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Compared with conventional phased array radar, the collocated multiple-input multiple-out (C-MIMO) radar is envisioned to offer greater freedom in waveform design and can simultaneously manage different beams to track multiple targets in the simultaneous multi-beam (SM) working mode. In this study, aiming at the multiple targets tracking (MTT) problem, a joint beam selection integrated with power and bandwidth allocation (JSPBA) scheme for the C-MIMO radar is proposed in the SM mode. By incorporating the modified particle filter, the predicted conditional Cramer–Rao lower bound (PC-CRLB) is calculated, which gives a measure of the best achievable performance for targets tracking. Then, the optimisation model is established with the aim of improving the worst case of PC-CRLB to achieve better performance of the worst-case tracking. Next, a three-step solution method is proposed to solve the JSPBA problem by converting the non-convex problem into a series of convex problems. At last, after the solutions are fed back to the control centre to guide the beam generation in the next tracking epoch, a cognitive tracking system is established. Simulation results confirm the superiority of the proposed method in improving the MTT performance in C-MIMO radar system.

The authors present cognitive automotive radar (CARr) as a significant capability to the sensing technology suite of autonomous driving vehicles. CARr is a closed-loop intelligent radar system utilising the automotive frequency bands of 24-25 and 76-77 GHz for the purposes of ground vehicle target signature identification. The authors consider specific cases of ground vehicle recognition and ground vehicle class identification in the presence of aspect angle uncertainty using forward-looking automotive radar. The transmit-adaptive waveforms are based from signal-to-noise ratio and mutual information optimisation metrics. In this study, two new adaptive waveform techniques with the flexibility to accommodate angular uncertainty probability distributions are introduced. The classification performance of these new waveforms is compared against the receive-adaptive wideband pulsed and other transmit-adaptive waveforms in the presence of angular uncertainties characterised by the uniform and truncated normal distributions. To ensure the validity of results, high-fidelity electromagnetic simulated radar cross-section signatures generated from scaled-to-true-physical-size ground vehicle computer-aided design models are utilised.

A joint radar-communication (JRC) system with both radar sensing and communication abilities is proposed to improve spectrum utilisation efficiency. The transmitter of the JRC consists of multiple antenna subarrays transmitting orthogonal waveforms. If the communication receivers are in radar sidelobe directions, the communication data symbols are embedded in the magnitude ratio as well as the phase shift between transmit waveform pairs. In the case of the communication receivers in radar main lobe direction, the data symbols are embedded in the phase shift between transmit waveform pairs only to preserve optimum radar target detection performance. Novel symbol mapping constellation scheme is designed to achieve a high data transmission rate while maintaining a relatively low symbol error rate. The simulation results show that with medium pulse repetition frequency radar waveforms used, the data transmission rate of the proposed JRC system is in the range of Mbits/s.

A fundamental problem in the fusion of wireless communications and radar is to design suitable waveforms that can be simultaneously used for information transmission and radar sensing. In this study, the authors extend the orthogonal frequency division multiplexing (OFDM) waveform by embedding communication codes to communication-embedded OFDM chirp waveforms for delay-Doppler radar applications. The waveforms are characterised by jointly utilising the advantages of classic phase modulation in communications and chirp frequency modulation in high-resolution radar. The integrated radar-communication system scheme is formulated, which can operate as wireless communications and delay-Doppler radar simultaneously. In a generic monostatic radar setting, a closed-form expression is derived to evaluate the ambiguity function of the designed waveforms, along with the average and variance analysis of the ambiguity function.

In this study, the authors present monopulse beam synthesis methods with sparse elements robust to the antenna module failure. The monopulse beam radar generates two beams (sum/difference beams) simultaneously and it requires a large number of antenna elements in antenna arrays. However, it is desirable to reduce the number of active antenna elements. Furthermore, in many practical applications, some of antenna elements may experience the module failure. Accordingly, to design beams robust to the module failure and reduce the number of active antenna elements simultaneously, the authors propose a modified reweighted L1 minimisation methods in which the Bayesian-inference-based failure probability is exploited. The authors also discuss how the proposed sparse beam synthesis method can be carried out successfully in conjunction with the array failure diagnosis based on the Bayesian compressive sensing.

The imaging performance of a sparse antenna array depends on the arrangement of the transmitting and receiving elements. In this study, the authors systematically extend the work presented by Caba and Boreman by a constraint optimisation of the Y-shaped antenna arrangement. This will lead to an improved point-spread function with reduced sidelobes. It was found that a 30% improvement of the imaging performance using backprojection techniques could be achieved compared with conventional array designs. The optimised sparse antenna array has been used in a simulation study to evaluate its performance for radar-based structural health monitoring of wind turbine blades. Depending on the damage position, either close to the front or back side of the rotor blade, the localisation error has been quantified as a function of its generally unknown effective relative permittivity.

