Abstract: A low profile, dual purpose antenna for simultaneous UHF and LF use has two coplanar antenna elements, one of which is circular and the other of which is a concentric annulus separated from it by a dielectric, as well as a third, linear antenna element extending from the center of the circular element. The circular element serves both to assist in tuning the UHF section of the antenna and as a voltage probe for the electrostatic component of the LF signal. Integrated within the antenna housing is a high input impedance, low noise amplifier for bandwidth limiting the LF signals. A coaxial feeder cable serves to connect both UHF and LF sections of the antenna to external equipment. Entry for the coaxial feeder cable into the antenna housing is through a threaded collar, which also acts as a single point fixing of the antenna to the roof of a vehicle.

Abstract: A method of determining the position of an object comprising the steps of: producing a plurality of hyperbolic electromagnetic wave patterns; calculating from said patterns at least three lines of position; identifying the lane of each line of position by two independent methods; comparing the size of the area enclosed by the lines of position based on the lanes identified by a first of said methods with the size of the area enclosed by the lines of position identified by a second of said methods and producing therefrom an indication as to whether the lanes identified by the first method are more likely to be correct than those identified by the second method; and computing the position of the object using the lines of position based on the lanes identified as being more likely to be correct.