Patent ID: 8497815

Claim:
A dielectrically loaded multifilar helical antenna for operation at a frequency in excess of 200 MHz, comprising: a dielectric core of a solid material having a relative dielectric constant greater than 5, the material of the core occupying the major part of the volume defined by the core outer surface, and a three-dimensional antenna element structure disposed on or adjacent an outer surface of the core having at least first and second pairs of elongate conductive substantially helical antenna elements centred on a common axis, each of which elements has a feed end and a linked end, the linked ends of each pair being linked together by a linking conductor, wherein the helical elements of the first said pair form part of a first conductive loop and the helical elements of the second said pair form part of a second conductive loop, and wherein, at an operating frequency at which the antenna is resonant in respect of axially directed circularly polarised radiation, each said conductive loop has an electrical length of substantially (2n−1)/2 times the wavelength, where n is an integer and wherein voltage maxima are present substantially at said feed end of each of said elements.