Due to the complex time-varying environments and the unknown target information, the uncertainty of target information is introduced into the echo signal. Owing to the uncertainty of target information, the number and operating modes of antenna array elements allocated for pattern synthesis are uncertain. Hence to reduce the influence of uncertainty of target information and save the antenna array elements, in the light of the uncertainty of the number and the distribution of the array elements in working state, a novel fuzzy random chance-constrained programming model of opportunistic digital array radar antenna aperture resource management is proposed. Moreover, this model can determine the information of radar target from the echo signal by reasonable resource management and allocation under the condition that the specified confidence levels are satisfied. Meanwhile, for solving the multi-object model, the fuzzy random simulation is integrated into fast and elitist non-dominated sorting genetic algorithm (NSGA_II) to compose a hybrid intelligent optimisation algorithm. Finally, two simulations are carried out to verify the validity of this model.

Specific emitter identification has attracted much attention of researchers in recent decades. This technology distinguishes different emitters by exploiting the unintentional modulation (UIM) contained in the signal. Heretofore, evaluation of UIM for pulse compression signals had not been properly solved, since previous evaluating results generally rely heavily on intentional modulation, and cannot solely and sufficiently describe the characteristics of UIM. In this study, the authors propose a novel feature extraction method which can naturally suppress intentional modulation, and meanwhile characterise the UIM. The proposed method utilises the facts that spectrum symmetry is an intrinsic and widespread property of modulated signals; and this symmetry will break when the UIM arises. By properly evaluating the spectrum asymmetry, the frequency-domain asymmetry distribution feature is derived. Experiments on real-world data demonstrate that the proposed feature outperforms conventional features in dealing with pulse compression signals. This study offers an effective way to extract UIM features from modulated signals, thus having broad applications to modern radar emitters.

Operating mode identification of multi-function radars (MFRs) is critical in radar threat evaluation and electronic jamming decisions. The hidden Markov model (HMM) in conventional methods relies on the MFR prior knowledge and cannot accurately describe the MFR signal sequence with regularity. An identifying method is presented that is based on predictive state representation (PSR) models without the help of prior information, which is unlikely to be obtained. Simulations of synthetic MFR signals are used to demonstrate the applicability of the novel method and to summarise the training parameter setting principles, which are of practical significance in applications of the method. The PSR-based method is shown to be more effective than the HMM-based methods, in particular when applied to the radar signal sequence with unknown regularity. The method also contains a novel approach to reducing the dimension of the system-dynamics matrix, which enables the algorithm to perform well in conditions of heavy noise. Simulation results attest to the validity of the proposed method. With the proposed method, the operating modes of radars can be identified accurately, which is significant in supporting adaptive countermeasures against MFRs.

The use of multi-carrier waveforms, such as Orthogonal Frequency Division Multiplexing (OFDM) as used in radio communication, for radar operations has gained strong interest recently. While the authors have completed research on using multi-carrier waveforms for simultaneous radar and communications operations, this study focuses on the recent research on using these waveforms for communications. Namely, they demonstrate how to employ OFDM to modulate Multi-Frequency Complementary Phase Coded sequences for wireless communications.

Increasing congestion of the electromagnetic spectrum has spurred investigation into approaches that provide more efficient spectrum use. While many approaches focus on some type of orthogonality in time, frequency, or coding, another less explored option is mixed modulation of two complementary signals through intentional modulation of pulse. This study discusses intentional modulation of a linear frequency modulated (LFM) chirp radar pulse with a communications signal in order to conduct complementary activities with a combined signal. In order to reduce cross-interference between the signals, the communications message employs spread-spectrum encoding (binary M-sequences) and new modulation scheme with reduced phase change to modulate the LFM waveform. Preferred pair of M-sequences exhibit excellent auto-correlation and low cross-correlation properties that lend themselves to simultaneous transmission of channelised communication signals. The proposed approach is to modulate a radar signal with preferred pair M-sequences using binary reduced phase shift keying modulation that provides a low throughput, communications signal that could be used for administrative or navigation purposes. To measure effect on radar performance, comparison of the radar ambiguity function for the LFM signal is contrasted with combined radar-communication signal.

