Radar Technology

In this book “Radar Technology”, the chapters are divided into four main topic areas: Topic area 1: “Radar Systems” consists of chapters which treat whole radar systems, environment and target functional chain. Topic area 2: “Radar Applications” shows various applications of radar systems, including meteorological radars, ground penetrating radars and glaciology. Topic area 3: “Radar Functional Chain and Signal Processing” describes several aspects of the radar signal processing. From parameter extraction, target detection over tracking and classification technologies. Topic area 4: “Radar Subsystems and Components” consists of design technology of radar subsystem components like antenna design or waveform design

Coherence-factor-based rough surface clutter suppression for forward-looking GPR imaging

We present an enhanced imaging procedure for suppression of the rough surface clutter arising in forward-looking ground-penetrating radar (FL-GPR) applications. The procedure is based on a matched filtering formulation of microwave tomographic imaging, and employs coherence factor (CF) for clutter suppression. After tomographic reconstruction, the CF is first applied to generate a "coherence map" of the region in front of the FL-GPR system illuminated by the transmitting antennas. A pixel-by-pixel multiplication of the tomographic image with the coherence map is then performed to generate the clutter-suppressed image. The effectiveness of the CF approach is demonstrated both qualitatively and quantitatively using electromagnetic modeled data of metallic and plastic shallow-buried targets

