J.E. Cilliers

Pulse Compression Sidelobe Reduction by Minimization of L/sub p/-Norms

Most modern radar systems make extensive use of pulse compression techniques. This paper presents a technique for the design of mismatched receive finite impulse response (FIR) filters based on the minimization of Lp -norms of the sidelobes. The goal of the minimization process is to reduce the range sidelobe levels of the convolution of the transmit pulse and the receive filter. A closed-form solution is derived for the least-squares case (which is equivalent to the L2-norm) and an expression for the optimization of the higher order norms is developed. The solutions for the higher order norms have to be obtained by means of iterative numerical methods. The effect of using receive filters which are longer than the transmit pulses is also investigated. Results are presented for linear FM transmit waveforms having time-bandwidth products ranging from 10 to 100 in combination with selected values of the norm order ranging from 2 to 200. Receive filter lengths up to three times the transmit pulse lengths are investigated. Results are presented which highlight the tradeoffs between sidelobe level, mismatch loss and mainlobe width. The effect of Doppler shift on the sidelobe response of these receive filters is also investigated.

High range resolution X-band urban radar clutter model for a DRFM-based hardware in the loop radar environment simulator

This paper describes measurements of urban ground clutter made from the CSIR campus in Pretoria, South-Africa. The measurements were made using a wideband X-band radar. The radar clutter is analysed and a Doppler spectrum based clutter model is derived. The clutter model is optimised for implementation on a digital radio frequency memory (DRFM) based hardware in the loop (HIL) radar environment simulation system. The clutter model was compared to a different measurement in the dataset and it was found to provide an accurate fit to urban ground clutter for the low grazing angles under consideration. The coherent component matched that of the data, while the slow diffuse component matched well for low clutter bandwidths of less than 1 Hz. For clutter bandwidths larger than 1 Hz there was approximately a 2 dB mismatch in the spectral tails.

Active calibration target for bistatic radar cross-section measurements

Either passive calibration targets are expensive and complex to manufacture or their bistatic radar cross section (RCS) levels are significantly lower than the monostatic RCS levels of targets such as spheres, dihedral, and trihedral corner reflectors. In this paper the performance of an active calibration target with relative high bistatic RCS values is illustrated as a reference target for bistatic RCS measurements. The reference target is simple to manufacture, operates over a wide frequency range, and can be configured to calibrate all four polarizations (VV, HH, HV, and VH). Bistatic RCS measurements of canonical targets, performed in a controlled environment, are calibrated with the reference target and the results are compared to simulated results using FEKO.

FM band commensal radar technology used for the detection of small aircraft and the measurement of propeller modulation

Commensal radars (CR) depend on transmitters of opportunity whilst having no impact on the systems the transmitters are serving. This paper presents initial trials conducted to investigate the performance of an FM radio band based CR system against smaller aircraft. We present the detection range results and also demonstrate that we could accurately determine the rotation rate of the aircrafts propeller.

Comparing different numerical methods for RCS prediction of a realistic electrically large complex airframe with measured data

Radar Cross Section (RCS) plays a significant role in radar design and modern electronic warfare. Important radar research fields like Non-Cooperative Target Recognition (NCTR) exploit the RCS signature of a target for identification. Different computational electromagnetic (CEM) techniques can be used to predict the RCS of targets. This paper investigates the accuracy and efficiency with which various asymptotic and full wave numerical methods can predict the RCS of a realistic, electrically large, complex airframe, validated against measured data.

Dynamic radar calibration using an airborne active calibration target

Modern trends in radar and electronic warfare applications require detail information on target scattering signatures, especially calibrated Radar Cross Section (RCS) information of targets in a realistic, dynamic environment. In this paper an active calibration target will be employed to calibrate a ground to air radar system, allowing dynamic RCS measurements.

Hardware in the loop (HIL) generation of airborne clutter using a sum of complex sinusoids technique

This paper describes the simulation of a non-symmetrical Doppler spectrum for an airborne radar scenario using a sum of complex sinusoids (SOC) technique. The low complexity generation of this class of spectrum is required for the generation of synthetic clutter for the testing of airborne radar systems using digital RF memory (DRFM) based hardware in the loop (HIL) test systems.