The conventional sidelobe blanking system, known as the Maisel sidelobe blanker, uses two receiving channels with different gains to detect the presence of a jammer. The Maisel system is an ad-hoc detector without any optimality properties. Yet, it has been successfully utilised in numerous operational systems. Here, the authors study the optimum Neyman–Pearson type sidelobe blanking (SLB) detectors for the Swerling target models to assist the design of Maisel blankers. The authors note that the optimal sidelobe blankers are of theoretical interest, since they require the knowledge of target and jammer parameters, which are typically not available at the radar site. The main goals of the present study are (i) to derive the optimal Neyman–Pearson detectors for SLB, (ii) to examine the performance gap between the optimal and Maisel detectors, and (iii) to develop objective criteria for the design of Maisel blankers that provides a guarantee on the gap to the optimality. Ready-to-use computer programs to assist the design process are also provided.

Skywave over-the-horizon radar (OTHR) plays an important role in the out-of-sight surveillance. However, the operational performance will severely degrade due to transient interferences. Previous works concentrate on time-domain methods to achieve transient interference suppression. However, time-domain methods are usually time-consuming and suffer performance loss when several discontinuous transient interference segments occupy parts of coherent processing interval. In fact, most transient interferences are spatially structured and can be cancelled at adaptive beamforming stage. In this study, the adaptive beamforming is adopted and a space-time cascade processing procedure is proposed for transient interference suppression. In the procedure, the sidelobe transient interferences are cancelled by adaptive beamforming and the mainlobe transient interferences are suppressed by a modified time-domain method. The proposed procedure is in accordance with the regular processing procedure of skywave OTHR and can provide reliable performance with small extra computational costs. The performance of the proposed procedure is evaluated using experimental data recorded by a trial skywave OTHR and the results verify the feasibility and effectiveness of the proposed procedure.

The authors develop a novel phase-modulation based dual-function system with joint radar and communication platforms. A bank of transmit beamforming weight vectors is designed such that they form the same transmit power radiation patterns, whereas the phase associated with each transmit beam towards the intended communication directions belongs to a certain phase constellation. During each radar pulse, a binary sequence is mapped into one point of the constellation which, in turn, is embedded into the radar emission by selecting the transmit weight vectors associated with that constellation point. The communication receiver detects the phase of the received signal and uses it to decode the embedded binary sequence. The proposed technique allows information delivery to the intended communication receiver regardless of whether it is located in the sidelobe region or within the main radar beam. Three signalling strategies are proposed which can be used to achieve coherent communications, non-coherent communications, and non-coherent broadcasting, respectively. It is verified that the proposed method provides improved bit error performance as compared to previously reported sidelobe modulation based dual-functionality techniques.

Orthogonal frequency division multiplexing (OFDM) linear frequency modulation (LFM) waveform is widely studied due to its application potentials in multiple-input–multiple-output (MIMO) radar, but its effective design is still a challenge. Considering the critical role, the pulse compression property of spatial synthesised signals plays in MIMO radar, a detailed analysis is made using OFDM LFM signals, resulting in the radical reasons for the high grating sidelobes. Then, a joint optimisation method for OFDM LFM signal design based on genetic algorithm and sequential quadratic programming is proposed to degrade the sidelobe level dramatically. Furthermore, to nullify the grating sidelobes thoroughly, a modification is performed through optimising the relaxed frequency steps of the OFDM LFM waveform, which involves a balance between sidelobe property and orthogonality. Numerical results validate the theoretic analysis and show the superior performance of the designed OFDM LFM waveforms in pulse compression properties of spatial synthesised signals.

In this study, a new kind of knowledge-aided (KA) permutation test (PT) detector is proposed for the problem of performance deterioration of the PT in complex non-homogeneous clutter environments. The proposed detector consists of two parts, a data selector and a conventional PT. The data selector uses the geographic information system (GIS) to select the reference cells which have similar clutter characteristics with the cell under test. Samples from the reference cells selected by the data selector are used to determine the detection threshold of the PT. Because the PT is a non-parametric method, the proposed detector can maintain a constant false alarm rate without knowing the clutter's distribution type, which is very important in complex clutter environments. Considering the computation complexity of the PT, the authors also provide an implementation algorithm for the PT called ‘valid strategy method’, which is more efficient than the direct calculation method. In order to prove the excellent performance of the KA-PT detector, this detector is compared with some conventional detectors in terms of the false-alarm number and detection probability with the real data collected by IPIX radar. The results show that incorporating the non-parametric method with the prior GIS can significantly improve detectors’ performance in practice.

