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Often, the monitoring systems solution of remote sensing problems, recognition (classification, discrimination) of radar objects using radio polarimetry methods is required in real time mode with the display of the current information on the radar monitor. Monitoring systems can be either stationary (more often terrestrial) or mobile (based on various transport vehicles). When designing such systems, along with ensuring the required speed and performance of the computer, it is also important to ensure the unification of the units and assemblies, the reduction of weight and size characteristics, simplification of the tuning, increase of the operational reliability. In this case, the use of blocks of digital information processing is required. When digitally processing polarized signals, it is necessary to convert the input analog signal to digital form, i.e. to sampled by time and frequency and perform level quantization. The peculiarities of the discretization of the radar polarized signal over time are considered in the article. Analytical expressions for the input polarized signal are derived with considering the geometric parameters of the polarization ellipse. Formulas are given for the in-phase and quadrature components of the polarized signal, for a complex signal envelope. It is alleged that quadrature processing of the polarized signal leads to a decrease in the requirements for analog-to-digital conversion chips due to a significant reduction in the sampling frequency. After the transformations presented in the article, electronic components, which are already in production by Russian companies in the radio electronic industry, can be used in monitoring systems. The transformations of a polarized signal in the time domain described in the article lead to certain transformations in the frequency domain. We are talking about converting the two-side signal spectrum into a one-side spectrum with its transfer to the video frequency region. Such a conversion helps to reduce the sampling rate from gigahertz to megahertz. Analytic expressions in the time domain are accompanied in the article by a graphic interpretation of the signal spectra in the frequency domain. A scheme for demodulating the in-phase and quadrature components of the polarized signal is given. Functional features of filtering units in the scheme are described, the attention of the designers of the digital signal processing systems to the requirements of the Kotel'nikov's sampling theorem is emphasized.

This thesis analyzes and develops waveforms and signal processing techniques that are used to improve the performances of range, velocity, and direction-of-arrival (DOA) estimation for multiple-input-multiple-output (MIMO) radar systems with colocated transmit and receive antennas. The main contributions of this work consist of four parts, which are summarized as follows. The starting point of this work is MIMO radar waveform design. The freedom to transmit non-coherent waveforms, i.e., the waveform diversity, enables many new features for MIMO radar to improve target detection and parameter estimation. However, it also introduces new challenges for the waveform design, e.g., minimiz-ing the cross-ambiguity functions (CAF’s). To tackle this problem, we consider the extension of two frequency-hopping waveforms from single-input-single-output (SISO) radar to MIMO radar, the Costas array coded (CAC) waveforms and the quadratic congruence coded (QCC) waveforms. Exhaustive search is carried out for suboptimal solutions to .nding a set of codes that mutually exhibit least cross-ambiguity properties. The general problem of the code selection for global optimum is formulated as an open question. The suboptimal Costas and quadratic congru-ence codes are used throughout this thesis when other designs are considered. The second contribution of this thesis is on receiver instrumental variable .lter (IVF) design for joint range and Doppler sidelobe suppression. The commonly used matched .lter (MF) maximizes the signal-to-noise ratio (SNR) of its output. However, it is ine.cient in improving the signal-to-clutter ratio (SCR). Alterna-tively, an IVF enables a trade-o. between the SNR and SCR at the receiver. We .rst analyze the performances of existing range domain only IVF designs using integrated sidelobe level (ISL) constraint and zero sidelobe (ZS) constraint, respec-tively. The results indicate the possibility of using phased-array radar for improved performance. Then a rectangular area centered at the origin on the range-Doppler plane is considered for joint clutter sidelobe suppression, where both MIMO and phased-array radar are considered. Closed-form solutions and simulation results are provided. The conclusion is then drawn in a trade-o. manner. Compromis-ing the waveform diversity, the phased-array radar design turned out to be more e.cient in terms of sidelobe suppression, SNR loss, and computational complexity. Another advantage introduced by MIMO radar waveform diversity is the .exible design of transmit beampatterns, which is the topic of the third part of this thesis. Existing works have provided many solutions. However, little attention has been paid to several aspects of the performance such as the ripple within the energy focusing section, the sidelobe attenuation, and the transition bandwidth. Hence, we propose a feasibility problem (FP) formulation based on the nonlinear mapping from MIMO radar transmit beampattern design to multiple-input-single-output (MISO) .nite impulse response (FIR) .lter design. One of the advantages of the proposed method is that it takes quantitative controls of the above parameters in the design. Moreover, the minimum number of transmit antenna to achieve a given transmit beampattern is obtained. Via simulations, the transmit beampattern formula, which has a similar form as Kaiser’s formula, is obtained for antenna selection given a set of design speci.cations. In addition, a robust design method is proposed. The robust design establishes a trade-o. between the radio-frequency ampli.er (RFA) requirements and the number of transmit antennas. It also leads to signi.cant relaxation of waveform correlation requirements. As a result, the robust design uses a set of easily generated and wildly used linear frequency modulated (LFM) waveforms to achieve the transmit beampattern identical to that designed under ideal orthogonality assumption. The last contribution of this thesis is presenting a fairer comparison between MIMO and phased-array radar. Throughout this thesis, the performance of phased-array radar is considered in comparison with MIMO radar in various aspects. The most signi.cant di.erence between the two systems is that phased-array radar transmits coherent waveforms whereas MIMO radar transmits non-coherent wave-forms. Implicitly, it is the coherent gain versus the diversity gain. The two systems establish a trade-o. for researchers and engineers to choose under di.erent objec-tives, design environments, and given conditions. Via the comparisons on the basic system models, receiver identi.ability, receiver IVF design, and transmit beampat-tern design, we conclude that MIMO radar outperforms phased-array radar when multiple targets exist whereas the latter outperforms the former when one is dealing with only a single target. ELECTRICAL and ELECTRONIC ENGINEERING

