Radar waveform diversity has received considerable attention in recent years due to increasing spectral congestion and the burgeoning capabilities of digital waveform generation. The promise of waveform diversity is far greater utilization of available degrees of freedom to enhance sensing performance and to even facilitate new operating modes. This tutorial provides an overview of this very broad topic, from the basic principles upon which it is founded to the myriad different areas being explored in research for practical sensing applications.

Overview of radar waveform diversity

Radar reflectivity of land and sea

This paper is focused on the design of phase sequences with good (aperiodic) autocorrelation properties in terms of peak sidelobe level and integrated sidelobe level. The problem is formulated as a biobjective Pareto optimization forcing either a continuous or a discrete phase constraint at the design stage. An iterative procedure based on the coordinate descent method is introduced to deal with the resulting optimization problems that are nonconvex and NP-hard in general. Each iteration of the devised method requires the solution of a nonconvex min–max problem. It is handled either through a novel bisection or an FFT-based method respectively for the continuous and the discrete phase constraint. Additionally, a heuristic approach to initialize the procedures employing the $l_p$ -norm minimization technique is proposed. Simulation results illustrate that the proposed methodologies can outperform some counterparts providing sequences with good autocorrelation features especially in the discrete phase/binary case.

A Coordinate-Descent Framework to Design Low PSL/ISL Sequences

Photonic-based instantaneous frequency measurement (IFM) of unknown microwave signals offers improved flexibility and frequency range as compared with electronic solutions. However, no photonic platform has ever demonstrated the key capability to perform dynamic IFM, as required in real-world applications. In addition, all demonstrations to date employ bulky components or need high optical power for operation. Here we demonstrate an integrated photonic IFM system that can identify frequency-varying signals in a dynamic manner, without any need for fast measurement instrumentation. The system is based on a fully linear, ultracompact system based on a waveguide Bragg grating on silicon, only 65-μm long and operating up to ∼30 GHz with carrier power below 10 mW, significantly outperforming present technologies. These results open a solid path towards identification of dynamically changing signals over tens of GHz bandwidths using a practical, low-cost on-chip implementation for applications from broadband communications to biomedical, astronomy and more.

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Wideband dynamic microwave frequency identification system using a low-power ultracompact silicon photonic chip

Robust and effective detection of a marine target is a challenging task due to the complex sea environment and target's motion. A long-time coherent integration technique is one of the most useful methods for the improvement of radar detection ability, whereas it would easily run into the across range unit (ARU) and Doppler frequency migration (DFM) effects resulting distributed energy in the time and frequency domain. In this paper, the micro-Doppler (m-D) signature of a marine target is employed for detection and modeled as a quadratic frequency-modulated signal. Furthermore, a novel long-time coherent integration method, i.e., Radon-linear canonical ambiguity function (RLCAF), is proposed to detect and estimate the m-D signal without the ARU and DFM effects. The observation values of a micromotion target are first extracted by searching along the moving trajectory. Then these values are carried out with the long-time instantaneous autocorrelation function for reduction of the signal order, and well matched and accumulated in the RLCAF domain using extra three degrees of freedom. It can be verified that the proposed RLCAF can be regarded as a generalization of the popular ambiguity function, fractional Fourier transform, fractional ambiguity function, and Radon-linear canonical transform. Experiments with simulated and real radar data sets indicate that the RLCAF can achieve higher integration gain and detection probability of a marine target in a low signal-to-clutter ratio environment.

Radon-Linear Canonical Ambiguity Function-Based Detection and Estimation Method for Marine Target With Micromotion

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.

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

The test and evaluation of modern radars using hardware in the loop simulators requires the use of wideband high-fidelity, digital radio frequency memories (DRFM) in order to generate realistic target returns. Important aspects of wideband DRFM design on a printed circuit board are highighted and the architecture of the DRFM that was implemented using commercial-off-the-shelf components is presented. The spurious free dynamic range of the DRFM was characterised as -47 dBc worst case over an instantaneous bandwidth of 800-MHz. An experimental pulse-Doppler radar was used to compare the fidelity of the returns from the DRFM and an optical delay line.

Design and performance of wideband DRFM for radar test and evaluation

In this issue, "Best of the Web" presents online radar reflectivity databases, which are free of charge to the international research community. Databases such as these are used for the characterization of interference (including noise, sea clutter and land clutter, among others) in radar systems, and the development of signal processing techniques that reduce the detrimental effects of this unwanted interference. The data can also be used for the development and evaluation of signal processing techniques aimed at detecting and tracking man-made objects by separating targets from interference based on Doppler and amplitude characteristics. These signal processing techniques include moving target indication (MTI), pulse-Doppler, space-time adaptive processing, track-before-detect (TkBD), and constant false alarm rate (CFAR) processing.

DataWare: Sea Clutter and Small Boat Radar Reflectivity Databases [Best of the Web]

Copyright: 2012 IET. First published at IET Radar Conference, Glasgow, United Kingdom, 23-25 October 2012

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Hardware in the loop radar environment simulation on wideband DRFM platforms

It is well known that full-wave and asymptotic computational electromagnetics (CEM) methods have different benefits and disadvantages [1], [2], [3], but these factors are usually considered from a theoretical and not an application point of view. Even though asymptotic CEM methods are considered to be too inaccurate for many applications, their application to the radar cross section (RCS) analysis of electrically large objects can lead to significant insights for both the design of a radar system and the development of doctrine associated with a specific platform. The aim of this paper is to illustratively evaluate the Multilevel Fast Multipole Method (MLFMM), Physical Optics (PO) and Shooting and Bouncing Rays (SBR) methods in terms of their suitability for simple RCS investigations which might be encountered in radar applications. (5 pages)

Jacques E. Cilliers

Papers

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

Design and performance of wideband DRFM for radar test and evaluation

DataWare: Sea Clutter and Small Boat Radar Reflectivity Databases [Best of the Web]

Hardware in the loop radar environment simulation on wideband DRFM platforms

Comparison of MLFMM, PO and SBR for RCS investigations in radar applications