This study investigates the potential advantages conveyed by the exploitation of polarimetric diversity in Passive Coherent Location (PCL) system exploiting Digital Video Broadcasting – Terrestrial (DVB-T) signals. To this purpose, different polarimetric detection schemes are considered that jointly exploit the signals collected at different receiving channels characterised by differently polarised antennas. A performance analysis has been carried out using experimental data collected by a passive radar system developed by Fraunhofer, namely PARASOL. This PCL system employs two orthogonal linearly polarised receiving channels (horizontal and vertical). The results obtained against cooperative targets demonstrate that a Polarimetric Generalised Likelihood Ratio Test (P-GLRT) detection scheme provides a remarkable improvement in terms of target detection capability as compared to the single-polarisation operation and the non-coherent integration of the results obtained at the available polarimetric channels.

Antipersonnel landmines have been indiscriminately used since World War II, and their long-term persistence in the ground creates a barrier to development in a large number of countries and forces people to live in constant fear. There is a growing demand for reliable landmine detection and localisation systems to return affected areas to their normal use. Due to its ability of detecting both metallic and non-metallic objects, ground penetrating radar (GPR) is a meaningful method for detecting landmines that may allow faster and safer operations. Unlike common clutter objects, most landmines can be modelled as multiple layered dielectric cylinders that cause multiple interfering reflections and result in features with a characteristic angular pattern. Due to this, landmines are expected to produce signatures that present some discriminant features that could be used for reducing the GPR false alarm rate. In this study, measurements of three inert landmines have been carried out to study and characterise landmine signatures as a function of polarisation angle and aspect angle.

Klein Heidelberg (KH) was a German WW2 bistatic radar system that used the British Chain Home radars as its illumination source. A paper published in 2010 presented information from previously classified sources on its origins and performance. Subsequently, some further information has been found, in particular concerning the dates by which the different KH stations become operational and their performance. This study summarises this new information, and discusses the dates by which each KH station was operational, the evidence for its effectiveness and the countermeasures considered by the British against KH.

The negative effects wind farm clutter has on the performance of radar systems for air traffic control and air surveillance is well known in the radar research community and several mitigation techniques have been proposed to address this problem. These include bi- and multistatic radar systems providing multiple views of the area under surveillance, and hence potential additional information that can be used to improve the receiver performance. This study presents the analysis of a set of experimental data collected simultaneously by two radar systems, one operating at S-band and one at X-band, of echoes from an operational wind farm in the UK near Oxford. This analysis presents several parameters extracted from the time domain data and the Doppler spectra, such as Doppler centroid and bandwidth of the micro-Doppler signature as well as amplitude statistics of the time domain returns. These parameters are characterised using data recorded at mono- and bistatic nodes, as well as at different polarisation combinations.

This study investigates the causes and effects of signal mismatch on the performance of a passive bistatic radar that employs reference signal reconstruction processing on a moving receiver platform. In addition to the transmitter's imperfections, namely carrier frequency offset and sampling clock drift, motion induced Doppler is taken into consideration and compensated. Signal processing approaches are used that exploit the unique characteristics of the terrestrial digital video broadcast waveform in order to compensate for the combined effects of transmitter mismatch and the motion induced Doppler. The proposed methods are tested on real-field measurements acquired in Germany and Australia for single frequency network and multiple frequency network, respectively. The results demonstrate superior performance in terms of delay–Doppler discrimination.

The simultaneous lobing technique, also known as monopulse technique, has been widely used for fast target localisation and tracking purposes. Many works focused on accurately localising one or two targets lying within a narrow beam centred around the monopulse antenna boresight. In this study, a new approach is proposed, which uses the outputs of four antennas to rapidly localise two point targets present in the hemisphere. If both targets have the same elevation angle, the proposed scheme cannot detect them. To detect such targets, a second set of antennas is required. In this study, to detect two targets at generalised locations, the antenna array is divided into multiple overlapping sets each of four antennas. Two algorithms are proposed to combine the outputs from multiple sets and improve the detection performance. Simulation results show that the algorithm is able to localise both targets with <2° mean square error in azimuth and elevation.