Compressive Sensing and Its Applications in Automotive Radar Systems

Die Entwicklung in Richtung zu autonomem Fahren verspricht, künftig einen sicheren Verkehr ohne tödliche Unfälle zu ermöglichen, indem menschliche Fahrer vollständig ersetzt werden. Dadurch entfällt der Faktor des menschlichen Fehlers, der aus Müdigkeit, Unachtsamkeit oder Alkoholeinfluss resultiert. Um jedoch eine breite Akzeptanz für autonome Fahrzeuge zu erreichen und es somit eines Tages vollständig umzusetzen, sind noch eine Vielzahl von Herausforderungen zu lösen. Da in einem autonomen Fahrzeug kein menschlicher Fahrer mehr in Notfällen eingreifen kann, müssen sich autonome Fahrzeuge auf leistungsfähige und robuste Sensorsysteme verlassen können, um in kritischen Situationen auch unter widrigen Bedingungen angemessen reagieren zu können. Daher ist die Entwicklung von Sensorsystemen erforderlich, die für Funktionalitäten jenseits der aktuellen advanced driver assistance systems eingesetzt werden können. Dies resultiert in neuen Anforderungen, die erfüllt werden müssen, um sichere und zuverlässige autonome Fahrzeuge zu realisieren, die weder Fahrzeuginsassen noch Passanten gefährden. Radarsysteme gehören zu den Schlüsselkomponenten unter der Vielzahl der verfügbaren Sensorsysteme, da sie im Gegensatz zu visuellen Sensoren von widrigen Wetter- und Umgebungsbedingungen kaum beeinträchtigt werden. Darüber hinaus liefern Radarsysteme zusätzliche Umgebungsinformationen wie Abstand, Winkel und relative Geschwindigkeit zwischen Sensor und reflektierenden Zielen. Die vorliegende Dissertation deckt im Wesentlichen zwei Hauptaspekte der Forschung und Entwicklung auf dem Gebiet der Radarsysteme im Automobilbereich ab. Ein Aspekt ist die Steigerung der Effizienz und Robustheit der Signalerfassung und -verarbeitung für die Radarperzeption. Der andere Aspekt ist die Beschleunigung der Validierung und Verifizierung von automated cyber-physical systems, die parallel zum Automatisierungsgrad auch eine höhere Komplexität aufweisen. Nach der Analyse zahlreicher möglicher Compressive Sensing Methoden, die im Bereich Fahrzeugradarsysteme angewendet werden können, wird ein rauschmoduliertes gepulstes Radarsystem vorgestellt, das kommerzielle Fahrzeugradarsysteme in seiner Robustheit gegenüber Rauschen übertrifft. Die Nachteile anderer gepulster Radarsysteme hinsichtlich des Signalerfassungsaufwands und der Laufzeit werden durch die Verwendung eines Compressive Sensing-Signalerfassungs- und Rekonstruktionsverfahrens in Kombination mit einer Rauschmodulation deutlich verringert. Mit Compressive Sensing konnte der Aufwand für die Signalerfassung um 70% reduziert werden, während gleichzeitig die Robustheit der Radarwahrnehmung auch für signal-to-noise-ratio-Pegel nahe oder unter Null erreicht wird. Mit einem validierten Radarsensormodell wurde das Rauschradarsystem emuliert und mit einem kommerziellen Fahrzeugradarsystem verglichen. Datengetriebene Wettermodelle wurden entwickelt und während der Simulation angewendet, um die Radarleistung unter widrigen Bedingungen zu bewerten. Während eine Besprühung mit Wasser die Radomdämpfung um 10 dB erhöht und Spritzwasser sogar um 20 dB, ergibt sich die eigentliche Begrenzung aus der Rauschzahl und Empfindlichkeit des Empfängers. Es konnte bewiesen werden, dass das vorgeschlagene Compressive Sensing Rauschradarsystem mit einer zusätzlichen Signaldämpfung von bis zu 60 dB umgehen kann und damit eine hohe Robustheit in ungünstigen Umwelt- und Wetterbedingungen aufweist. Neben der Robustheit wird auch die Interferenz berücksichtigt. Zum einen wird die erhöhte Störfestigkeit des Störradarsystems nachgewiesen. Auf der anderen Seite werden die Auswirkungen auf bestehende Fahrzeugradarsysteme bewertet und Strategien zur Minderung der Auswirkungen vorgestellt. Die Struktur der Arbeit ist folgende. Nach der Einführung der Grundlagen und Methoden für Fahrzeugradarsysteme werden die Theorie und Metriken hinter Compressive Sensing gezeigt. Darüber hinaus werden weitere Aspekte wie Umgebungsbedingungen, unterschiedliche Radararchitekturen und Interferenz erläutert. Der Stand der Technik gibt einen Überblick über Compressive Sensing-Ansätze und Implementierungen mit einem Fokus auf Radar. Darüber hinaus werden Aspekte von Fahrzeug- und Rauschradarsystemen behandelt. Der Hauptteil beginnt mit der Vorstellung verschiedener Ansätze zur Nutzung von Compressive Sensing für Fahrzeugradarsysteme, die in der Lage sind, die Erfassung und Wahrnehmung von Radarsignalen zu verbessern oder zu erweitern. Anschließend wird der Fokus auf ein Rauschradarsystem gelegt, das mit Compressive Sensing eine effiziente Signalerfassung und -rekonstruktion ermöglicht. Es wurde mit verschiedenen Compressive Sensing-Metriken analysiert und in einer Proof-of-Concept-Simulation bewertet. Mit einer Emulation des Rauschradarsystems wurde das Potential der Compressive Sensing Signalerfassung und -verarbeitung