Common-Aperture Dual-Polarized Transceiver Antenna Systems for Millimeter-Wave Polarimetric Radar
Douglas, Tanner
2022
Abstract
The millimeter-wave radar is one of the key sensor technologies utilized in the automotive industry for advanced driver assistance systems and autonomous vehicles. Its ability to leverage phenomena such as the Doppler effect and the polarization of electromagnetic waves make it an extremely versatile sensor, capable of detecting position and velocity of potential roadway obstacles, as well as distinguishing between obstacles of different types (pedestrians, other vehicles, etc.) based on their polarization responses. Additionally, its relative insensitivity to precipitation and fog allows for all-weather operation, even in conditions that severely inhibit visibility. However, radar is not a perfect all-encompassing sensing solution; in particular, its most significant drawback is imaging resolution inferior to that of optical sensors like cameras and lidar. A radar’s resolution is closely linked to its antenna system. Angular resolution is improved with a narrow antenna beam, which translates to a large effective aperture. Similarly, fine range resolution is achieved using the frequency-modulated continuous-wave technique, which requires high transmit-to-receive antenna isolation. Typically, this isolation is accomplished with spatial separation between elements. Limited available mounting space on most vehicles prohibits the large antenna system size mandated by these requirements. The focus of this dissertation is the development of an antenna system architecture which provides a very narrow beam and high isolation, while supporting dual-polarized transmit and receive capability for polarimetry applications. The use of a common transmit/receive aperture makes the antenna system relatively compact while eliminating parallax. The shared aperture is a single dielectric lens, which focuses at both the transmit and receive feeds by means of a novel polarization-independent spatial power divider. This device was designed using concepts from the flourishing field of electromagnetic metamaterials and metasurfaces, and can be constructed using standard semiconductor fabrication techniques. While modern automotive radars operate at the 79 GHz band, there is a strong interest in exploring higher millimeter-wave frequencies (particularly the 230 GHz band) for future systems. The shift to a shorter wavelength will result in improved angular and range resolution while reducing antenna size. Therefore, separate versions of the common-aperture dual-polarized transceiver antenna system have been designed for operation at the two bands. One of the challenges of moving to higher frequency is the availability and performance of millimeter-wave electronics and waveguide components. In support of high frequency dual-polarized radar antennas, an orthomode transducer with a simple structure has been designed for reduced fabrication complexity at the 230 GHz band. Additionally, there is currently a lack of data on the backscattering properties of many target classes at 230 GHz. The antenna and orthomode transducer designs of this work have been incorporated as part of the front ends of radar systems operating at this band. As a demonstration of the utility of 230 GHz radar, as well as the antenna system itself, a set of polarimetric backscattering measurements of several road surfaces is presented. Such data can be used to inform algorithms for discrimination between different surfaces, and assessment of road conditions. Another topic in this dissertation is the design of a low-profile passive reflector, which can enable radar sensors to detect and identify road markings, a task currently handled only by cameras. As an appendix, a planar antenna system with high isolation for wireless communication and radar applications at 6 GHz is presented.Deep Blue DOI
Subjects
Antennas Radar Polarimetry Full-Duplex Electromagnetic Metamaterials and Metasurfaces Waveguides Microfabrication
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