Radar detection of small maritime targets is of great interest in the context of coastal and port security for prevention of activities such as smuggling and piracy. Multistatic radar and forward scatter radar offer detection advantages compared with conventional monostatic systems, such as advantageous multi-perspective target view for the former and target radar cross-section enhancement for the latter. In this study, experimental results are presented to characterise simultaneous measurements investigating the detection of a small inflatable boat by a multistatic radar and a forward scatter radar. These results are believed to be the first example of simultaneous experimental comparison of such systems.

We define commensal sensors (CSs) as a class of EM sensor that use the emissions of other systems to fulfil their sensing function, without having any impact or collaboration with the emitter of opportunity. The jamming of CS systems, and possible Electronic Protection (EP) responses to such jamming have not received more than a passing reference in the open literature. The authors examine a specific case of a sensor exploiting FM Band transmissions, with a multi-receiver configuration (single transmit site, many spatially distributed receivers) and find that although modest jammer power can be very effective in jamming a single node of the CS, the unknown geometry and frequencies of operation of the CS will make it difficult to jam in practice. Simple null steering by the CS receivers is very effective. The authors also note that the CS sensor system requires excellent electronic support (ES) to be aware of electronic attack. The study reviews the tactical situation, and the very sparse literature. This is followed by some analysis of the effect of noise jamming, followed by simulations of jamming, with and without receiver null steering, as well as some self-protection jamming.

The X-band coherence statistical characteristics related to the height of ambiguity, polarisation and resolution in two typical forested areas are investigated, using X-band multi-baseline polarimetric synthetic aperture radar interferometry (PolInSAR) data acquired by an automobile-based interferometric synthetic aperture radar (InSAR) system. The influences of the polarisation and resolution on coherence are carefully analysed. The results show that the volume decorrelation in forested areas is independent of the polarisation and the coherence decreases with the reduction of the resolution. In addition, an empirical coherence model in relation to the height of ambiguity, resolution, forest height and range slope is proposed, according to the coherence statistical characteristics of the experimental data. The model can be used to calculate the mean coherence of forested areas under a specific system baseline and therefore it can play an important role in X-band InSAR baseline configuration for forest mapping.

Coprime arrays have been recently proposed as effective sparse configurations suitable for radar beamforming and angle-of-arrival estimation applications. In this study, a new approach for passive beamforming using coprime arrays is presented. In particular, a new detection strategy is proposed, which outperforms the coprime processors presently available in the literature, both in terms of peak sidelobe ratio and integrated sidelobe ratio, without giving rise to ‘ghost’ targets in presence of multiple interferers. The advantage of the proposed detector is demonstrated through the simulation of appropriate array scanned responses and receiver operating characteristic curves.

This study considers the problem of wideband direction of arrival (DOA) estimation for spatial optical beam-forming network (SOBFN). Since its system configuration is different from that of the traditional microwave beam-forming networks, the authors first establish the observation model of SOBFN when multiple broadband signals are received. Two kinds of DOA estimation strategies are proposed for wideband direction finding based on the established signal model. The proposed methods decompose the wideband array output into narrowband outputs in several discrete frequency bins. Then, they take advantages of the spatial sparsity of the discrete narrowband observation models to estimate the spatial power spectrum, either coherently or non-coherently. A coarse DOA estimate is obtained via peak-searching in the reconstructed spectrum. The preliminary result is then refined by a linear interpolation procedure. Profound experiments are carried out to demonstrate and compare the performance of the two strategies. Simulation results show that the proposed approaches can achieve wideband DOA estimation of high precision and super-resolution for SOBFN. Moreover, coherent process is proved to have superior performance than the non-coherent strategy.