The authors propose a two-stage approach to design radar dynamic environmental knowledge base (DEKB), which provides a priori information for knowledge-based (KB) signal processing and radar system design. Specifically, the first stage is to use historical knowledge such as maps to establish the static environmental knowledge base (SEKB), which is the initial state of the DEKB. The second stage is to employ radar returns and other sensors information to update the knowledge base dynamically. Moreover, an exemplar establishment of the SEKB based on real scene and a specific update method based on two Anderson–Darling tests are introduced. Finally, as an application of the DEKB, the authors present a new KB constant false alarm rate (CFAR) detector utilising multidimensional knowledge from the DEKB. The performance of the new detector is analysed by real radar data, collected by a linear frequency-modulated continues wave radar, and compared with the classical cell averaging CFAR detector and the KB CFAR detector which uses only one kind of knowledge.

The anti-jamming methods available in multistatic radar are mostly based on data fusion processing and therefore do not fully explore its anti-jamming ability. In the view of multistatic radar, the echoes of real targets received by the widely separated receivers would be independent from each other due to the independence of target radar cross sections in different scattering directions. However, the deception jamming received by the same receivers would be highly correlated since the jamming signals transmitted to different directions are identical. Therefore, real targets would differ from false targets in the spatial scattering property in multistatic radar. By exploiting this phenomenon, a new signal fusion-based method for discriminating active false targets from desired real targets is proposed in this study based on Neyman–Pearson lemma. In this method, false targets are identified by correlation test between the complex envelopes of arbitrary two targets in different receivers. The new method can discriminate false targets generated by deception signals with arbitrary modulation. The closed-form expression for the rejection probability of false targets is derived. Both theoretical analysis and simulations verify the feasibility of the proposed method.

In monostatic continuous wave (CW) radar the dominant waveform is periodic linear frequency modulation, mostly because its stretch processing requires sampling rate much lower than the bandwidth. In a bistatic scene a clean copy of the transmitted signal, required in stretch processing, is not available to the receiver. That opens the competition for other periodic waveforms. The authors study describes and demonstrates, through bistatic field trials, the good performances of bi-phase and tri-phase CW waveforms. Among their advantages are sidelobe-free range response, availability at all prime lengths and ease of synchronisation. Successful bistatic operation is a prerequisite for multistatic systems.

Owing to the closed spacing of the transmitting and receiving antennas, the colocated multiple-input multiple-output (MIMO) radar is easier to be blocked by jamming. The signal model of MIMO radar in active jamming scenario is different from that under the target-like interferences. The jamming echo caused by the radiate signal of the jammers includes the information of receiving array, but not the transmitting array. After match filters and beamforming, the output jamming power of the MIMO radar is related to the number of elements and spacing of the transmitting array. This study provides a potential method to suppress the active jamming by designing the suitable transmitting array. Compared with phased array radar, the proposed method can get improved performance for conventional beamforming or adaptive beamforming performance degradation cases. The effectiveness is verified by numerical simulation results.

This study deals with the problem of spectrum sensing and spectrum sharing for cognitive radar operating in spectrally dense environments. The authors focus on how compressed sensing in spectrum sensing can allow a significant reduction in acquisition time reducing the cost for high-resolution analogue-to-digital converters. They derive an algorithm for estimating the channel parameters that characterise the behaviour of the primary user of the channel and also define a spectrum-sharing method to minimise the interference between the radar and the primary user.

By jointly utilising the advantages of cognitive radar with situational awareness due to closed-loop control and frequency diverse array (FDA) with range-angle-dependent beampattern, this study proposes a cognitive FDA radar with situational awareness. Different from conventional phased-array, FDA offers a range-dependent beampattern. The proposed cognitive FDA radar can avoid undesired strong interferences and focus to the desired targets through the presented closed-loop control algorithm. This algorithm aims to maximise the receiver output signal-to-interference-plus-noise ratio (SINR) performance by iteratively optimising the frequency increment in a closed-loop manner. That is, the cognitive FDA radar can adaptively change its frequency increment according to the environment and thus better performance can be obtained. The cognitive FDA radar performance is evaluated by examining the SINR and direction-of-arrival (DOA) estimation mean square errors. How the performance depends on the FDA frequency increment is also investigated. Simulation results show that the cognitive FDA radar yields much better SINR performance and thus higher DOA estimation precision than basic FDA and conventional phased-array radars.

International audience; Multilateration and automatic dependent surveillance-broadcast systems are used in air traffic control to detect, locate and identify cooperating aircraft using signals emitted by airborne transponders and received by dedicated ground stations. In areas with a high traffic density, these stations may receive simultaneously several superimposed signals. Present operational systems use only one receiving channel connected to a non-directional antenna. When the received replies are superimposed, that is, 'garbled', their detection and/or decoding are severely affected in nowadays equipment. The aim of this study is to transform the single channel problem into a multiple channels problem in order to solve it using specific knowledge about the Mode S signals. In fact, the multiple channels problem is a typical signals separation problem applied to Mode S mixture for which several algorithms already exist. The authors' algorithm, named projection algorithm (PA) single antenna, is based on the existing PA and can be easily implemented on existing receiving stations. The effectiveness of their method is demonstrated using real data collected from their experimental receiver.

