Dish Reflector For A High Gain Antenna

Abstract

A dish reflector for a high antenna formed by a plurality of generally triangular petals joined edgewise to form a quasi-paraboloid configuration.

Description

FIELD OF THE INVENTION

The present invention relates generally to antennas, and more particularly, to a dish reflector for a high-gain antenna.

The invention described herein was made in the performance of work under a NASA contract and is subject to the provisions of Section 305 of the National Aeronautics and Space Act of 1958, Public Law 85-568 (72 Stat. 435/ 42 U.S.C. 2457).

BACKGROUND OF THE INVENTION

A high-gain antenna is an obvious necessity to provide an intelligible signal when the received electromagnetic energy is at a relatively low power level. For example, an ordinary television antenna having relatively low-gain characteristics is perfectly satisfactory to produce intelligible sound and a clear television picture when located within line of sight of a conventional television transmitting station. On the other hand, a television or other communication signal transmitted from a satellite in orbit obviously arrives at an intercepting antenna with a relatively low power level of electromagnetic energy wherefore the use of a high-gain antenna is imperative. Commonly, such a high-gain antenna takes the form of a relatively large size paraboloid reflector which receives the radiated electromagnetic energy over its entire surface and in accordance with the general reflective characteristic of a paraboloid, reflects such energy to a collector located at its focal point.

Recently, proposals for the wide dissemination of educational information to remote areas have included the provision of a plurality of television receivers arranged in such remote areas to receive the television signal emanating from a satellite. The number and remote locations of these plural receiving stations present practical problems in the shipping, local installation and cost. More particularly, both the size and shape of a true paraboloid do not lend themselves readily to mass production techniques; thus the cost is high. If a unitary structure, shipping and handling are a problem; if composed of a plurality of compound curvature sections, yet added cost and assembly complexity appear.

SUMMARY OF THE PRESENT INVENTION

Accordingly, it is the general objective of the present invention to provide a high-gain antenna which incorporates a dish reflector formed from a number of parts capable of fabrication by mass production techniques wherefore the costs are minimized and the elements can readily be shipped in their disassembled form in a relatively compact light weight package but subsequently assembled and installed in operating condition quickly, easily, and with assurance of high-gain performance.

Generally, the dish reflector is formed by the assembly of a plurality of generally triangular reflector petals in substantially edgewise, abutting relationship to form a dish in the form of a quasi-paraboloid. Generally the term, "quasi-paraboloid," refers to a dish reflector structure wherein a section line extending outwardly from the center of the antenna through the center of one of the petals has an approximate parabolic configuration whereas a section line transverse to such outwardly extending line remains substantially rectilinear. More particularly, the generally paraboloid curvature of each individual petal outwardly from the center of the reflector dish is determined by the precise positions of connection of adjoining petals and is designed to minimize the phase errors resultant from the departure of the reflector conformation from that of a true paraboloid.

In order to simplify and reduce manufacturing costs of the dish reflector, each of the petals is initially formed, in one case, by a simple blanking operation, in a flat, generally triangular form from sheet aluminum, steel, or other material having a highly reflective surface and in particular being capable of bending during assembly to form the ultimate quasi-paraboloid shape. During the blanking operation, holes are formed along the edges of the petals in predetermined calculated disposition so that upon subsequent assembly of the petals in edgewise abutting relation through the use of nuts and bolts, pop rivets, or other connecting means, the desired quasi-paraboloid conformation will automatically be achieved thus eliminating the need for any skill or technical know-how on the part of the person assembling the structure.

Preferably, rim segments are arranged to receive the outer edges of the triangular petals during installation and adjacent rim segments are in turn joined by the simple bolted connection of angular corner brackets thereto so as to function as assembly jigs during the assembly operation and to subsequently function as a rigid exterior rim structure for the dish reflector enabling it to withstand mechanical shock and also enabling appropriate mounting of the dish reflector in the desired disposition for optimum reception of the electromagnetic radiation.

Obviously, the disassembled petals, rim segments, and corner brackets can be shipped in a rather compact package even though the ultimate size of the assembled dish reflector is relatively large, yet upon arrival, use of but simple tools by a relatively unskilled person enables erection of the dish reflector in a period of less than two hours. Because of the pre-established petal dimensions and the holes therein which control the configuration of the assembled reflector, the desired high-gain is assured.

The quasi-paraboloid configuration can obviously be obtained in other specific fashions, one example being the edgewise connection of a plurality of generally triangular reflective petals to preformed, rigid ribs projecting radially in a generally parabolic configuration, enabling the elimination of the exterior rim segments.