in einem realistischeren Szenario demonstriert. Die Entwicklung und Validierung des zugrunde liegenden Sensormodells wird ebenso dokumentiert wie die Entwicklung der datengetriebenen Wettermodelle. Nach der Betrachtung von Interferenz und der Koexistenz des Rauschradars mit kommerziellen Radarsystemen schließt ein letztes Kapitel mit Schlussfolgerungen und einem Ausblick die Arbeit ab.Developments towards autonomous driving promise to lead to safer traffic, where fatal accidents can be avoided after making human drivers obsolete and hence removing the factor of human error. However, to ensure the acceptance of automated driving and make it a reality one day, still a huge amount of challenges need to be solved. With having no human supervisors, automated vehicles have to rely on capable and robust sensor systems to ensure adequate reactions in critical situations, even during adverse conditions. Therefore, the development of sensor systems is required that can be applied for functionalities beyond current advanced driver assistance systems. New requirements need to be met in order to realize safe and reliable automated vehicles that do not harm passersby. Radar systems belong to the key components among the variety of sensor systems. Other than visual sensors, radar is less vulnerable towards adverse weather and environment conditions. In addition, radar provides complementary environment information such as target distance, angular position or relative velocity, too. The thesis ad hand covers basically two main aspects of research and development in the field of automotive radar systems. One aspect is to increase efficiency and robustness in signal acquisition and processing for radar perception. The other aspect is to accelerate validation and verification of automated cyber-physical systems that feature more complexity along with the level of automation. After analyzing a variety of possible Compressive Sensing methods for automotive radar systems, a noise modulated pulsed radar system is suggested in the thesis at hand, which outperforms commercial automotive radar systems in its robustness towards noise. Compared to other pulsed radar systems, their drawbacks regarding signal acquisition effort and computation run time are resolved by using noise modulation for implementing a Compressive Sensing signal acquisition and reconstruction method. Using Compressive Sensing, the effort in signal acquisition was reduced by 70%, while obtaining a radar perception robustness even for signal-to-noise-ratio levels close to or below zero. With a validated radar sensor model the noise radar was emulated and compared to a commercial automotive radar system. Data-driven weather models were developed and applied during simulation to evaluate radar performance in adverse conditions. While water sprinkles increase radome attenuation by 10 dB and splash water even by 20 dB, the actual limitation comes from noise figure and sensitivity of the receiver. The additional signal attenuation that can be handled by the proposed compressive sensing noise radar system proved to be even up to 60 dB, which ensures a high robustness of the receiver during adverse weather and environment conditions. Besides robustness, interference is also considered. On the one hand the increased robustness towards interference of the noise radar system is demonstrated. On the other hand, the impact on existing automotive radar systems is evaluated and strategies to mitigate the impact are presented. The structure of the thesis is the following. After introducing basic principles and methods for automotive radar systems, the theory and metrics of Compressive Sensing is presented. Furthermore some particular aspects are highlighted such as environmental conditions, different radar architectures and interference. The state of the art provides an overview on Compressive Sensing approaches and implementations with focus on radar. In addition, it covers automotive radar and noise radar related aspects. The main part starts with presenting different approaches on making use of Compressive Sensing for automotive radar systems, that are capable of either improving or extending radar signal acquisition and perception. Afterwards the focus is put on a noise radar system that uses Compressive Sensing for an efficient signal acquisition and reconstruction. It was analyzed using different Compressive Sensing metrics and evaluated in a proof-of-concept simulation. With an emulation of the noise radar system the feasibility of the Compressive Sensing signal acquisition and processing was demonstrated in a more realistic scenario. The development and validation of the underlying sensor model is documented as well as the development of the data-driven weather models. After considering interference and co-existence with commercial radar systems, a final chapter with conclusions and an outlook completes the work

