US 2991474 A
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Description (OCR text may contain errors)
July 4, 196 J. R. DONNELLAN ETAL 2,991,474
SINGLE SPIRAL LINEARLY POLARIZED ANTENNA Filed D80. 29, 1959 14 E T s X v Z I I y 2| 21 l3 E UTILIZATION DEVICE IEIEZE Z l8 I9-20 8 L I INVENTORJ JOHN R. DONNELLAN 2l BORIS SHELEG UTILIZATION BYMM/ ATTORNEY United States Patent Ofifice Patented July 4, 1961 2,991.4 SINGLE SPIRAL LINEARLY POLARIZED ANTENNA The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.
This invention relates to spiral antenna systems in general and in particular to an arrangement for obtaining linear polarization from a comparatively simple system requiring only one spiral antenna element as well as only a simple planar reflector.
The spiral antenna element, which is described as a two conductor interwound planar Archimedian spiral, has several unique characteristics which can be utilized to good advantage. Among these an important feature of such an antenna element is its ability to couple to the far field in controllable phase, as a result of which a selected phasing may be obtained at any point in the far field. When two such elements cooperate in coupling to the far field and couple in opposite polarization sense, the circularly polarized coupling of the elements resolves itself into linear polarization wherein the plane of such linear polarization is readily adjustable at will, This arrangement produces an antenna which has very desirable properties, particularly when several such pairs of antenna elements are combined and the relative phasing of the pairs is adjusted, it then is possible to produce large angle scanning of a linearly polarized antenna beam as well as control the plane of polarization. Such an arrangement, however, does have the requirement for coperative pairs of spiral antenna elements. Although in many instances the use of two such elements is of no particular disadvantage, in the arrangement mentioned above where elements are employed to produce scanning or a plurality of elements are employed to produce sharper beams than those possible with single elements, the many elements required make it desirable to have some arrangement whereby a reduction in the quantity thereof is possible. Thus, it appears desirable to obtain some arrangement whereby each element produces a field which is linearly polarized rather than the normal circularly polarized field.
It is, accordingly, an object of the present invention to provide a spiral antenna system wherein each spiral antenna element is caused to provide a linearly polarized radiation field.
Another object of the present invention is to provide a single element spiral antenna system wherein the field produced thereby is linearly polarized.
Other and further objects and features of the present invention will become apparent upon careful consideration of the accompanying description and drawings wherein:
FIG. 1 indicates in general a spiral antenna element.
FIG. 2 indicates an arrangement in accordance with the teachings of the present invention whereby such a single spiral antenna element may be utilized for electromagnetic wave coupling with a linearly polarized far field.
FIG. 3 shows a side view of the arrangement of FIG. 2 whereby a more accurate indication of the relative positioning of the various components of the apparatus of FIG. 2 is possible. The drawing is not to scale as to component dimensions, however.
In accordance with the basic teachings of the present invention an antenna system is provided wherein a linearly polarized field is obtained from a single spiral antenna element. It has been discovered that such a result is obtained by placing a reflector on one side of the spiral antenna element to limit the far field therefrom to one side of the spiral and by inserting a grating between the reflector and the spiral element.
Referring now to FIG. 1 of the drawing there is shown a basic spiral antenna element having two conductors 10 and 11 disposed upon a suitable backing plate 12. The
two conductors are insulated from each other and typically wound in such a way as to produce an Archimedian spiral wherein the two conductors spiral uniformly outward from a small central radius to a larger outer radius. Typically the two conductors could be produced by printed circuit techniques as thin conductors remaining on a backing plate after the application of the printed circuit process. Such an antenna will radiate when the circumference is of the order of a Wave length and produces a symmetrical field which is a somewhat flattened hourglass pattern. The field of the antenna of FIG. 1 is basically circularly polarized in a sense depending upon the manner in which the spiral evolves from the center to the outer points being termed either right or left-hand polarization.