BRIEF DESCRIPTION OF THE DRAWINGS

The stated objective of the invention and the manner in which it is achieved as summarized hereinabove will become more readily apparent from a perusal of the following detailed description of exemplary embodiments of the invention illustrated in the accompanying drawings wherein:

FIG. 1 is a perspective view of a microwave antenna incorporating a dish reflector in accordance with the present invention,

FIG. 2 is an enlarged, fragmentary, sectional view taken along line 2--2 of FIG. 1 illustrating certain structural details of the dish reflector,

FIG. 3 is another enlarged, fragmentary, sectional view taken along line 3--3 of FIG. 1 illustrating yet further structural details,

FIG. 4 is an exploded view of the parts indicating the manner of assembly of the dish reflector of FIG. 1,

FIG. 5 is a three-axis diagram explanatory of the manner in which gain of the reflector is maximized, and

FIG. 6 is an exploded, perspective view similar to FIG. 4 of the parts of a modified dish reflector embodying the invention.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS OF THE INVENTION

With initial reference to FIG. 1, a high-gain antenna is illustrated and includes in accordance with the present invention, a dish reflector 10 whose interior surface is formed from highly reflective material, and specifically has the conformation of a quasi-paraboloid which conformation will be more precisely defined hereinafter. Three supporting legs 12 project upwardly from a rigid base 14 to engage and support the rim of the dish reflector 10 in proper orientation so that the Z axis of the quasi-paraboloid, as indicated in FIG. 1, is directed towards a satellite or other source of radiation which is to be reflected by the reflector towards a suitable collector 16 supported by suitable arms 18 projecting upwardly and inwardly from spaced points on the rim of the reflector so that such collector will reside also on the Z axis and more particularly at the focal point of the quasi-paraboloid so that, as will be explained in greater detail hereinafter, and as in the case of true paraboloid reflectors, the reflected electromagnetic energy will be focused at such collector 16 whose output in turn after appropriate electronic processing is fed through a feed line indicated at 20 to a conventional television set (not shown). It will be obvious that the collected energy can alternatively provide an input signal to a sound receiver or other form of electronic equipment and such receiving equipment forms no part of the present invention, in and of itself. Furthermore, as will be apparent, a simple electronic reversal enables delivery of energy to the antenna dish for transmission rather than reception of electromagnetic energy.

As specifically illustrated in FIG. 1, the dish reflector 10 is formed by ten petals 22 of highly reflective material, each petal subtending an angle of 36.degree. at its central apex and curving outwardly so that in central section through its altitude defines substantially a parabola, as shown in FIG. 2. A section line at right angles or transverse to the altitude of each triangular petal 22 on the other hand is rectilinear as shown in FIG. 3 so that slight deviations from a true paraboloid result. The described and illustrated conformation of all of the reflector petals 22 is the same and the totality of the conformation of the 10 petals is encompassed by the mentioned term, "quasi-paraboloid."

Preferably, the individual petals 22 are formed from rather thin and flexible aluminum sheet (e.g., 0.040 inch) and to add structural rigidity to the arrangement, the outer edge or base of each triangular petal is supported in a slot 24 at one side of a boxlike rim segment 26 which is preferably formed as an extruded aluminum section (see FIG. 4) and the closely abutting ends of adjoining rim segments 26 are in turn joined rigidly by angular corner brackets 28 which encompass the adjacent rim segments and are joined to the rim segments and the outer corners of the petals 22 by suitable nuts and bolts indicated at 30. In turn, the adjoining edges of the petals 22 have a plurality of holes 32 at spaced intervals therealong and are arranged in overlapping relation as shown in FIG. 3 so that they can be joined by the application of pop rivets 34, as shown, or alternatively by any other form of connecting means such as a simple nut and bolt arrangement.

Preferably, as illustrated in FIG. 4, each of the individual, generally triangular petals 22 is initially formed by blanking in essentially a flat configuration, but since it is formed from slightly flexible material such as the thin aluminum mentioned hereinabove, each petal is capable of being bent in single curvature so that the altitude of the assembled triangular petal will approximate the parabolic configuration described hereinabove and shown in FIG. 2, while retaining a rectilinear disposition in the transverse direction as shown and described in connection with FIG. 3. The desired configuration is obtained in accordance with the present invention by precisely positioning the holes along the adjacent edges of the petal sections so that when the pop rivets 34 are applied thereto, the individual petals 22 are bent to the desired singly curved conformation.

The assembly operation is extremely simple once the petals 22 have been so formed with the required exterior dimensions and the desired hole dispositions. Initially, two of the rim segments 26 are assembled with the angular corner bracket 28 and two adjacent petals 22 are then slipped into the adjoining rim segments so as to lie in edgewise overlapping relationship. The bolts 30 are manually applied to the bracket segments and other corners of the petals. The first pop rivet 34 is then applied to the outermost, overlapping holes 32 of the two petals, the desired registration of the holes being readily attained by a slight bending of the adjacent petals. Thereafter, additional pop rivets 34 or other connecting means are applied in succession to the registering holes 32 in the adjacent petals 22 and upon completion of the riveting operation, the desired quasi-paraboloid configuration is attained. It is to be particularly noted that the bracket 28 and rim segments 26 function, during such assembly operation, as assembly jigs to facilitate ease and rapidity in the assembly of the dish reflector.

When the assembly is completed, even though the petals 22 themselves are relatively thin material, the rim segments 26 and brackets 28 joined thereto form a mechanically rigid structure so that the assembled dish reflector 10 will retain its shape regardless of weather conditions or mechanical shock.

