Autonomous Vehicles: MMW Radar Backscattering Modeling of Traffic Environment, Vehicular Communication Modeling, and Antenna Designs

77 GHz Millimeter-wave (mmWave) radar serves as an essential component among many sensors required for autonomous navigation. High-fidelity simulation is indispensable for nowadays’ development of advanced automotive radar systems because radar simulation can accelerate the design and testing process and help people to better understand and process the radar data. The main challenge in automotive radar simulation is to simulate the complex scattering behavior of various targets in real time, which is required for sensor fusion with other sensory simulation, e.g. optical image simulation. In this thesis, an asymptotic method based on a fast-wideband physical optics (PO) calculation is developed and applied to get high fidelity radar response of traffic scenes and generate the corresponding radar images from traffic targets. The targets include pedestrians, vehicles, and other stationary targets. To further accelerate the simulation into real time, a physics-based statistical approach is developed. The RCS of targets are fit into statistical distributions, and then the statistical parameters are summarized as functions of range and aspect angles, and other attributes of the targets. For advanced radar with multiple transmitters and receivers, pixelated-scatterer statistical RCS models are developed to represent objects as extend targets and relax the requirement for far-field condition. A real-time radar scene simulation software, which will be referred to as Michigan Automotive Radar Scene Simulator (MARSS), based on the statistical models are developed and integrated with a physical 3D scene generation software (Unreal Engine 4). One of the major challenges in radar signal processing is to detect the angle of arrival (AOA) of multiple targets. A new analytic multiple-sources AOA estimation algorithm that outperforms many well-known AOA estimation algorithms is developed and verified by experiments. Moreover, the statistical parameters of RCS from targets and radar images are used in target classification approaches based on machine learning methods. In realistic road traffic environment, foliage is commonly encountered that can potentially block the line-of-sight link. In the second part of the thesis, a non-line-of-sight (NLoS) vehicular propagation channel model for tree trunks at two vehicular communication bands (5.9 GHz and 60 GHz) is proposed. Both near-field and far-field scattering models from tree trunk are developed based on modal expansion and surface current integral method. To make the results fast accessible and retractable, a macro model based on artificial neural network (ANN) is proposed to fit the path loss calculated from the complex electromagnetic (EM) based methods. In the third part of the thesis, two broadband (bandwidth > 50%) omnidirectional antenna designs are discussed to enable polarization diversity for next-generation communication systems. The first design is a compact horizontally polarized (HP) antenna, which contains four folded dipole radiators and utilizing their mutual coupling to enhance the bandwidth. The second one is a circularly polarized (CP) antenna. It is composed of one ultra-wide-band (UWB) monopole, the compact HP antenna, and a dedicatedly designed asymmetric power divider based feeding network. It has about 53% overlapping bandwidth for both impedance and axial ratio with peak RHCP gain of 0.9 dBi.PHDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/163001/1/caixz_1.pd

Propagation and scattering of electromagnetic waves in low THz band in automotive radar applications

This thesis, firstly, due to the lack of knowledge in influence of harsh outdoor environment on the performance of the low-THz automotive sensors, the investigation has been done to demonstrate the performance of low-THz sensors in the presence of different radome contaminants (mud, oil, grit, etc.) and various weather conditions (rain, snow, fog, etc.) to prove the feasibility of using low-THz frequencies (100 GHz -1 THz) in automotive radar in uncontrolled environmental conditions. Secondarily, this thesis reports and discuss the important and yet unsolved task on automotive surface recognition and shows the possibility of using Low THz radar for road surface classification by exploring the radar signal backscattering from surfaces with different roughness, and finally this thesis demonstrate the novel approach to surface classification based on the analysis of radar images obtained using the low THz imaging radar and demonstrate the advantage of low THz radar for surface discrimination for automotive sensing. The proposed experimental technique in combination with a convolutional neural network provides high surface classification accuracy

Design Data Collection with Skylab Microwave Radiometer-Scatterometer S-193, Volume 1

