Frequency independent log periodic slot multi-mode antenna array

BACKGROUND OF THE INVENTION

An H-guide is an open type of transmission line comprised of two conductive plates separated by a dielectric strip. The propagation of hybrid modes in an H-guide waveguide is explained in “The H-guide a Waveguide for Microwaves”, by F. J. Tischer, 1956 IRE Convention Record, pt. 5, pp. 44-47.

It is known to propagate microwaves within an H-guide to diminish possible heat losses in the two conductive plates.

It is also known to make a cylindrical H-guide microwave antenna as disclosed in Pat. 3,233,242 to George N. Voronoff.

SUMMARY OF THE INVENTION:

The present invention is comprised of six identical triangular elements, with coinciding apices, wrapped on a cone.

Each element consists of two parallel electrically conductive plates, with a dielectric slab disposed between them. Two rows of slots lie on log periodically expanding circles; and when the elements are wrapped on a cone, the shorter slots lie closer to the apex of the cone than the longer slots.

The antenna array receives excitation from H-guide type waveguides which are created by the dielectric slabs which may be placed between the joints of any two elements.

Because the excitation occurs between any two elements, pairs of rows of slots are excited rather than individual rows. This “aperture sharing” technique permits a broader beam angle than heretofore possible.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a side view, partially in cross-section, of a preferred embodiment of the invention;

FIG. 2 is an exploded view of one of the elements which comprise the embodiment of FIG. 1; 55

FIG. 3 is a top view of the embodiment of FIG. 1; and

FIG. 4 is a perspective view, partially in cross section of a second embodiment of the invention.

DESCRIPTION OF THE PREFERRED ₆₀EMBODIMENTS

FIG. 1 and FIG. 3 show a conical array 26 consisting of six identical elements 25, one of which is shown in FIG. 2.

Referring to FIG. 2, element 25 is comprised of two ⁰⁰ parallel truncated triangular conductive plates 10 and 16. Plate 16 has log periodically expanding slots 11 cut into it so that the shorter slots lie near the virtual apex of the tuncated triangle, and the longer slots lie near the base of the tuncated triangle.

Spacer bars 12 maintain a separation between conductive plates 10 and 16. In one embodiment of the invention, spacer bars 12 are a dielectric material which can be used for exciting the antenna.

Referring to FIG. 1 and FIG. 2, excitation normally occurs via dielectric slab 13 which acts as an H-guide type waveguide between conductive plates 10 and 16. Blocks 14 and strip 15 form a launcher for propagating electromagnetic waves along dielectric slab 13.

_lg Absorbers 24, which may be made of Eccosorb LS-26, or aluminum backed Resonant Solid Absorbers RS-C, or RS-X manufactured by B. F. Goodrich, load the antenna array, prevent energy leakage and provide insulation between the adjacent elements 25 of antenna 26. Slot 17 2θ is provided to hold absorbing material 24, such as Eccosorb LS-26, to provide termination.

Cap 18 is provided, as shown in FIG. 1 and FIG. 3, for streamlining in the event that antenna array 26 is mounted on the nose of an aircraft.

FIG. 3 also shows an element 25 consisting of two rows of log periodically expanding slots cut into conductive material 10.

FIG. 4 shows a second embodiment of the invention.

Two semicircular conducitve plates 19 and 20 are dis30 posed in space parallel to one another. Slots 11, cut into plate 19, expand log periodically from the center of the semicircle to its perimeter. Spacers 23 separate the two semicircular plates.

Dielectric slabs 13 are placed between each row of 35 slots. For excitation, launcher 21 is fastened to the outer perimeter of the semicircle. Dielectric slab 13 is removed, and a longer dielectric slab 22 is inserted in its place. Thus dielectric slab 22 causes H-guide type hybrid waves to propagate between plates 19 and 20 causing 40 “aperture sharing” to occur.

It should be noted that any number of dielectric slabs 13 may be removed and replaced by excitation slabs 22 and launchers 21.

Obviously many modifications and variations of the present invention are possible in light of the above teach⁴⁵ ings. It is therefore to be understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

The invention described herein may be manufactured and used by or for the Government of the United States ⁵⁰ of America for governmental purposes without the payment of any royalties thereon or therefor.