Assymetrical folded half-dipole and linear extension antenna array

This disclosure is concerned with a linear antenna array mounted on a conductive longitudinal boom, as in a Yagi-type array or the like, having a plurality of assymmetrical transversely extending folded half dipoles and linear extensions thereof disposed at successive longitudinally spaced locations along the boom, with the folded half dipoles of successive antennas extending from opposite sides of said boom.

The present invention relates to linear antenna arrays and the like, being 
more particularly directed to arrays as of the Yagi and related types 
employing folded type dipoles and linear elements. 
In my earlier U.S. Pat. No. 4,218,686, issued Aug. 19, 1980, an 
advantageous antenna of this type is described in which assymetrical 
linear elements interact with folded dipoles to compensate for the 
unbalance of the folded dipole antenna feed and thereby to provide 
improved radiation pattern, impedance matching, and other performance 
characteristics over relatively wide frequency bands. This technique 
involved interaction with "hot" and ground sides of a full folded dipole 
fed by conventional coaxial feed techniques. 
There are occasions where it is advantageous not to have both "hot" and 
ground folded dipole antenna loops and where conventional parallel or 
coaxial feed and matching techniques are not suitable. In accordance with 
the present invention, the assymmetrical phenomenon of said Letters Patent 
is combined in a novel manner with a plurality of successive folded 
half-dipoles ("hot" side loops only) and linear extensions thereof to 
achieve the highly novel result of enabling the use of a vastly simplified 
feed construction providing matching over multi-frequency bands of 
somewhat more limited extent. 
An object of the invention, accordingly, is to provide such a novel 
multi-folded half-dipole array suitable for use with a single conductive 
boom and in configurations such as of the Yagi type, to attain the 
above-described and other advantages. 
A further object is to provide a novel antenna array of more general 
applicability, as well. 
Other and further objects are explained hereinafter and are more 
particularly pointed out in connection with the appended claims. 
In summary, however, from one of its aspects, the invention embraces a 
linear antenna array comprising a conductive boom extending along a 
longitudinal line, and a plurality of transversely extending folded 
half-dipoles and assymmetrical-length extensions of an arm thereof, 
disposed at successive longitudinally spaced locations along the boom, 
with the end of the said folded half dipole from which the extension 
continues being connected to the boom, and the other end of the folded 
half-wave dipole being disposed laterally spaced from the boom, successive 
antenna folded half-dipoles extending from opposite sides of the boom, and 
conductive means extending substantially parallel to and laterally of the 
boom interconnecting the said other ends of successive folded half-wave 
dipoles. Preferred best mode embodiments are hereinafter set forth.

Referring to the drawing, a single longitudinally extending conductive boom 
support is shown at 1 mounting at successive spaced longitudinal locations 
a plurality (shown as three) of "driven" antennas I, I' and I", each 
comprising a half only ("hot" side) of a folded dipole loop L, L' and L", 
each disposed extending transversely from a side of the boom, and with one 
of the free ends of each of which connected to the boom, as at 2, 2' and 
2", from which connection there extends transversely from the other side 
of the boom 1, linear antenna extensions E, E' and E", respectively. In 
accordance with the invention, the other free ends 4, 4' and 4" of the 
respective succesively mounted folded half dipole loops L, L' and L", are 
bent laterally outward of the boom 1 and are interconnected by conductive 
straps C, C', serving as the other feed conductor for the dipole loops, 
supported upon insulator blocks B, and extending substantially parallel to 
the boom 1 but laterally spaced therefrom. The folded half-dipole loop 
antennas L, L', and L" are preferably oriented with the plane of their 
loops substantially orthogonally intersecting the line of the boom 1. 
The invention, as before stated, in its best mode, uses assymetrical 
lengths of loop L and linear extension E, from an arm thereof; of loop L' 
and extension E'; and of loop L" and extension E", with the lengths of 
antennas I, I' and I" being successively longer (corresponding to 
successively lower frequencies in a predetermined band). Surprisingly, 
excellent impedance matching is achievable when successive loops L, L', L" 
extend from opposite sides of the boom from the preceding antenna, and 
with the boom and substantially parallel strap connectors C--C' serving as 
the feed. 
Considering the VHF television band from channel 7 to channel 13, as an 
example, loop L may be 121/2" with the linear extension E from its inner 
arm being of non-symmetrical length, about 15% longer, namely about 
143/8"; loop L', 13", with extension E', 151/2"; loop L", 133/4" and 
extension E", 16". The longitudinal spacing between the successive 
antennas may be 15" (about a twentieth of the wavelength). As shown, 
parasitic directors D or reflectors R may be connected to the boom beyond 
the driven elements for additional directivity and reduced back lobes. 
While three driven elements are shown in the linear array, two elements may 
be used and more than three, if desired. Further modifications will also 
occur to those skilled in the art and are considered to fall within the 
spirit and scope of the invention as defined in the appended claims.