J. C. Smit

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.

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.

X-Band high range resolution radar measurements of sea surface forward scatter at low grazing angles

Radar measurements of a radar calibration sphere test target suspended in sea surface multipath propagation conditions are reported. Wideband measurements together with high range resolution (HRR) processing were employed to resolve the direct reflection component and sea surface reflected multipath components of the received signal. The temporal correlation characteristics of the resolved single bounce multipath signal component are investigated, which shows that a strong temporal correlation in the sea surface forward scatter component exists. Based on this measurement, we propose a temporal correlation extension to an existing low-angle propagation model, together with a correlation filter structure to realize the correlation extension in computer simulation.

On the gain in recognition performance due to the addition of polarisation in an X-band High Range Resolution radar evaluated for F-18 and F-35 targets using asymptotic EM techniques

This paper addresses the prediction of the maximum gain in recognition performance of a High Range Resolution (HRR) X-band radar when use is made of the full polarisation matrix, as compared to the linear polarisations. The study was conducted for the F-35 and FA-18F. Use is made of the information theoretic concept of mutual information (MI) to perform this analysis. Returns from the targets were simulated using an asymptotic RCS prediction code. The information content of the two targets is compared for various polarisations.

Bistatic RCS measurements in a compact range

This paper illustrates the feasibility to perform bistatic RCS measurements in a conventional monostatic compact range that has been reconfigured to perform bistatic measurements at relatively large bistatic angles. The bistatic RCS measurements are conducted by illuminating the target with an incident plane wave generated by an offset parabolic reflector. The bistatic scattering of the target is measured with a wideband double-ridged horn receive antenna that is positioned at the side of the chamber at various fixed bistatic angles. In this study bistatic RCS measurements were conducted on canonical structures as well as a realistic complex scale aircraft model. The bistatic RCS measurements are compared to the full-wave multi-level fast multipole method (MLFMM) in FEKO.

Comparison of various CEM methods to predict RCS of lossy dielectrics

The accuracy with which various full-wave and asymptotic CEM techniques can calculate the RCS of lossy dielectric objects is investigated. This is conducted through comparison to measured RCS data. The investigated methods include MLFMM, FEM, PO and RL-GO. Different lossy dielectric materials are used to construct canonical targets. The RCS of these targets are measured in a compact range at the University of Pretoria, South Africa. The material properties of these lossy dielectrics are accurately characterised using a waveguide technique. Accurate CAD models of the dielectric objects are constructed and used for simulations. The calculated RCS results are compared to the measurements to determine the accuracy of the various methods. The performance and computational efficiency of these methods are also investigated.

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.