M.R. Inggs

Evaluation of coherent netted radar carrier stability while synchronised with GPS-disciplined oscillators

In this paper the dual-mixer time delay (DMTD) technique is used to characterize netted radar carrier stability. Moreover, the performance of synchronization via twisted-pair (TP) cable was compared to that of GPS-disciplined oscillators (GPSDO). This was done using an experimental coherent netted radar (NetRAD), developed at University College London (UCL), UK, and quartz-based GPSDOs, developed at the University of Cape Town (UCT), South Africa. NetRAD was configured as a DMTD test bench, using the existing radar hardware. Parameters such as time and frequency offset, time deviation and Allan deviation were extracted through post-processing of the sampled IF signal. Zero-range measurements conducted under laboratory conditions are presented alongside field measurements conducted over a base-line of 100 metres. Performance of the UCT GPSDOs and the reference TP cable systems were comparable in terms of frequency stability and phase jitter. However, as was expected, the GPSDO time sync was much less precise.

Neural approaches to ship target recognition

This paper summarizes current research into the applications of neural networks for radar ship target recognition. Three very different neural architectures are investigated and compared, namely; the feedforward network with backpropagation, Kohonens (1990) supervised learning vector quantization network, and Simpsons (see IEEE Trans on Neural Networks, vol.3, no.5, p.776-787, 1992) fuzzy min-max neural network. In all cases, preprocessing in the form of the Fourier-modified discrete Mellin transform is used as a means of extracting feature vectors which are insensitive to the aspect angle of the radar. Classification tests are based on both simulated and real data. Classification accuracies of up to 93% are reported.

FOPEN capabilities of commensal radars based on whitespace communication systems

The use of passive or parasitic radars has been an active area of research recently. Such radars mostly depend on communication emitters of opportunity. One recent development in the field of communication engineering is the newly adopted standards for whitespace communication which frees the usage of analog TV bands. These bands because of their low-frequency nature, are suitable for foliage penetration (FOPEN). This paper investigates the use of whitespace communication for commensal use as a FOPEN radar system. It proposes the architecture of such an integrated communication radar (COMMRAD) system and concludes that such an FOPEN system is possible using the whitespace bands.

Processing alternatives in OFDM radar

OFDM radar has been studied in the last years for its suitability to combine communication and radar applications simultaneously. In this paper, we discuss the processing applicable to a train of OFDM pulses as from a radar prospective. We will focus on two different solutions. The first solution operates on the time domain signal while the second solution processes the signal in the frequency domain. We show that both solutions can be implemented by means of DFT and IDFT operations, which make them efficient in real time. We demonstrate that both achieve the same gain in SNR and we give examples based on simple scenarii.

Information sensing for radar target classification using compressive sensing

Target detection and classification are two major uses of a Radar system. The usual way a Radar (or any sensor-system) operates is by sensing data from the environment and then processing the data to extract useful information from it. The current work investigates the use of compressive sensing (CS) to directly sense application-specific information from the scene. This is achieved by a modified version of CS which we term as transform domain CS (TD-CS). We show the use of TD-CS in extracting classification specific information from a single dispersive scatterer based scene. It was shown that TD-CS preserves classifiability of the scenes as measured by simple Euclidean distance as well as by the Bhattachharya distance. Hence, the proposed scheme not only reduces the sampling rate required, it also directly gives the features important to classify a target.

Measurements of bistatic radar sea clutter

Bistatic radar is a technique of considerable potential importance and interest. Despite this, current understanding of the properties of bistatic clutter, and in particular, bistatic sea clutter, is limited at best. We present some results of a recent trials campaign to gather bistatic sea clutter data, and to analyse the data in order to develop models to represent bistatic radar sea clutter. The results indicate that the shape parameter of the compound K distribution model fitted to the data tends to be higher for the bistatic clutter than for the equivalent monostatic clutter. This suggests that a bistatic geometry may allow a lower detection threshold for a given probability of false alarm, and hence give improved detection performance of weak targets against a clutter background compared to the conventional monostatic geometry.

A Cramer Rao analysis on receiver placement in a FM band Commensal Radar system based on Doppler only measurements

This paper investigates the theoretical placement of receivers in an Commensal Radar (CR), Doppler only tracking system with a single transmitter multiple receiver configuration. Theory, based on the Fisher Information matrix (FIM), is developed to derive the theoretical achievable bound for a given receiver configuration and used as a basis to select the optimal receiver placement. Theoretical concepts such as Shannon entropy and Cramèr-Rao analysis are explained and used in the selection process of receiver positions. Further, we show that time history information of a target can cumulatively be used together with FIM that will improve the Cramèr-Rao bound. Lastly, we use the theory developed to evaluate receiver placement combinations by means of a simulation and provide insight on the method of selecting receivers that would minimise the error performance of a Doppler only tracking system. The demonstrations used here are typical of a CR using FM Broadcast emissions.

NetRAD multistatic sea clutter database

This paper describes a multistatic, sea clutter and vessel database, assembled using the three node, S Band radar, known as NetRAD (for, “Netted Radar”). This data was collected in the United Kingdom and South Africa during 2009-201. It is the intention of the investigators and sponsors of this work to make the raw data available to individuals and organisations interested in processing this multistatic data in support of the development of the understanding of sea clutter and vessel properties in the multistatic configuration.

Hardware cancellation of the direct coupling in a stepped CW ground penetrating radar

A stepped CW ground penetrating radar using UHF frequencies is being developed by the University of Cape Town. One of the major problems encountered is a large direct coupling between the transmit and receive antennas. This coupling limits the dynamic range of the system by inserting a large signal into the receiver. The hardware implementation of a digitally controlled RF cancellation circuit is discussed. This RF system comprises of an analogue bi-phase modulator used as a wideband phase-shifter and a PIN diode attenuator. This system, controlled by a PC, was attached to the front end of the SFCW radar. Results of the cancellation circuit used to cancel a cable over a 200 MHz bandwidth and a coupling vector are presented.<<ETX>>

Drill head mounted obstacle avoidance radar

Horizontal drilling in soft soil provides an efficient and cost effective solution for the installation of utilities. However, with the increased congestion of underground utilities, the probability of damaging mislocated or unknown utilities increases, reducing the financial benefits of this technology and increasing the possibility catastrophic damage such as striking gas lines. It is hence important to develop instrumentation that is capable of locating obstacles lying along the bore paths. This paper discusses the development of a obstacle avoidance system based on ground penetrating radar technology. The system is a stepped frequency continuous wave (SFCW) radar that has been designed to fit within a standard 2.75 inch diameter drill head. The only above-ground components are the human machine interface (HMI) and power supply. Communication and power are transmitted underground via a wireline technique. An advanced demonstration model has been built and tested. The paper provides an overview of the requirements of an obstacle avoidance radar system. This is followed by a brief discussion of radar and antenna development required to implement the system. Finally results of indoor and outdoor field trials will be provided.