This thesis illustrates the necessity and design process of performance improvement for radar detection by using novel CFAR detectors. A qualitative discussion of the need for and applications of conventional CFAR detectors is presented first. Typical applications are given as examples of where the radar system may be utilized. A closer look under the Swerling 2 assumption is presented as well. The second portion of the thesis generally introduce the underlying electromagnetic theories that radar detection is built upon. The radar range equation, radar cross section, noise in systems, and vehicular applications are explained. The portion focuses on the radar detection. MASTER OF ENGINEERING (EEE)

The emerging photonics-based radar breaks the bandwidth limitations of traditional radar, making it possible to achieve a high range resolution. While, the angular resolution of a photonics-based radar is still limited by the size of its equivalent aperture. To achieve both high range and angular resolution, we propose a super-resolution radar detection method that is achieved by a photonics-based phased array radar applying two-dimensional multiple signal classification (2D-MUSIC) algorithm. The broad bandwidth enabled by the photonics-based system can ensure a high range resolution, and the 2D-MUSIC method helps to achieve a high angular resolution. Feasibility of the proposed method is experimentally verified through a photonics-based 1×4 phased array radar with a bandwidth of 4 GHz (22-26 GHz). With the capability for highly precise target detection in both range and angular direction, the proposed scheme has great potential in future radar applications.

Spectrum sharing between cellular and radar systems is an emerging area of research. Deploying commercial wireless communication services in radar bands give wireless operators much needed additional spectrum to meet growing bandwidth demands. However, to enable spectrum sharing between these two fundamentally different systems interference concerns must be addressed. In order to assess interference concerns we design a three-dimensional (3D) channel model between radar and cellular base stations (BSs) in which the radar uses a two-dimensional (2D) antenna array and the BS uses a one-dimensional (1D) antenna array. We formulate a line-of-sight (LoS) channel and then propose an algorithm that mitigates radar interference to BSs. We extend the previously proposed null space projection algorithm for 2D channels to 3D channels and show that effective nulls can be placed by utilizing both the azimuth and elevation angle information of BSs. This results in effective interference mitigation. In addition we show that the 3D channel model allows us to accurately classify the size of radar’s search space when null space projection algorithm is used for interference mitigation.

We present a deep learning approach to design tensorial metasurfaces for radio-frequency (RF) applications, such as communications and radar, that have strict radiation requirements. Such intelligent RF surfaces require significant manual tuning of several constituent meta-atom designs to realize the required phase shift or polarizability. In this context, meta-atoms that comprise multiple layers are considerably more challenging but have the advantage of implementing complex, tensorial electromagnetic (EM) responses. In this paper, to reduce the design time and optimization overhead, we employ a deep convolutional generative adversarial network (DC-GAN) to perform inverse design, i.e. generate single-and multi-layer meta-atom shapes based on the desired radiation pattern. Further, our DCGAN architecture includes a separate, simulator convolutional neural network that allows for quick validation of the response of the synthesized meta-atom shape. We generated spectral responses for training by feeding parametric variations of twelve published meta-atom designs to a full-wave EM simulator. Numerical experiments indicate that meta-atom designs generated by the DC-GAN differ from co-polarization and cross-polarization transmission responses obtained via EM simulators by less than 1 dB.

Self-interference stemming from transmission power leakage to the receiver deteriorates the performance of linear frequency modulated continuous wave (LFMCW) radar. Therefore, how to increase the isolation between the transmitting and receiving antennas becomes a major problem for the improvement of LFMCW radar. In this paper, we adopt a microwave adaptive interference cancellation system based on down-conversion, and propose to use a phase shifter to offset the phase shift caused by the circuit delay and components in the down-conversion circuit, thereby improving the self-interference cancellation ratio. Experiments are conducted to evaluate our methods. The results show that, compared with the traditional delay-based compensation method, our phase-offset based method can increase the interference cancellation ratio (ICR) by 15dB under the condition of wired interference coupling and 10dB under the wireless coupling condition.

Integrated radar and communication (IRC) systems are promising in the next generation wireless communication networks. However, to realize high level security of information transmission in IRC systems is challenging due to the large transmission power and the open unguided nature of the wireless channels. In this paper, the secure precoding and artificial noise (AN) techniques are investigated to improve the secrecy rate of a multiple-input multiple-output IRC system with multiple eavesdroppers. The formulated secrecy rate maximization problem is non-convex due to the logarithmic of the determinant that exists in the objective function. Instead of using Taylor series approximation of the non-convex elements, we propose to linearize two log-det terms to tackle this challenging problem. After linearization, an alternating optimization algorithm is proposed to solve the primitive problem. Moreover, a first-order approximation is employed to handle the quadratic constraint on radar detection performance. The suboptimal secure precoding and AN scheme can be obtained for maximizing the information security transmission rate of the legitimate receiver while ensuring the performance of radar detection. Simulation results are presented to validate the performance of our proposed design.

Large antenna arrays have been always exploited for radar applications in order to provide very high spatial resolution, beam-forming and null-steering. These capabilities have been found to be extremely appealing for communication systems too because of their potential to provide highly-directive beams as the best solution to reduce interference and increase the overall capacity, allowing spectral reuse through spatial diversity. Nowadays the big challenge is not only related to the maximization of the overall system performance - which have been proven to be very effective when considering full-phased/full-digital architectures - but is mainly focused on the economic side: the real goal is to keep cost and energy consumption sufficiently low to obtain affordable products. This work focuses on millimeter-wave wireless systems (nun-Waves), and presents an overview of the application scenarios for 5G (and beyond) networks, together with the main related challenges and finally explores some techniques that can be adopted to design energy- and cost-efficient phased array antennas.

