Log periodic rotating antenna

BACKGROUND OF THE INVENTION

This invention pertains to an antenna system support structure, particularly useful as a rotating log periodic antenna.“°

Log periodic antennas are generally characterized by a number of substantially parallel dipole radiating elements each respectively having a length, and being disposed at spacings, defined by a given relationship from one to the ₂next. Characteristically, these radiating elements have ° consisted of long, hollow, tubular members which are cantilevered to extend out from a common “spine” or support boom. Thus, such an array becomes quite ponderous as the radiating elements become longer and longer, θθ

Heretofore, antenna systems, and particularly rotating antenna systems, have been handicapped by their structural configurations whereby their weight, bulk, and awkwardness serve to handicap their employment. In directional antenna systems to be rotated to a desired _3gazimuth, the radiating array structure should be as little subject to weather conditions, such as icing, high winds, or both, whereby it can remain directionally oriented without undue strain on the structure.

Inasmuch as the spacing between the dipole radiating 40 elements will be dictated by the radiating array, in many instances, such as where the spacing is a logarithmic function, the spacing between each adjacent pair of elements will not be the same as between other adjacent pairs of radiating elements. Further, it is necessary, for electrical 43 reasons, to ensure that structure adjacent to the radiating elements be placed clear of adjacent support structure so as not to create undue interference with such structure.

In the past this requirement has necessitated additional expense in the fabrication of the support boom structures. 50

SUMMARY OF THE INVENTION AND OBIECTS

According to the present invention, the array supporting structure serves to space the radiating array above the plane of the support boom structure so as to mini- 55 mize certain of the foregoing and other problems heretofore experienced and to permit a simplified boom construction to be utilized.

In addition, according to the invention, the array supporting system serves to permit a substantial reduction in θθ the projected area of the booms so as to minimize the effects of wind. The radiating array participates as a part of the support system to ease the load otherwise acting upon the cantilevered outer ends of the booms whereby the bulk and mass of the booms may be reduced. 33

Accordingly, it is a general object of the invention to provide an improved antenna system.

Another object of the invention is to provide an improved antenna system characterized by a radiating array supported above the plane of the support booms so 70 as to minimize electrical and mechanical interference therebetween, and organized in a manner serving to ac2 complish the above and other objects as will become more clearly apparent from the following description, considered in conjunction with the drawing.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a perspective view showing the upper portion of a support tower and radiating array supported according to the invention.

FIGS. 2 and 3 are respectively enlarged detailed sections taken along the lines 2—2 and 3—3 of FIG. 1.

FIG. 4 is a side elevation view of the structure shown in FIG. 1.

FIG. 5 is an enlarged detailed perspective view showing the portion designated by the line 5—5 of FIG. 4.

FIG. 6 is an enlarged detailed view taken along the line 6—6 of FIG. 4.

FIG. 7 is an enlarged side elevation view taken in the zone bounded by the line 7—7 of FIG. 4.

FIG. 8 is a plan view of FIG. 4 viewed from above.

FIG. 9 is an enlarged detailed view in the zone bounded by the line 9—9 of FIG. 8.

FIG. 10 shows an enlarged plan view, viewed from above, taken along the line 10—10' of FIG. 7.

FIG. 11 is an enlarged perspective view of the detail as shown in the region bounded by line 11—11 of FIG. 1.

FIG. 12 is an enlarged perspective view showing the detail for connection being made between radiator elements and feed lines.

FIG. 13 is an enlarged detailed perspective view showing the manner of spacing feed lines from the boom structure and from support bridles as shown in the region 13—13 of FIG. 4.

FIG. 14 is a plan view of a portion of one of the support booms.

FIG. 15 is an enlarged detailed view of the portion bounded by line 15—15 of FIG. 14.

FIG. 16 is a transverse section view taken along the line 16—16 of FIG. 15.

FIG. 17 shows a diagram for explanation of forces acting upon a support boom structure, according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

In general, as will be described in more detail further below, there has been provided an antenna system to be carried atop a support tower and which is provided with a radiating array configuration of spaced flexible radiating elements. The array supporting construction is characterized as having a periphery configuration on the order of but not substantially greater than the periphery of the array configuration, and the array supporting construction serves to support the plan of the radiating array in a spaced relation above the support structure.

Thus, each of the booms is inclined upwardly so that the applied compressive forces from the load of the array are directed longitudinally along each boom toward a common axis of rotation. The load of the array also applies an upwardly acting component or moment of force to the cantilevered unsupported outer ends of the booms so as to counteract the bending stresses which are otherwise acting downwardly upon these portions of the booms. In this manner, bending stresses in the booms are relieved.

