Sequential Along-Track Integration for Early Detection of Moving Targets

This paper concerns the joint multiframe sequential target detection and track estimation in early-warning radar surveillance systems. The rationale for applying sequential procedures in such a scenario is that they promise a sensitivity increase of the sensor or, alternatively, a reduction in the time needed to take a decision. Unlike previous works on sequential radar detection, the attention is not restricted to stationary targets, namely position changes during the illumination period are allowed. Starting from previous sequential rules, different truncated sequential strategies are proposed and assessed: they are aimed at orienting the sensor resources towards either the detection or the track estimation or the position estimation. Bounds on the performances of the proposed procedures in terms of the system parameters are derived and computational complexity is examined. Also, numerical experiments are provided to elicit the interplay between sensor-target parameters and system performances, and to quantify the gain with respect to other fixed-sample-size procedures. - Reference

Signal Synthesis and Receiver Design for MIMO Radar Imaging

Multiple-input–multiple-output (MIMO) radar is an emerging technology that has significant potential for advancing the state-of-the-art of modern radar. When orthogonal waveforms are transmitted, with $M+N$ ($N$ transmit and $M$ receive) antennas, an $MN$-element filled virtual array can be obtained. To successfully utilize such an array for high-resolution MIMO radar imaging, constant-modulus transmit signal synthesis and optimal receive filter design play critical roles. We present in this paper a computationally attractive cyclic optimization algorithm for the synthesis of constant-modulus transmit signals with good auto- and cross-correlation properties. Then we go on to discuss the use of an instrumental variables approach to design receive filters that can be used to minimize the impact of scatterers in nearby range bins on the received signals from the range bin of interest (the so-called range compression problem). Finally, we present a number of numerical examples to demonstrate the effectiveness of the proposed approaches.- Reference

Maximum Position Alignment Method for Noisy High-Resolution Radar Target Classification

In this paper, the alignment of noisy high-resolution radar signals using the maximum position method is studied. The relationship between the shift estimation and the signal-to-noise ratio is considered. As a result, two analytical expressions are obtained that approximate the root-mean-square error of the difference in the shift estimation with and without noise. These two expressions allow us to improve the understanding of the sensitivity to noise of the Maximum Position alignment method. - Reference

Imaging Simulation of Bistatic Synthetic Aperture Radar and Its Polarimetric Analysis

Employing the 3-D mapping and projection algorithm (MPA), an imaging simulation of bistatic synthetic aperture radar (BISAR) observation over a complex scenario is developed. Based on the explicit expression of the point target response of stripmap BISAR imaging, raw data are efficiently generated from the scattering map precalculated by MPA. Some examples of BISAR image simulation are studied. The polarimetric characteristics of a BISAR image are then discussed. It is found that some typical polarimetric parameters such as Cloude's $alpha$, $beta$, and $gamma$ might become unable to describe the scattering mechanism under bistatic observation. A transform of unified bistatic polar bases for a BISAR image is proposed. The parameters $\alpha$, $\beta$ , and $\gamma$ are modified to retain the property of orientation independence in the bistatic circumstance. Analysis of simulated images shows that the redefined $\alpha$, $\beta$ , and $\gamma$ after the unified bistatic polar bases transform well describe different scattering mechanisms in BISAR imaging. It provides a primary tool for BISAR image interpretation and terrain classification. Reference

Whitening Dual-Polarized Weather Radar Signals With a Hermitian Transformation

Oversampling weather radar signals in range and then whitening these signals has been shown to improve the accuracy of spectral moments. For dual-polarized radar, the polarimetric variables depend upon information gleaned from the cross correlation of the different received signals. Theoretical improvements to the polarimetric variables have been provided to date, but experimental evidence of improvements through whitening has been limited. This paper provides an analysis of the effects of whitening on the estimated cross correlation along with experimental results of whitening applied to polarimetric variables. Different whitening transformations based solely on covariance matrix inversions will be shown to affect the copolar correlation of the whitened data. A Hermitian symmetric whitening transformation will be shown to produce better estimates of polarimetric variables obtained from whitened data than the original whitening transformation defined for use with range oversampling.Reference

Holographic Research to Enhance Aircraft Antennas

The US Air Force has funded researchers at HRL Laboratories in Malibu, California to work on innovative new holographic techniques to create antennas that do not detract from an aircrafts aerodynamics.

The team are working on holographic impedance surfaces that will make antennas completely flush with the surface of the aircraft while still maintaining or even enhancing current protruding antenna capabilities.

The team are building the surfaces out of metallic materials on a substrate.

Programme manager at the Air Force Office of Scientific Research, Dr Arje Nachman said that the technology offers several benefits.

"One attractive benefit offered by these interesting surfaces is that if the tail of an aircraft obstructs the beam of an antenna then the tail can be covered by a suitably crafted impedance surface in such a way that the antenna beam flows around the tail as if the tail weren't there," Nachman said.

The HRL team is now trying to extend the capabilities of the electromagnetic impedance and experiment with practical implementations of it.

The researchers plan to create new kinds of unit cells and are also seeking new mapping techniques that allow those cells to be positioned over complex objects.

By Daniel Garrun.