In this paper, a dual-band photonics-based radar system used for precise displacement measures in a multitarget scenario is described. The radar was designed for monitoring applications to prevent both structural failures of buildings and landslides. The radar system exploits the technique of stepped frequency continuous wave signal modulation and the displacement of the targets is evaluated through differential phase measurements. In this work, encouraged by the results already achieved in the single-target scenario, we present an investigation extended to the case of multiple targets. We aim to evaluate the accuracy of the displacement estimation both from a simulated and experimental point of view, and to understand how multiple targets impact on the final estimate of displacements. Simulation results demonstrate that it is possible to achieve a typical accuracy of less than 0.2 mm for distances up to 400 m. These results are confirmed by preliminary experimental outcomes, which take into account different operative conditions with multiple targets. Finally, concluding remarks and perspectives draw the agenda for our future investigations.

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.

Multiple-input multiple-output (MIMO) radars have attracted much attention for their superior ability to enhance a system's performance. In this study, the authors' goal was the study of the spatial multiplexing gain of MIMO radars with widely separated antennas (WS-MIMO), which the authors showed that is equal to the number of unambiguously detectable targets. They obtained this number from two different aspects: first, by defining the ambiguity function of a WS-MIMO radar in the case of multiple targets, suitable for such purpose; Second, by modelling the MIMO radar system with a MIMO wireless channel. They showed that a MIMO radar is indeed a MIMO wireless system communicating the information about the existence of the targets. By such modelling, they could easily make the relation between dual concepts of MIMO radar and MIMO communication, one of which is the multiplexing gain.

Recent changes in U.S. policy call for spectrum sharing between radar and wireless communications. In order to inform choices of protection criteria for a radar sharing spectrum with communications systems, this paper models communications interference and its effects on a cell-averaging adaptive-threshold radar detector. First, we propose a statistical model for communications interference based on existing models and original simulations, and we find support for both Gaussian and non-Gaussian models, depending on the application. Then, we assess the impact of communications interference on radar detection. Our results suggest that when interference is not well modeled as white Gaussian noise, mean interference-to-noise ratio (INR) is not sufficient to characterize interference effects on radar, and additional interference characteristics such as kurtosis/impulsiveness and coherence time can significantly impact radar performance. We also find degradation in radar performance in relatively low-INR Gaussian interference (e.g., about $-6$ to $-\text{2 dB}$ mean INR at the output of the matched filter).

Purpose This paper aims to present an approach of utilizing multiple-input multiple-output (MIMO) radar concept to enhance pedestrian classification in automotive sensors. In a practical environment, radar signals reflected from pedestrians and slow-moving vehicles are similar in terms of reflecting angle and Doppler returns, inducing difficulty for target discrimination. An efficient discrimination between the two targets depends on the ability of the sensor to extract unique characteristics from each target, for example, by exploiting Doppler signatures. This study describes the utilization of MIMO radar for Doppler measurement and demonstrates its application to improve pedestrian classification through actual laboratory measurements. Design/methodology/approach Multiple non-modulated sinusoidal signals are transmitted orthogonally over a MIMO array using time division scheme, illuminating human and non-human targets. The reflected signal entering each of the receiving antenna are combined at the radar receiver prior to Doppler processing. Doppler histogram was formulated based on a series of measurements, and the Doppler spread of the targets was determined from the histograms. Results were compared between MIMO and conventional single antenna systems. Findings Measurement results indicated that the MIMO configuration provides able to capture more Doppler information compared to conventional single antenna systems, enabling a more precise discrimination between pedestrian and other slow-moving objects on the road. Originality/value The study demonstrated the effectiveness of using MIMO configuration in radar-based automotive sensor to enhance the accuracy of Doppler estimation, which is seldom highlighted in literature of MIMO radars. The result also indicated its usefulness in improving target discrimination capability of the radar, through actual measurement.

Frequency diverse array (FDA) can produce a range-angle-dependent beampattern due to the employment of a small frequency increment across the array elements. By utilizing this characteristic, this letter devises an FDA and multiple-input multiple-output hybrid radar to jointly estimate the ranges and angles of multiple targets via optimal transmit beamspace design. A uniform elemental power constraint is adopted as the optimization criterion is to minimize the mutual coherence of the sensing matrix using a sparse model and to achieve high-resolution estimation in both range and angle dimensions. A cyclic optimization approach based on power method-like is further developed to solve the non-convex design problem. The excellent performance of the proposed approach is demonstrated via computer simulations.

In this paper, we experimentally demonstrate a radar signal distribution over optical networks. The use of fiber enables us to distribute radar signals to distant sites with a low power loss. Moreover, fiber networks can reduce the radar system cost, by sharing precise and expensive radar signal generation and processing equipment. In order to overcome the bandwidth challenges in electrical switches, a semiconductor optical amplifier (SOA) is used as an all-optical device for wavelength conversion to the desired port (or channel) of a wavelength division multiplexing (WDM) network. Moreover, the effect of chromatic dispersion in double sideband (DSB) signals is combated by generating optical single sideband (OSSB) signals. The optimal values of the SOA device parameters required to generate an OSSB with a high sideband suppression ratio (SSR) are determined. We considered various parameters such as injection current, pump power, and probe power. In addition, the effect of signal wavelength conversion and transmission over fiber are studied in terms of signal dynamic range.

