Adaptive OFDM Radar for Target Detection and Tracking

We develop algorithms to detect and track targets by employing a wideband orthogonal frequency division multiplexing: OFDM) radar signal. The frequency diversity of the OFDM signal improves the sensing performance since the scattering centers of a target resonate variably at different frequencies. In addition, being a wideband signal, OFDM improves the range resolution and provides spectral efficiency. We first design the spectrum of the OFDM signal to improve the radar\u27s wideband ambiguity function. Our designed waveform enhances the range resolution and motivates us to use adaptive OFDM waveform in specific problems, such as the detection and tracking of targets. We develop methods for detecting a moving target in the presence of multipath, which exist, for example, in urban environments. We exploit the multipath reflections by utilizing different Doppler shifts. We analytically evaluate the asymptotic performance of the detector and adaptively design the OFDM waveform, by maximizing the noncentrality-parameter expression, to further improve the detection performance. Next, we transform the detection problem into the task of a sparse-signal estimation by making use of the sparsity of multiple paths. We propose an efficient sparse-recovery algorithm by employing a collection of multiple small Dantzig selectors, and analytically compute the reconstruction performance in terms of the $ell_1$-constrained minimal singular value. We solve a constrained multi-objective optimization algorithm to design the OFDM waveform and infer that the resultant signal-energy distribution is in proportion to the distribution of the target energy across different subcarriers. Then, we develop tracking methods for both a single and multiple targets. We propose an tracking method for a low-grazing angle target by realistically modeling different physical and statistical effects, such as the meteorological conditions in the troposphere, curved surface of the earth, and roughness of the sea-surface. To further enhance the tracking performance, we integrate a maximum mutual information based waveform design technique into the tracker. To track multiple targets, we exploit the inherent sparsity on the delay-Doppler plane to develop an computationally efficient procedure. For computational efficiency, we use more prior information to dynamically partition a small portion of the delay-Doppler plane. We utilize the block-sparsity property to propose a block version of the CoSaMP algorithm in the tracking filter

Frequency Diverse Array Radar: Signal Characterization and Measurement Accuracy

Radar systems provide an important remote sensing capability, and are crucial to the layered sensing vision; a concept of operation that aims to apply the right number of the right types of sensors, in the right places, at the right times for superior battle space situational awareness. The layered sensing vision poses a range of technical challenges, including radar, that are yet to be addressed. To address the radar-specific design challenges, the research community responded with waveform diversity; a relatively new field of study which aims reduce the cost of remote sensing while improving performance. Early work suggests that the frequency diverse array radar may be able to perform several remote sensing missions simultaneously without sacrificing performance. With few techniques available for modeling and characterizing the frequency diverse array, this research aims to specify, validate and characterize a waveform diverse signal model that can be used to model a variety of traditional and contemporary radar configurations, including frequency diverse array radars. To meet the aim of the research, a generalized radar array signal model is specified. A representative hardware system is built to generate the arbitrary radar signals, then the measured and simulated signals are compared to validate the model. Using the generalized model, expressions for the average transmit signal power, angular resolution, and the ambiguity function are also derived. The range, velocity and direction-of-arrival measurement accuracies for a set of signal configurations are evaluated to determine whether the configuration improves fundamental measurement accuracy

An investigation of a frequency diverse array

This thesis presents a novel concept for focusing an antenna beam pattern as a function of range, time, and angle. In conventional phased arrays, beam steering is achieved by applying a linear phase progression across the aperture. This thesis shows that by applying an additional linear frequency shift across the elements, a new term is generated which results in a scan angle that varies with range in the far-field. Moreover, the antenna pattern is shown to scan in range and angle as a function of time. These properties result in more flexible beam scan options for phased array antennas than traditional phase shifter implementations. The thesis subsequently goes on to investigate this phenomenon via full scale experimentation, and explores a number of aspects of applying frequency diversity spatially across array antennas. This new form of frequency diverse array may have applications to multipath mitigation, where a radio signal takes two or more routes between the transmitter and receiver due to scattering from natural and man-made objects. Since the interfering signals arrive from more than one direction, the range-dependent and auto-scanning properties of the frequency diverse array beam may be useful to isolate and suppress the interference. The frequency diverse array may also have applications to wideband array steering, in lieu of true time delay solutions which are often used to compensate for linear phase progression with frequency across an array, and to sonar, where the speed of propagation results in large percentage bandwidth, creating similar wideband array effects. The frequency diverse array is also a stepping stone to more sophisticated joint antenna and waveform design for the creation of new radar modes, such as simultaneous multi-mode operation, for example, enabling joint synthetic aperture radar and ground moving target indication