It is within the further contemplation of the invention herein that the three longitudinally extending boom-forming elements are characterized by triangular cross-section defined by a plurality of boom-forming elements. The booms are oriented whereby the base of the triangular cross-section appears at the top of the boom, while the apex of the triangular cross-section is disposed at the bot3,553,701 tom of the boom. In this manner, greater strength of boom structure is obtained and the bulk of the boom may be reduced so as to aid in minimizing the effects of wind acting upon the antenna system.

Referring in greater detail to the construction, there is shown in FIG. 1 an antenna system including generally a support tower assembly 11, including the usual guy wires 12 secured thereto, and a rotatably disposed antenna assembly 13. Antenna assembly 13 comprises both the radiating array 14 and the array supporting assembly 16.

In general, as will be understood by those skilled in antenna systems, the radiating elements 17 function as dipoles fed by feed lines 18 which are, in turn, electrically coupled to return lines 19 returning along the central boom 21 and ultimately downwardly along the axis of rotation of antenna assembly 13 to a balun (not shown).

In an antenna system of the type described, it is important that the support structure not interfere, either electrically or mechanically, with the radiating array while holding the array in transmitting position.

Accordingly, each of three support booms 21, 22, 23 has been angled slightly upwardly at an angle, on the order of 1.4° to the horizontal and from booms 21-23 array 14 is supported out of the plane of the booms as now to be described.

Atop support tower 11 means have been provided to collect and support the root portions of each of the three booms 21-23 in a rotatable mounting arrangement whereby the overturning moment to be experienced by the mounting bearing assembly has been minimized for improved functioning of the bearing and rotatable drive, and for the additional advantage of foreshortening support tower 11.

Thus, as best shown in FIGS. 7 and 10, at the top of the main portion of support tower 11, a bearing assembly 24 supports a mounting cage 26 for receiving and supporting the root portion of each of booms 21-23.

As arranged herein, these root portions of booms 21-23 are carried substantially contiguous to the bearing assembly 24 whereby the overturning moment experienced by bearing assembly 24 will be minimal. Bearing assembly 24 includes base plate 27 secured to the upper ends of a number of cross braces 28. Base plate 27 carries the stationary race 29 of a ball bearing assembly which further includes a rotatable race 31. Race 31 is subdivided into a relatively smooth upper portion and a lower portion which has been provided with drive teeth 32 which serve to engage the pinion 33 of a drive motor 34. As thus arranged, motor 34 can readily rotate the outer race 31 with respect to stationary race 29 and, by means now to be described, rotate the array supporting assembly 16 (FIG. 1).

Thus, the two portions of rotatable race 31 are joined by means of bolts 36 which serve to clamp a mounting ring 37 tightly to an annular protective skirt 38 which covers, and protects from the elements, the entire bearing assembly 24.

Mounting ring 37, in turn, supports three lower rail stubs 39 of a cross-section configuration adapted to receive and be bolted to the lower rails 41 of each of booms 21-23. In addition, mounting ring 37 carries the cage-like support structure consisting of cross braces 42 which are joined at their upper ends in mutual support to a triangularly shaped frame 43, each element of which is of a box construction or square tube construction to provide considerable strength thereto. Frame 43 carries upper rail stubs 44 secured thereto, as by welding, for example, which serve to receive the two upper rails 46 of each of booms 21-23. Accordingly, it will be readily apparent that each boom 21-23 includes three longitudinally extending boom-forming elements, such as the rails 41, 46, arranged to provide a triangular cross-section disposed in a manner to orient the base of the triangle at the top of the boom and the apex at the bottom so as to increase the strength of each boom without increasing the mass or size of same. Rails 41, 46 are spaced apart by means of the boom braces 47 uniformly angled back and forth between the rails along the length of each boom 21-23. Thus, the manufacture of the booms can be accomplished in conventional style, and by virtue of elevating the radiating array above the array supporting booms, the manufacture of these booms 21-23 can be accomplished without consideration as to whether or not the radiating elements 17 may be mechanically or electrically interfered with by the structure of the boom due to the fact that the spacing between elements 17 is based upon a logarithmic relationship, whereas the spacing between boom braces 47 is maintained at a uniform constant relationship.

In copending application Ser. No. 648,475 of William L. Werner for a “Log Periodic Rotating Antenna,” which is assigned to the assignee herein, a rotatable log periodic antenna array has been disclosed wherein the radiating elements each comprise a pair of wire portions to be supported at their outer ends to diverge at a relatively narrow angle from each other. The radiating elements are supported by a cable coupled to support each of the wire portions. The main supporting cable is disposed between the ends of the radiating elements to provide the major support for the radiating elements. The outer ends of the radiating elements are additionally supported variously by another cable or other means as disclosed therein.

