Abstract: A single element, multi-frequency dipole antenna including two substantially equal arm sections of conductive material extending co-axially in a straight line in opposite directions from each other, each arm section being a mirror image of the other arm section throughout its entire length, each arm section including at least two contiguous shorter sub-sections of j.sub.1, j.sub.2, . . . j.sub.n lengths, wherein j.sub.1 represents the length of the innermost sub-section, sub-sections terminated by discontinuities wherein j.sub.1 represents the 1/4 wavelength of the highest resonant frequency and each consecutive-integer sequence of j sub-sections represent the 1/4 wavelength of lower resonant frequencies.

Abstract: A dual frequency feed element for a parabolic reflector antenna system, comprising a conductive cavity having a central axis, the cavity mounted at the focal point of a parabolic reflector surface and defined about its outer perimeter by an upstanding cavity wall, and having a closed cavity floor and an open top directed toward the reflective surface, a dual frequency radiating element centrally disposed in the cavity and arranged to radiate a first low frequency signal out through the cavity open top to the antenna surface, a conductive floor fixed below the radiating element a distance in relation to the radiant energy for the first low frequency signal, and disposed in the cavity transverse to the central axis thereof to reflect radiant energy for the first signal and, a frequency selective surface fixed below the radiating element, apart from the conductive floor, and transverse to the central axis of the cavity to reflect radiant energy for the second, higher frequency signal while simultaneously being i