In view of the fact that the assembled dish reflector 10 is a quasi-paraboloid, the path lengths of radiation from a plane wave front reflected at different points to the focus will have regular variations in comparison to the corresponding path lengths utilizing a true paraboloid. Such differences in path lengths will in turn result in slight phase errors of the reflected electromagnetic energy, but by suitable design criteria to be described in detail hereinafter, these phase errors are minimized so that the realizable gain of the ten petal antenna as specifically described hereinabove is reduced by no more than a fraction of a decibel below that achievable by a perfect paraboloid.

More particularly, and with reference to the diagrammatic showing of FIG. 5, the distance traveled bu an electromagnetic wave from an XY plane 36 through the focal point 38 of the quasi-paraboloid will initially travel a distance [F - Z (y)] to a point 40 on the reflective petal 22 and will thereafter travel from this point 40 to the focal point 38 a distance, L = ([F - Z (y)].sup.2 + x.sup.2 + y.sup.2).sup.1/2, the total distance, d, being equal to the sum, [F - Z(y)] + ([F - Z(y)].sup.2 + x.sup.2 + y.sup.2).sup.1/2. It being known that the distance from a plane through the focus to a perfect paraboloid and thence to the focal point is equal to 2F (F being the focal distance as indicated) in accordance with the general definition of a paraboloid, the difference in distance which we will refer to as the phase error distance will be (2F - d). In order to minimize the phase error as desired, it is merely necessary then to determine the amount of bending of the petal 22 to provide a dimension Z.sub.min (y) such that the quantity, ##SPC1## is a minimum, r.sub.o being the radius of the antenna, and w(y) the half-width of a single petal.

Knowing the value Z.sub.min (y), it is then but a simple geometric transformation to find the precise shape of a petal 22 and the hole dispositions to produce the requisite amount of bending to provide Z.sub.min (y) and the consequent minimized phase error. By way of example, in one particular dish reflector designed for operation at 2.62 GHz with a reflector diameter of approximately 7 feet, the individual petals 22 as stamped in their flat triangular form had an altitude of 43.5 inches and the precise X and Y dimensions of the individual petal holes, as indicated in FIG. 4, were as follows measured from the center or apex of the triangular petal outwardly:

X Y 0.487 0.500 1.462 3.504 2.437 6.516 3.412 9.546 4.386 12.598 5.361 15.677 6.255 18.531 7.229 21.680 8.123 24.606 9.017 27.575 9.910 30.589 10.804 33.655 11.697 36.768 12.509 39.656 13.322 42.587

the mechanical tolerances in the hole dispositions was maintained at 0.005 inch which is well within the capability of standard mass production blanking techniques and with this particular reflector configuration, an antenna gain of 32 dB was attained which is but 0.9 dB below that of a perfect paraboloid. It will be apparent that if the dish reflector is made with an increased number of sections, yet higher gain can be realized, but in view of the close approximation to that of a perfect paraboloid with use of but 10 petals the described structure was considered entirely adequate and of course enables the assembly operation to proceed quite rapidly, and as previously mentioned, such assembly can be achieved by an unskilled laborer in less than 2 hours, and the resultant reflector dish has excellent gain.

The number of petals can accordingly be changed without departing from the spirit of the invention and other changes such as integrating the rim segments with the petals will similarly suggest themselves. Additionally, the petals and supports therefor can be considerably modified while retaining the quasi-paraboloid conformation. By way of example, in FIG. 6, petals 42 formed of expanded metal which is flexible and highly reflective are joined at their edges by machine screws 44 to radially extending parabolic ribs 46 formed from rigid metal straps with suitable threaded holes therein. A radial section through each petal 42 is substantially parabolic but a transverse section is substantially rectilinear as in the first embodiment so that the simple structural but excellent gain characteristics are again achieved.

Additional modifications and/or alterations can obviously be made without departing from the spirit of the invention. Accordingly, the foregoing description of but two embodiments of the invention is to be considered as purely exemplary and not in a limiting sense, and the actual scope of the invention is to be indicated only be reference to the appended claims.

Claims

What is claimed is:

1. A dish reflector for a high-gain antenna which comprises

a plurality of generally triangular reflective petals and

means connecting said petals in edgewise overlapping relation to form a quasi-paraboloid with a line extending centrally outward through each petal being of generally parabolic form and a transverse line being substantially rectilinear,

said connecting means including a plurality of connecting members joining the overlapping edges of said petals through registered holes therein at predetermined dispositions which define the ultimate assembled quasi-paraboloid conformation of the reflector.

2. A dish reflector according to claim 1 wherein

the generally parabolic curvature of each petal outwardly is such that the phase errors of reflected electromagnetic energy at the focus of the quasi-paraboloid are minimized.

3. A dish reflector according to claim 1 which comprises

a rigid rim connected to the exterior edges of said petals to provide structural rigidity.

4. A dish reflector according to claim 3 wherein

said rim includes a plurality of rim segments slotted to receive the outer edges of said petals and joined at the extremities by angular corner brackets.

5. A dish reflector according to claim 1 wherein

said petals, prior to connection by said connecting means, are in the form of flat sheets of flexible material.

6. A dish reflector according to claim 1 wherein

said petals are formed of flexible material.