Piet van Genderen

Doppler Tolerance of OFDM-coded Radar Signals

This paper proposes a new concept of radar coding using OFDM signals. The Doppler tolerance of such a radar is expressed as a function of Doppler frequency and time delay. In order to set a limit to the compression loss due to Doppler, it is shown that the target speed that can be allowed for a single pulse should be limited

Ground penetrating impulse radar for land mine detection

The video impulse ground penetrating radar (GPR) system for detection of small and shallow buried objects has been developed. The hardware combines commercially available components with components (e.g. antennas) specially developed or modified for being used in the system. The GPR system has been designed to measure accurately electromagnetic field backscattered from subsurface targets in order to allow identification of detected targets through solution of the inverse scattering problem. The GPR has been tested in different environmental conditions and has proved its ability to detect small and shallow buried targets.

A communication waveform for radar

This paper discusses some opportunities created by using Orthogonal Frequency Division Multiplexing signals for radar and communication at the same time. Two examples of opportunities in radar are proposed, i.e. solving the unambiguous radial speed in a single transmission and improving the signal-to-background contrast. The performance of the data link is analyzed and shown to be useful.

Radar response approximations for buried plastic landmines

This paper analyzes the early-time radar response of buried penetrable targets such as plastic landmines. The Born approximation is used to derive simple analytical expressions relating target and soil properties to the early-time response. Understanding these dependencies is crucial for target identification under varying soil conditions. The derived expressions include the transfer function and the impulse response of a penetrable target embedded in an unbounded homogeneous lossy medium and illuminated by a uniform plane wave. Using a truncated circular cylinder having the dimensions of a PMA-3 mine as an example, the early time responses predicted by the Born approximation are compared against responses obtained by three-dimensional finite-difference time-domain (FDTD) simulations. The results demonstrate that with the Born approximation it is possible to predict the general shape of the target response, i.e. the number of amplitude peaks, as well as the amplitudes of those peaks that relate to backscatter from the top of the example target. To improve the fit between the predicted and simulated responses, two phenomenologically motivated modifications to the early-time response expressions are proposed. The modified expressions are able to accurately predict not just the general shape of the early-time response, but also the influence of the host medium conductivity on the target impulse response.

Compensation of Range Migration for Cyclically Repetitive Doppler-Sensitive Waveform (OFDM)

Range migration, which occurs for targets with high velocity when the radar range resolution is high, is solved by exploiting the cyclically repetitive waveform-namely, orthogonal frequency division multiplexing. The proposed technique is based on a signal processing method that solves the Doppler ambiguity by exploiting the Doppler sensitivity of the multicarrier spread spectrum structure. The new method extends the availability of narrowband delay-Doppler processing to a wider range of waveform and target parameters.

Frequency agile stepped OFDM waveform for HRR

High Range Resolution (HRR) is an important feature for radar, aiming at target classification. The range resolution is inversely proportional to the bandwidth of the transmitted signal. Pulse burst waveforms can achieve HRR at low expenses when the carrier frequency increases from one pulse to the next, stepping and synthesizing the wide bandwidth. In such a stepped frequency approach the resolution is determined by the bandwidth of the total pulse burst. With the Orthogonal Frequency Division Multiplexing (OFDM) waveform, the time/frequency pattern of the transmitted radar signal is fully flexible while the waveform can be generated easily by IFFT. The novelty of this paper is to demonstrate how the combination of frequency agility and HRR processing into one system can benefit from the OFDM flexibility. An elementary scenario with a single stationary or low speed point target is assumed.

Analysis of the influence of mine and soil properties on features extracted from GPR data

This paper presents a parametric study on the influence of target and soil properties, including depth of burial, on features extracted from ground penetrating radar (GPR) data. Understanding this influence is crucial for designing a classifier that uses these features for mine detection and identification. Two types of features have been studied. These are the Wigner-Ville distribution and geometric moments. Using a fast forward modeling program, synthetic GPR data were created for six buried objects, including two plastic minelike objects, for a wide range of soil properties and depths of burial. Both non-lossy and lossy soils were considered. From the computed data the above features were extracted and correlated with each other. The results show that the Wigner-Ville distribution performs much better in discriminating between objects than geometric moments. Furthermore, the features were found to be practically invariant to changes in mine-soil permittivity contrast and depth of burial provided that the soil is non-lossy. In the presence of losses, the GPR pulse is reshaped at the air-ground interface and as it propagates through the soil. As a result of the reshaping, the target response and hence the features can differ substantially from the non-lossy case.

The Cavity Magnetron: Not Just a British Invention [Historical Corner]

It is a common belief by many people that the resonant-cavity magnetron was invented in February 1940 by Randall and Boot from Birmingham University. In reality, this is not the full story. Rather, it is a point of view mostly advocated by the winners of the Second World War, who gained a great benefit from this microwave power tube (thanks to a two-orders-of-magnitude increase of power) in the Battle of the Atlantic, in night bombing until the final collapse of the German Reich, and in many other operations. This paper discusses the contributions by other nations, mainly France, but also Germany, Japan, The Netherlands, the Czech Republic, the USSR, and even more, to the cavity magnetron and to its roots.

Experiments showing an improvement of angular resolution by LMMSE-based processing

Azimuth target resolution is of crucial importance in many applications of radar. The primary radar parameter affecting the azimuth resolution is the antenna beamwidth. However, in practice, standard signal processing techniques require the distance between targets to be more than one resolution cell. This can prove inadequate for several relevant applications. This paper describes the results obtained from experiments aimed at testing the capabilities of angular resolution between targets separated by less than the beamwidth in azimuth by means of linear minimum mean square error, LMMSE, -based processing. Results show the capabilities of this technique of separating targets in such a scenario. The processing scheme shows a strong improvement in the resolution capability with respect to standard techniques.

Ultrawideband spiral antenna used for stepped frequency radar

This paper refers to a special type of antenna, called frequency independent antenna, used in Stepped Frequency Continuous Wave (SFCW) radar employed for humanitarian demining. The radar transmits 128 frequencies within the frequency range from 400 MHz to 4845 GHz, in groups of 8 simultaneously transmitted frequencies. It has been built at the International Research Center for Telecommunications transmission and Radar (IRCTR), Delft University of Technology.