Video synthetic aperture radar (ViSAR) can produce sequential images at a high frame rate, which provides a persistent surveillance over a region of interest. However, due to position changes of different apertures, most of existing imaging algorithms fail since the orientation and resolution of each frame image will change accordingly. In this article, based on the high centre frequency characteristic of ViSAR, an interpolation-free algorithm for persistent multi-frame imaging is proposed. The proposed algorithm can be implemented by only two-dimensional fast Fourier transforms without any image post-processing, thus both the efficiency and quality of imaging are obtained at the same time. Simulation and real data results have verified the effectiveness of the proposed algorithm.

Despite rapid developments in global navigation satellite system (GNSS), positioning in urban canyons is a big challenge for civil receivers. Low accessibility to the sky, multipath, weak signal and blocking incidents are the major problems of positioning in these environments. This study proposes a robust adaptive joint tracking architecture to improve the tracking and positioning results of the receiver. In this architecture beside the conventional tracking architecture, one adaptive tracking method works to aid the computation of the code phase error in weak channels. To increase the availability of the satellites above the receiver, global positioning system and Russian GLobal NAvigation satellite system integration is utilised. Different tests in static mode including blocking, multipath and weak-signal scenarios and a dynamic test in an urban environment are included. Experimental results show that the joint adaptive receiver could find the position with more than 31 and 14% improvements in RMS error rather than conventional receiver during the static multipath and dynamic tests, respectively. How the proposed method solves the fault propagation problem of vector tracking is also shown using a simulated scenario.

Increasing demand for wireless communications services within the spectrum bands that are most conducive to operating cellular and mobile broadband systems is aggravating frequency congestion within the electromagnetic spectrum. Primary–secondary spectrum sharing can be exploited to alleviate spectrum congestion by allowing secondary systems to access opportunistically the allotted frequency band of a primary system. In this study, the feasibility of spectrum sharing between air traffic control (ATC) radar and long-term evolution (LTE) wireless communications systems is investigated through waveform-level simulations and link budget analyses. Numerical results show that with moderate frequency and range separation, spectrum sharing between a scanning ATC radar and a single LTE cell in L-band is possible, though both systems are ultimately subject to quantified performance degradations due to the impact each has on the other.

Range estimation is an important issue of radar system, and its performance is mainly limited by the transmitting bandwidth. To improve the range resolution, the existing approaches often either occupied wider bandwidth or employed some non-linear techniques which cause high complexity. The wider the transmitting bandwidth has not only the more the network resource takes but also the easier the radio frequency interference (RFI) is introduced. The authors propose a new radar system by utilising jointly the compressive sensing (CS) and the proposed virtual expanding technique, referred to as the compressing sensing and virtual expanding (CSVE) radar system. The proposed CSVE radar system not only provides high-range resolution with low cost by saving transmitting bandwidth but also is robust to the bad effect of the RFI by utilising a pre-detection phase at the transmitter and a detection phase at the receiver. Simulation results validate the superiority of the proposed CSVE radar system over both the high-resolution techniques such as Capon, multiple signal classification and matched filter, and the CS step-frequency radar system.

In this study, the authors tackle the bearings-only target motion analysis problem, which is to estimate the position and velocity of a target using bearing measurements. They consider a target which is highly manoeuvrable. This study introduces the modified range-parameterised extended Kalman filter (MRPEKF), which consists of a number of independent EKFs, each with a different initial range estimate. The MRPEKF uses the filter re-initialisation strategy to track a highly manoeuvring target. They further introduce the method to improve the efficiency of the MRPEKF. They verify the effectiveness of their MRPEKF by comparing it with the IMM KF using simulations.

This study reports on a novel technique for the estimation of the target total rotational velocity of a non-cooperative target. The technique makes use of the second-order local polynomial Fourier transform to estimate the hitherto unknown component of the velocity vector in the radar line-of-sight direction, and three-dimensional (3D) interferometric inverse synthetic aperture radar (ISAR) imaging the target. The aspect-independent 3D size and shape of a target – an important metric for automatic target recognition – can thus be estimated. Cross-range focus in the component 2D ISAR images is also improved in the process. Results obtained from extensive simulations demonstrate the feasibility of the proposed approach.