A STUDY ON SERIES SLOT ARRAY ANTENNA DESIGN METHODOLOGY AND ITS APPLICATION TO DUAL LINEAR POLARIZATION

학위논문 (박사)-- 서울대학교 대학원 : 전기·컴퓨터공학부, 2014. 2. 남상욱.본 논문에서는 임의의 선형편파 발생을 위한 직렬 슬롯 배열안테나 설계 방법을 제시하였다. 45도 기울어진 선형편파 발생이 가능하고 동시에 임피던스 정합, 균일전장 분포를 형성할 수 있도록 '교차 리액턴스 슬롯 쌍'을 기본 방사체로 제안하였다. 이 기본 방사체를 이용하면 개별 방사 슬롯 간의 간격이 관내 파장의 반 파장 간격으로 위치시킬 수 있기 때문에 grating lobe를 억제할 수 있다. 또한, 제안한 안테나 설계 기법은 기판 집적 도파관 기술 (substrate integrated waveguide, SIW)을 통해 구현하였고 전장 시뮬레이터 및 제작, 측정을 통해 설계 기법의 적합성을 검증하였다. 먼저, Ka-밴드 용 선형 및 평면 배열안테나를 설계하였다. 45도 선형편파를 발생시키기 위해 적층의 SIW 구조로 배열안테나를 구현하였으며 균일 전장이 발생되는 원리를 등가회로 및 임피던스, 전류 순환 방정식을 이용하여 검증하였다. 나아가, 전자장 시뮬레이터를 통한 결과와 비교•분석하였다. 두 번째로, 낮은 부엽레벨을 가지도록 개별 방사체의 전장 계수 조절 방법을 제안하였다. 각 직렬 방사 슬롯을 흐르는 모드 전류의 크기를 조절하기 위해 개별 방사체의 위치를 중심선을 따라 이동시킬 수 있다. 이러한 옵셋 조절 방법을 이용하여 ‒20 dB 및 ‒26 dB Dolph-Chebyshev 계수를 가지는 선형 배열안테나를 설계하였고 제안한 방법의 효용성을 제작 및 측정을 통해 검증하였다. 마지막으로, ±45도 이중 선형편파 발생을 위한 설계 기법을 제안하였다. 동일한 개구면을 공유하는 두 선형편파 간의 격리도를 최대화하기 위해 교차 슬롯 간에 수직 조건을 만족할 수 있도록 기판의 유전율 및 방사 SIW의 폭을 결정하였다. 나아가 제안한 설계 기법을 8 × 8 이중 평면 모노펄스 안테나 설계에 응용하였다. 모노펄스 동작을 위해 기존의 금속 도파관 전송선로를 이용해 제작된 비교기를 결합하였으며 반사손실, 방사패턴, 이득 등의 전기적인 결과를 확인하였다.1. Introduction 1 1.1 Conventional Slot Array Antennas for Linear Polarization 3 1.2 Substrated Integrated Waveguide (SIW) Technology 5 2. Linear Slot Array Antenna for 45º-Inclined Linear Polarization 9 2.1 Introduction 9 2.2 Proposed Antenna Configuration 10 2.2.1 Single Slot Module and Impedance Extraction 11 2.2.2 Alternating Reactance Slot Pair 14 2.2.3 Equivalent Circuit Analysis using Recursive Formulas 17 2.2.4 Centered-Inclined Series-to-Series Coupling Slot 20 2.3 Simulation and Measurement 22 2.4 Summary 25 3. Planar Slot Array Antenna for 45º-Inclined Linear Polarization 30 3.1 Introduction 30 3.2 Proposed Antenna Configuration 33 3.3 Feeding Network Design and Analysis 35 3.4 Coupling and Radiating Slot Arrangement for In-Phase Excitation 41 3.5 Wideband Coax-to-SIW Transition Design and Analysis 42 3.6 Simulation and Measurement 48 3.6.1 Uniform Electric Field Distribution 48 3.6.2 Back-to-Back Coax-to-SIW Transition 52 3.6.3 Reflection Coefficient, Gain, and Radiation Patterns 54 3.7 Summary 57 4. Excitation Control Method for Low Sidelobe Level 63 4.1 Introduction 63 4.2 Axial Displacements for Excitation Control 66 4.3 Design Procedure for Excitation Control 73 4.4 Simulation and Measurement 77 4.5 Summary 82 5. Dual Linear Polarized SIW Monopulse Antenna for Tracking Radar 85 5.1 Introduction 85 5.2 Design Considerations for Dual LP Radiating SIWs 88 5.3 The Proposed Dual LP 8 by 8 SIW Monopulse Protptype Antenna 92 5.3.1 Folded Short-Circuited Stubs 95 5.3.2 Shunt-to-Series Coupling Slots 96 5.3.3 Series-to-Series Coupling Slots 97 5.4 RWG Comparator for Monopulse Operation 98 5.5 Experimental Results 103 5.5.1 Dual LP SIW Sub-Array Antenna 103 5.5.2 Dual LP SIW Monopulse Antenna 107 5.6 Summary 109 6. Conclusion 116Docto

Hybrid Beam-Steering OFDM-MIMO Radar: High 3-D Resolution With Reduced Channel Count

