US2856605A - Antenna - Google Patents

Description

Oct ,1958 E. R. JACOBSEN 2,856,605

ANTENNA Filed Jan. 15, 1958 INVENTOR. ERL/NG R. JA COBSEN United States Patent'Ofilice A 2,856,605 Patented Oct. 14, 1958 ANTENNA Erling R. Jacobsen, Falls Church, Va. Application January 15, 1958, Serial No. 709,160 12 Claims. (Cl. 343-807) This invention relates to antennas and is particularly applicable to broad band antennas intended for frequencies greater than 50 megacycles.

It has been found that a broader band characteristic can be achieved by folding the elements of a simple dipole antenna to define interwound spirals lying in a single plane. While higher operating frequencies then become possible, extremely high standing wave ratios have been found to occur at certain values of frequency within the desired band. it has also been found that a standing wave ratio at a particular fequency value can be made to approach a mathematically determined average over the entire band of desired frequencies by the addition of capacity to the outer portions of the spiral elements of such an antenna. Such lumping capacity however, will not assure the elimination of the hole effects which become apparent from the gain-frequency curves of antennas thus constructed.

It is among the objects of the present invention to provide an antenna having an axis and comprising two mutually insulated strips of conductive material interwound about the axis and having varying finite width components parallel to the axis, so that the added capacity will increase at a predetermined rate, outwardly from the proximate portions of the strips. A substantially mean input impedance can thus be achieved throughout. the band, permitting improved transmission line matching and a more effective transfer of power.

The strips of this antenna are preferably spirally interwound, identical elements, of varying width. The width components preferably vary progressively, diverging outwardly with respect to the axis. Each of the strips preferably has an edge lying in a plane, and the widths of the strips are preferably perpendicular to this plane. The antenna is preferably symmetrical with respect to its axis, the proiiiinate ends of the strips lying equidistant from the axis and being disposed at 180 with respect thereto.

A more complete understanding of the invention will follow from a description of the accompanying drawing wherein:

Fig. 1 is a perspective view of an antenna constructed accordance with the present invention;

Fig. 2 is a sectional elevation taken along line 2-2 of Fig. l; and

Fig. 3 is a fragmentary perspective view on an enlarged scale depicting the construction to better advantage.

The antenna depicted in the drawing is composed of a pair of conductive strips and 12 spirally interwound and mutually insulated. The lower edges of the strips as shown in Fig. 2 lie substantially in a plane and are embedded in an insulating base 14 which may be composed of a thermoplastic or thermosetting material. The material constituting this insulating base 14 may vary widely so long as it serves the function of holding the convolutions of the interwound strips in spaced relationship and insulated one from the other.

1.0 and 12 are equidistantfrom' the axis 20 of the antenna and disposed at 180 with respect thereto. The strips 10 and 12 may be composed of sheet aluminum, for example, cut so as to diverge from their narrow proximate ends 16 and 18 to their remote ends 22 and 24. This divergence may be rectilinear or curvilinear but it is preferably progressive. Where the upper edges of the strips are curvilinear, they may assume exponential, hyperbolic or parabolic forms, for example, or such other forms as will produce desired band pass characteristics.

The interwinding of the conductive strips may also vary, the spiral configuration contemplating such forms as Archimedian, exponential, or otherwise, selected to produce the desired capacity effects.

The antenna may be terminated in balanced resistances if desired, or it may be nnterminated. Where the antenna is terminated in balanced resistances, they may be selected to effect the loading and isolation of the antenna as well as the configuration of the gain-frequency curve. It is also contemplated that directional and additional loading efiects may be achieved by the use of a cavity or plane reflecting element.

The present invention is particularly well suited for broad band antennas designed for frequencies above 50 megacycles. Actually, the greatest advantages of antennas of this type will be realized at frequencies above megacycles. As a specific example of an antenna incorporating the present invention, the design of an antenna covering a band of to 1000 megacycles with a gain deviation of +4 decibels and -9 decibels as compared with a conventional dipole antenna can be as follows: The conductive strips can be cut from a sheet of aluminum 37 feet long, diverging in width from one-quarter inch to four inches. The two elements can then be interwound in the form of Archimedian spirals with a spacing of one-quarter inch between convolutions. The overall diameter of the resulting antenna will be approximately 15 inches. The radiation pattern of. such an antenna will be essentially constant over all frequencies within. the band for which it was designed, having a major lobe characteristic which drops off not more than 8 decibels in any direction 45 from the antenna axis.

Whereas the width of each interwound strip is preferabl disposed parallel to the axis as depicted in Fig. 2, it is contemplated in some forms of the invention that other angular dispositions be employed, but in any event, there will always be a finite component of width parallel to the axis.

Whereas only one specific form of the invention has been shown and described, variations are contemplated within the scope of the appended claims.

I claim:

1. An antenna having an axis and comprising two mutually insulated strips of conductive material interwound about said axis and having varying finite Width components parallel to said axis.

2. An antenna as set forth in claim 1 wherein strips are spirally interwound.

3. An antenna as set forth in claim 1 strips are identical.

4. An antenna as set forth in claim 1 width components vary progressively.

5. An antenna as set forth in claim 1 strips diverge outwardly.

6. An antenna as set forth in claim 1 strips have widths parallel to said axis.

7. An antenna as set forth in claim 1 strips are equal in length.

8. An antenna as set forth in claim 1 said wherein said wherein said wherein said wherein said wherein said wherein said 3 strips have proximate ends disposed at 180 relative to 11. An antenna as set forth in claim 1 wherein each said axis. of said strips has a varying width.

9. An antenna as set forth in claim 1 wherein said 12. An antenna as set forth in claim 1 wherein said strips have proximate ends equidistant from said axis. antenna is symmetrical with respect to said axis.

, 10. An antenna as set forth in claim 1 wherein each 5 of said strips has an edge lying in a plane. N0 references lt d.

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