Evaluation of phase-frequency instability when processing complex radar signals

A new radar system for digital signal processing before detection is proposed. These are the guidelines for selecting an intermediate frequency for signal processing. The features of signal processing in the case of echo-signal selection by the features of the correlation properties of their complex bypass are described. This paper presents the study of ambiguity function (AF) when processing complex radar signals. In this work, the AF synthesis was performed considering non-determined components and the presence of phase-frequency instability. The received result enhances the potentials for distinguishing an incoherent radar signal. The numerical simulation results of received AF are presented. Considering fluctuation components in the complex AF, depending on the laws of the distribution of amplitude and frequency fluctuations and their parameters, allowed to get the gain in the width of the main lobe from the units to tens of times. Paper represents original analytical expressions for AF of radio-signals modulated by narrow band random processes with various distribution laws

1-D broadside-radiating leaky-wave antenna based on a numerically synthesized impedance surface

A newly-developed deterministic numerical technique for the automated design of metasurface antennas is applied here for the first time to the design of a 1-D printed Leaky-Wave Antenna (LWA) for broadside radiation. The surface impedance synthesis process does not require any a priori knowledge on the impedance pattern, and starts from a mask constraint on the desired far-field and practical bounds on the unit cell impedance values. The designed reactance surface for broadside radiation exhibits a non conventional patterning; this highlights the merit of using an automated design process for a design well known to be challenging for analytical methods. The antenna is physically implemented with an array of metal strips with varying gap widths and simulation results show very good agreement with the predicted performance

Beam scanning by liquid-crystal biasing in a modified SIW structure

A fixed-frequency beam-scanning 1D antenna based on Liquid Crystals (LCs) is designed for application in 2D scanning with lateral alignment. The 2D array environment imposes full decoupling of adjacent 1D antennas, which often conflicts with the LC requirement of DC biasing: the proposed design accommodates both. The LC medium is placed inside a Substrate Integrated Waveguide (SIW) modified to work as a Groove Gap Waveguide, with radiating slots etched on the upper broad wall, that radiates as a Leaky-Wave Antenna (LWA). This allows effective application of the DC bias voltage needed for tuning the LCs. At the same time, the RF field remains laterally confined, enabling the possibility to lay several antennas in parallel and achieve 2D beam scanning. The design is validated by simulation employing the actual properties of a commercial LC medium

A Survey on Fundamental Limits of Integrated Sensing and Communication

The integrated sensing and communication (ISAC), in which the sensing and communication share the same frequency band and hardware, has emerged as a key technology in future wireless systems due to two main reasons. First, many important application scenarios in fifth generation (5G) and beyond, such as autonomous vehicles, Wi-Fi sensing and extended reality, requires both high-performance sensing and wireless communications. Second, with millimeter wave and massive multiple-input multiple-output (MIMO) technologies widely employed in 5G and beyond, the future communication signals tend to have high-resolution in both time and angular domain, opening up the possibility for ISAC. As such, ISAC has attracted tremendous research interest and attentions in both academia and industry. Early works on ISAC have been focused on the design, analysis and optimization of practical ISAC technologies for various ISAC systems. While this line of works are necessary, it is equally important to study the fundamental limits of ISAC in order to understand the gap between the current state-of-the-art technologies and the performance limits, and provide useful insights and guidance for the development of better ISAC technologies that can approach the performance limits. In this paper, we aim to provide a comprehensive survey for the current research progress on the fundamental limits of ISAC. Particularly, we first propose a systematic classification method for both traditional radio sensing (such as radar sensing and wireless localization) and ISAC so that they can be naturally incorporated into a unified framework. Then we summarize the major performance metrics and bounds used in sensing, communications and ISAC, respectively. After that, we present the current research progresses on fundamental limits of each class of the traditional sensing and ISAC systems. Finally, the open problems and future research directions are discussed

