US3394377A - Slot antenna mounted within openwork support tower - Google Patents

Description

July 23, 1968 A. ALFORD 3,394,377

SLOT ANTENNA MOUNTED WITHIN OPENWORK SUPPORT TOWER Filed March 30, 1965 FIG! INVENTOR ANDREW ALFORD ATTORNEYS United States Patent 3,394,377 SLOT ANTENNA MOUNTED WITHIN OPENWORK SUPPORT TGWER Andrew Alford, Winchester, Mass. (299 Atlantic Ave., Boston, Mass. 02110) Filed Mar. 30, 1965, Ser. No. 443,907 5 Claims. (Cl. 343767) ABSTRACT OF THE DISCLOSURE The present invention relates in general to electromagnetic energy transduction and more particularly concerns a novel slotted cylinder mounted within a triangular tower and coacting with the tower to form a mechanically rugged compact radiating system having substantially omnidirectional radiation characteristics in the horizontal plane. The invention is especially useful in connection with radiating UHF television signals at great heights and coacting with a number of similarly mounted slotted cylinders appropriately fed to form a high gain radiation system etficiently directing energy toward the desired listening area from a mechanically rugged structure capable of withstanding severe weather conditions.

The transmission range of UHF television signals is normally limited to approximately line of sight. Accordingly, range is maximized by locating the transmitting antenna as high as practical while efiiciently illuminating the desired listening area with sufficient energy. Since the attenuation of UHF energy a8 a function of distance from the radiator is greater than that of VHF energy, achieving a given quality of television reception over a given area requires more effective radiated power at UHF than is required at VHF. Since raising the actual transmitter power is costly and limited by practical considerations, raising effective radiated power to desired levels at UHF is advantageously accomplished by using high gain antennas. Although high gain may be achieved by using multi-element antennas, serious mechanical problems are introduced when it is desired to support a heavy multi-element antenna at the great heights normally desired for satisfactory television coverage.

The nature of the problem will be better appreciated when it is recognized that stacking twelve or more elements over a twelve or more wavelength height at the top of a mast may be required to obtain the desired gain. Such a mast sufficient to support the multi-element load would have dimensions large enough to interfere with the radiation characteristics of the radiating elements.

Accordingly, it is an important object of this invention to provide UHF electromagnetic transduction means that is mechanically rugged and may comprise a large number of individual stacked radiating elements to achieve high gain in a rugged mechanical assembly at great heights.

It is another object of the invention to achieve the preceding object with a relatively compact structure eX- hibiting substantially omnidirectional radiation characteristics in the horizontal plane.

According to the invention, a slotted cylindrical radiating element is situated within a skeletal triangular tower much nearer to one of the three supporting posts than the others with the slot facing away from the said one supporting post so that the slotted cylindrical radiator coacts with the tower to provide a radiation pattern that is essentially omnidirectional in the 'horizontal plane;

Numerous other features, objects and advantages of the invention will become apparent from the following specification when read in connection with the acc0mpanying drawing in which:

FIG. 1 is a perspective view of a slotted cylinder in a triangular tower section embodying the principles of the invention; and

FIG. 2 is a graphical representation of the omnidirectional radiation characteristic of the embodiment of FIG. 1 when dimensioned for operation at 1000- megacycles.

With reference now to the drawing and more particularly to FIG. 1 thereof, there is shown a perspective view of an embodiment of the invention. Only a single section of a tower of triangular cross section is shown so as not to obscure the principles of the invention. A complete tower comprises a number of such sections cascaded which sections are essentially similar. Thus, a typical triangular tower section will include vertical poles 11, 12 and 13 joined together by upper horizontal bars 14, 15 and -16 by lower horizontal bars 17, 18 and 19 and by cross struts 21, 22 and 23. A ladder 24 is mounted adjacent to vertical pole 12 to provide access for servicing a radiating element. The slotted cylindrical radiator 25 is supported closely adjacent to pole 11 with its vertical slot 26 (FIG. 2) facing away from vertical .pole 11 and including the plane that perpendicularly bisects horizontal bars 15 and 18. Antenna 25 is shown fed at the bottom by a coaxial transmission line 27. The slotted cylindrical radiator is preferably of the type disclosed in Alford US. Patent No. 2,611,867.