Fall detection is an area of increasing interest in independence-assisting remote monitoring technologies for the elderly population. Immediate assistance following a fall can lower the risk of medical complications, thus saving lives and reducing the associated health care costs. Therefore it is important to detect a fall as it happens and promptly mobilise first responders for proper care and attendance to possible injury. Radar offers privacy and non-intrusive monitoring capabilities. Micro-Doppler signatures are typically employed for radar-based human motion detections and classifications. Proper time–frequency signal representation is, therefore, required from which important features can be extracted. Missing or noise/interference corrupted data can compromise the integrity of micro-Doppler signatures and subsequently confuse the classifier. In this study, the authors restore the time–frequency signatures associated with human motor activities, such as falling, bending over, sitting and standing, by using a hybrid approach of compressive sensing and multi-window analysis based on Slepian or Hermite functions. Because time–frequency representations of many human gross-motor activities are sparse and share common support in joint-variable domains, the multiple measurement vector approach can be effectively applied for fall classification in both cases of full data or compressed observations.

Unobtrusive and continuous monitoring of cardiopulmonary activity at a distance provides a potential tool in making health care and emergency delivery more efficient. Doppler radar remote sensing of vital signs has shown promise to this end, with proof of concept demonstrated for various applications such as more comfortable monitoring for many people. In this study, the authors present a second-order cyclostationary model for the returned amplitude and frequency modulated radar signal, which is contaminated with various noises, body motion artefacts and dc offset, to extract vital signs. They validate their model with confidence interval extraction from 500 simulation runs and also with 50 experiment runs on a female student using a miniaturised non-contact heartbeat and respiration monitoring radar system based on the quadrature Doppler effect.

A simple modification of a minimum-based constant false alarm rate detector for Pareto clutter models is examined in this study. This has been motivated by the need to develop improved detection processes to operate in high grazing angle clutter as exemplified by returns acquired from the Defence Science and Technology Organisation's Ingara radar. A minimum-based detector has the greatest resilience to clutter transitions and interfering targets. However, it has been shown recently that a minimum-based detector for the Pareto environment has a tendency to saturate. Using a simple transformation, progress is made towards the development of a useful incoherent detection scheme. Its performance is then analysed in both synthetic and real clutter.

This paper concerns experimental investigation of the frequency-domain approach to target scene sensing using ultra-wideband orthogonal frequency division multiplexing software-defined radar. Individual spectral components of the radar signal (sub-carriers) are analysed with the aim of performing their adaptive selection and establishing similarity of the observed response to the previously collected responses of various target scenes. By performing this analysis, the authors are effectively utilising frequency diversity of targets for detection purposes. A low-power, short-range radar system built at Miami University is used to apply this approach to target detection with generalised-likelihood ratio test (GLRT) and frequency profile matching (FPM). Experimental results indicate good promise of FPM, which performed equally to, or outperformed GLRT in all scenarios. Results of correct detection and false alarm rates are shown and discussed, along with theoretical descriptions of the detection approaches.

High target speed, long pulse duration or wide signal bandwidth may cause noticeable scale effect on radar echoes, for which the conventional narrowband matched filter may introduce an obvious signal-to-noise ratio (SNR) loss for target detection. To obtain the ideal SNR gain in the above scenarios, a novel long-time coherent integration method has been proposed, namely wideband-scaled Radon-Fourier transform (WSRFT). The proposed WSRFT can compensate the scale effect not only on the single pulse but also among the multiple pulses in a long coherent integration time. Furthermore, the performance comparison between the proposed WSRFT and the existing Radon-Fourier transform method is given. Finally, some numerical experimental results are also provided to demonstrate the effectiveness of the proposed WSRFT method.

This study presents a time division multiplexing (TDM) multiple-input–multiple-output (MIMO) digital beamforming (DBF) radar concept based on a single transceiver (one transmitter and one receiver). Compared with a conventional MIMO DBF radar system with M-element transmitting array and N-element receiving array, the proposed concept can reduce the number of transmitter/receivers from M + N to 2 for a drastic cost reduction. In addition to theoretical analysis and numerical simulation, an experimental TDM MIMO DBF radar demonstrator is realised and tested for verification using real data. Numerical analysis and experimental results show that the proposed concept can achieve considerable higher angular resolution at lower cost compared to conventional DBF radar concepts using the same antenna array with one-way or two-way beamforming.

