system is analyzed, and explicit expressions are obtained for the net increase in the residue clutter power due to timing jitter. The increase in mean-square error is found to be proportional to the jitter variance, with the two jitters contributing almost equally. The system analyzed can have either a recursive or nonrecursive MTI filter, and the latter includes the familiar two- and three-pulse canceller as special cases. The increase in residue clutter power for a three-pulse canceller is about 4.8 dB worse than that for a two-pulse canceller     

Design and Evaluation of an Adaptive MTI Filter

The design and evaluation of an adaptive moving target indicator (MTI) filter, the adaptive canceler for extended clutter (ACEC) is dealt with, taking into consideration adaptivity to clutter mean Doppler frequency. This consideration is one of the most important operational requirements in adaptive MTI's and permits a relatively simple hardware implementation as compared to more general optimization and adaptivity criteria (briefly described). The ACEC's algorithm compensates in real time for the clutter mean Doppler frequency. Performances have been obtained by digital computer simulation in various operational conditions.     

Design of MTI Radar on the Basis of Detection Probability

A single (quadrature) channel moving target indicator (MTI) radar system employing a tapped delay line filter is analyzed. The point of view taken is that of optimal clutter rejection in conjunction with subsequent receiver decision operations. The random nature of the spread of target Doppler shifts is taken into account. Based on the above, a procedure is presented by means of which the detection probability can be numerically evaluated for an optimized filter frequency response.     

Maximizing the Usable Bandwidth of MTI Signal Processors

A technique is presented for maximizing the percentage of usable Doppler bandwidth throughout which a radar return can be detected while maintaining an acceptable clutter suppression. The technique employs the weighted Chebyshev approximation to the design of a transversal high-pass digital filter which has an optimal passband ripple for a given number of filter weights and associated integration gain consistent with the required increase in signal-to-noise ratio needed for acceptable probabilities of detection and false alarm. Conventional approaches to the design of a movingtarget arget indictor (MTI) filter which maximizes the improvement factor by clutter suppression typically improve the signal-to-background noise ratio over less than 50 percent of the range between dc and the pulse-repetition frequency fT. This technique can increase the usable bandwidth to 80 percent or more of fT. Two examples are included which utilize parameter values from the Army Missile Command's experimental radar and demonstrate the interactive influence of such filter parameters as the number of weights, passband ripple and bandedge, and stopband attenuation and cutoff.     

The Effect of Staggered PRF's on MTI Signal Detection

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.     

Improvement Factor of the Phase-Sensitive Noncoherent MTI

The phase-sensitive noncoherent MTI detects targets by relative motion between the target and an extended clutter background. In this type of MTI, the phase of the target is compared with the phase of the clutter in an adjacent range bin. Theoretical analysis of the system's performance is presented. The improvement factors for single- and double-delay periodic filters are derived and computational results are included.     

Properties of Staggered PRF Radar Spectral Components

Expressions for moving target indicator (MTI) improvement factor limitation due to pulse repetition frequency (PRF) staggering and loss of target detectability for various values of Doppler frequency in the passband are presented. It is also shown that the product of variance of stagger periods and clutter variance is an important parameter determining the performance of a staggered PRF MTI radar.     

A Comparison of Noncoherent and Coherent MTI Improvement Factors

An analysis based on statistical considerations and Monte Carlo simulations indicates that a noncoherent moving target indicator (MTI) using a linear envelope detector differs from one using a square law envelope detector. The square law envelope detector is usually described in the literature because of ease of analysis, and it is commonly stated or implied that the results are the same for the two cases because of the similar spectral characteristics of the detectors. A comparison is made between the two noncoherent MTIs and the coherent MTI in terms of clutter attenuation and MTI improvement factors.     

New Clutter Rejection Waveforms for Long-Range Radar

A frequent compromise in the design of long-range search radars has to be made between the maximum unambiguous detection range and the achievable coherent clutter rejection performance. A new class of waveforms is introduced which offers the designer a previously unavailable flexibility in arriving at radar designs with improved clutter rejection without seriously affecting the maximum unambiguous search range. The key to these new waveforms is the recognition that a class of useful N-pulse, nonrecursive, moving target indicator (MTI) canceler designs exists which only requires the radar to transmit a total of N -1 (nonuniformly spaced) pulses.     

Performance Degradation of MTI Circuits Due to Amplitude Limiting

The loss in output signal-to-noise ratio (SNR) due to amplitude limiting is obtained for a radar circuit consisting of a bandpass limiter, coherent demodulator, matched filter, and moving-target-indicator (MTI) filter. The circuit is used in scanning MTI radars. The tandem connection of the limiter and coherent demodulator is a model for the saturation of the intermediate-frequency (IF) demodulator of an MTI radar. Results on special functions are used to obtain simple formulas for the loss in output SNR relative to a linear IF demodulator when the input SNR is less than -15 dB and the number of hits per 3-dB beamwidth exceeds 15.     

Airborne adaptive MTI scheme with preventing the whitening of thetarget

A new airborne MTI scheme that applies to non-homogeneous clutter environment is presented. Results of simulation have proved that the scheme has a superior ground clutter suppression performance and can effectively prevent the whitening of a target     

CTD MTI Radar Filter with Charge-Transfer Inefficiency Compensation

The design and implementation of a second-order nonrecursive moving target indication (MTI) radar filter using commercially available charge-transfer devices as delay lines are described. A simple technique is included to compensate for the device charge-transfer in-efficiency and its sensitivity is analyzed. Experimental laboratory tests and results in an operating radar system are reported showing the good performance of the realized MTI radar filter.     

Super resolution feature extraction of moving targets

High range resolution (HRR) moving target indicator (MTI) is becoming increasingly important for many military and civilian applications such as the detection and classification of moving targets in strong clutter background. We consider the problem of extracting the HRR features of moving targets with very closely spaced scatterers in the presence of strong stationary clutter, where the range migration and Doppler frequency are taken into account. A relaxation-based algorithm, which is robust and computationally simple, is proposed to deal with the above problem. Numerical results have shown that the proposed algorithm exhibits super resolution and excellent estimation performance     

An Adaptive MTI for Weather Clutter Suppression

A digital realization of an adaptive clutter-locking loop is presented. The purpose of the loop is to estimate the mean Doppler frequency of the clutter. The clutter spectrum is then shifted toward the zero Doppler by this estimate. A fixed moving target indicator (MTI) canceler following the loop suppresses the shifted clutter. Experimental simulations illustrate the feasibility of the loop. Results indicate that the proposed canceler works significantly better than a fixed canceler, while not as well as the 10-pulse moving target detector (MTD) processor. However, the complexity of the MTD is significantly more than the relatively simple adaptive processor presented here.     

MTI Processing and Weibull-Distributed Ground Clutter

It is shown that the Weibull-distributed ground clutter obeys a Weibull distribution after processing by the double canceler moving target indicator (MTI).