US2688082A - Antenna system - Google Patents

Description

W. DARLING ANTENNA SYSTEM Aug. 31, 1954 Filed June 8, 1953 TTOR NE Y Patenteol Aug. 31, 1954 ANTENNA SYSTEM Woodrow Darling, Merchantville, N. J., assigner to Radio Corporation of America, a corporation of Delaware Application June 8, 1953, Serial No. 360,254

Claims.

This invention relates to antenna arrays, and particularly to antenna arrays especially suitable for broadcasting broadband signals, such as television picture and sound signal transmission.

A tower type of construction for such antenna arrays offers numerous important advantages. These towers usually consist of three or four corner legs and suitable bracing members for added rigidity. Some of the advantages of this type of construction are: (l) stability under high wind velocities is obtained; (2) transmission lines and junction boxes for the transmission line network to feed the antenna elements may be located inside of the tower, and (3) the vertical aperture of the antenna may be increased by simply making the tower high and providing and feeding more layers of radiators, with the concomitant result that the vertical beam width is narrowed and a greater proportion of the energy is radiated in the direction where it is most useful.

The structure required to support an antenna having the required gain can be made to support other radiating systems at only a slight additional cost. The tower type of construction lends itself to multiple uses, such as an amplitude modulation (AM) radiator and to support antennas for frequency modulation (FM) and other television (TV) stations. The use of a single tower by two or more TV stations is especially desirable because all receiving antennas are automatically oriented in the right direction for all channels so used. The advantages of multiple usage in many installations oifset the inherent expensiveness of such structures.

The interior of the tower can be made available for access to the antennas. Thus,one antenna can be serviced or repaired without inconvenience to the schedules of other stations using the same tower. The interior of the tower allows more room for multiplicity of feed lines and connections required in the use of a great number of radiators.

An object of this invention is to provide a novel television broadcast antenna system having improved horizontal pattern characteristics.

Another object of the invention is to provide an improved tower supported antenna array which is especially adapted to be excited in phase rotational fashion, also termed turnstile feeding.

A further object of the invention is to provide an antenna system which permits two different radio frequency signals to be broadcast simultaneously from the same aperture, while at the same time attaining an extremely high order of decoupling between the radio frequency sources.

Briefly, in accordance with this invention, there is provided a tower supported antenna array including yconductive surface elements or screens mounted around a supporting tower and forming a rectangle or square in cross-section. The antenna elements are half wavelength dipoles mounted out from the corners of the rectangle formed by the conductive surface elements, with each dipole element parallel to one of the conductive surface elements and different dipole elements parallel .to different conductive surface elements. The conductive surface elements or screens are either electrically connected to the tower or to each other, or both, at the vertical edges thereof.

The antenna array of this invention is especially adapted to be fed in phase rotational fashion, and the resulting horizontal pattern circularity is held within Very narrow limits of variation. However, should it be desirable to use a directional pattern in the horizontal plane and phase rotational feeding, the antenna of this invention can be employed with many benefits.

An outstanding advantage of the antenna of this invention is that two separate sources ofradio frequency energy can utilize the same antenna aperture. The desirability of such an arrangement can be appreciated by noting that often an additional broadcasting service can be added to an existing antenna tower. In other words, two diierent television broadcasting signals can be simultaneously broadcast from the same portion of a tower previously used for only one broadcasting service. Further, should the broadcaster of television programs desire to use separate antennas for the video signal and the accompanying sound transmission, this invention allows two sets of antennas broadcasting these two different signals to utilize a single aperture on one tower structure. As well as obtaining double use of the same aperture, the antenna system of this invention provides a very large amount of decoupling between the two separate radiating systems.

A more detailed description follows in conjunction with theaccompanying drawing, in which:

Figure l is a top plan view of one layer of an omnidirectional antenna array according .to the invention;

Figure 2 is a side elevation of a portion of a representative array in accordance with ,the invention; and

Figure 3 is a cross-sectional plan view of .an-

other layer of an antenna array taken along the line 3-3 of Figure 2.

