Antennas and Dielectric Characterization Techniques for Future Automotive Communications and Driving Assistance Systems

Abstract

Improving vehicular safety can be accomplished by the provision of advanced sensors and communication systems. This thesis deals with problems associated with automotive radar sensors and 5G vehicular communication systems, such as vehicle-to-everything and vehicle-to-satellite connectivity. In particular, wideband dielectric characterization methods for 5G and radar band, as well as novel antenna systems for 5G communication and satellite communication on the move are investigated. To study the effects of the windshield or moonroof on antennas placed behind them, a broadband (1-35 GHz) dielectric characterization technique for measuring low-loss dielectric slabs is presented. The technique uses a coplanar waveguide (CPW) transmission line sample holder for measurements. The technique is suitable for the characterization of brittle materials like glass as it does not require complicated sample machining and preparation. The windshield of the vehicle is of particular importance as it is one of the few locations in the vehicle that can be used for mounting antennas without destroying their radiation performance. Consequently, a novel 5G millimeter wave (28 GHz) antenna system that can be directly placed against vehicle windshield for vehicle-to-everything is designed, fabricated, and tested. The 5G millimeter wave band is specifically important to vehicular communication due to the low latency (millisecond range) at this band. The design achieves both wide angular coverage and high gain through a compact multi-array design. Each array is designed to have a fixed beam direction using a separate feeding network with sufficient beamwidth so that the overall pattern guarantees simultaneous coverage in the elevation plane while providing a high passive antenna gain. Mounting the antenna behind the laminated windshield has been investigated and proven to have a negligible effect on the antenna matching and a minor effect on the radiation pattern. Non-terrestrial vehicular connectivity fills in the gaps that the common vehicle-to-everything communications fails to cover such as underserved and rural areas. A wideband circularly polarized (CP) patch arrays in X- and Ku-bands for vehicular satellite communication are presented. The arrays have a modular design that enables the scalability of the array and simplicity of digital control and dc bias lines routing. A 2×2 array is designed and fabricated with a 3-dB axial ratio band of 10.7‒13 GHz and controlled by a beamformer integrated circuit mounted on an interposer. A 4×4 array made of four 2×2 arrays is designed, fabricated, and tested both in free space and in the presence of the moonroof laminated glass. With the decent performance of the array in the presence of laminated glass, it can be installed behind vehicles’ moonroofs for satellite communication without the need to modify the vehicle's exterior design. As a part of improving vehicular radar sensing, two dielectric characterization techniques at the vehicular radar operating frequency band (77 GHz) to characterize vehicular paint are developed. This is due to the fact that modern vehicular radars are mounted behind the bumper or the emblem of the vehicle, which gets painted. The developed techniques target different types of paint: a coplanar waveguide resonator technique for low-loss paint samples (most regular paints and clearcoats) and a rectangular waveguide technique for high-loss paint samples (most metallic paints). Both techniques are used for testing actual paint samples.