This study presents the signal processing techniques applied on a 9.4/18.8 GHz harmonic radar, which is used to investigate behaviours of small insects such as bees, beetles and butterflies. It is still a challenge to achieve high accuracy and long detection range simultaneously in a harmonic pulse radar system. The authors combine the spread spectrum technology with the classic pulse harmonic radar system to overcome the dilemma between accuracy and detection range. The processing gain of the pseudo-random code from the spread spectrum technology is used to increase the sensitivity and makes the system able to detect the signal with the weak power strength below the system noise level. To eliminate the effect caused by the local leakage, the signal-processing method provided to cancel the leakage through applying the symmetric property of the autocorrelation function of the pseudo-random code. In the field tests, the proposed system achieves a 60 m detection range within 1 m ranging accuracy by using 1.75 W transmitting power corresponding to 40.430 dBW equivalent-isotropically radiated power (EIRP). It is estimated to extend to at least 900 m detection range by using a 3 kW transmitting power corresponding to 72.771 dBW EIRP.

A coherent two-dimensional (2D) multiple signal classification (MUSIC) processing for the simultaneous estimation of angular and range target positions has been presented. A 2D spatial smoothing technique is also introduced to cope with the coherent behaviour of the received echoes, which may result in a rank deficiency of the signals covariance matrix. The algorithm is analysed with respect to its application to coherent multiple-input multiple-output (MIMO) arrays. The extended baseline which is synthesised can indeed be used to further improve the performance of the system. The results of the algorithm are shown for both simulated and experimental data scenarios. In the latter case, the data are collected by a frequency-modulated continuous wave radar with MIMO functionality that has been designed and realised in cooperation with TNO, the Netherlands. © The Institution of Engineering and Technology 2014.

Terrain-scattered interference (TSI), that is, jammer signals reflected on the earth's surface, is a significant problem to military airborne radar. In auxiliary beam TSI suppression, the TSI in the main radar beam is estimated by a single or several auxiliary beams and is subtracted from the main beam channel. The signal to subtract is the auxiliary beam signals fed through an estimate of the ‘reflection system’, which describes scattering on the surface. The authors first present results on the structure of this TSI suppression, on the estimation of the reflection system and on the quality of the estimate. Then the authors derive theoretical expressions for the signal-to-interference plus noise ratio (SINR) and the remaining TSI power for a single auxiliary beam. Since the SINR is directly connected to the radar performance, it can be seen what factors affect the performance and how. It was noted that when the estimated reflection system is missing one or more delays of the true system, the TSI filter cannot suppress the TSI signal completely. This phenomenon, which is called ‘TSI leakage’, has a very large impact on the performance. The SINR cannot be kept constant. Instead, an ‘SINR improvement’ can be defined.

The authors investigate the role of correlated waveforms in transmit–receive beam pattern performance of colocated multi-input multi-output (MIMO) radar, which presents many advantages by waveform diversity. The mutual orthogonality among the transmitted waveforms is often assumed but cannot be achieved in practice due to the limitation of signal duration and hardware precision. The authors introduce a common model considering the waveform correlation and propose a matched processing structure for the next estimation of parameters. The sufficient statistic for direction estimation is derived, and the transmit–receive beam pattern related to the waveform correlation matrix is obtained. This work mainly studies the effects of transmitting correlated waveforms with all kinds of correlation forms on beam pattern level. By employing these theoretical results, four numerical examples are performed further to obtain both qualitative and quantificational analyses of MIMO radar transmit–receive beam pattern performance with respect to the changing of the cross-correlation levels of the transmitted waveforms, which can provide a good guidance for orthogonal waveform design when considering MIMO radar beam patterns.

This study focuses on estimation of clutter degrees of freedom (DOFs) for airborne multiple-input multiple-output (MIMO)-phased array radar. Firstly, two equivalent clutter models are presented, according to the transmitting subarray beampattern and synthetic-phased centre, and based on the basic steering vector. Secondly, a convenient estimating rule of clutter DOFs for airborne MIMO-phased array radar under arbitrary transmitting subarray structures is presented and proofed strictly. Finally, the simulated results indicate that airborne MIMO-phased array radar is effective both in spatial selectivity and clutter suppression, and the clutter DOFs under arbitrary transmitted subarray structures can be estimated by the proposed rule exactly. The proposed models and rule are suitable for both conventional-phased array radar and airborne MIMO radar with uniform or non-uniform transmitting subarray and sparse array, and they are valuable for the improvement of space-time adaptive processing algorithm performance.

