MTI Loss with Coherent Integration of Weighted Pulses

A moving target indicator (MTI) preceding a coherent integrator causes a degradation in the signal-to-noise ratio (SNR). This negative effect can be reduced by weighting of the MTI output pulses before the integration process. Two examples are given which show the improvement in SNR and detection probability as a result of this weighting.     

MTI Target Visibility

The available target Doppler space over which the target-to-clutter lutter improvement factor is equal to or greater than a design value based on the conventional moving target indicator (MTI) improvement factor I is investigated. Quantitative results are given for case of a zero-mean Gaussian spectrum using binomial weighting.     

Some Results on Pulse-Burst Radar Design

Pulse-burst radar attempts to capitalize on the advantages of both low and high PRF radar while minimizing their disadvantages. Optimization procedures are applied to the choice of transmitter signal and receiver weighting. The results are compared to the use of Tschebyscheff transmitter weighting with an optimized receiver. The effects of various design and operational parameters are indicated. The performance of pulse-burst radar is qualitatively compared to that of conventional low and high PRF Doppler radar. It is concluded that pulse-burst radar offers the possibility of achieving a solution to the MTI problem under operational conditions where conventional Doppler radars fail.     

Quantization Requirements in Digital MTI

To minimize hardware complexity, it is desirable to implement a digital moving target indicator (MTI) with the fewest number of quantization levels. The reduction of the clutter cancellation ability of single-and double-canceller MTI's is discussed with binominal weighting as a function of the number of levels and the spacing of the levels. The method of analysis is applicable to more complex MTI's as weil as nonuniform quantizers.     

中等PRF机载PD雷达频域恒虚警处理性能计算

 一、引言 在中等脉冲重复频率（PRF）工作时,MTI-FFT-CFAR是PD或MTD雷达信号处理器的一种典型结构。Lawrence和Moore对MTD雷达在地杂波和气象杂波背景中的检测性能的计算中,假设了邻近距离单元中的杂波样本是独立同分布的（iid）。而在MTI-FFT-频域单元平均CFAR处理器中,频域单元的杂波样本明显偏离iid假设。门     

Weighting Factor and Transmission Time Optimization in Video MTI Radar

In an earlier paper by the author the problem of determining the optimum symmetrical weighting factors for a video MTI radar was discussed. This paper extends this work so as to remove the symmetrical restriction from the problem. In addition, for a staggered pulse system, optimum times of transmission are determined. In the earlier paper a global solution to the restricted optimization problem was achieved. In this paper only a locally optimum solution is achieved for the more general problem.     

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.     

Elimination of Blind Velocities of MTI Radar by Modulating the Interpulse Period

The performance of a coherent MTI is determined by two sets of parameters: the interpulse periods and the weighting coefficients. The latter are expressed in terms of the former so as to maximize clutter attenuation. Interpulse periods are optimized so as to remove blind velocities. The many local optima of the interpulse periods have improvement factors that show differences of up to 6 dB for a 5-pulse canceler. A computer program has been developed that combines random search and the gradient method to produce points that combine a high value of the improvement factor with good blind speeds performance.     

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.     

Performance Compparison of Optimum and Conventional MTI and Doppler Processors

The performance of an optimum radar signal processor and more conventional techniques (such as MTI, adaptive MTI, and cqherent integration) are compared. A mathematical method is suggested and applied to several cases of practical interest. A number of operative conditions are discovered in which the conventional processing techniques give very poor performance and the optimum radar processor becomes necessary.     

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.     

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.     

An MTI Technique for Processing Radar Measurements of a Waking Reentry Body

A processing technique based on pulse-cancellation techniques familiar in moving target indicator (MTI) radar is proposed for separating (in Doppler) echoes of a reentry body traveling at hypersonic velocities from those of its lower velocity turbulent wake appearing in the same range cell. The cancellation technique is implemented by forming the sum of the products of binomial weighting coefficients of alternating sign with the complex echoes of a small number of closely spaced transmitted coherent pulses; thereby, in effect, synthesizing a digital canceler. The ability of the two-and three-pulse canceler to estimate body RCS in the presence of attached wake is demonstrated by employing coherent burst data collected by the AMRAD radar for a mission flown at the White Sands Missile Range. Estimates of body RCS obtained from the two-and three-pulse canceler compare favorably to the corresponding estimates obtained from a 30-pulse Doppler periodogram for this mission. Expressions for both the achievable wake rejection ratio and the mean and standard deviation of the body power estimate of the N-pulse canceler are derived as a function of the wake parameters, assuming Gaussian wake statistics.     

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.     

Clutter suppression using recursive and nonrecursive MTI filters

The author calculates the effectiveness of clutter suppression of a moving-target-indicator (MTI) filter in tandem with a fast-Fourier-transform (FFT) Doppler filter bank, taking into account the transient response of the MTI filter. Both recursive and nonrecursive filters are considered. The analysis is extended to the high-pulse-repetition-frequency (PRF) case with clutter fold over. The results can be used to select key design parameters, including the MTI filter, the window size, and the initial transient segment to be discarded. Numerical examples are included     

Ambiguity Resolution for Satellite Doppler Positioning Systems

The implementation of satellite-based Doppler positioning systems frequently requires the recovery of transmitter position from a single pass of Doppler data. The least-squares approach to the problem yieds conjugate solutions on either side of the satellite subtrack. It is important to develop a procedure for choosing the proper solution which is correct in a high percentage of cases. A test for ambiguity resolution which is the most powerful in the sense that it maximizes the probability of a correct decision is derived. When systematic error sources are properly included in the least-squares reduction process to yield an optimal solution the test reduces to choosing the solution which provides the smaller valuation of the least-squares loss function. When systematic error sources are ignored in the least-squares reduction, the most powerful test is a quadratic form compasison with the weighting matrix of the quadratic form obtained by computing the pseudoinverse of a reduced-rank square matrix. A formula for computing the power of the most powerful test is provided. Numerical examples are included in which the power of the test is computed for situations that are relevant to the design of a satellite-aided search and rescue system.     

Development of airborne moving target radar for long range surveillance

The following topics are discussed in the context of the development of an airborne moving target radar for long range surveillance: US Navy long range shipborne radar; Cadillac I airborne early warning (AEW) radar; Cadillac II airborne early warning (AEW) radar; airborne moving target indicating (AMTI) radar; related post-war radar activities; and the invention of the displaced center antenna. Among the topics studied is the use of a monopulse antenna in an MTI radar to remove the degradation of the MTI caused by rapid scanning of the antenna. A method of using a monopulse antenna for motion compensation in airborne MTI is discussed.<>     

Constrained Improvement MTI Radar Processors

A new class of staggered PRF MTI radar processors is developed in this paper. These processors are constrained to achieve a specified value of MTI improvement and, subject to this constraint, minimize variations in processor response as a function of target Doppler frequency. The selection of both filter weights and PRF stagger sequences is discussed and a number of representative designs are presented.