Broadband spiral antenna with provision for mode suppression

Claim 2

An improved spiral antenna comprising six equiangular arms equally spaced circumferentially apart about a center, first means electrically connecting together the inner ends of a pair of adjacent arms, second means connecting together the inner ends of the pair of arms opposite to the first connected pair of arms, means applying high-frequency energization between said first and second means to energize the antenna for producing electromagnetic radiation therefrom, and suppression means disposed substantially at a radius of 0.6 wavelength of antenna energizatIon from the antenna center about the center adjacent each arm for suppressing electromagnetic radiation at a radius greater than 0.6 wavelength to thus suppress Mode 5 radiation from the antenna.

Claim 3

The antenna of claim 1 further defined by means defining an electrically conducting ground plane in close proximity to one side of said antenna adjacent each arm thereof whereby said antenna radiates away from said plane.

Claim 4

The antenna of claim 1 further defined by said suppression means comprising an annular absorber of a material absorbing electromagnetic radiation disposed against one side of the antenna and having an inner diameter in the range of 0.6 to 0.8 wavelength.

Claim 5

The antenna of claim 2 further defined by said suppression means comprising a plurality of resistors connected one between each antenna arm and said ground plane at a radius in the range of 0.6 to 0.8 wavelength and said arms terminating at such connections.

Claim 6

An improved unidirectional frequency-independent antenna comprising six equiangular spiral antenna arms disposed in substantially planar array and spaced equally apart about a center, means electrically connecting together a first pair of antenna arms adjacent said center and connecting together the pair of antenna arms opposite said first pair, means applying high-frequency electrical energization between said connections to directly energize said two pairs of arms and parasitically energize the two remaining unconnected antenna arms whereby said antenna is energized to radiate in Mode 1 and Mode 5 regions, means defining an electrically conducting ground plane in close proximity to one substantially planar side of the antenna, and radiation suppression means disposed between said antenna and ground plane radially outward of the Mode 1 radiation region of the antenna and suppressing Mode 5 radiation whereby substantially only Mode 1 radiation occurs.

Claim 7

An improved unidirectional frequency-independent antenna comprising six equiangular spiral antenna arms disposed in substantially planar array and spaced equally apart about a center, means electrically connecting together a first pair of antenna arms adjacent said center and connecting together the pair of antenna arms opposite said first pair, means applying high-frequency electrical energization between said connections to directly energize said two pairs of arms and parasitically energize the two remaining unconnected antenna arms whereby said antenna is energized to radiate in Mode 1 and Mode 5 regions, means defining an electrically conducting ground plane in close proximity to one substantially planar side of the antenna, and radiation suppression means disposed between said antenna and ground plane radially outward of the Mode 1 radiation region of the antenna and suppressing Mode 5 radiation whereby substantially only Mode 1 radiation occurs.

Claim 8

The antenna of claim 5 further defined by said radiation suppression means being disposed radially outward of the antenna from the center thereof substantially 0.6 wavelength of the highest operating frequency of energization of the antenna.

Claim 9

The antenna of claim 6 further defined by said radiation suppression means comprising a material having a high loss tangent for high-frequency energization disposed in a ring between said antenna arms and said ground plane and extending radially outward from substantially 0.6 wavelength to 0.9 wavelength of the highest operating frequency of energization of the antenna.

Claim 10

The antenna of claim 5 further defined by said suppression means comprising resistors connected between said antenna arms and said ground plane and said arms terminating at said resistor connections.