Reduced-dimension space-time adaptive processing (STAP) techniques are often used in multichannel wide-area surveillance airborne systems to suppress ground clutter. However, it is well known that their performance degrades to some extent in non-homogeneous environments because of inaccurate estimation of the interference covariance matrix from secondary data. In this study, the authors propose an algorithm which applies Kalman filtering to suppress ground clutter based on the data model of radar echoes from multichannel wide-area surveillance systems. Since the proposed algorithm does not need to estimate the interference covariance matrix, it has a major advantage when processing the data from non-homogeneous environments. Simulated data from phased-array multifunctional imaging radar (PAMIR) system and real data from an X-band wide-area surveillance system are used to validate the proposed algorithm. The results show that the new algorithm works well in both radar systems.

A modification of the classical orthogonal frequency division multiplexing signals is discussed that allows for the creation of a set of perfectly orthogonal transmit signals sharing the same bandwidth. These signals can be employed for performing radar measurements with multiple transmitters being simultaneously active, for example, in radar networks or multi-input multi-output radar applications. Since all the signals of the individual transmitters occupy the full available bandwidth, no deterioration of the achievable range resolution occurs. This study comprises both the theoretical considerations as well as the verification simulations and measurements. A particular focus is on the requirements regarding the frequency and time synchronisation of the individual signals and their impact on the achievable performance. The influence of possible Doppler shifts is also considered. Finally, a performance comparison with classical code-based multiple user access techniques is provided. The achieved results demonstrate that the proposed multi-carrier waveforms clearly outperform the classical code-based approach under realistic assumptions of synchronisation accuracy.

There is continuing interest in the development of large-area active microwave panels for use as switchable windows, 'wallpaper', reflectors or radar-absorbent materials. The density of active devices on such panels may range from a few hundred to tens of thousands per square metre but there is no published information about the reliability of such panels in practice and the effects on their performance of cumulative device failure. A preliminary analysis of such effects in terms of panel radar cross-section and power consumption is provided.

A study of robust detection scheme for continuous wave noise radars is presented. The probability density function (PDF) of the noise at the input of the radar is not usually Gaussian and has heavy tails generated by impulse interferences. Although the PDF of interferences at the output of the noise radar correlator is Gaussian, impulse interferences increase the processing floor, and thus decrease the overall radar sensitivity. The proposed robustification applied to the correlator's input signal increases the radar sensitivity in the presence of impulse interferences, and does not introduce any significant losses if the input noise is purely Gaussian.

Quadrature phase discriminators, the core of wideband instantaneous frequency measurement (IFM) receivers and multiple base-line interferometry for accurate direction finding (DF), were invented in 1957, by S.J. Robinson of Mullard Research Laboratories (MRL). Digital instantaneous frequency measurement (DIFM) receivers have been universally used operationally for wideband monitoring of radar environments in naval, airborne and ground-based electronic support measures (ESM) systems all over the world for over 50 years. Their importance is such that many countries have developed their own IFM manufacturing capability with just minor architectural changes to the original design. This study describes the invention sequence, the development history, IFM design and performance principles, its general use and limitations in modern electronic warfare (EW) systems and ends with a projection for the future.

Two essential requirements of a non-communications electronic support system are a high probability of intercept and a high probability of detection against scanning microwave band emitters. High probability of intercept is typically achieved using a wideband receiver whereas high probability of detection requires a narrowband receiver. Achieving both has hitherto required the use of multiple receivers in a cascaded or channelised architecture. To minimise the cost for radar warning receivers and anti-radiation systems, the authors propose that a single scanning narrowband receiver with inherently high probability of detection can achieve a high probability of intercept by using an optimised search strategy to control its frequency scan pattern. In this study the authors have presented a new approach to assessing the performance of strategies based on probability of intercept and demonstrated the use of an evolutionary algorithm to optimise receiver search strategies. The optimised strategies show a significant performance improvement over traditional scheduling approaches.

Spectral constraints placed on radar systems by regulatory agencies require the design of highly linear amplifiers. Spectral spreading in power amplifiers is a result of transistors operated in the non-linear regime to optimise efficiency. Various methods are employed by power amplifier designers to maximise both linearity and efficiency. The methods of predistortion, feedforward, envelope tracking, Doherty and `linear amplification using non-linear components` are discussed in this article. Trade-offs and challenges inherent in these design approaches are surveyed.

