Wideband planar automotive antennas for use in conjunction with polymeric composite structures

Automotive wireless communications have rapidly developed in recent years with the emergence of many new communications technologies. Only a couple of decades ago most vehicles were fitted with only one antenna for AM and FM radio reception. By comparison, today's cars may be fitted with a multitude of antennas to communicate at many different frequencies for a wide variety of applications.

This thesis proposes the use of wideband planar antennas in conjunction with polymeric composite panels to meet the communication requirements of vehicles both now and into the future. Sheet Moulding Compound (SMC) is a mature composite technology which is widely used in the automotive industry to form external car body panels by compression moulding. An SMC body panel could be utilized to create an RF-transparent aperture in a vehicle's body structure. A wideband antenna could be attached to the underside of such a panel, or embedded into it during the compression moulding process. This would create a multifunctional antenna component which, when painted, would be indistinguishable from an ordinary section of bonnet, roof or trunk.

The research presented in this thesis covers a variety of related topics. The electrical and mechanical properties of SMC are examined using various techniques. Optimal manufacturing process parameters are determined, which produce minimal deformation on an embedded antenna substrate during the compression moulding process. The effect of automotive paints on the impedance and radiation behaviour of planar antennas is determined by experimental means, including those paints which have a 'metallic' effect.

Two wideband antennas designed for vehicular use are proposed - the Optimised PICA and the WiPlaVe antenna. The antennas are low profile, fabricated on low-cost FR-4 substrates, and provide an impedance match over a wide range of frequencies of interest in the automotive environment. A novel diplexer-divider-combiner device is presented. The device is implemented by exploiting Complimentary Split Ring Resonators, and improves the radiation performance of the WiPlaVe antenna at low frequencies.

The overall performance of the proposed wideband vehicular antenna solution is validated by simulation and measurement in a variety of circumstances. A wideband antenna is embedded into the surface of an SMC ute tailgate component, and the radiation of the structure is characterized in an anechoic chamber. The effect of bending a wideband antenna is also evaluated by simulation and measurement. CST Microwave Studio© is employed to simulate the O-PICA antenna on a full-size vehicle with an SMC roof panel. The same full-sized configuration is implemented in hardware with a GPS receiver. A comparison of the performance of the O-PICA antenna for GPS purposes is made against a commercial GPS patch antenna. The O-PICA antenna is found to provide comparable GPS performance with the commercial narrowband antenna, demonstrating the value of the integrated wideband vehicular antenna proposal.