Studies have demonstrated the usefulness of micro-Doppler signatures for classifying dynamic radar targets such as humans, helicopters, and wind turbines. However, these classification works are based on the assumption that the propagation channel consists of only a single moving target. When multiple targets move simultaneously in the channel, the micro-Dopplers, in their radar backscatter, superimpose thereby distorting the signatures. In this paper, we propose a method to detect multiple targets that move simultaneously in the propagation channel. We first model the micro-Doppler radar signatures of different movers using dictionary learning techniques. Then, we use a sparse coding algorithm to separate the aggregate radar backscatter signal from multiple targets into their individual components. We demonstrate that the disaggregated signals are useful for accurately detecting multiple targets.

In order to meet the demands of “Internet above the clouds,” we propose a multiple-antenna aided adaptive coding and modulation (ACM) for aeronautical communications. The proposed ACM scheme switches its coding and modulation mode according to the distance between the communicating aircraft, which is readily available with the aid of the airborne radar or the global positioning system. We derive an asymptotic closed-form expression of the signal-to-interference-plus-noise ratio (SINR) as the number of transmitting antennas tends to infinity, in the presence of realistic co-channel interference and channel estimation errors. The achievable transmission rates and the corresponding mode-switching distance-thresholds are readily obtained based on this closed-form SINR formula. Monte-Carlo simulation results are used to validate our theoretical analysis. For the specific example of 32 transmit antennas and four receive antennas communicating at a 5-GHz carrier frequency and using 6-MHz bandwidth, which are reused by multiple other pairs of communicating aircraft, the proposed distance-based ACM is capable of providing as high as 65.928-Mb/s data rate when the communication distance is less than 25 km.

Multiple-input multiple-output (MIMO) radar enjoys the advantage of increased degrees-of-freedom and spatial diversity gain, but it cannot effectively resolves the targets closely spaced in the same angle cell (but different range cells). Frequency diverse array (FDA)-MIMO radar can handle this problem by exploiting its range-dependent beampattern. FDA-MIMO radar was, thus, suggested for range–angle estimation of targets. Nevertheless, it is necessary to provide theoretical performance analysis for such a relatively new radar technique. Since multiple signal classification (MUSIC) algorithm is widely adopted in most of the FDA-MIMO literature, this paper derives the Cramer–Rao lower bound and mean square error expressions in MUSIC-based range–angle estimation algorithms for a general FDA-MIMO radar. Furthermore, the corresponding range and angle resolution thresholds in target detection and localization are also derived. Numerical results verify that the FDA-MIMO indeed outperforms conventional MIMO radar in both range–angle estimation and resolution threshold performance.

As the use of automotive radar increases, performance limitations associated with radar-to-radar interference will become more significant. In this paper, we employ tools from stochastic geometry to characterize the statistics of radar interference. Specifically, using two different models for the spatial distributions of vehicles, namely, a Poisson point process and a Bernoulli lattice process, we calculate for each case the interference statistics and obtain analytical expressions for the probability of successful range estimation. This paper shows that the regularity of the geometrical model appears to have limited effect on the interference statistics, and so it is possible to obtain tractable tight bounds for the worst case performance. A technique is proposed for designing the duty cycle for the random spectrum access, which optimizes the total performance. This analytical framework is verified using Monte Carlo simulations.

Increasing safety and automation in transportation systems has led to the proliferation of radar and IEEE 802.11pbased dedicated short-range communication (DSRC) in vehicles. However, current implementations of vehicular radar devices are expensive, use a substantial amount of bandwidth, and are susceptible to multiple security risks. In this paper, we use the IEEE 802.11 orthogonal frequency-division multiplexing communications waveform, as found in IEEE 802.11a/g/p, to perform radar functions. In this paper, we present an approach that determines the mean-normalized channel energy from frequencydomain channel estimates and models it as a direct sinusoidal function of target range, enabling closest target range estimation. In addition, we propose an alternative to vehicular forward collision detection by extending IEEE 802.11 DSRC and WiFi technology to radar, extending the foundation ofjoint communications and radar frameworks. Furthermore, we perform an experimental demonstration near DSRC spectrum using IEEE 802.11 standard compliant software defined radios with potentially minimal modification through algorithm processing on frequency-domain channel estimates. The results of this paper show that our solution delivers sufficient accuracy and reliability for vehicular RADAR if we use the largest bandwidth available to IEEE 802.11p (20 MHz). This indicates significant potential for industrial devices with joint vehicular communications and radar capabilities.

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.

Frequency modulation continuous wave (FMCW) radar receivers generally suffer from transmitter leakage due to insufficient TX-to-RX isolation. One of the effective approaches to solving this problem is using reflected power cancelers (RPCs) that cancel the leakage from the transmitter adaptively. In this paper, a linear time invariant (LTI) model of the RPC is derived in order to carry out a comprehensive study of the mechanism of leakage cancelation and output noise performance for CW radar applications. Loop frequency responses for receiving signal, loop stability, and the influence of dc offset of IQ mixer are analyzed by a simplified transfer function. A detailed noise model of the RPC is established based on the LTI model to study the output noise components of the RPC under a large incident leakage, then the internal noise cancelation mechanism is elucidated. A prototype with its operating frequency range from 820 to 1020 MHz at UHF band is implemented. Measured loop frequency responses are in agreement with simulation results obtained with the proposed model. Furthermore, measured cancelation ratios for leakages of different ramp rates comply with the normalized power gain at corresponding frequency offsets. The input-referred receiving noise of the RPC prototype is measured to be −155 dBm/Hz at 100-kHz offset under +10-dBm incident leakage power. The proposed LTI model provides a useful tool for the design of high-performance RPC for FMCW systems in different application environments.