Referring to Figure 1, there is shown a top plan view of a tower mounted antenna system according to this invention. A tower II is shown of square cross-section a-nd is preferably straight sided for the portion of its length occupied by the antenna system. Although not shown on the drawing, the interior of tower can be used for access to the antenna for servicing purposes, and would be provided with hardware for mounting the necessary transmission line. The tower II may be used also as a low frequency radiator (for example, for amplitude modulated broadcasting) or solely as a support for one or more very-high frequency antenna systems such as that of this invention.

Arranged around the periphery of the tower II are conductive surface elements I5. These elements I5 may be constructed of thin sheet metal or other conductive material, but from a practical standpoint are constituted by a plurality of conductors forming a network, grid, or screen approximating a sheet reflector surface. The spacing between conductors in such screening should be less than 005k, preferably no more than 0.03 at the operating frequency. 'I'he screens forming the conductive surface elements l5 could be effected by welding conductors directly to the tower Il; but to make the screens I5 more flexible in application to different tower structures, they are preferably made separate and self-supporting.

The conductive screens I5 are preferably between 0.4 and 0.6K in width. For one application of the invention, the conductive screens I5 may be discontinuous between adjacent layers of the antenna array, while for another embodiment to be described below, the screens I5 would extend throughout the entire length occupied by the antenna array. The width of the screens I5 thus varies for about 9 ft. for channel 2 to about 21/2 ft. for channels ll, 12 and 13 for veryhigh frequency television broadcasting. The screens I5 are used to keep radiation out of the tower and thus prevent changes in the impedance due to coupling of antenna elements with objects inside the tower; hence, if only one element were used on the tower, the tower would be screened on all sides.

Dipole antenna elements 2|, 22 are mounted on supports 23, 24 out from the corners of the tower II, and both elements 2|, 22 together are a half wavelength long electrically. The supports 23, 24 space the electrical centers of the half wave dipoles 2l, 22 a distance between 0.2 and 0.3K from the corners of the tower and form angles of substantially 135 with respect to the planes of the conductive screens I5.

Although the dipoles 2| and 22 are shown as being linear rods, for broadband operation such as is encountered in television picture transmission, it is preferable to use a dipole structure employing a plurality of conductors in pyramid configuration or several conductors extending outwardly from the electrical center of the dipoles fanned apart at the ends, or other known broadband element structures.

Electrical excitation of the dipole elements is accomplished by using equal length feed lines joining oppositely positioned pairs of dipoles (for example, 2Ic, 22a and 2Ic, 22e) to common junction boxes.

Referring to the dipole elements 2Ia, 22a, a coaxial transmission line 33 is led through one of the support members, shown here as member 24a, and the metallic sheath conductor of line 33 is connected to one dipole element 22a, while the inner conductor of the coaxial line 33 is connected to the other dipole element 2Ia. Both connections are made at the adjacent ends of the dipole elements 2Ic, 22a where they are mounted on the support members 23a, 24a. The dipole elements associated with the opposite phase, that is, dipole elements 2Ic, 22e in Figure 1, are connected through a coaxial transmission line 34 to a source of voltage of the same phase as that supplied to the last transmission line 33. However, these last dipole elements 2Ic, 22c are connected in reverse sense, that is, the coaxial transmission line 34 is led through the supporting member 23e, and the metallic sheath conductor of line 34 is connected to the dipole element 2Ic, while the inner conductor of the transmission line 34 is connected to the other element 22e. On the other two corners of the tower I I, the two sets of dipole elements 2 Ib, 22h and 2Id, 22d are respectively connected in opposite sense through coaxial transmission lines 35, 36 to another source of voltage which is displaced in time phase by from that to which the rst two sets of dipole elements 2Ic, 22a and 2Ic, 22e were connected.