When a number of radiating elements are stacked and fed by an appropriate arrangement of coaxial cables, it is preferred that the coaxial cables rise vertically closely adjacent to the vertical pole furthest from the radiating element 25 and the ladder 24. For a structure comprising a stacked array of sections like that shown in FIG. 1 this vertical pole would be pole 13. It is also preferred that the specific feeder to the bottom of a radiating element be dressed closely along a horizontal strut to the element feedpoint from the vertical pole, typically along strut 19 from vertical pole 13.

A large number of like slotted cylinders may be located one above the other at the top of the radiating tower at two wavelength intervals to provide increased gain. By appropriately controlling the relative phase of energy applied to the different elements, the vertical directivity of an array of elements may be control-led in accordance with known principles. The radiating structure thus formed is characterized by high radiation efiiciency, desired directivity, high gain and mechanical ruggedness. By locating the antenna within the triangular tower severe stresses caused by heavy wind loading are relatively loW and deicing or other weather protective apparatus may be conveniently added to the slotted cylindrical radiator without detracting from the desired mechanical or electrical characteristics of the apparatus. Still another feature of the invention resides in the convenient and relatively safe access for servicing, for practical towers may be made which permit service personnel to function from the inside of the tower supported by temporary platforms which may be laid on the struts.

Referring to FIG. 2, there is shown the radiation pattern in the horizontal plnae of the structure illustrated in FIG. 1 with the diameter of the vertical poles 11, 12 and 13 1% inches, with the separation between adjacent vertical poles 22 /2 inches, with the separation between slotted cylindrical antenna 25 and vertical pole 11 1.46 inches, and with slotted cylinder 25 having a slot a little less than two wavelengths long, about 4 wavelength 3 wide and the cylinder diameter being about wavelength e M. a H

The specific embodiment described herein is by way of example only. It is evident that those skilled in the art may now make numerous modifications of and departures from the specific embodiment described herein without departing from the inventive concepts. Consequently, the invention is to be construed as limited solely by the spirit and scope of the appended claims.

What is claimed is: 1. Electromagnetic transduction apparatus comprising, means defining a supporting tower of triangular cross section comprising three vertical conducting membersat the vertices of the triangular cross section interconnected and supported by supporting links, conducting means defining only a single verticalradiating slot in any one horizontal plane, means for supporting said conducting means with said slot generally parallel to and inside of said vertical members and much closer to one of said members than the others with said vertical slot separated from said one member by an electrically opaque portion of said conducting means, said conducting means coacting with said supporting tower to provide a radiation characteristic in the horizontal plane that is substantially omnidirectional. 2. Electromagnetic transduction apparatus in accordance with claim 1 wherein said conducting means defining a vertical radiating slot comprises means defining a conducting cylindrical surface formed with vertical radiating slot embracing the plane perpendicularly bisecting a first side plane between said others of said members and passing through said one member,

a portion of said conducting cylindrical surface being between said slot and said one member.

3. Electromagnetic transduction apparatus in accordance with claim 2 wherein said supporting tower is of equilateral triangular cross section.

4. Electromagnetic transduction apparatus in accordance with claim 3 wherein said supporting tower comprises three upper horizontal links, three lower horizontal links and three diagonal links with each diagonal link extending diagonally upward from near the junction of a respective lower horizontal link with a respective vertical member near the junction of a respective upper horizontal link with a vertical member adjacent to said respective vertical member.

5. Electromagnetic transduction apparatus in accordance with claim 4 and further comprising,

a ladder section immediately adjacent to a ladder-adjacent one of said vertical members adjacent to said one vertical member which ladder is parallel to the plane joining said ladder-adjacent one of said vertical members and said one vertical member.

References Cited UNITED STATES PATENTS 2,611,867 9/1952 Alford 343770 2,771,606 11/ 1956 Kandoian 343890 3,254,343 5/1966 Laub et a1 343890 FOREIGN PATENTS 832,564 4/1960 Great Britain. 1,122,510 5/1956 France.

ELI LIEBERMAN, Primary Examiner.

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