The author has identified the following significant results. Observations with S-193 have provided radar design information for systems to be flown on spacecraft, but only at 13.9 GHz and for land areas over the United States and Brazil plus a few other areas of the world for which this kind of analysis was not made. Observations only extended out to about 50 deg angle of incidence. The value of a sensor with such a gross resolution for most overland resource and status monitoring systems seems marginal, with the possible exception of monitoring soil moisture and major vegetation variations. The complementary nature of the scatterometer and radiometer systems was demonstrated by the correlation analysis. Although radiometers must have spatial resolutions dictated by antenna size, radars can use synthetic aperture techniques to achieve much finer resolutions. Multiplicity of modes in the S-193 sensors complicated both the system development and its employment. An attempt was made in the design of the S-193 to arrange optimum integration times for each angle and type of measurement. This unnecessarily complicated the design of the instrument, since the gains in precision achieved in this way were marginal. Either a software-controllable integration time or a set of only two or three integration times would have been better

Radar and microwave radiometric techniques for geoscience experiments

Radar backscattering data for farm crop

The probability of detecting and tracking RADAR targets in clutter at low grazing angles

Modern military acquisition and tracking RADARs are required to operate against aircraft and missiles specifically designed to have minimal radar cross section (RCS) and which fly at very low level to take maximum advantage of terrain screening. A model for predicting system performance is necessary for a range of terrain types in varying precipitation and seasonal cultural conditions. While the main degradation is from surface clutter and denial of sightline due to terrain and other local obstructions, several other factors such as multipath propagation, deliberate jamming and even operator performance contribute to the total model. The possibility that some radars may track obscured targets, however briefly, by using the diffraction path, is of particular interest. Although this report critically examines each of the contributory factors in order to select optimum values for inclusion in an overall computer prediction model; a new surface clutter model is specifically developed for sloped terrain using actual clutter measurements. The model is validated by comparison with an extensive survey of worldwide clutter results from both published and unpublished sources. Certain constraints have been necessary to restrict the study to a manageable size, while meeting the requirements of the sponsors. Attention is therefore focussed upon performance prediction for typical mobile tracking radar systems designed for operation against small RCS low level targets flying overland

Site specific radar coverage and land clutter modelling

The objectives of this minor dissertation were to investigate relevant theory, models and processes required for the development of a site specific radar coverage and land clutter modelling tool. Various sources of digital elevation model (DEM) and land cover (LC) data were investigated. It was found that the ASTER GDEM and SRTM 30 m DEM datasets can be used to characterise land topography for all intended areas of interest. It was also found that two LC datasets, namely the National Land Cover 2009, and GlobeLand30 m data sources can be used to characterise land cover for all intended areas of interest. For each terrain type found in the GlobeLand30 or NLC 2009 datasets, a decision was made as to which of the terrain types for each land clutter model matches the land cover data terrain type the closest. These classifications were presented in the form of tables. It was concluded that the SRTM 30 m DEM dataset and the GlobeLand30 LC dataset should be used as they are currently the highest quality DEM and LC datasets that are freely available that covers all intended areas of interest. Numerous monostatic land clutter models exist in literature that address specific cases of clutter types and behaviours. Nine such land clutter models were investigated. Measured land clutter data collected over various terrain types in the Western Cape region of South Africa are compared to simulated backscatter data from these land clutter models. From insights gained from the literature study as well as the analysis of these comparisons, a classification was made on each model's compatibility and validity for different grazing angles and frequency ranges. A classification table was presented indicating the appropriate land clutter models to use in order of their validity, with respect to different grazing angle regions and frequency ranges

Applications of ground-based radar to mine slope monitoring

"Slope failure accidents were responsible for about 12% of U.S. surface mine fatalities from 1995 to 2003. Small surface movements on a mine highwall may be precursors of failure that, if detected, could provide sufficient warning to enable workers and machinery to be withdrawn to safety. Radar interferometry offers the necessary precision to detect these movements. Radar has some advantages over other methods in its ability to cover large surface areas for true two-dimensional monitoring day and night under almost any weather condition. Radar's active transmit/receive mode of operation provides for more direct sampling than passive optical methods that depend on solar illumination. Improvements in microprocessor speeds and capacities have led to the development of a number of small, portable, ground-based systems. Such systems are now being deployed at several locations around the world. As part of an ongoing study of monitoring technologies, researchers from NIOSH and Brigham Young University, Provo, UT, cooperated to assess the feasibility of using interferometric radar to monitor mine slope stability. Field tests of a device incorporating prototype equipment were successful in that small, centimeter-scale displacements on rock slopes were detected." - p. NIOSHTIC-

