Abstract: The present invention provides an antenna dielectric having a thickness of less than 3 mm, having a relative dielectric permitivity approaching that of air whereby circuit and transmission line losses are minimised. In accordance with another aspect of the invention, there is provided an antenna ground plane substrate comprising an expanded polystyrene substrate produced by a two-stage moulding process. The two-stage polystyrene is coated with a conductive coating to provide a conductive surface of uniform smoothness and of light weight.

Abstract: The present invention provides an antenna dielectric having a thickness of less than 3 mm, having a relative dielectric permitivity approaching that of air whereby circuit and transmission line losses are minimised. In accordance with another aspect of the invention, there is provided an antenna ground plane substrate comprising an expanded polystyrene substrate produced by a two-stage moulding process. The two-stage polystyrene is coated with a conductive coating to provide a conductive surface of uniform smoothness and of light weight.

Abstract: A radio frequency antenna arrangement comprising an array of radiating elements, such as radiating antenna patches, which are co-located in a circuit, such as a microstrip circuit, with feeder elements which couple electromagnetic radiation to the radiating elements. The antenna arrangement has an electrically conductive backplate located behind the circuit, which acts as a groundplane and which is separated from the circuit by a dielectric layer. To reduce electromagnetic interference from the feeder elements which could disrupt the antenna pattern an electrically conductive screen is located directly in front of the feeder elements of the circuit but selectively exposes the array of radiating elements. The screen is spaced from the feeder elements and is not electrically connected to the backplate so that the screen, feeder elements and backplate do not form a triplate structure.

Abstract: A radio frequency antenna arrangement for selective operation at orthogonal polarizations of electromagnetic radiation. The antenna arrangement comprises at least one radiating element, such as one or more antenna patches, each having a vertical polarization feed point and a horizontal polarization feed point. The arrangement also includes a vertical feeder circuit for coupling a radio frequency modulated electromagnetic signal to the vertical polarization feed point of the or each radiating element, a horizontal feeder circuit for coupling a radio frequency modulated electromagnetic signal to the horizontal polarization feed point of the or each radiating element and a terminating resistive load. A switch mechanism is provided for selectively coupling the electromagnetic signal to one of the horizontal feeder circuit or the vertical feeder circuit and for selectively coupling the load to the other of the horizontal feeder circuit or the vertical feeder circuit.