US 4,608,572 A · Broad-band antenna structure having frequency-independent, low-loss ground plane

Abstract

To optimize antenna bandwidth and efficiency in broad-band antenna elements of the planar, multiarm spiral and log periodic types, a conically shaped ground plane characterized by progressively sized circumferential chokes, is arranged on a common axis with the axial center of the spiral or log periodic elements so that the electrical spacing between the excited regions of the log periodic of spiral elements and the ground plane maintains a constant one-quarter wavelength relationship. The progressively sized circumferential chokes on the ground plane cut off the flow of excessive radial currents along the ground plane surface to achieve an improved mix of excitation and reexcitation modes. In one embodiment, the circumferential chokes on the conical ground plane are partially shunted by shunting strips that electrically or capacitively bridge the choke walls to reestablish limited radial currents along the ground plane for sustaining certain desirable antenna modes. In another disclosed embodiment, the equivalent one-quarter wavelength relationship between the driven spiral or log elements and the reflecting ground plane is maintained in an antenna structure in which the driven elements are disposed on the surface of a dielectrically shaped cone and the ground plane and progressively sized circumferential chokes are arranged in a generally planar array. In still another disclosed embodiment, the circumferential, progressively sized chokes are disposed on the interior reflective surface of a center-fed antenna horn, wherein the array of chokes has the effect of broad-banding the otherwise inherently narrow band characteristics of the horn.

Claims27

Dependent claims

An antenna structure comprising:

a directional, frequency-repeating, broad-band driven element arranged around an axis of antenna directivity and having excitation characteristics that vary with the radius from said axis, said excitation characteristics concentrating relatively higher signal frequencies in regions of said element proximate said axis, and concentrating progressively lower signal frequencies in regions of increasing radius from said axis out to a perimeter of said element;
a matching broad-band reflective ground plane formed around said axis and so arranged with said element that signal energy is reflected by said ground plane back toward said element generally along said axis, said ground plane having an array of circumferential chokes proximate said axis and matching the relatively higher signal frequencies of excitation on said element in said regions thereof proximate said axis, and said chokes on said ground plane progressively increasing in size with increasing radius so as to match the progressively lower frequencies of excitation at regions of said element of corresponding radius out to said perimeter of said element, said circumferential chokes limiting the inducement of radial currents on said ground plane;
and
shunt means associated with said chokes for controlled shunting of radial currents on said ground plane.

1 more element

An antenna structure comprising:

a directional, frequency-repeating, broad-band driven element arranged around an axis of antenna directivity and having excitation characteristics that vary with the radius from said axis, said excitation characteristics concentrating relatively higher signal frequencies in regions of said element proximate said axis, and concentrating progressively lower signal frequencies in regions of increasing radius from said axis out to a perimeter of said element;
and
a matching broad-band reflective ground plane formed around said axis and so arranged with said element that signal energy is reflected by said ground plane back toward said element generally along said axis, said ground plane having an array of circumferential chokes proximate said axis and matching the relatively higher signal frequencies of excitation on said element in said regions thereof proximate said axis, said chokes on said ground plane progressively increasing in size with increasing radius so as to match the progressively lower frequencies of excitation at regions on said element of corresponding radius out to said perimeter of said element, the terminal portions of said circumferential chokes that are positioned nearest to said driven element collectively defining the effective surface of said reflective ground plane, said circumferential chokes limiting the inducement of radial currents on said ground plane.

Dependencies are inferred from the claim text.

Broad-band antenna structure having frequency-independent, low-loss ground plane

Life of this patent

Broad-band antenna structure having frequency-independent, low-loss ground plane

Life of this patent

Abstract

Claims27