The modulated wideband converter (MWC) is well-known for a sub-Nyquist wideband sampling capability based on compressed sensing (CS) theory. In this paper, our goal is to use the MWC as a base to design a sub-Nyquist radar electronic surveillance (ES) system. Our focus is then to extend the capabilities of the previous MWC system in order to meet the challenges, i.e., a very long acquisition time, a much larger simultaneous monitoring bandwidth, and a faster digital signal processing receiver. To this end, we present a new performance analysis framework and then a new digital domain receiver. The proposed performance analysis framework will be useful in comparing signal-acquisition performance of the proposed ES system with those of other sub-Nyquist receivers, including those of the classical Nyquist rate receivers, without resorting to extensive simulations. This framework can also be used to study the complex interplays of important system parameters of MWC, such as the sampling rate, the number of parallel channels, the period of Pseudo random sequence, and thus guides us in selecting the right system dimensions and parameters for desired performance. Radar surveillance application has its inherent needs for very long acquisition time and simultaneous monitoring of very large frequency range. To meet this challenge, a fast signal recovery system needs to be developed, so that radar signal logistics can be retained and recovered from compressed samples. We have proposed a split and synthesis process in which the radar signal recovery problem over a long signal acquisition time can be divided into many small CS signal recovery problems, and the solutions for small pieces are put together later on at the end. In addition, a sub-sampling method is proposed to have the multiple measurement vector problem complete signal recovery faster without noticeable performance loss.

[EN] Multiple-input multiple-output (MIMO) radars have been shown to improve target detection for surveillance applications thanks to their proven high-performance properties. In this paper, the design, implementation, and results of a complete 3-D imaging frequency-modulated continuous-wave MIMO radar demonstrator are presented. The radar sensor working frequency range spans between 16 and 17 GHz, and the proposed solution is based on a 24-transmitter and 24-receiver MIMO radar architecture, implemented by timedivision multiplexing of the transmit signals. A modular approach based on conventional low-cost printed circuit boards is used for the transmit and receive systems. Using digital beamforming algorithms and radar processing techniques on the received signals, a high-resolution 3-D sensing of the range, azimuth, and elevation can be calculated. With the current antenna configuration, an angular resolution of 2.9° can be reached. Furthermore, by taking advantage of the 1-GHz bandwidth of the system, a range resolution of 0.5 m is achieved. The radio-frequency front-end, digital system and radar signal processing units are here presented. The medium-range surveillance potential and the high-resolution capabilities of the MIMO radar are proved with results in the form of radar images captured from the field measurements.

Wireless local positioning systems are based on measurements of signal time of flights and/or bearing angles to determine the position of an active transmitter in 3-D space. Traditional time-of-flight and angle measurements with such positioning systems require many data samples at high rates to fulfill the Nyquist criterion. Moreover, in multipath channels the ability of classical signal processing methods to resolve the delay and bearing vectors of the multiple transmission paths is strictly limited by the radio frequency bandwidth and aperture size. In this paper, we show that the wireless channel is ideally suited for the application of compressed sensing. We can thus reduce the number of samples without major losses in localization performance, or we can improve the resolution. After introducing a general model of a localization task with multipath propagation, and following the definition of key parameters of existing systems, we review the necessary data processing stages with compressed sensing and verify its excellent applicability. Finally, measurements are presented to verify the theoretical predictions experimentally.

The target detection problem in multi-static passive radar systems (MS-PRS) is investigated, where multiple transmitters operate at a single frequency and a single multi-antenna radar receiver processes the received signals. In contrast to multi-frequency MS-PRS, the detector design is challenging due to the fact that the detector sees a mixture of transmitted signals which may not be separately treated. We propose the design of generalized likelihood ratio test (GLRT) receivers to optimize the detection performance. The beamformers at the radar receiver are optimized so that the received signals can be seen as statistically independent signals from multiple reference channels and a surveillance channel. The detector optimization problem is accurately approximated with a convex optimization algorithm. It is analytically shown that the performance of the proposed GLRT receiver approaches that of the active radar. Computer simulations verify the analytical results.

This paper presents a rotatable cyclic Vernier digital-to-time converter (DTC) with 1.8 ps timing resolution on an 80 ns time scale. The proposed DTC features high timing resolution, and can be utilized in beam-steering arrays, which is infeasible for ordinary Vernier DTCs. The proposed DTC was implemented within a passive time-equivalent direct-sampling ultra-wideband impulse-radio radar system and was fabricated in 65 nm CMOS technology. This radar system is capable of quantizing direct-sampled impulse waveforms to provide full degrees of freedom for backend digital signal processing. The measured differential nonlinearity/integral nonlinearity of the DTC was +4.6/−3 and 12.4/−9.4 where the LSB was 1.8 ps, and the total power consumption was 133 mW. Also, a new method for localization between wireless sensor nodes of equivalent-time direct-sampling radar is presented in this paper; this method can theoretically achieve resolution as high as that of regular radar.

The mitigation of third-order intermodulation distortion produced by a nonlinear tunable bandpass filter (BPF) in a digital receiver channel is demonstrated. An iterative solution is proposed, in the use of the least-mean-square algorithm, as an effective way to allow the correction coefficients to adapt to the changes in the system characteristics when the center frequency is changed. Results are shown using a two-pole, varactor-loaded BPF, and an Analog Devices AD9371 transceiver.

