US2237936A - Radio antenna - Google Patents

Description

April 1941- A. H. JACKSON 20231936 RADIO ANTENNA Filed July 29, 1939" s Sheets-Sheet 1 .17 fgigl J5 15 L i, 10

a y a -12? INVENTOR Alcrmzderflhckaan April 1941- A. H. JACKSON 2.237.936

RADIO ANTENNA Filed July 29, 1959 3 Sheets-Sheet 2 1.5

Jay. 5.

INVENTOR Alexan darli. Ja (755012 Patented Apr. 8, 1941 UNITED STATES PATENT OFFICE RADIO ANTENNA Application July 29, 1939, Serial No. 287,261

2 Claims.

This invention is for a radio antenna and relates to an antenna structure especially designed for short Wave radiation.

Heretofore open structural steel towers have been used in radio broadcasting as a mast to support radiating wires extending from the tower to an adjoining structure or located between towers. More recently open structural steel towers themselves have been used as vertical radiators. In the former case the tower was purely a mechanical support and in the latter case the tower is an electrical part of the station and its height is correlated to the wave length of the station.

According to the present invention a structural steel tower is used in a somewhat different relation in that it provides a support to secure elevation for a short wave antenna which is carried at the top of it and provides also the necessary reflecting area or capacity relation between the antenna and ground to enable the short wave antenna to operate efficiently when so elevated. The invention is especially important where the radiating system comprises a plurality of separate radiators which are excited in out-of-phase relation to secure a controlled field pattern or beam.

According to the present invention, an open structural steel tower is provided, the height and dimensions of which are determined more or less according to the location of the station, a higher tower being provided in low lands or level country and, as a general rule, a tower of less height being used where the station is on high terrain. The short wave antenna construction, preferably comprising a plurality of correlated short wave radiators, is supported on the top of the tower. In order to provide a uniform horizontal reflecting surface for radiation, my invention contemplates the provision of a large structural metal platform at the top of the tower structure which platform is more or less completely covered with metal to provide an area of large extended surface under the antenna. The tower with its platform thus becomes not only a complete support for the radiators, but provides a reflector for the radiators. The invention enables'short wave radiators to be located at a desired elevation above the ground but still provides adequate refleeting surface immediately below the short wave radiators and at the same time enables a relatively light open framework having a minimum of wind resistance to be used to secure these advantages.

My invention may be more fully understood by reference to the accompanying drawings in which Figure 1 is a side elevation of a tower and antenna construction embodying my invention;

Figure 2 is a detailed view of a typical radiator such as the tower is designed to support;

Figure 3 is a top plan view of the tower as shown in Figure 1 on a slightly larger scale and with the radiators removed;

Figure 4 is a view of the top of the tower with the platform and radiators both removed;

Figure 5 is a view similar to the upper part of Figure 1 showing a modified arrangement wherein the platform is insulated from the tower;

Figure 6 is a view similar to Figure 4 of the arrangement wherein insulators are employed;

Figure '7 is a detailed view showing one of the supporting insulators in the arrangement employed in Figures 5 and 6; and

Figure 8 is a detailed view of the hold-down insulators at the center of the upper part of the tower shown in Figure 5.

