Christoph Gierull

Performance analysis of fast projections of the Hung-Turner type for adaptive beamforming

Abstract Eigenvector-based projection methods are currently popular in direction-of-arrival (DOA) estimation and adaptive nulling of interference. The most significant problem with these methods is their very high computational load, particularly when used for large arrays of many elements. In this paper, we present a statistical performance analysis of a fast projection method of the Hung-Turner type (HTP) when used for interference cancellation, which overcomes the critical computational intensity. It is shown that the resulting normalized signal-to-noise-plus-interference-ratio (SNIR) for the HTP is a special case of that from the sample matrix inversion method with diagonal loading (LSMI). An analytical expression for the probability density function of the normalized SNIR is derived, from which the independency of performance of the interference power can be seen. The optimum number of snapshots, the achievable rate of convergence and the resulting loss of SNIR for arbitrary interference environments can be predicted from this analysis. As the ideas of interference suppression and high-resolution angle-of-arrival estimation are closely related, the presented results can also be translated to the superresolution problem.

High-resolution wide-swath SAR

This chapter presents the principle of high-resolution wide-swath synthetic aperture radar (SAR), a means for imaging wide areas at high resolution. The material covers the limitations of achieving wide-swath and high-resolution with a traditional SAR, the basic idea of using a multi-aperture SAR to overcome this limitation and current implementations where multi-aperture (or multiple antenna) systems collect data in an ideal configuration. Overviews of approaches to processing data collected in nonideal configurations, such as when the data are collected with non-uniform sampling and/or when they are collected with a squinted system, are then introduced. Armed with an overview, the chapter introduces the theory of multi-aperture SAR processing with the objective of generalizing the concept of high-resolution wide-swath to higher resolution, wider-swath SAR. This enables application of the added degrees of freedom to other modes such as spotlight and high-resolution stripmap. In order to present the theory and the generalizations, and in consideration of possible future systems, the theory is derived in the wavenumber domain for wideband and/or widebeam, space-based systems with special cases for narrowband systems presented as appropriate. In contrast to much of the current literature, the theory views the antenna patterns as the key provider of the additional degrees of freedom and proposes to utilize other pattern characteristics in addition to the phase-centre separation to improve imaging. For this reason, special care is taken in developing the antenna pattern dependence in the signal model. The approach for signal reconstruction focuses, mainly, on the minimum mean-square error method as it is quite general and includes, as special cases, the well-known projection approach as well as the space-time adaptive processing (STAP) approach. Further, it inherently, simultaneously improves the geometrical and radiometrical resolution due to favourable weighting by the antenna pattern and a less aggressive ambiguity prescription as compared to other techniques. The approach also naturally incorporates other more generalized system configurations where, for instance, the antenna patterns have, not only different phase-centres, but also different shapes or different pointing directions. As an added feature, the presented method is robust against matrix inversion problems which can render the projection approach intractable. The special case of a phased-array multi-aperture system is presented.

Radar multi-platform system for air surveillance

The chapter is about air surveillance system composed of several platforms equipped with primary and secondary radars. Currently, air situational awareness is obtained by data fusion of platform tracks exchanged via normalized Tactical Data Links. The performances of air surveillance can be significantly improved, taking into account the game changing due to telecommunication progress: High Data Rate network is now available on almost all the multiplatform systems, even those composed of mobile platforms as ships and aircrafts. Via HDR network, platforms can share plots (raw detections) of all their radars and a common improved air picture can be elaborated by plot data fusion on each platform. The first section presents the objectives of multiplatform air surveillance system in civil and military domains. The second section describes the theoretical multi radar performance gains under the hypothesis that the HDR network is perfect (no loss, no delay) and that the radar plots of all the platforms are exchanged. The third section describes the evolution of architectures for civil and military multiplatform systems over a 40 years period. For the upgraded multiplatform architecture, the fourth section presents its external interface and its main functions. The fifth section provides some examples of western multiplatform systems and gives some results of performance gains obtained by a multiplatform system in development. Finally, multiplatform systems future challenges are discussed in the sixth section.