Random Sidelobes Research Articles

A Random Antenna subset selection jamming method against multistatic radar system

Multistatic radar system (MSRS) is considered an effective scheme to suppress mainlobe jamming, since it has higher spatial resolution enabling jamming cancellation from the spatial domain. To develop electronic countermeasures against MSRS, a low complexity random array subset selection (RASS) jamming method is proposed in this paper. In the RASS jammer, elements of the array antenna are activated randomly, leading to stable mainlobe and random sidelobes, which is different from the traditional jammer that applies the complete antenna array enjoying constant mainlobe and sidelobes. We study the autocorrelation matrix of RASS jamming signals received by radars, and derive its rank, revealing that the rank of jamming subspace is increased thus severely degrading the performance of jamming cancellation. Moreover, we calculate the output jamming to signal-and-noise ratio (JSNR) after the subspace-based jamming suppression methods used in MSRS with the proposed jamming method, which demonstrates that the rank increasing property invalidates such suppression methods. Both simulation and experiment results verify our analytical deduction and exhibit the improved countermeasure performance of our proposed RASS jamming method compared to the traditional jammers.

Comparison of Correlation-Based OFDM Radar Receivers

Various correlation-based receivers have been proposed in passive bistatic and active monostatic radar exploiting orthogonal frequency-division multiplexing communications signals, but too little has been dedicated to establishing their relations and advantages over each other. Accordingly, this article provides an analytical comparison of the common filters in such waveform sharing scenarios, along with a performance analysis regarding three criteria: computational complexity, signal-to-interference-plus-noise-ratio, and resilience to ground clutter. The last two especially assess the possible detrimental effects of the random sidelobes (or pedestal) induced by the data symbols in the range-Doppler map. Although simulations show that none of the filters performs unanimously better, the ones employing circular correlations globally evidence attractive results.

STATISTICAL PROPERTIES OF RANDOM SPARSE ARRAYS

Theoretical models that can be used to predict the range of mainlobe widths and the probability distribution of the peak sidelobe levels of two-dimensionally sparse arrays are presented here. The arrays are considered to comprise microphones that are randomly positioned on a segmented grid of a given size. First, approximate expressions for the mean and variance of the squared magnitude of the aperture smoothing function are formulated for the random arrays considered in the present study. By using the variance function, the mean value and the lower end of the range i.e., the first 1 per cent of the mainlobe width distribution, can be predicted with reasonable accuracy. To predict the probability distribution of the peak sidelobe levels, distributions of levels were modelled by using a Weibull distribution at each peak in the sidelobe region of the mean squared magnitude of the aperture smoothing function. The two parameters of the Weibull distribution were estimated from the means and variances of the levels at the corresponding locations. Next, the probability distribution of the peak sidelobe levels were identified by following a procedure in which the peak sideload level was determined as the maximum among a finite number of independent random sidelobe levels. It was found that the model obtained from that approach predicts the probability density function of the peak sidelobe level distribution reasonably well for the various combinations of the two different numbers of microphones and the various grid sizes tested in the present study. The application of these models to the design of random, sparse arrays having specified performance levels is discussed.

Equivalence of adaptive array diagonal loading and omnidirectional jamming

Diagonal loading, where a diagonal matrix is added to the estimate of the covariance matrix, is often used in adaptive arrays to minimize the array's responsiveness to random fluctuations in the estimate of the interference environment. Poor estimates of the covariance matrix often result in high random sidelobes in the sample matrix inversion (SMI) adapted pattern. It is shown in this communication that an omnidirectional spread of uniform jammers arriving at a linear array of half-wavelength spaced elements with cosine element patterns also produces a diagonal matrix. This equivalence of form is useful in visualizing the effects of diagonal loading and understanding the resulting patterns.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Observation and explanation of an unusual feature of random arrays with a nearest-neighbor constraint

When a nearest-neighbor constraint (which prevents elements from lying closer than some specified distance from each other) is imposed on a large random planar array of isotropic radiators, the corresponding radiation pattern contains a region around the main beam where random sidelobes are suppressed. This effect is mostly clearly manifested if the array is densely packed, i.e. if the array contains nearly the maximum number of elements consistent with the chosen constraint. A theory to account for this effect is developed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Radar Performance Review in Clear and Jamming Environments

The performance of electronically scanned radar systems is evaluated for clear and barrage jamming environments. Radar figures of merit in jamming are derived for search and track modes and are directly related to antenna pattern relative sidelobe levels. A random sidelobe model is analyzed with various numbers of independent jammers. Probability distributions of detection probability are derived to determine detection performance versus average jamming level and number of jammers.