The paper proposes a cooperative scheme for the coexistence of a multiple-input-multiple-output (MIMO) communication system and a matrix completion (MC) based, collocated MIMO (MIMO-MC) radar. To facilitate the coexistence, and also deal with clutter, both the radar and the communication systems use transmit precoding. For waveform flexibility, the radar uses a random unitary waveform matrix. We prove that for such waveforms and any precoding matrix, the error performance of MC is guaranteed. The radar transmit precoder, the radar subsampling scheme, and the communication transmit covariance matrix are jointly designed in order to maximize the radar SINR, while meeting certain communication rate and power constraints. The joint design is implemented at a control center, which is a node with whom both systems share physical layer information, and which also performs data fusion for the radar. We provide efficient algorithms for the proposed optimization problem, along with insight on the feasibility and properties of the proposed design. Simulation results show that the proposed scheme significantly improves the spectrum sharing performance in various scenarios.

Coexistence between 802.11 wireless local area network (WLAN) and radars operating in co/adjacent channel scenarios (notably 5GHz) is a problem of considerable importance that requires new innovations. We propose a modified Wi-Fi link design that mitigates the interference from a pulsed search radar such that the WLAN network continues to operate outside the exclusion region. For low density parity check encoding adopted in high throughput WLANs such as 802.11n and.11ac, the modified receiver includes a new interleaver and a log-likelihood ratio (LLR) mapping function to mitigate the impact of radar interference. Two detection approaches are proposed to detect the radar pulse interference to Wi-Fi; time domain cyclic prefix auto-correlation detection and frequency domain data subcarrier based detection. The detection approaches are derived analytically and their performances are evaluated via simulation. We investigate the impact of interleaver length and LLR mapping function parameters via simulations to obtain the desirable frame error rate. Under the known radar pulse arrival at the Wi-Fi receiver, the modified system can significantly mitigate the radar interference for all interference to noise ratio (INR) values by using the frame interleaver. Using the radar pulse detectors in the system, the modified system can mitigate the interference at high and low INRs, while it can partially mitigate the interference in the range of 3

Ground Penetrating Radar (GPR) is a well-received non-destructive technique for the detection of underground utilities, such as water/gas pipes, sewers, power cables, and telecommunication ducts. However, radar signatures of plastic pipes are generally weak when the surrounding soils are attenuative and/or the pipe and soils have similar electromagnetic characteristics. In order to increase the radar visibility of these pipes, attaching Radio-Frequency (RF) tags to them is a useful method. In this paper we designed two types of Bowtie-Omega shaped RF tags. The finite element method (FEM) simulation and measurement of the designed tags show strong resonances in the GPR spectrum, and by conducting GPR B-scans stronger radar signatures are observed when the RF tags are buried in our 2.0 × 1.5 × 0.75 m tank filled with dry sand. Furthermore, we implement a simple processing procedure based on Short-time Fourier Transform (STFT), by which strong time-frequency domain response of the tags is clearly seen at those designed resonant frequencies, and disappear when tags are not inserted. The resulting detection of the hollow plastic pipe in both time and frequency domains due to the co-located tag is evidently enhanced.

To improve the availability of limited spectral resources and construct a cost-efficient platform simultaneously performing both radar and communication functions, the orthogonal frequency division multiplexing (OFDM) integrated radar and communication system (IRCS), which is referred to as OFDM-IRCS, is provided. For the frequency sensitive target and frequency selective fading channel, it is able to improve the radar and communication performance by efficiently employing the limited transmit power in the OFDM-IRCS. To this end, we propose two optimal waveform design methods that meet different users’ demands. First, the Cramer-Rao bounds (CRBs) for estimating range, velocity and target scattering coefficients with integrated OFDM waveform are derived. And the channel capacity in communication is formulated. Then, the multiobjective optimization problem is devised, and the adaptive weighted-optimal and Pareto-optimal waveform design approaches are proposed to simultaneously improve the estimation accuracy of range and velocity in radar and the channel capacity in communication. Finally, several numerical examples are presented to demonstrate the effectiveness of the proposed design methods.

In this paper, a new Ka-band Doppler radar with an ability to remotely monitor respiration rate, heartbeat rate (HR), and heart rate variability (HRV) is presented. Exploiting the advantage of high sensitivity of Ka-band radar in sensing of chest-wall movement, we make more accurate reconstruction of cardiopulmonary activities from low-quality received signal. The advantage of using Ka-band radar is obtained by paying a penalty, which is harmonic interferences that make measuring of cardiopulmonary details infeasible in lots of real scenarios. In this paper, by using a more complete model of return signal, a new routine is introduced for the robust detection of breathing and HR that extremely alleviates the problems associated with harmonic interferences. Besides, a more suitable model is proposed, which can cover time-variability cardiorespiratory features. Taking advantage of this model and based on the unconditional orthonormal representation of band-limited signals, a filter with time-varying coefficients is proposed to extract HRV. This extraction is done without resorting to tracking HR trace that makes it more precise and robust than the conventional approach. The indicated filter enables us to suggest a novel approach to remove random body motion effects. By experimental data, the applicability of the new radar for a wide range of real world scenarios is investigated, and its advantages beside conventional approaches are proved practically in different aspects.

We provide an overview of several high-tech antenna apertures and antenna front ends, developed and realized by IMST (in some cases in cooperation with partners) over a time span of more than 15 years. These front ends have become key components for bandwidth-hungry applications such as mobile/nomadic satellite communication terminals (satcom-onthe-move) and radar systems. Satcom terminal data throughput for multimedia services provided via satellite links is increasing rapidly. Such terminals require highly complex radio-frequency (RF) systems capable of tracking satellites despite movements of the mobile terminal platform. Depending on the type of platform (land mobile, maritime, or aeronautical), the requirements for these front ends and the resulting complexity can vary. This also applies to radar sensors for automotive applications and unmanned aerial vehicle (UAV) platforms, for example. In all of these front ends, the antenna architecture is always based on a phased/steerable array topology. Such systems are, in general, complex configurations: they require not only RF circuitry but also complex baseband processing and highly accurate sensor platforms to perform adequate beam steering and tracking. The overall design must be cost-effective, a very demanding requirement. Through the years, IMST has developed a customized set of highly specialized skills to address all of these challenges.

