C.J. Baker

A Multistage Processing Algorithm for Disturbance Removal and Target Detection in Passive Bistatic Radar

The paper examines the problem of cancellation of direct signal, multipath and clutter echoes in passive bistatic radar (PBR). This problem is exacerbated as the transmitted waveform is not under control of the radar designer and the sidelobes of the ambiguity function can mask targets including those displaced in either (or both) range and Doppler from the disturbance. A novel multistage approach is developed for disturbance cancellation and target detection based on projections of the received signal in a subspace orthogonal to both the disturbance and previously detected targets. The resulting algorithm is shown to be effective against typical simulated scenarios with a limited number of stages, and a version with computational savings is also introduced. Finally its effectiveness is demonstrated with the application to real data acquired with an experimental VHF PBR system.

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.

Measurement and analysis of ambiguity functions of passive radar transmissions

Passive coherent location (PCL) radar systems make use of broadcast or communications illuminators of opportunity in a bistatic configuration. In order to understand the performance limitations of this type of radar it is necessary to know the ambiguity properties of these waveforms, and how they vary with the form of modulation and with the bistatic geometry. This paper presents and analyses the ambiguity functions of a set of off-air measurements of signals that might be used for PCL systems. We find that the ambiguity behavior of analog modulation formats, such as FM radio or analog television, depend significantly on the instantaneous program content, and can be very poor, for example during pauses in speech. Digital modulation formats, in contrast, are much more favorable and much more constant with time. This suggests that the choice of signals to be used for PCL may be made on a dynamic basis, according to the modulation and bistatic geometry.

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.

Evaluation of WiFi beacon transmissions for wireless based passive radar

Wireless transmissions are a potentially powerful and widely available source of transmissions for passive radar detection. In this work we have carried out a detailed study on the use of IEEE 802.11 (WiFi) transmissions in a passive radar system. The WiFi transmission sequence has been found to be complex and dependent on the user environment but is dominated by direct sequence spread spectrum (DSSS) and orthogonal frequency division multiplexing (OFDM) signals. An ambiguity function analysis of the DSSS based WiFi beacon signal has been carried out followed by field measurements using a wireless based passive radar system. Range and Doppler characterization of this system is reported and compared with the theoretical predictions. Detection of moving human targets has been achieved for the first time using 802.11 transmissions. This work shows that this technique has considerable promise for a low cost and widely deployable detection and tracking system.

Frequency diverse array with beam scanning feature

In this paper, the radiation characteristics of frequency diverse array (FDA) are explored by EM simulation. An intuitive beam scanning feature is observed from the transient field simulation results. The scanning speed is proved to be related to the frequency increment between two neighboring elements. Moreover, the relation between beam angle and time is derived for pulsed applications and verified mathematically.

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.

Radar Micro-Doppler Signature Classification using Dynamic Time Warping

This paper describes the first feasibility study using dynamic time warping (DTW) to classify the micro-Doppler signature (μ-DS ) for radar automatic target recognition (ATR). Real radar data has been used in the testing, and the performance of the DTW classifier has been benchmarked against the conventional k-nearest neighbour (k-NN) algorithm. The basic theory behind the μ-DS is introduced, and aspects of the phenomenon that could cause difficulties for classifiers are highlighted. We explain how DTW can cope with these difficulties and achieve successful classification of three target classes. A correct classification rate exceeding 0.8 has been achieved, leading to the conclusion that this technique shows considerable promise for application in radar ATR systems.

Template Based Micro-Doppler Signature Classification

The micro-Doppler signature of a target is a time varying frequency modulation imparted on the radar echo signal by moving components of the target. Battlefield radar output the baseband signal as audio and soldiers listening on headphones are able to identify the target from its micro-Doppler signature. Automation of this capability is desirable for improved reliability and reduction in classification time. For the first time dynamic time warping (DTW), a speech recognition technique, has been applied to the problem. Its performance has been compared with the common k-nearest neighbour (k-NN) classification method since both approaches utilise a template library

Lessons for Radar

Echolocating mammals such as bats, whales and dolphins have been using waveform diversity for over 50 million years. Synthetic systems such as sonar and radar have existed for fewer than 100 years. Given the extraordinary capability of echolocating mammals it seems self-evident that designers of radar (and sonar) systems may be able to learn lessons that may potentially revolutionize current radar-based capability leading to truly autonomous navigation, collision avoidance, and automatic target classification. Echolocating mammals have been little studied in relation to the operation of radar and sonar systems. In this article, we introduce a range of strategies employed by bats and consider how these might be exploitable in the radar systems of tomorrow. Specifically, we concentrate on the functions necessary for autonomous navigation. Echolocating mammals are known to vary their waveforms via modification to the pulse-repetition frequency (PRF), also known to biologists as pulse-repetition rate (PRR), power, and frequency content of their transmitted waveforms. This has enabled them to evolve highly sophisticated orientation techniques and the ability to successfully forage for food. Moreover, recent developments in technology mean that it is now possible to replicate these parametric variations in synthetic sensing systems such as radar and sonar.