Patent ID: 6552693
Filing Date: 2003-04-22
Classification: H01Q

Abstract:
An antenna having an operating frequency in excess of 200 MHz comprising a cylindrical insulative body having a central axis and formed of a solid material which has a relative dielectric constant greater than 5, the outer surface of the body defining a volume the major part of which is occupied by the solid material, a conductive sleeve on the cylindrical surface of the insulative body, a conductive layer on a surface of the body which extends transversely of the axis, the conductive sleeve and layer together forming an open-ended cavity substantially filled with the solid material, and a feeder structure associated with the cavity, wherein the relative dielectric constant and the dimensions of the cavity are adapted such that the electrical length of its circumference at the open end is substantially equal to a whole number (1, 2, 3, . . . ) of guide wavelengths around the circumference corresponding to the operating frequency, wherein the antenna has a radiation pattern for circularly polarised radiation at the operating frequency, which pattern is cardioid-shaped with its maximum along the axis of the insulative body outwardly away from the open end of the cavity.