Analytical evaluation of ILM sensors, volume 1

The functional requirements and operating environment constraints are defined for an independent landing monitor ILM which provides the flight crew with an independent assessment of the operation of the primary automatic landing system. The capabilities of radars, TV, forward looking infrared radiometers, multilateration, microwave radiometers, interferometers, and nuclear sensing concepts to meet the ILM conditions are analyzed. The most critical need for the ILM appears in the landing sequence from 1000 to 2000 meters from threshold through rollout. Of the sensing concepts analyzed, the following show potential of becoming feasible ILM's: redundant microwave landings systems, precision approach radar, airborne triangulation radar, multilateration with radar altimetry, and nuclear sensing

Microwave remote sensing of snowpacks

The interaction mechanisms responsible for the microwave backscattering and emission behavior of snow were investigated, and models were developed relating the backscattering coefficient (sigma) and apparent temperature (T) to the physical parameters of the snowpack. The microwave responses to snow wetness, snow water equivalent, snow surface roughness, and to diurnal variations were investigated. Snow wetness was shown to have an increasing effect with increasing frequency and angle of incidence for both active and passive cases. Increasing snow wetness was observed to decrease the magnitude sigma and increase T. Snow water equivalent was also observed to exhibit a significant influence sigma and T. Snow surface configuration (roughness) was observed to be significant only for wet snow surface conditions. Diurnal variations were as large as 15 dB for sigma at 35 GHz and 120 K for T at 37 GHz. Simple models for sigma and T of a snowpack scene were developed in terms of the most significant ground-truth parameters. The coefficients for these models were then evaluated; the fits to the sigma and T measurements were generally good. Finally, areas of needed additional observations were outlined and experiments were specified to further the understanding of the microwave-snowpack interaction mechanisms

Measurement and modelling of bistatic sea clutter

There is a growing interest in bistatic radars; however, such systems cannot reach their full potential unless the designer has a proper understanding of the environment in which they operate. Rather little information has been published on bistatic clutter and out-of-plane bistatic sea clutter in particular. This is due to a number of factors including the inherent complexity of conducting bistatic radar trials and the resulting lack of high quality bistatic data. In this thesis the collection and analysis of a unique set of bistatic sea clutter data is described. To achieve this objective a novel multistatic radar system was developed. The nodes do not need to be physically connected. This system has a peak transmitted power of more than 500 W. Synchronisation in time and frequency was achieved using GPS disciplined oscillators built and designed at the University of Cape Town. Using the above system simultaneous bistatic and monostatic sea clutter and target signatures were recorded in the UK and South Africa at various geometries and weather conditions. Parts of this unique data set related to out-of-plane bistatic sea clutter was analysed in this thesis. The data covered both co- and cross-polarised sea clutter data at low grazing angles with bistatic angles between 30° and 120°. Data sets covering a range of conditions with sea states from 2 – 5. Using the recorded data it was shown that the ratio of the bistatic normalised radar cross section to the monostatic normalised radar cross section dropped as the scattering angle was increased until the scattering angle was around 90°. Furthermore, the cross-polarised bistatic normalised radar cross section was found to be larger than the cross-polarised monostatic normalised radar cross section when the scattering angle was around 90°. A new empirical model for predicting bistatic normalised radar cross section has been developed. The model is applicable to both in-plane and out-of-plane geometries. The model was able to provide a good fit to both UCL and external data. The temporal correlation properties of both monostatic and bistatic data were studied. It was found that the speckle component of both bistatic and monostatic clutter decorrelated in tens of milliseconds, with the decorrelation time longer for bistatic clutter. The texture of both bistatic and monostatic clutter had similar autocorrelation functions and had similar decorrelation times. By comparing the texture and intensity autocorrelation functions it was concluded that the compound model still holds. It was also found that bistatic clutter was less ‘spiky’ than monostatic clutter particularly at horizontal polarisation. This was due to the reduction in the intensity of the spikes due to specular reflections. By combing the effects of the reduction in reflectivity and spikiness it was shown that a bistatic radar would require a smaller signal to interference ratio than a monostatic radar for the same probability of detection and probability of false alarm. This was more evident at angles close to 90° and for horizontal polarisation. In summary this thesis reports the collection and analysis of novel simultaneous monostatic and bistatic sea clutter and target data. This was achieved by the development of a unique multistatic radar system. This work has resulted in significant advances in both netted radar technology and understanding of bistatic sea clutter