US2972146A - Folded dipole antenna with internally mounted loading means - Google Patents

Description

Feb. 14, 1961 s x 2,972,146

FOLDED DIPOLE ANTENNA WITH INTERNALLY MOUNTED LOADING MEANS Filed July 29, 1959 INVENTOR HAROLD A. SAXE BY {7% M.

ATTORNEY United States Patent Ofitice 2,972,146 Patented Feb. 14, 1961 FOLDED DIPOLE ANTENNA WITH INTERNALLY MOUNTED LOADING MEANS Harold A. Saxe, Whippany, N.J., assignor to Western Electric Company, Incorporated, New York, N.Y., a corporation of New York Filed July 29, 1959, Set. No. 830,281

2 Claims. or. 343-749 This invention relates to a folded dipole antenna and more particularly to a folded dipole antenna having loading circuits mounted therein.

An object of the invention is to provide a new and improved folded dipole antenna.

Another object of the invention is the provision of a folded dipole antenna having loading circuits to physically shorten the elements for permitting operation of a parasitic array where wind velocities or limited space prohibit the use of full-length beams.

A further object of the invention is to provide a folded dipole antenna which offers improved radiation eificiency, harmonic suppression and weather resistance.

Apparatus illustrating certain features of this invention may include a primary and a secondary active means for transmitting and receiving electromagnetic waves. The secondary active means includes two spaced, axially aligned members mounted parallel to and insulated from the primary means. Loading circuits are connected between the ends of the active means.

More particularly apparatus illustrating certain features of the invention may include a primary tubular active element, and a pair of loading circuits respectively mounted within, and insulated from, the outer ends of the primary element. One terminal of each of the circuits is connected electrically to each of the ends of the primary element. A pair of secondary active elements are fixed to and insulated from the primary element, the secondary elements being axially aligned with their common axis parallel to the axis of the primary element. The other terminal of each of the circuits is connected electrically to each of the outer ends of the secondary elements to complete an electrical path between the primary element and the secondary elements.

A complete understanding of the invention may be had from the following detailed description of a specific embodiment thereof when read in conjunction with the appended drawing, in which:

Fig. 1 is a front elevational view of a preferred embodiment of the antenna;

Fig. 2 illustrates an enlarged fragmentary sectional view of a portion of Fig. l; and

Fig. 3 shows an enlarged sectional view taken along line 33 of Fig. 2.

Referring to the drawing, wherein like reference characters designate like or corresponding parts throughout the several views, there is shown in Fig. l a folded dipole antenna,-designated generally by the numeral 11, having a primary tubular active element 12 and a pair of axially aligned and spaced secondary tubular elements 13. The secondary elements 13 are of a smaller diameter than and fixed spatially to the primary element 12 by insulated connectors 14 so that the common axis of the secondary elements 13 is spaced from, and parallel to, the axis of the primary element 12. Of course, the diameter, length and spacing of elements 12 and 13 may be varied in accordance with desired impedance, directional and radiating properties.

Loading coils, designated generally by the numeral 15, including a winding 16 and a core 17 (Figs. 2 and 3) of an insulating material, such as hard rubber or the like, are mounted removably within the outer ends of the primary element 12. The core 17 is fixed to a disk 18 of an insulating material, such as hard rubber, which may be fitted removably within an annular member 19 to form a weather-tight seal between the member 19 and the disk 18. The annular member 19 may be of the same material as the primary element 12 and is fitted removably within it -to form a weather-tight seal between the element 12 and the member 19, thus effectively sealing the ends of the element 12.

One end of the winding 16 is fixed to the annular member '19 by welding or the like, While the other end of the winding 16 is engaged to the secondary element 13 by means of a threaded member 21 (Figs. 2 and 3). Hence, it is apparent that the loading coil 15 may be replaced simply by removing the annular member 19, the disk 18, and substituting the coil 15 with a different coil having an impedance characteristic as desired.

A transmitting or receiving unit, not shown, to be used in conjunction with the antenna is connected electrically thereto by leads 22, Fig. 1.

'For antenna physical lengths of one-fourth wave length or less, it is advisable to use tuned circuits of lumped constants at the ends of the elements to improve radiation efliciency. Since the tuned circuit would be positioned within one of the elements 12 or 13, it would be protected from weather conditions, thereby maintaining the antenna resonance virtually constant under extreme temperature and humidity changes. Alternatively, the ends of the folded dipole antenna 11 may be loaded by short loops of wire or other conductive material insulated and placed inside the radiating elements 12 or 13.

The loading coils 15, or other loading circuits, provide an inductive or capacitive load which simulates a short or an open circuit, depending on the frequency applied to, and the length of, the elements 12 and 13. Consequently, the use of the loading coils 15 causes the radiation of harmonic frequencies to be reduced and most of the antenna resonant frequencies to be harmonically unrelated. Hence, the antenna 11 may be used for multiband operation on frequencies which are not exact multiples of the lowest frequency. It may also be used as a single band antenna capable of limiting harmonic radiation.

Also, the antenna loading may be adjusted for operation on frequencies which either are or are not exact multiples of the lowest tuned frequency of the antenna. By electrically loading the ends of the antenna rather than loading its center, a larger portion of antenna radiation current can be utilized in signal transmission.

It should be understood that the loading coils 15 may be positioned within the secondary elements 13 if the size of the coils 15 and elements 13 permit.

It should be further understood that the above-described embodiment of the invention is merely illustrative and that numerous modifications may be made within the spirit and scope of the invention.

What is claimed is:

1. In a folded dipole antenna having a hollow elongated active element and a loading circuit mounted therein, a loading circuit support for mounting within the active element which comprises a core of insulating material, an insulating disk fixedly engaged to the core, and a conductive annular member coaxially surrounding the disk, the annular member being of a size for reception within the end of the active element such that the core and the loading circuit are sealingly disposed completely within the element.

2. In a folded dipole antenna having hollow elonmaterial, an insulating disk fixedly engaged to the core and having an aperture formed therethrough, and a conductive annular member coaxially surrounding the disk for connection to one end of the loading circuit to be supported, the other end of the circuit being disposed sea-lingly through the aperture formed through the disk 10 2,744,248

and connected electrically to the secondary active element, the annular member being of a size for reception within the end of the primary active element such that the core is sealingly disposed completely within the element.

References Cited in the file of this patent UNITED STATES PATENTS Warren Feb. 7, 1933 Ehrbar et al. Jan. 12, 1954 Cupec May 1, 1956

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