Abstract: A retroreflective material in which the coating used to produce or enhance retroreflectivity and which bridges at least some of the gaps between the beads is treated and/or removed to produce areas of contrast which may represent patterning and/or graphical and/or pictorial matter without significantly affecting the retroreflective properties of the beads, if at all, and/or which may result in a different colour to conventional silvery grey coloured retroreflective materials.

Abstract: A microwave antenna comprising a dielectric substrate, carrying on one side thereof a microstrip antenna suitable for operation within a first frequency band and on the other side thereof a conductive ground plane, a first microwave feed coupled between the microstrip antenna and the ground plane for conducting microwave signals in the first band, at least one radiation aperture formed in the ground plane for operation within a second frequency band and arranged to communicate with a resonant microwave cavity defined between the ground plane and a conductive enclosure arranged to extend therefrom, and a second microwave signal feed coupled between the ground plane and the said enclosure for conducting microwave signals in the second band.

Abstract: An antenna suitable for the generation of a circularly polarized annular radiation pattern comprising a substrate spaced apart from a ground plane by a layer of dielectric material, the substrate being arranged to carry on one side thereof a conductive layer in which a plurality of radial slots is defined equiangularly disposed to extend outwardly from a central region of the substrate, and on the other side thereof a microstrip feed line arrangement via which the radial slots are arranged to be fed with microwave energy for the generation of a horizontally polarized radiation pattern and via which an edge slot defined between the peripheral edge of the layer and the ground plane is arranged to be fed with microwave energy for the generation of a vertically polarized radiation pattern whereby the horizontal pattern and the vertical pattern in combination afford the circularly polarized annular radiation pattern.

Abstract: In a prior form of stripline antenna, the strip turns through successive right-angle corners to form successive multi-cornered cells in which the lengths of the longitudinal and transverse strip sections are such that the summed radiation from each cell radiates in the same direction and with the same polarization direction. In the present disclosure, the distribution of radiated power along the array is varied, e.g. to maximize it at the center, by varying the absolute lengths of these strip sections as between cells while maintaining their required relationships, e.g. by progressively increasing these lengths towards the center of the array in order to increase the radiated power accordingly. This compares with the previously known method, viz varying the strip width.

Abstract: Stripline antenna arrays of the type in which the strip turns through successive right-angle corners to form successive four-cornered cells, the lengths of the longitudinal and tranverse strip sections being such that the summed radiation in each cell has the same polarization direction, viz vertical, horizontal or circular, radiating in the broadside direction effect arbitrary polarization directions radiating in any direction in the plane (x-z) normal to the array which contains the array axis, by using cells having six potential right-angle corner sites and strip sections of appropriate lengths. The number of actual corners may reduce to four; e.g. where strip-section lengths reduce to zero.