Michael Inggs

Stepped-frequency processing by reconstruction of target reflectivity spectrum

This paper describes a processing technique for combining stepped-frequency waveforms efficiently to obtain higher range resolution. Essentially this method involves the reconstruction of a wider portion of the targets reflectivity spectrum by combining the individual spectra of the transmitted narrow-bandwidth pulses in the frequency domain. This paper describes the signal processing steps involved, and shows simulation results which validate and illustrate the method.

High resolution SAR processing using stepped-frequencies

This paper demonstrates a method to produce high resolution SAR images using stepped-frequencies. An advantage of the stepped-frequency approach is the reduction of the instantaneous bandwidth and sampling rate requirements of the radar system, as well as the possibility of skipping frequencies that might be corrupted due to external interfering frequency sources. The technique described involves the construction of a wide-bandwidth chirp pulse produced from a burst of narrow-bandwidth chirp pulses transmitted at stepped-frequency intervals. A description of this technique is given and simulation results are shown.

Ship target recognition using low resolution radar and neural networks

The classification of ship targets using low resolution down-range radar profiles together with preprocessing and neural networks is investigated. An implementation of the Fourier-modified discrete Mellin transform is used as a means for extracting features which are insensitive to the aspect angle of the radar. Kohonens self-organizing map with learning vector quantization (LVQ) is used for the classification of these feature vectors. The use of a feedforward network trained with the backpropagation algorithm is also investigated. The classification system is applied to both simulated and real data sets. Classification accuracies of up to 90% are reported for the real data, provided target aspect angle information is available to within an error not exceeding 30 deg.

Passive radar using a software-defined radio platform and opensource software tools

This paper presents a prototype passive radar system that utilises FM radio transmitters for target detection. The system is based on the Universal Software Radio Peripheral (USRP) hardware platform and the opensource GNURadio software-defined radio (SDR) toolkit. The hardware components that were required to implement the passive radar receiver are introduced. The signal processing software that was written to make target detection possible is briefly discussed. The experimental site and the geometry of the receiver, transmitters in the area, and incoming air traffic are described. The experimental data and the results after performing the required signal processing is presented. It is shown that the passive radar system has the ability to detect commercial passenger aircraft at short ranges.

A quantitative method for mono- and multistatic radar coverage area prediction

The prediction of radar coverage as a function of the position of the radar has always been a key step in radar network planning. In the past, simple geometric models backed up by the deployment of siting radars were the only options for potential site evaluation, but the development of sophisticated propagation models (e.g. AREPS [1]) has moved the technology forward to another level of prediction accuracy. Modelling takes into account atmospheric refraction, as well as terrain effects and clutter. In previous papers [2], [3] we have shown that the modelling can also cater for multistatic radar systems. In this paper we have extended our modelling to give a statistical measure of the effectiveness of a site that measures the signal to noise ratio (SNR) or (for multistatic radar) the signal to interference ratio (SIR) over regions of interest. The area is pixellated into values of SNR and SIR, and pixels meeting the required SNR and / SIR are counted. We show some results for a multistatic radar. We conclude by indicating how we plan to include ground clutter. We mention how this method of obtaining quantitative coverage performance can be used with all forms of radar, and will be able to improve future networks of cognitive radars.

High range resolution radar using narrowband linear chirps offset in frequency

This paper introduces a method to combine a number of narrow-bandwidth chirp pulses stepped in frequency in order to achieve high range resolution in SAR images. The limitations of this method are discussed, as well as some of the design constraints appropriate to designing a high-resolution stepped-frequency SAR system. Results obtained from processing simulated and E-SAR data are presented and discussed.

High resolution VHF SAR processing using synthetic range profiling

This paper demonstrates the use of stepped-frequency waveforms to obtain high resolution SAR images without imposing severe instantaneous bandwidth requirements on the radar system. Although azimuth compression and motion compensation are essential to obtain high resolution SAR images, this paper only discusses how to obtain high range resolutions. Especially at VHF frequencies it is very difficult to obtain high range resolutions, because the effective pulse bandwidth required would amount to a large percentage of the centre frequency. After briefly introducing the theory of synthetic range profiling as applied to SAR, this paper goes on to discuss the synthetic range profile of an A320 Airbus, which serves to demonstrate the feasibility of synthetic range profiling. More attention is then given to simulation results, which introduce the problems encountered when sampling the returning echo waveforms.

Development of a low cost SFCW ground penetrating radar

Due to their system complexity and high component cost, stepped frequency continuous wave radars have not been popular in the ground penetrating radar industry. However, over the last decade the cost of RF technologies has decreased considerably, making it more feasible to make SFCW GPRs. This paper discusses the implementation and development of a low cost SFCW GPR using digital radio technology, a homodyne single channel receiver and a digital signal processor. The radar operates over a bandwidth from 490 MHz to 780 MHz and is capable of taking a single depth profile measurement using 256 frequency steps in less than 0.5 seconds. The results of field trials are also presented.

Impact of the Doppler modulation on the range and Doppler processing in OFDM radar

Orthogonal frequency division multiplexing (OFDM) radar is highly appropriate in applications where communication and radar functionalities are intended simultaneously. The same waveform and the same infrastructure are used, reducing hardware complexity. In this paper, we focus on the radar processing of a pulsed waveform, where the pulses are composed of several OFDM symbols. We derive a novel signal processing scheme that retrieves an estimate of the range and the radial velocity when the target is a point scatterer. Rather than a processing based on correlation functions we exploit the phases of the subcarriers and our knowledge of the phase codes. Then, we discuss the impact of the Doppler modulation within the individual pulses and we show how the use of identical sequences (IS) for the phase codes can mitigate the degradation of the retrieval in the range Doppler image. Lastly, we propose two alternative methods that retrieve an unambiguous estimate of the Doppler frequency.

A simulation of synthetic range profile radar

Synthetic range profiling is a technique where high range resolution is obtained by transmitting a series of pulses at different frequencies, and then using signal processing to form a high resolution image of target reflectivity along the range axis. The technique is basically an extension of pulse compression theory. This paper summarises the theory and describes a simulation system used to determine whether existing radars are suitable for synthetic range profiling. A discussion on the interpretation of range profiles is included.<<ETX>>