H.D. Griffiths

Frequency diverse array radars

This paper presents a generalized structure for a frequency diverse array radar. In its simplest form, the frequency diverse array applies a linear phase progression across the aperture. This linear phase progression induces an electronic beam scan, as in a conventional phased array. When an additional linear frequency shift is applied across the elements, a new term is generated which results in a scan angle that varies with range in the far-field. This provides more flexible beam scan options, as well as providing resistance to point interference such as multipath. More general implementations provide greater degrees of freedom for space-time-frequency-phase-polarization control, permitting novel concepts for simultaneous multi-mission operation, such as performing synthetic aperture radar and ground moving target indication at the same time.

Radar Spectrum Engineering and Management: Technical and Regulatory Issues

The radio-frequency (RF) electromagnetic spectrum, extending from below 1 MHz to above 100 GHz, represents a precious resource. It is used for a wide range of purposes, including communications, radio and television broadcasting, radionavigation, and sensing. Radar represents a fundamentally important use of the electromagnetic (EM) spectrum, in applications which include air traffic control, geophysical monitoring of Earth resources from space, automotive safety, severe weather tracking, and surveillance for defense and security. Nearly all services have a need for greater bandwidth, which means that there will be ever-greater competition for this finite resource. The paper explains the nature of the spectrum congestion problem from a radar perspective, and describes a number of possible approaches to its solution both from technical and regulatory points of view. These include improved transmitter spectral purity, passive radar, and intelligent, cognitive approaches that dynamically optimize spectrum use.

Knowledge-based radar signal and data processing: a tutorial review

Radar systems are an important component in military operations. In response to increasingly severe threats from military targets with reduced radar cross sections (RCSs), slow-moving and low-flying aircraft hidden in foliage, and in environments with large numbers of targets, knowledge-based (KB) signal and data processing techniques offer the promise of significantly improved performance of all radar systems. Radars under KB control can be deployed to utilize valuable resources such as airspace or runways more effectively and to aid human operators in carrying out their missions. As battlefield scenarios become more complex with increasing numbers of sensors and weapon systems, the challenge will be to use already available information effectively to enhance radar performance, including positioning, waveform selection, and modes of operation. KB processing fills this need and helps meet the challenge.

Multi-mission multi-mode waveform diversity

Previously, the authors presented a novel method for achieving range-dependent beamforming through the use of a frequency diverse array. The frequency diverse array concept was developed using a quasi-stationary waveform assumption. This concept can be extended to non-continuous wave signals for narrowband and wideband applications such as moving target indication (MTI) and synthetic aperture radar (SAR). Alternative implementations are described, which offer the potential for achieving MTI and SAR simultaneously.

Challenge problems in spectrum engineering and waveform diversity

We describe and discuss some of the current challenges facing radar that result from continued spectral encroachment, which necessitating enhanced robustness to interference, agile waveform-diverse operation, and greater synergy between the signal processing and the physical radar/environment. Subsequently, specific research topics are suggested in which spectrum engineering and waveform diversity may yield viable solutions. In so doing, this paper also provides an introduction to the special session on radar spectrum engineering and waveform diversity affiliated with NATO Task Groups SET-182 and SET-179, respectively.

Knowledge-based resource management for multifunction radar: a look at scheduling and task prioritization

In this article, we consider two related aspects of radar resource management, scheduling and task prioritization. Two different methods of scheduling are examined and compared and their differences and similarities highlighted. The comparison suggests that prioritization of tasks plays a dominant role in determining performance. A prioritization scheme based on fuzzy logic is subsequently contrasted and compared with a hard logic approach as a basis for task prioritization. The setting of priorities is shown to be critically dependent on prior expert knowledge. By assessing the priorities of targets and sectors of surveillance according to a set of rules it is attempted to imitate the human decision-making process such that the resource manager can distribute the radar resources in a more effective way. Results suggest that the fuzzy approach is a valid means of evaluating the relative importance of the radar tasks; the resulting priorities have been adapted by the fuzzy logic prioritization method, according to how the radar system perceived the surrounding environment.

Bistatic radar using satellite-borne illuminators

Bistatic radar has long been recognised as an interesting variant of radar, with a number of potential advantages for air defence. Space-based radar is seen by the US Department of Defense as a key technique for future AMTI and GMTI applications, and the DISCOVERER II programme is indicative of current thinking, aiming ultimately at a network of several tens of satellites. This system would also involve bistatic receivers to give near-continuous surveillance. The purpose of this paper is to present a system concept for a bistatic radar using a satellite-based illuminator of opportunity and a static ground-based receiver. The paper presents system design and performance calculations, and describes experiments to be performed.

The Signal and Interference Environment in Passive Bistatic Radar

We present a review of the properties of some signals that may be used as illuminators of opportunity in passive bistatic radar systems. It is shown that such signals are not ideal for radar purposes, though modern digital modulation formats are to be preferred, since their ambiguity performance is better and in general does not vary with time. However, with any type of signal the ambiguity performance is also a strong function of bistatic geometry. We also consider the direct signal, multipath and interference environment, and show both by analysis and experiment that this will in general be severe, requiring of order 80 dB or more of suppression to achieve acceptable target detection results, and even then an effective receiver noise figure of order 20 -30 dB should be used in performance calculations.

Classification of Unarmed/Armed Personnel Using the NetRAD Multistatic Radar for Micro-Doppler and Singular Value Decomposition Features

In this letter, we present the use of experimental human micro-Doppler signature data gathered by a multistatic radar system to discriminate between unarmed and potentially armed personnel walking along different trajectories. Different ways of extracting suitable features from the spectrograms of the micro-Doppler signatures are discussed, particularly empirical features such as Doppler bandwidth, periodicity, and others, and features extracted from singular value decomposition (SVD) vectors. High classification accuracy of armed versus unarmed personnel (between 90% and 97% depending on the walking trajectory of the people) can be achieved with a single SVD-based feature, in comparison with using four empirical features. The impact on classification performance of different aspect angles and the benefit of combining multistatic information is also evaluated in this letter.

Bistatic MIMO radar space-time adaptive processing

Bistatic multiple-input multiple-output (MIMO) radar systems have the advantages of both bistatic radar and MIMO radar. In addition, the transmit angle can be obtained by processing the receive data. In this paper, bistatic MIMO and space-time adaptive processing (STAP) are applied to ground moving target indication (GMTI). It is shown that the clutter spectrum is a curve in 3-dimensions (transmit angle, receive angle and Doppler frequency) after compensation. The performances of single input multiple-output (SIMO) and MIMO cases are compared. The results show that the bistatic MIMO-STAP outperforms its SIMO counterparts in both signal interference and noise ratio (SINR) and SINR loss.