US 3362026 A
Description (OCR text may contain errors)
-w 1 1968 v. c. SMITH, JR., ETAL 3,362,026
SHORTENED LOG PERIODIC ANTENNA Filed Jan. 27, 1965 INVENTORS LAN JEN CHU, VALOR C.SMITH,JR.
ATTORNEYS United States Patent SHORTEN ED The present invention relates to log periodic antennas and, more generically, to antennas of the type in which an array of dipoles of different dimensions is employed for directional and other radiational characteristics.
While the invention will be more particularly described in connection with its preferred and optimal application to log periodic antennas, in which the spacing and dimensions of the dipoles are adjusted in accordance with a logarithmic law of variation, it will be apparent that the techniques here-involved may also be employed with other types of dilferent length dipole arrays for useful purposes, also. Turning, however, to the preferred application of substantially log periodic arrays, the present invention is directed to obviating the required large dimensions of the dipoles inherent in particularly low-frequency log periodic structures. In summary, this result is attained through the shortening of the dipole structures in physical dimensions, but the resonating of the same with the aid of added inductive and capacitative structures that enable a smaller-sized antenna to give results equivalent to conventional large-size arrays of this character.
A further object of the invention is to provide a new and improved antenna structure of more general utility, as well.
Additional objects will be apparent in the following descriptions and in the appended claims.
The invention will now be described in connection with the accompanying drawing, the single figure of which is a fragmentary isometric view illustrating the invention as applied to a substantially log periodic antenna.
Referring to the drawing, a pair of substantially parallel longitudinal strip feed conductors is shown at 1-1' having longitudinally spaced transversely extending (preferably orthogonally to the longitudinal direction of the conductors 1-1) dipole extensions 2, 2, 4, 4, 6, 6 that, in accordance with conventional practice, would be of successively decreasing lengths and separations in accordance with the log periodic law, or some other desired law of variation. In accordance with the present invention, the norm-ally required length of the dipole elements is considerably shortened by dividing the dipole extensions into segments supported in-line by insulating separators, In connection with the oppositely extending pair of transverse dipole extensions 2 and 2', for example, these are respectively shown divided into segments 20-20" and -30 connected by insulating spacers 21 and 31. Although the overall length of the elements 2 and 2' is made much smaller than the normal length required, as before explained, electrical equivalence to the longer length is elfected by providing conductive inductance jumpers 5 and 5 joining the respective segments 20-20 and 30-30, and, at the outer ends of the segments 20 and 30, capacitative means in the form of a plurality of conductors 22 and 22 extending generally forward in the space between the dipoles 2-2' and the next longitudinally spaced dipoles 4-4. Similar comments apply to the structures of the succeeding elements 4-4, 6-6, etc. By adjusting the number or dimensions of conductors 22 and 22, shown extending substantially orthogonally to the dipole elements 2 and 2 in the longitudinal direction, and/or 3,362,026 Patented Jan. 2, 1968 the orientation of the conductors, ditferent values of capacitance can be loaded upon the elements and can thus be appropriately tuned with the inductance provided by the jumpers 5 and 5, and the segments 20-20 and 30-30, to produce resonance equivalent to that of a much longer dipole pair. Thus, by changing the value of capacitance, as by using successively fewer and/or shorter conductors (shown as two at the ends of the elements 4-4 and one at the ends of the elements 6 and 6), and by appropriate orientation of these elements, such as the acute angle convergence orientation of the single elements at the ends of the dipoles 6 and 6', such tuning may be effected in accordance with the log periodic law, or any other desired law.
It should be noted, thus, that the log periodic law can even be attained with dipoles 2-2', 4-4 of substantially the same length, since these may be differently tuned with the corresponding inductance and capacitance device to achieve the same electrical result as different dimensioning of the elements.
Through this technique, very much smaller arrays have been constructed to produce the same kinds of performance heretofore attainable with very sizable structures. As an example, highly successful log periodic radiation results have been attained in the VHF band with tubular conductors 1 and 1 spaced to maintain the plane of the dipoles 2, 4, 6 about one foot above the plane of the elements 2, 4', 6', with the elements 2-2' extending 30 feet and a total of nine pairs of dipole elements longitudinally extending over a distance of about thirty six feet. This is contrasted with arrays having dipole elements of two or more times this length.
Modifications will occur to those skilled in the art and all such are considered to fall within the spirit and scope of the invention as defined in the appended claims.
What is claimed is:
1. An antenna having, in combination, a pair of substantially parallel longitudinal conductors having opductors having oppositely transversely extending pairs of dipole extensions spaced longitudinally therealong, certain of the dipole extensions being divided into segments by insulator means with the segments being joined by inductive means, and capacitative means extending in the space between the outer ends of certain of the dipole extensions and the next longitudinally spaced pair of dipole extensions, the said certain divided extensions being tuned with the corresponding inductive and capacitative means to produce different elfective lengths of successive dipole extensions substantially in accordance with the log periodic law.
3. An antenna as claimed in claim 2 and in which the inductive means comprises a conductive jumper connecting the divided dipole extension segments.
4. An antenna as claimed in claim 2 and in which the capacitative means comprises conductor extension means extending generally in the longitudinal direction.
5. An antenna as claimed in claim 4 and in which successively dilferent numbers and/or dimensions of conductor means are employed in successive pairs of dipole extensions to effect successively difierent tuning of the successive extensions.
6. An antenna as claimed in claim 5 and in which the conductor extensions extend substantially orthogonally to the dipole extensions.
7. An antenna as claimed in claim 4 and in which the conductor extensions extend at an acute angle to the dipole extensions.
4 References Cited UNITED STATES PATENTS 3,259,904 7/1966 Blonder et'al. 343-7925 3,276,028 9/1966 Mayes et al. 343-792.5 3,277,487 10/ 1966 Berry, et al 343-7925 ELI LIEBERMAN, Primary Examiner.