Referring to the drawings, 2 designates a rigid open structural steel tower of any suitable design and of such height as may be required to secure the desired elevation of the radiator. The particular open structural steel tower shown in Figure 1 is of a generally pyramidal form which is square in horizontal cross section having four corner supports 3 with diagonal bracing 4 and cross bracing 5. The upper part of the tower comprises four upwardly and outwardly divergent supporting arm portions 6, one of these arms being located on each corner of the tower. As shown in Figure 4, they extend outwardly on the diagonals of the tower so as to provide a maximum spread in proportion to the cross section of the upper part of the tower from which the arms start. The arms in effect constitute outwardly divergent continuations of the corner columns or supports 3. The several arms are tied together by horizontal braces l. Secured to the top of the several arms and joining them together is a framework forming an extended platform of an area considerably larger than the area of the tower and over which a continuous open. metal covering as hereinafter more fully described is secured to provide what is sometimes referred to as a reflector in short wave broadcasting and which is sometimes referred to as a counterpoise. although its function is probably somewhat different from the function of the conventional counterpoise of long wave broadcasting. In the form illustrated this platform comprises a frame 3 secured to the arms 6 and from which the platform is extended. In the illustrated form the platform sets on and is secured to the frame 8 and is preferably formed of intersecting light structural sections. The platform is preferably of circular contour having a peripheral frame In and cross bracing ll. Spread over substantially the entire area of the platform are strips of heavy screening or expanded metal l2. The screening or expanded metal l2 provides a large distributed capacity with relatively little weight and enables rain or snow to pass through it. At one point in the platform is an opening I 3 forming a hatch through which one may climb the ladder in the tower and up one of the leg extensions 6 to gain access to the top of the platform. On the platform are catwalks I l. The catwalks M are covered with relatively heavier grating. They afford access to obstruction lights [5 on the top of the platform and also enable one to walk about the central portion of the platform to have access to the antennae.

The platform 9 provides the support for the radiating antenna. The antenna may comprise a supporting post It having a plurality, preferably four, radiating elements I I carried thereon in such manner that each is electrically separate from the other. The post I 6 passes between supporting beams !8 on the platform 9 and the post extends down between plates I carried on the beams 13 shown in Figure 1. The lower end of the post It is provided with a flanged terminal Ell and guy rods 2| extend from the flanged terminal .20 to the top frame 8 to support the post. Additional guy rods 2| connected to the frame 8 and to member 22 further support the antenna structure.

The antenna structure may be of any suitable or preferred construction, the particular construction illustrated being a construction designed for and currently used by the Civil Aeronautics Authority of the Department of Commerce and forms no part of the present invention per se. It is illustrated merely for the purpose of enabling my invention to be more fully understood. In this form of antenna, the post I6 is hollow metal tubing having radial arms I6. At the outer end of each arm I6 is an enlargement [Ba and this enlargement carries upper and lower insulator assemblies I1. Passing through the insulator assemblies is a metal conductor constituting the antenna I1. tal conductor I la passes through the tubular arm I6 and conduits, not shown, lead down through the post it to a system of antenna leads, not shown.

The radiators H for short wave broadcasting I are only a few feet long. They ordinarily extend an equal distance above and below the horizontal arm on which they are carried. In the particular installation illustrated in the drawings, the radiating element I! would be in the neighborhood of approximately 12'. This is referred to not by way of limitation, but as showing the relative length of the radiating elements in proportion to the other parts of the installation. The lower ends of the'radiating elements terminate, of course, above the top of the platform 9 so that there is a very appreciable clearance space between the lower ends of these radiating elements and the platform. In the particular installation shown, there are four of the radiators ll equidistantly spaced. As will be understood by those skilled in the art, the several radiators are excited in a manner to produce a directional pattern. The platform 9 has a relatively large area as compared with the maximum A horizondistance between any two of the radiating elements I! so as to secure effective and directionally controlled radiation. The platform 9 preferably extends over an area considerably greater than the area of the base of the supporting tower and of course considerably greater than the area of the upper portion of the tower. By providing four upwardly extending arms which also extend outwardly from each corner of the tower, the mechanical problem of supporting so large a platform is taken care of. The antenna itself is supported in the platform without any special relation to the columns or legs of the tower. While the antenna structure in the particular form illustrated is shown in the exact center of the tower, the platform enables the antenna to be otherwise located or enables a plurality of independently supported radiating elements to be provided at different points over the area of the platform. By having the platform at the extreme top of the tower, so that the tower is flat and free of any part of the tower projecting through it, the field pattern of the radiating system may be accurately established.