Monopulse radars are used to track targets that appear in the look direction beam width. The distortion of the tracking information produced when high power interference signals (jamming) are introduced through the radar antenna can cause severe erroneous outcomes from the monopulse tracking processor. This leads to errors in the target tracking angles that may cause target mistracking. New monopulse radar structures that utilizes an empirical mode decomposition (EMD) based denoising processor are presented in this paper. EMD filtering is carried out for the complex radar chirp signal with subsequent detrending, thresholding, and denoising processes. These processes are used to decrease the noise level in the radar processed data to improve the signal to noise ratio. The performance enhancement using the monopulse radar tracking system with EMD based filtering is included using the standard deviation angle estimation error (STDAE) for different jamming scenarios and different target SNRs. STDAE shows that the new EMD based system works well in the case of main beam interference and side lobe interference for the conventional processor and, in the case of the spatial adaptive processor, is effective in the case of main lobe interference.

This study mainly deals with the problem of multiple-input multiple-output (MIMO) radar in compound-Gaussian clutter-dominated scenario with unknown covariance matrix. The general MIMO model, with widely separated sub-arrays and co-located antennas at each sub-array, is adopted. First, the signal model is developed to compound-Gaussian clutter, and then, the generalised likelihood rate test (GLRT) and Rao detectors are derived with known covariance matrix. To make the detectors fully adaptive, the secondary with signal-free data is collected to estimate the covariance. A thorough performance assessment is also given, which considers the sense with co-located antennas configuration of transmitters and receivers array. Via several numerical examples, it is shown that the derived GLRT and Rao detectors can provide excellent detection performance in spikier clutter compared with the detector, which is derived by Jian Li in Gaussian clutter. To this end, the Rao detector outperforms best.

Passive radars have been known to the scientific community since their first application as a system to detect bombers by means of shortwaves radiated by radio broadcasting towers in 1935, although they lately raised a renewed interest among researchers for some specific features that make them more appealing than classic active radar systems. In fact, having the transmitter and receiver located at two different positions, and the adoption of signals carrying other kinds of information such as GSM (either classical or the 1800/1900 MHz DCS version) or UMTS waveforms, makes passive radar virtually undetectable and economically advantageous. A measurement system used to characterise the clutter from a GSM/DCS and UMTS-based passive radar is presented. The main objective is to study the statistical properties of the clutter signals, find theoretical models fitting the measured clutter data and analyse the differences between the modulated carriers of the two different standards.

Range sidelobes, a major shortcoming of radar pulse compression, are often reduced through the use of mismatched filters. The authors propose to blank the remaining sidelobes by using two or more mismatched filters, whose sidelobes are designed to peak at different delays. The authors show how to design such filters and present promising simulation results with two or more mismatched filters.

The extension of the dynamic range performance of existing radar systems is integral to the requirement for current sensors to see deeper into clutter, that is, to detect weak signals (e.g. small targets) in the presence of strong interference (e.g. urban clutter signals). The rationale behind this requirement is that this additional capability greatly enhances the utility of military and commercial systems. Two approaches to improving the dynamic range of modern radar and surveillance receivers are described: (1) linearisation of intermodulation distortion (IMD) using digital post-distortion algorithms and (2) linearisation of IMD using frequency retranslation mixer (FRM). The experimental results presented illustrate that the digital post-distortion and FRM approaches are effective in providing IMD improvements for the hardware and test scenarios measured. The improvements measured ranged from 15 to 35 dB for narrowband signals to 2–6 dB for frequency-modulated continuous wave (FMCW) wideband signals. The digital post-distortion approach provided the greatest performance improvement when the input signals were between the analogue-to-digital converter full range and 20 dB below that level. The improvements measured for the FRM linearisation approach ranged from 20 to 25 dB for the narrowband two-tone tests and 16–18 dB for the wideband FMCW signal chirps.

This paper reports on the design and initial evaluation of a low-cost multistatic radar system that exploits digital components. The system is based on a commercial-off-the-shelf and open architecture approach, using a direct digital synthesiser, a field programmable gate array and a digital signal processor as core components. Instrument function testing, calibration and the results of the initial field tests are reported. Some of the first multistatic experimental results are reported and demonstrate a number of aspects of the performance of such a configuration. The advantages and limitations of a low-cost digital radar design are discussed and further system development possibilities outlined. This system will enable the collection of a wide range of novel multistatic data and has the potential to demonstrate a number of new radar applications.

A novel approach to the design of spatial arrays is presented. The hybrid array beamformer consists of a sparse array in which some of the elements are arranged periodically, thus creating a periodic sub-array. The outputs of the sparse and periodic arrays are then fused to create a beampattern with good resolution and low peak sidelobe levels. This approach is seen as matching the performance of standard periodic arrays but with a significant saving in terms of the required number of elements. Applications include sonar, radar and ultrasonic systems