Hybrid couplers are essential devices in various microwave circuits and systems, such as radar systems and beam forming networks. The development of this device is necessary along with the development of the new communication standards for the most modern guiding structures. One of the most recent and promising guiding technologies is the ridge gap waveguides, which is expected to play an essential role in the millimeter wave and submillimeter wave applications, not only the 5G communications but also other future communication. Therefore, standards are recommended to make use of the high-frequency guiding structures. In this paper, a design procedure for the hybrid couplers is presented. The frequency band of interest is centered at the 15 GHz, which can be deployed for both the 5G mobile communication and the airborne radar applications. The proposed design is fabricated and measured. The measured and simulated results are in excellent agreement.

This paper presents a 2-GS/s 8-bit 16 $\times$ time-interleaved (TI) analog-to-digital converter (ADC) for a millimeter-wave pulsed radar baseband system-on-chip (SoC). To suppress sampling timing errors among sub-ADCs, a foreground timing-skew calibration technique with small additional circuits is proposed. Measured spurious-free dynamic range and signal-to-noise distortion ratio at 1-GHz full Nyquist is, therefore, enhanced by 16 and 11 dB, respectively. Unlike conventional calibration techniques based on redundant ADCs or complicated digital calculations, additional circuit components are only several small resistors and a capacitor, resulting in only 0.4% area penalty. This area saving enables the compact integration of the radar baseband SoC with digital beamforming, where eight-channel TI-ADCs occupy the dominant chip area otherwise. Even though this is foreground, no system performance is sacrificed because the calibration sequence is closed loop and fast enough to be executed during an existing calibration interval in a periodic beam transmission sequence. The TI-ADCs are embedded on industrial SoC in a 40-nm CMOS process. The power consumption including the input buffer and the reference buffer is 54.2 mW from a 1.1-V supply, and figure of merit is 355 fJ/conversion step.

In this paper, we present a highly integrated and miniaturized Ka-band stepped frequency radar that can be used for un-manned aerial vehicle applications. The microwave portion of the radar is integrated onto a low temperature co-fired ceramic multi-chip module, utilizing a triple-print gold thick-film metallization, allowing for wire-bonding and solder capabilities. In addition to miniaturization, a metal seal frame was designed to surround the individual microwave circuits providing isolation barriers to reduce electromagnetic coupling within the system and disturbances from outside interferers. The radar implementation is based on a previous Ka-band radar system designed at the University of Oklahoma using connectorized commercial-off-the-shelf components. This new design results in a 64 times size reduction in foot-print area, half the power consumption, and greater than a 10 times weight reduction compared to the previous implementation. To ensure desired system performance is maintained, both radars were subjected to a direct loop-back test and the intermediate frequency output spectrums, prior to base-band down-conversion, are recorded and compared. Both outputs contain a spectrally pure tone at 12.8 GHz near the expected power indicating that the new radar performs as intended and is comparable to its predecessor. The packaging techniques presented show extreme promise for system integration and miniaturization of future radar and communication systems following the trend to reduce size, weight, and power.

We report recent progress towards miniaturizing and packaging an ultra wideband (UWB) radar developed for measurements of ice and snow over the 2–18 GHz range. The initial objective of this work is the close integration of the radar's RF section (composed of a receiver and a low-power transmitter) while maintaining or enhancing its electrical performance. First, we describe a connectorized reference system developed to serve as a performance benchmark for transmit and receive signal chains. Next, we discuss the use of drop-in modules to achieve a significant size reduction of the RF front-end. These modules are based on packaged chips and arranged in a planar configuration. We present system-level performance metrics of the reference system justifying the need for further integration. We briefly discuss other potential applications of the miniaturized radar and the direction of future packaging efforts as we work toward our future goal of integrating the complete radar “from antenna to bits” by using a system-in-package approach.

In this paper, the concept of phase modulated MIMO radars is explained and demonstrated with a 28-nm CMOS fully integrated 79-GHz radar SoC. It includes two transmitters, two receivers, and the mm-wave frequency generation. The receivers’ outputs are digitized by on-chip ADCs and processed by a custom designed digital core, which performs correlation and accumulation with a pseudorandom sequence used in transmission. The SoC consumes 1 W to achieve 7.5 cm range resolution. A module with antennas allows for 5° resolution over ±60° elevation and azimuth scan in 2 $\times $ 2 code domain MIMO operation. A 4 $\times $ 4 MIMO system is also demonstrated by means of two SoCs mounted on the same module.

To improve the effectiveness of limited spectral resources, an adaptive orthogonal frequency division multiplexing integrated radar and communications waveform design method is proposed. First, the conditional mutual information (MI) between the random target impulse response and the received signal, and the data information rate (DIR) of frequency selective fading channel are formulated. Then, with the constraint on the total power, the optimization problem, which simultaneously considers the conditional MI for radar and DIR for communications, is devised, and the analytic solution is derived. With low transmit power, the designed integrated waveform outperforms the fixed waveform (i.e., equal power allocation). Finally, several simulated experiments are provided to verify the effectiveness of the designed waveform.

