VE1BLL, Higgler; Thanks For the Responce. Some futher background info.
Vehicle: Open Top LeMans LMP2 SportsCar, All of the Chassis and bodywork is Carbon fibre composite (no metal Roll Cage, all Carbon ). The car has no roof, think of a two seater F1 Car with body work covering all of the wheels.
Data Telemetry TX(Car); 5 Watts, 458.575MHz, 1/4 Wave Dipole, Mounted behind rear roll hoop. ( cant go any higher )
Data Telemetry RX(Base station); Two Dipole antennas, approximatly 2m long and seperated by 1.5m, feeds into a diversity reception modem.(To help with Multi-path issues)
Voice Radio RX/TX (Car); TX 7.5 Watts, 180 MHz, 1/2 Wave Dipole, mounted in centre front of car. ( Very limtied other location to mount )
Voice Radio RX/TX Base Station; TX 10 Watts, 180 MHz, Single dipole antenna, Approx 1.5m length.
Maxium Range; Varies but in general a line of sight max range would be 1.5-2km.
Ground planes for both car antennas (data/voice)are simply as much copper tape as I can fit underneath the relavent area, this is currently not much but may be improved during the winter redesign. The Antenna sits in the middle of the copper patch and clamps through to the outside of the bodywork.
Vehicle Orientation; The nature of the circuits means that the cars can be at any angle relative to the base station, many circuits fold back on themselves or even run in reverse.
We have considered using a Yagi antenna for one of the diversity antennas and pointing it at the weakest area.
Sorry, Dont know what the loss component of the carbon fibre.
I am not familiar with patch antennae, We have complex compound curves of bodywork and many limitations on mounting positions, this may make such an antenna hard to fit, possibly. I shall look more at this sugggestion so that I am more up to speed with what you are suggesting, its a new field to me Im afraid

Cheers, John.