We report on the realization of a multichannel imaging radar that achieves uniform 2-D cross-range resolution by means of a linear array of a special form of leaky-wave antennas. The presented aperture concept enables a tradeoff between the available range resolution and a reduction in the number of channels required for a given angular resolution. The antenna front end is integrated within a multichannel radar based on stepped-carrier orthogonal frequency-division modulation, and the advantages and challenges specific to this combination are analyzed with respect to signal processing and a newly developed calibration routine. The system concept is fully implemented and verified in the form of a mobile demonstrator capable of soft real-time 3-D processing. By combining radio frequency (RF) components operating in the W-band (85-105 GHz) with the presented aperture, a 3-D resolution of less than 1.5° x 1.5° x 15 cm is demonstrated using only eight transmitters and eight receivers

Wide-Angle Multistatic Synthetic Aperture Radar: Focused Image Formation and Aliasing Artifact Mitigation

Traditional monostatic Synthetic Aperture Radar (SAR) platforms force the user to choose between two image types: larger, low resolution images or smaller, high resolution images. Switching to a Wide-Angle Multistatic Synthetic Aperture Radar (WAM-SAR) approach allows formation of large high-resolution images. Unfortunately, WAM-SAR suffers from two significant implementation problems. First, wavefront curvature effects, non-linear flight paths, and warped ground planes lead to image defocusing with traditional SAR processing methods. A new 3-D monostatic/bistatic image formation routine solves the defocusing problem, correcting for all relevant wide-angle effects. Inverse SAR (ISAR) imagery from a Radar Cross Section (RCS) chamber validates this approach. The second implementation problem stems from the large Doppler spread in the wide-angle scene, leading to severe aliasing problems. This research effort develops a new anti-aliasing technique using randomized Stepped-Frequency (SF) waveforms to form Doppler filter nulls coinciding with aliasing artifact locations. Both simulation and laboratory results demonstrate effective performance, eliminating more than 99% of the aliased energy

An experimental synthetic aperture SONAR

Aperture synthesis is a mature technique that has been used with success in a number of remote sensing fields. Sonars can also potentially benefit from the technique, though to date the limitations of slow acoustic propagation and difficulty in maintaining a stable platform has hindered investigation. This thesis investigates aperture synthesis for high resolution underwater imaging. A prototype sonar is designed and fabricated for the study. The performance of the sonar is assessed in both tank and sea trials and the results presented in this thesis

Mapping of Ice Sheet Deep Layers and Fast Outlet Glaciers with Multi-Channel-High-Sensitivity Radar

This dissertation discusses the waveform design, the development of SAR and clutter reduction algorithms for MCRDS radars that are developed at CReSIS to map the ice-sheet bed, deep internal layers and fast-flowing outlet glaciers. It is verified with survey data that the sidelobe level of the designed tapered linear chirp waveform is lower than -60dB for reliable detection of deep ice layers close to the bed. The SAR processing is implemented in f-k domain with motion compensation. Very weak echoes from the deepest parts of Jakobshavn channel are detected for the first time using large synthetic aperture length. A beam-spaced clutter-reduction algorithm is developed to reduce the distributed across-track ice clutter encountered in sounding fast outlet glaciers by estimating the clutter power as a function of depth. On average this method is able to reduce ice clutter by 10dB over Hanning weighting with the MCRDS radar's multi-channel data

Radar Imaging in Challenging Scenarios from Smart and Flexible Platforms

undefine

Transient displacement analysis using double-pulsed ESPI and fringe processing methods

This thesis deals with techniques for the displacement measurement of fast transient phenomena using ESPI. Four main contributions are presented. First, a computer model for speckle noise and ESPI fringe generation is proposed. An assessment methodology for speckle noise reduction algorithms is then derived using the computer model. Then the noise in the ESPI fringe patterns is analysed using computer generated speckle and several solutions for its reduction are proposed and assessed. Finally, a fast electro-optical system is presented as a solution to the unambiguous phase extraction problem from a single interferogram. With this novel system, whole field transient displacements occurring in time intervals as short as 20ns can be successfully registered and retrieved. [Continues.