By means now to be described, the entire load of the radiating elements can be supported from their tip ends by a single cable 48.

Thus, each of booms 21-23 angles slightly upwardly relative to the horizontal and extends radially outwardly from the axis of rotation of array 14. For example, as noted in FIG. 7, the upwardly divergent angle is indicated by phantom lines as at reference numeral 49 as being on the order of 1.4°. Radiation array 14 consists of the transversely extending radiating elements 17. Each radiating element 17 (FIG. 9) consists of a pair of wire portions 51 held at the tip end 52 of element 17 by an assembly 53 of suitable insulative material pivotally mounted in a conventional device 54 attached to dielectric cable 48.

The inner ends of radiating elements 17 are coupled (FIG. 12) to feed lines 18 by means of spreader insulative bars 56 which serve to spread and properly separate and evenly tension the inner ends of wire portions 51. Bars 56 are pivotally supported on the opposite ends of a joiner bar 57, of insulative material, whereby the entire dipole radiating element 17 has been formed.

Feed lines 18 are supported equi-distant from the inner ends of wire portions 51 by means of the feed jumper bars 58 which carry a swaged fitting 59 at their outer ends to make contact with the feed lines 18.

By disposing feed lines 18 in spaced relation above and along boom 21, it will be apparent that the foregoing connections made with feed lines 18 by radiating elements 17 can be made without regard to the spacing and construction of interfering parts of boom 21. Accordingly, at the outer end of feed lines 18 (FIG. 5), each line 18 is coupled by means of a swaged fitting 61 to a tension equalizing assembly 62. Assembly 62 consists of the pair of insulative bars 63 pivotally coupled to straps 64 at one end and to a support yoke 66 at the other. An eyebolt 67 anchors yoke 66 from an upwardly extending extension 68 of rigid, rectangular cross-section whereby the outer supported end of lines 18 terminates in modest spaced relation above boom 21.

Feed lines 18 are held in substantially constant spaced relation with respect to boom 21 along its length by means of a clamping assembly 69 comprised of a pair of crossed I shaped braces 71 pivotally supported at their opposite ends respectively to upper rails 46 and to an insulator member 72 which serves to dispose one of feed lines 18 centrally of a large opening 73 therethrough as by means

3,553,701 of the stand-off insulators 74, 76 swaged onto feed lines 18.

Feed lines 18 extend from the outer tip of boom 21 as shown in FIG. 5 rearwardly of the radiating array 14 along boom 21, as supported by the apparatus shown in FIG. 13, to the axis of rotation of array 14 and continues on rearwardly to be electrically coupled to radiating elements 17 located between booms 22, 23. Means are provided for tensioning that portion of feed lines 18 extending forwardly from the axis of rotation of array 14 in a manner independent of the means for tensioning feed lines 18 in the rear portion thereof. Thus, feed lines 18 may be considered as having been mechanically divided into a major portion extending forwardly of the axis of rotation of array 14 and a minor portion extending rearwardly from the axis of rotation.

The major and minor portions of feed lines 18 are independently tensioned by attachment to means located at the axis of rotation of array 14 and are electrically connected by means of the jumper lines (FIG. 7) 77. Thus, the ends of lines 18 for the major portion thereof are secured to a support tower extension, or mast 78 comprised of a trio of upwardly extending rails 79 mounted in vertically disposed rail stubs 81. Insulators 82, pivotally secured at each end, engage and hold a loop 83 of each feed line 18 as formed by doubling a portion of the feed line back upon itself and employing a swage fitting 84 to form the loop 83. A jumper line 77 is also swaged, by as the fitting 86, onto feed line 18 so as to provide electrical coupling with the rear or minor portion of feed lines 18.

Tensioning of the latter is similarly accomplished and accordingly need not be described in further detail, other than to note the pair of stabilizer plate 87 anchored by the eyebolt 88 secured to one of rails 79. Jumper lines 77 are held clear of rails 79 by means of stand-off insulators 89.

Means serving to couple the rear end of feed lines 18 is best shown in FIG. 11 and consists of a tension equalizer assembly 91 comparable to the equalizer assembly 62 as previously described. Laterally extending wire portions 51 of the rearmost radiation element 17 are held by means of the rhombus-shaped insulator plate 92 as described earlier above relative to insulator 72 in FIG. 13. In the present instance, however, electrical coupling to wire portions 51 from feed lines 18 has been made by utilizing jumper wires 93.

