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Nonlinear adaptive processing using sparse arrays has received a fair amount of attention in the radar community recently because it is possible to exploit more spatial degrees of freedom for beamforming than a conventional linear processor would allow. However, the practical difficulties of nonlinear adaptive beamforming have received little consideration in the literature. This paper will describe...
This paper describes fully adaptive nonlinear space-time processing on nested arrays. Nested arrays are sparse arrays that in conjunction with nonlinear processing of the received signals enable more adaptive degrees of freedom than a conventional linear beamformer would allow. The Space-Time Adaptive Processing (STAP) architecture proposed in this paper consists of a nested array that samples received...
In theory, nonlinear adaptive beamforming techniques which form an extended virtual array from a sparsely populated physical array offer significantly enhanced adaptive degrees of freedom towards mitigating environmental interference as opposed to conventional linear beamformers. A neglected practical issue however, central to the implementation of nonlinear beamformers in radar, is an accurate determination...
This paper describes the multirate processing of random signals sampled on nested intervals. Nested sampling intervals consist of nonuniformly spaced samples formed by concatenating two or more smaller intervals each with uniform sampling. By filtering a vectorized version of the signal power spectral density matrix, the input-output behavior of conventional filter banks can be replicated. This type...
Promising techniques have recently been developed for creating nulls in the transmit sidelobes of a radar by using the signal from a nearby auxiliary antenna. In operational settings, the performance of these nulling techniques will be sensitive to electromagnetic scattering from objects in the vicinity of the antennas. This paper presents a theoretical analysis of the impact of environmental and...
Many modern radar systems employ pulse compression to maximize the energy on target while maintaining high range resolution. For a solitary point target in white noise, employing a matched filter on receive will maximize the target signal-to-noise ratio (SNR) at the output of the receiver. The matched filter itself is a time-reversed version of the transmitted waveform which is convolved with the...
Modern radar systems often incorporate the ability to form nulls in the antenna transmit pattern. Transmit nulls can be used to suppress the returns from point clutter sources greatly and to reduce interference with neighboring emitters. To implement a transmit nulling capability, one practical technique is to provide independent phase control at each element of a phased array antenna. However, for...
This paper describes a method for constructing waveforms such that the individual radars in a spatial Multiple Input Multiple Output (MIMO) radar system can simultaneously transmit pulse compression sequences yet avoid interference with each other. The waveform design algorithm is based on the matrix representations of finite abelian groups.
The ability to create nulls in the transmit pattern of a phased array antenna has many applications for radar systems, including interference and clutter mitigation. Most nulling techniques introduce small perturbations in amplitude and phase, or phase-only, at each element of the phased array. For practical reasons, phase-only perturbations are desired and they create acceptable rms levels of null...
This paper describes a novel concept for performing adaptive transmit nulling in radars. Typically, the average depth of open-loop transmit nulls is limited by the Error Sidelobe Level (ESL) of an array. The ESL is determined by random errors in the array manifold, such as the residual calibration errors. Theoretically, it is possible to null below the ESL by using the backscatter from a target to...
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