The dipoles 2l, 22 on one pair of oppositely disposed corners (for example, those identified with the letter suixes a and c) are excited from one source of voltage, and the dipoles on the other two oppositely disposed corners (for example, those identified with the letter suffixes b and d) are excited by another source of voltage which is displaced 90 in time phase relative to the first source of voltage. These two sets of voltages produce currents in the dipole elements which induce radio frequency radiation fields, and these elds combine to produce apparent rotation of the total eld from all of the antenna elements at radio carrier frequency. This type of feed is termed phase rotational, progressive phasing or turnstile feed.

In regard to Figure l, it should be noted that if the feed cables for any opposite pair of dipole arms are interchanged; for example if the feed cable 33, 34 is reversed in its connection to the dipole arms 2Ic, 22a, 2Ic and 22a, then the phases of the two sources of radio frequency carrier indicated at the angles 0 and -90 must be interchanged.

Referring now to Figure 2, there is shown an elevation of an antenna array in accordance with this invention wherein two different sets of antenna elements are used in the same array aperture. One set of the antenna elements which would be coupled to a single source of radio frequency excitation will be arranged like those shown in Figure 1, while interspersed in alternate layers, a second set of dierently positioned antenna elements occupying the same aperture is coupled to a different source of radio frequency energy.

Referring to Figure 3, as well as to Figure 2, Figure 3 shows a top plan view of one layer of elements 2l', 22 along the line 3-3 of Figure 2 designated as layer III on the drawing. Layers I, III and V are, of course, identical and like the arrangement of Figure 3, while the alternate layers H, IV, etc., will be like the arrangement shown in Figure 1.

In the connections shown in Figure 3, the dlpole elements 2 I', 22 of each corner are disposed in a vertical plane which makes an angle of 90 with respect to the dipoles of a next adjacent layer up or dow-n (layer II or IV). Due to the connection of the transmission lines, the apparent rotation of the field in the arrangement shown in Figure 3 will be the reverse ofA that shown for the connection of lines and dipole elements of Figure l. One source of radio frequency energy is coupled to the odd numbered layers; that is, layers I, III, V, etc., wherein the positioning of the dipole elements 2l', 22 and their connection to the transmission lines 33', 34', 35 and 36 will be like that shown in Figure 3. The other source of radio frequency energy is coupled to the even numbered layers II, IV, etc., wherein the positioning and connection of the elements 2l, 22 and their associated transmission lines 33, 3d, 35 and 36 is like that shown in Figure l.

The spacing between adjacent layers coupled to the same radio frequency source is preferably made between 0.7 and 0.9i at the operating frequency to most efficiently utilize the vertical aperture occupied by the antenna array and to reduce radiation along the lengthwise axis of the tower l l.

Because of the opposite rotational sense of the two radiated fields, the voltages which the Figure l system induces in the layer of Figure 3 cancel at the final junction point. This has the effect of providing a very large amount of decoupling between the two interspersed radiating systems. Also, the fact that the most closely adjacent radiators of the two separate radiating systems are disposed in space quadrature and are at a null point in the pattern characteristic of the individual element of the other system further augments this decoupling.

When two sets of radiators are used in the same aperture, the screens l5 on the several sides of the tower extend throughout the entire length occupied by the array. If, however, the array is to be used for radiating energy from one source only in a given aperture, only alternate layers (for example, layers II, IV, etc., of Figure 2) would be employed and the screens l5 in each layer on the several sides of the tower need have a height of the order of only S/gx at the operating frequency with their centers at the center of the associated layer of radiating elements 2l, 22. In such an arrangement, there may be an interval between the screens of adjacent layers.

The antenna array of this invention may be used with feeding arrangements which achieve a specially shaped vertical pattern characteristic wherein the elements in one layer associated with the same radio frequency source are phased differently from those in another layer connected to the same source or wherein the elements in different layers are fed with different amounts of radio frequency energy.

What is claimed is:

l. An antenna system including a supporting tower structure, conductive surface elements having a width of substantially a half wavelength at the desired operating frequency, said conductive surface elements being mounted about said tower structure and forming a square at any transverse cross-section, a dipole element supported out from a corner of said square at a distance lying between 0.2 and 0.3i at the operating frequency, said dipole element having its arms parallel to the plane of one of said conductive surface elements, and means to couple a radio frequency transmission line' tolsaid dipole element.