Rearwardly of the tension equalizer assembly 91 attachment is made to a pair of parasitic radiator elements 94. Thus, spacer 96 of non-insulative material is clamped thereto and a longitudinal tug is thereby applied to feed lines 18 by bridling, or slightly angling the parasitic elements 94 rearwardly (FIG. 8). The longitudinal tug 100 (FIG. 11) need not be too great inasmuch as only the minor portion of the overall feed lines is required to be tensioned in this manner.

Accordingly, it is readily apparent that the rearmost radiator element, such as parasitic elements 94, have been coupled to the end of the minor portion of feed lines 18 for tensioning the minor portion of the feed lines while the major portion of feed lines 18 is tensioned by adjustment of the adjustable eyebolt 67 (FIG. 5). Tensioning of each of the two portions is essentially independent of the other whereby only a limited strain is applied to the tensioning radiator elements at the rear of array 14.

As in other log periodic antennas, return lines have been provided. Referring to FIG. 5, four return lines 19 are disposed and evenly tensioned by the dual tension equalizing assemblies 98, 99 mutually disposed at right angles to each other and adjusted in tension by means of the elongated eyebolt 101. Each assembly 98, 99 is comparable to those shown relative to the tension equalizer assembly 62 and need not be further described.

Means serving to maintain generally uniform spacing between return lines 19 along boom 21 comprises a num6 ber of devices as shown in FIG. 2 disposed at intervals along boom 21. Thus, each of these devices comprises in general an H shaped central supporting unit mounted for slight pivotal adjusting movements along the geometric center of the triangular cross-section of boom 21.

More particularly, an insulated spacer bar 103 supports each of two pairs of aluminum clamps 102, each of which has been formed with passages for engaging the return lines 19. Spacer bar 103 has been pivotally mounted at its ends respectively to a T-shaped metallic extension 104 and a metallic link 106. The extension T 104 and link 106 are, in turn, respectively coupled to insulators 107 which are each respectively engaged by adjustable mountings 109. In this manner, it will be apparent that return lines 19 will be carried centrally along boom 21 rearwardly toward the axis of rotation of array 14. Upon reaching the axis of rotation of array 14, return lines 19 change direction and pass downwardly of the main support tower 11.

Referring to FIGS. 7 and 10, means have been shown for making this transition and for suitably tensioning each of the two portions of return lines 19, i.e., the horizontal portion and the vertical portion. Thus, the four horizontal return lines 19 and four vertical return line portions 97 are each coupled (FIG. 7) to spreader bars 111. Each bar 111 serves to space the ends of its associated pair of return lines 19, 97 and the two bars 111 are each connected by a round rod 112 bent at a 90° angle and secured at its opposite ends respectively to each of the two bars 111. Rod 112 is, in turn, held under tension by means of the adjustable tension equalizing assembly 113.

Assembly 113 comprises two pairs of shackle links 114, each pair of which is coupled to a shackle 116 carried on the end of a pair of insulators 117 pivotally coupled, in turn, to stabilizer bars 118 held under adjustable tension by means of the eyebolt 119. Eye bolt 119 threadedly engages the transversely extending inverted angle mounting bar 121.

As thus arranged, it is apparent that return lines 19 make the transition from horizontal to vertical and extend downwardly as return line portions 97 centrally of the main support tower assembly 11 where, at their lower end, they ultimately reach a balun of conventional design (not shown).

Inasmuch as the radiating array 14 rotates relative to the stationary support tower assembly 11, in the manner described and shown in the above identified patent application, the vertically extending return line portions 97 will twist as a group. Accordingly, means are provided whereby the spacing remains constant between each of the return lines 97 during such twisting movement.

The twisting movement may occur roughly in the upper 25 feet of support tower assembly 11, whereas the remaining lower extent of the downwardly extending return lines 97 may be held stationary and substantially free of any twisting. The lower portion is mounted by the means shown in FIG. 3 centrally of support tower 11, whereas the upper portion of return lines 97 is carried by a portion of the structure shown in FIG. 3 but in an unanchored manner.

Thus, as described relative to the devices shown in FIG. 2, FIG. 3 similarly provides an H shaped spacer construction 122 constructed in the manner described relative to comparable components shown in FIG. 2. In the upper extent of tower assembly 11 the spacer construction 122 stands by itself supported merely by the downwardly extending return lines 97. The lower portions of the return lines 97 are firmly supported against twisting by the remainder of the apparatus shown in FIG. 3 which is comparable to that apparatus shown in FIG. 2 and need not be further described herein.