This paper describes a multi-purpose radar system suitable for applications with different requirements on dynamic range, resolution, and miniaturization degree. It utilizes a scalable sensor platform that includes a wideband 30.5-GHz voltage-controlled oscillator (VCO) as well as 61- and 122-GHz transceivers (TRXs) in a silicon-germanium BiCMOS technology. The proposed architecture enables the cascading of multiple TRXs and allows the implementation of MIMO radar systems in two different frequency bands by using a single VCO. The higher transmit output power of 11.5 dBm as well as receive gain of 24 dB make the 61-GHz TRX suitable for applications requiring a high dynamic range. The lower wavelength allows the integration of on-chip antennas in the 122-GHz TRX and enables, thus, a high miniaturization degree. The higher LO scaling factor makes the 122-GHz TRX also more attractive for high-resolution applications. A sweep bandwidth of 2.5 GHz generated by the VCO is scaled up to 10 GHz and results in a range resolution of 3 cm. The proposed TRXs are equipped with binary phase shift keying modulators as well as an I/Q receiver and can be utilized to build a flexible software-defined radar platform for range and distant-selective vibration sensors utilizing frequency-modulated continuous wave as well as pseudo-random noise radar techniques.

Although radar and communication systems so far have been considered separately, recent advances in passive radar systems have motivated us to propose a unified system, capable of fulfilling the requirements of both radar and communications. In this paper, we provide performance tradeoff analysis for a system consisting of a transmitter, a passive radar receiver, and a communication receiver (CR). The total power is allocated for transmitting the radar waveforms and information signals in such a way that the probability of detection (PD) is maximized, while satisfying the information rate requirement of the CR. An exact closed-form expression for the probability of false alarm (PFA) is derived, whereas PD is approximated by assuming that the signal-to-noise ratio corresponding to the reference channel is often much larger than that corresponding to the surveillance channel. The performance tradeoff between the radar and communication subsystems is then characterized by the boundaries of the PFA-rate and PD-rate regions.

In this article, an analytical method for radar electromagnetic compatibility (EMC) in complex environment is proposed to deal with the radar system-level EMC problem. The complete procedure of thi...

Snow avalanche is a natural phenomenon, which annually causes infrastructure damage and leads to human casualties in many countries all over the world. As a result, a detailed hazard mapping is required to be able to understand the avalanche risk levels. Also, the scarcity of the areas suitable for constructing infrastructures in the mountains places a high premium on providing high precision hazard mapping. This paper presents the design and development of an advanced phased array antenna for an FMCW radar to produce a high resolution image of snow avalanche in range and cross-range. The proposed antenna is a 16-element fully populated phased array with ±14° azimuth beamwidth and ±22.5° fixed elevation angle. The designed phased array antenna has 14.4 dBi gain and -20.3 dB sidelobe level. In this design, subarraying overlapping technique has been used to eliminate undesirable grating lobes by means of spatial antialias filtering. A phased array power divider is proposed to allow tapering of the amplitude of the elements to achieve low sidelobe level.

We present a photonic method for the generation of dual-chirp signals. In this approach, a single-tone RF signal is first modulated using a modulator in order to generate two optical carriers, which are further modulated by a linearly chirped signal by another modulator. Square-law detection in a photodiode then generates a dual-chirp signal whose center frequency and time-bandwidth product (TBWP) are fourfold increased. The dual-chirping and the improved TBWP can improve the range resolution of the radar system and help avoid the range measurement error caused by the range-Doppler coupling effect. The generation of bandwidth-quadrupled S-band dual-chirp waveforms is demonstrated experimentally. The processing of the dual-chirp signal is also discussed, in order to show its advantages over single-chirp signals. We believe that the proposed approach is a potential solution for the generation of dual-chirp signals with high center frequency and large bandwidth in modern radar systems.

The well-known range-Doppler coupling property of the chirp radar makes it more vulnerable to different types of deceptive repeater jammers that benefit from the pulse compression processing gain of the radar-matched filter. These jammers generate many false targets that appear before and after the true target. Therefore, the radar cannot distinguish the true target from the false ones. This paper reviews different self-protection repeater jammers and presents their pros and cons, in order to provide a reference for the study of jamming/anti-jamming methods.

Frequency-modulated continuous wave radar systems suffer from permanent leakage of the transmit signal into the receive path. Besides leakage within the radar device itself, an unwanted object placed in front of the antennas causes so-called short-range (SR) leakage. In an automotive application, for instance, it originates from signal reflections of the car’s own bumper. Particularly the residual phase noise of the downconverted SR leakage signal causes a severe degradation of the achievable sensitivity. In an earlier work, we proposed an SR leakage cancellation concept that is feasible for integration in a monolithic microwave integrated circuit. In this brief, we present a hardware prototype that holistically proves our concept with discrete components. The fundamental theory and properties of the concept are proven with measurements. Further, we propose a digital design for real-time operation of the cancellation algorithm on a field programmable gate array. Ultimately, by employing measurements with a bumper mounted in front of the antennas, we show that the leakage canceller significantly improves the sensitivity of the radar.

In the first part of the paper, we make a brief review on the coding and programmable metasurfaces recently proposed at microwave and terahertz frequencies, which are realized by distributing coding particles “0” and “1” with opposite reflection phases on surfaces with certain coding sequences. The powerful manipulations to microwaves and terahertz waves using the coding and programmable metasurfaces are presented. In the second part of the paper, we propose a new coding scheme for the generation of ring-shaped radiation pattern. Different coding strategies are provided to demonstrate the flexible controls of the size, position, and number of rings in the radiation patterns, including changing the periodicity of the gradient coding sequence and adding it with one or multiple periodic sequences. A new structure featuring low electromagnetic interference and ultrahigh efficiency is designed to implement the ring-shaped pattern, which shows highly consistent results to the theoretical results calculated by Fourier transform. We remark that such a ring-shaped radiation pattern may find a wide range of applications in radar detections.