Under some circumstances it is desirable to have the platform insulated from the tower. Where this is necessary, an arrangement such as that illustrated in Figures 5 to 8 inclusive may be provided. In the arrangement shown in these figures, the general arrangement is the same as previously described, there being a frame 8 formed of structural channels joined to the top of the four arms 6. At each corner of this square frame is a supporting insulator assembly which assembly as shown in Figure 7 comprises an insulator body 26 set in a cup 21, the cup 21 being secured to the frame 8. At the top of the insulator is a cap 28 having a projecting stud 29 thereon that passes through a perforated plate 30. The plate 30 is secured to the under side of a structural frame 8' which in turn is secured to the platform 9, the platform being similar to that previously described. Cooperating with the supporting insulator assembly at each corner of the top of the tower is a central hold-down insulator assembly. This hold-down insulator assembly, generally designated in Figure 5 by the reference numeral 3!, comprises a body of insulating material 32 having a metal cap 33 at the top thereof. A bolt 34 passes through the cap 33 and down through the insulator 32 and is secured at 35 to the tower structure. Around the base of the insulator 32 is a collar 36 having a plurality of sockets 31 into which are screwed tie rods 38. The upper ends of the tie rods pass through the supporting frame 8, as shown in Figure 8. The several corner insulator assemblied 25 serve to support the platform on top of the tower in insulated relation to the tower while the holddown insulator assembly 3! provides a means for tying the platform to the top of the tower but in non-conducting relation to the tower. The hold-down insulator assembly is in tension while the insulating element 32 thereof is in compression. The arrangement thus enables the necessary tension to be exerted to hold the platform down while the insulating body itself transmits a compressive load.

The modification illustrated in Figures 5 to 8, except for the fact of the platform being insulated from the tower, is generally the same as the form illustrated in Figure 1. By having the platform insulated from the top of the tower, the platform may, in operation, be at a potential'difference to both the radiator and the ground and provide an ungrounded as distinguished from a grounded counterpoise, or it may be grounded independently of the tower should it for any reason be desirable to have the counterpoise at ground potential and the supporting tower at a potential other than ground potential.

While I have illustrated and described certain specific embodiments of my invention, it will be understood that this is by way of illustration and that various changes and modifications may be made in the type of tower used and. in various other respects within the contemplation of my invention and within the scope of the following claims.

I claim:

1. An antenna structure for use in wireless transmission of signals comprising an open structural metal tower of generally pyramidal form having corner supports and diagonal and transverse bracing, upwardly and outwardly extending supporting arms at the top of the pyramidal tower forming offset extensions of the top of the tower, a structural metal frame at the top of said extensions, supporting insulators on said frame, a platform resting on said supporting insulators, a hold-down insulator connected with the frame and with the tower structure and a transverse radiator mounted on and carried by the platform.

2. Apparatus for use in short-wave broadcasting by means of which the effective horizon of the antenna is increased and the effect of local ground conditions is minimized, comprising an open structural load-carrying supporting tower, a structural metal platform at the top of the tower, the over-all area of which is substantially greater than the over-all transverse cross-sectional area of the structure of the tower at any point in its height and which overhangs the base of the tower in every direction, an open mesh conducting screen at the top of the platform secured thereto and forming a substantially plane reflecting surface for radio waves, the platform having intersecting structural members to sustain the screen and provide substantially continuous support therefor, and a short-wave antenna supported by the tower entirely, above the reflector and electrically insulated from the tower and the reflector.

ALEXANDER. H. JACKSON.

DISCLAIMER 2,237,936.-Alewander H. J aalcson, Pittsburgh, Pa. RADIO ANTENNA. Patent dated April 8, 1941. Disclaimer filed September 22, 1941, by the assignee, Blaw- Zfnom 0ompamy. Hereby enters this disclaimer as to claim 2 of said Letters Patent.

[Oficz'wl Gazette October 28, 1 941.]

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