2. An antenna system including a supporting tower `structure, conductive surface elements having a width of substantially ahalf wavelength at the desired operating frequency, said' -conductive surface elements being mounted about said tower structure and forming a square at any transverse cross-section, fou-r dipole elements arranged in a layer, each of said dipoles being supported out from the cornersof said square with their electrical centers ata distance lying between 0.2 and 0.3i at the operating frequency on the bisector of the angle between two of vsaid conductive surface elements, said dipole elements on each corner having their arms parallel to an adjacent conductive surface element, Withfadjacent dipole elementsv in said layer at right angles to each other and oppositelydisposed dipole elements in said layer parallel to each other.

3. An antenna system including a supporting tower structure, conductive surface elements having a width substantially a half wavelength at the desired operating frequency, said conductive surface elements being mounted about said tower structure and forming a square at any transverse cross-section, four dipole elements arranged in a layer, each of said dipoles being supported out from the corners of said square with their electrical centers at a distance lying between 0.2 and 0.3K at the operating frequency on the bisector of the angle between two of said conductive elements, said dipole elements on each corner having their arms parallel to an adjacent conductive surface element and means to couple radio frequency transmission lines to said elements to excite said dipole elements in phase progression.

4. An antenna system including a supporting tower structure, conductive surface elements having a width of substantially a half Wavelength mounted about the circumference of said tower structure to enclose the same, and forming a square at any cross-section, said surface elements extending throughout the entire length occupied by said antenna system, a first set of radiating elements arranged in layers and spaced center-to-center by a distance lying between 0.7 and 0.9i at the operating frequency, said first set of radiating elements comprising dipoles mounted out from the corners of said conductive surface elements a distance of 0.2 to 0.3% on the bisector of the angle between two of said conductive surface elements, said dipole elements on each corner being parallel to an adjacent conductive surface element and perpendicular to dipole elements on adjacent corners, a second set of radiating elements also arranged in layers but interspersed with the layers of said rst set of radiating elements and spaced center-to-center by a distance lying between 0.7 and 0.9 at the operating frequency, said second set of radiating elements comprising dipoles mounted out from the corners of said conductive surface elements a distance of 0.2 to 0.3i on the bisector of the angle between two of said conductive surface elements, said dipole elements on each corner lying in a vertical plane which is perpendicular to the dipoles in the next adjacent layer in a vertical direction.

5. An antenna system including a supporting tower structure, conductive surface elements having a Width of substantially a half wavelength mounted about the circumference of said tower structure to enclose the same and forming a square at any cross-section, said surface elements extending throughout the entire length occupied by said antenna system, a first set of radiating elements arranged in layers and spaced center-to-center by a distance lying between 0.7 and 0.9K at the operating frequency, said first set of radiating elements comprising dipoles mounted out from the corners of said conductive surface elements a distance of 0.2 to 0.3i on the bisector of the angle between two of said conductive surface elements, said dipole elements on each corner being parallel to an adjacent conductive surface element and perpendicular to dipole elements on adjacent corners, a second set of radiating elements also arranged in layers but interspersed with the layers of said first set of radiating elements and spaced center-to-center by a distance lying between 0.7 and 0.9i at the operating frequency, said second set of radiating elements comprising dipoles mounted out from the corners of said conductive surface elements a distance of 0.2 to 0.3i on the bisector of the angle between two of said conductive surface elements, said dipole elements on each corner lying in a vertical plane which is perpendicular to the dipoles in the next adjacent layer in a Vertical direction, and means to couple radio frequency transmission lines to the rst set of elements to excite said elements in a predetermined phase progression, and further means to couple separate radio frequency transmission lines to`said second set of elements to excite said second set of elements in phase progression opposite to that of said first set of elements.

No references cited.

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