Теоретико–експериментальне обґрунтування шляхів розширення функціональних можливостей метеорологічного радіолокатора та підвищення ефективності виявлення небезпечних метеорологічних явищ за рахунок використання поляризаційних властивостей зондувальних і відбитих сигналів

1. Доведено теоретично і підтверджено експериментально закон монотонної залежності спектральної диференціальної відбиваності від доплерівської частоти у дощі. 2. Теоретично і експериментально отриманий зв'язок нових доплерівсько- поляриметричних параметрів – диференціальної доплерівської швидкості DDV і нахилу спект- ральної диференціальної відбиваності SLP з інтенсивністю турбулентності і параметрами роз- поділу крапель дощу за розміром. 3. Створена концепція багатофункціонального доплерівсько-поляриметричного дистан- ційного зондування метеорологічних об’єктів для отримання інформації про мікроструктуру об’єкта і характеристики вітру в ньому. 4. Розроблена теорія доплерівсько-поляриметричного дистанційного зондування крапе- льних опадів мікрохвильовими радіолокаторами. 5. Розроблені математичні моделі зв'язку доплерівсько-поляриметричних вимірюваних параметрів з характеристиками мікроструктури і параметрами динаміки (вітер, турбулентність) метеорологічних об’єктів з урахуванням інерційності розсіювачів, режиму зондування, харак- теристик радіолокатора, особливостей обробки сигналів. 6. Розроблені нові методи: - дистанційного виявлення зон граду за даними доплерівсько-поляриметричного спосте- реження зони огляду; - дистанційного виявлення зон імовірного обледеніння за даними допплерівсько- поляриметричного спостереження зони огляду; - дистанційного виявлення зон небезпечної турбулентності з оцінкою її інтенсивності за даними доплерівсько-поляриметричного спостереження зони огляду; - автоматичного розпізнавання типу гідрометеорів за даними доплерівсько- поляриметричного дистанційного зондування; - непрямої оцінки ефективності методів і алгоритмів та виконані відповідні оцінки щодо розроблених нових методів. Значимість отриманих наукових результатів зумовлена тим, що вони складають теоре- тико-експериментальну основу створення багатофункціональної когерентно-імпульсної метео- рологічної радіолокаційної системи здатної надавати комплекс необхідної метеорологічної ін- формації для ефективного розв’язання актуальних задач не тільки авіації, але й енергопоста- чання, мореплавства, транспорту, агрокомплексу, рибальства, прогностичних гідрологічних та протиградових служб, радіозв’язку, зокрема супутникового, інших галузей економіки, діяль- ність яких істотно залежить від забезпечення достовірного вимірювання інтенсивності опадів, турбулентності, виявлення зон підвищеної електричної активності та інших небезпечних метеорологічних явищ

Suppression approach to main-beam deceptive jamming in FDA-MIMO radar using nonhomogeneous sample detection

Suppressing the main-beam deceptive jamming in traditional radar systems is challenging. Furthermore, the observations corrupted by false targets generated by smart deceptive jammers, which are not independent and identically distributed because of the pseudo-random time delay. This in turn complicates the task of jamming suppression. In this paper, a new main-beam deceptive jamming suppression approach is proposed, using nonhomogeneous sample detection in the frequency diverse array-multiple-input and multiple-output radar with non-perfectly orthogonal waveforms. First, according to the time delay or range difference, the true and false targets are discriminated in the joint transmit-receive spatial frequency domain. Subsequently, due to the range mismatch, the false targets are suppressed through a transmit-receive 2-D matched filter. In particular, in order to obtain the jamming-plus-noise covariance matrix with high accuracy, a nonhomogeneous sample detection method is developed. Simulation results are provided to demonstrate the detection performance of the proposed approach