Finally, each of the two-rearwardly-directed booms 22, 23 is electrically subdivided into discrete insulated sections by the insulative splice as shown in FIGS. 14-16. Each splice 123 comprises metallic adaptors 124 formed

3,553,701 at one end with a cylindrically shaped socket 126 or cup for receiving a solid cylindrically shaped bridging member 127 of rigid insulative material, and at is other end with a channeled stub rail 128 adapted to be bolted, as shown in FIG. 16, to the rail portions of a type forming booms 22, 23.

As is known, any time an elongated boom is supported in a cantilevered fashion from its end, the outer unsupported end of the boom is subject to considerable downward bending forces imposing severe stress on the boom structure as well as upon its mounting. Each of booms 21-23 is guyed from above, as shown in FIGS. 1, 4 and 8, by support cables 129, 131, 132, respectively, extending from the upper end of support tower extension 78 to a bridle 133 (FIG. 13). Cables 131 and 132 are, as shown in FIG. 4, subdivided by means of electrical insulators 134.

The outer unguyed end portion of each boom will normally experience downwardly acting bending stresses caused by the unsupported weight of such boom portions. The radiating array herein contributes counteracting forces forming an eccentric upwardly acting moment serving to relieve such bending stresses. Thus, referring to the diagram shown in FIG. 17, the supporting action derived from the array itself may be more clearly understood.

The unsupported “cantilevered” outer end portions, such as 145 in FIG. 17, including the outrigger 140 and array elements, tends to bend downwardly about a bending point 146 located along the centroid 147 of boom 145 and immediately beneath the point of support 148 supplied by the guying cable 129. Catenary support cables 48 (shown in FIG. 17 as a single cable 48' for diagrammatic purposes and clarity) when loaded by environmental forces imposed upon the array elements develop a force, f, acting mainly along the boom 21 toward the center of rotation of the array, but disposed above the centroid 147 of the boom so as to define an eccentric moment arm, L_b to develop a counteracting moment to that moment developed by the weight, F_g, of the boom portion 145 and the array portion acting about point 146. Thus, the counteracting moment acts upwardly substantially normal to the centroid axis 147.

Stresses effected by the array’s eccentric location with respect to the tilted booms are not restricted to point 146 alone. These stresses travel throughout the boom and their effect ends at the junction where all three booms come together.

Thus, by supporting the array above the booms, the array tends to contribute to its own support and it becomes possible to construct a boom of lighter weight material and of lower mass with a lower profile exposed to the wind.

Booms 21-23 are guyed from below by means of cables 136, 137 and 138 (FIG. 1) by means of the downwardly and outwardly diverging struts 139 which are also guyed in a triangular disposition by means of the cables 141.

It will be apparent that the arrangement of struts 139 and guying cables 136-138 and 141 are disposed beneath the level of bearing assembly 24 whereby booms 21-23 have been securely stabilized and advantageously supported while foreshortening the overall extent of support tower assembly 11.

From the foregoing, it will be readily evident that there has been provided an improved antenna construction providing a number of significant advantages, such as the provision of an arrangement whereby the boom construction may be of lesser mass and profile relieving critical requirements of material and construction which become quite significant, for example, where an antenna of the type described must be located in a remote geographical region and operated over long periods of time essentially without maintenance, observation or inspection.

It is further apparent the construction of each of booms 21-23 may be conventionally carried out without regard to any particular spacing of the radiating array elements 17. The manner of supporting the antenna for rotation serves to minimize the overturning moment which would otherwise act upon and impose severe requirements upon the bearing assembly located at the top of the support tower. Further, it will be appreciated that the radiating elements are supported at their ends solely by a single cable inasmuch as the load requirements applied to such cable have been significantly relieved by virtue of the arrangement shown. Thus, a single cable at the ends of each of the radiating elements becomes sufficient support and the array supporting construction is thereby provided with a periphery configuration on the order of but not substantially greater than the periphery of the radiating array configuration itself. As mentioned, this position of the radiating array to lie in a plane above the array supporting construction has served to minimize the expense involved in the construction of booms for supporting such arrays.

Further, by disposing the two rails of each boom at the top of the boom and the third rail, forming the apex of the triangular cross-section, beneath the boom, greater strength is achieved in each boom for the material used and enhances the advantages of less boom profile and less massive structure is attained. Finally, the manner of independently tensioning portions of the feed lines serves to permit less structure to be employed in tensioning the minor or rear portion of the feed lines 19 simply by attachment to parasitic elements such as the parasitic elements 94.