,With reference now to FIG. 2 of the drawing, the apparatus shown therein includes a single spiral antenna element 13 of the type discussed above and shown in FIG. I mounted in front of a reflector 14 which is of sufficient proportions as to effectively prevent radiation from the back side of the antenna 13 from directly reaching free space and returning it in the direction of the spiral element 13 and intervening grating structure indicated by the general numeral 15 which may achieve the form of a plurality of uniformly spaced parallel Wires 16 supported by a suitable frame-work 17. The wires 16 are closely spaced and may typically be attached to the frame 17 in such manner as to be insulated from each other and from the frame itself. The spacing of adjacent wires is substantially less than a wave length and substantially greater than the diameter of the wire. The grating 15 is placed between the spiral antenna element 13 and reflector 14 with the spacing of the grating 17 and the reflector 14 being a quarter wave-length at the frequency of operation. The spacing between the spiral antenna element 13 and the grating 15 is not particularly critical as to the conversion of circular polarization into linear however it does affect phasing and hence the plane of the polarization. Thus some convenient means for adjusting this spacing may be desired and is readily attainable by providing sliding mountings for the element 13. The phasing of the coupling at any point in the far field can be varied by merely rotating the spiral antenna element 13 about its axis perpendicular to the reflector 14 and the grating 15.
With reference now to FIG. 3 of the drawing, a somewhat diffcrent view of the apparatus of FIG. 2 is indicated showing the side of various components and indicating the spacing between the grating 15 and the reflector 14 to be a quarter wave-length, indicating further the spiral antenna element 13 and a typical mounting device 18 which is suitably arranged to maintain the desired relationship between the components mentioned in the foregoing. Physical connection of the spiral antenna element may be provided by means of the leads 19 and 20 which are connected to a suitable utilization device 21 which could be a receiver or a transmitter. In accordance with the previous discussion, rotation of the spiral antenna element as well as positioning relative to the grating 15 is obtained by means of a rod member 22 of suitable insulating characteristics which can be either rotated or moved axially typically from the back side of reflector 14 to position spiral antenna element 13 as desired.
In operation of the apparatus of the invention atransmitting situation may be assumed wherein thepoianzation of direct forward radiated energy is circular in such a sensethat viewedjfromthe forward side of the spiral looking toward the spiral the polarization canbar'epre sent'ed by a vector rotating in a clock wise' direction. With this situation the radiationfromithe back side of the spiral which impinges on the grating will also be seen from the forward side of the spiral as a vector rotating'in a clock-wise direction; however, the cornbination of the grating 15, andthe reflector 14 spaced a quarter wavelength apart reverses the rotational sense of the reflected radiation so that'the reflected radiation will be 'Seen'rrem the same position as above 'as a vector rotating in a counter clock-wisedirection. Therefore, the direct radiation and the reflected radiation are circularly polarized and, since there are no dissipative devices involved, they will be of substantially equal amplitude and opposite senses. The two polarization senses combine to give a linearly polarized output. The orientation of the linear polarization is a function of the spacing of the spiral from the grating and of the orientation of the wires of the grating. Thus, with the grating in a fixed position and the spiral a fixed distance from the grating, the spiral may be rotated in order to change the phase of the far field while maintaining the desired direction of linear polarization. Such an arrangement is particularly advantageous where scanning arrays requiring a plurality ot elem ents 13 are required because then such an array can be made with equal spacing of the centers of the elements in both directions.
Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore tobe understood that within the scope of the appended claims the invention may be practical otherwise than as specifically described.
. 4 What is claimed is:' 1."Arr'aritenna*system eomprism a spiralantennaelement, a reflector disposed on one side of the spiral antenna element 'and substantially parallel thereto, and a grating having a pluralityiof conductors disposed between said element and said reflector, 'a "quarter wavelength from said reflector. p 7
2. An antenna systemcomprising, aspiral' antenna element, a planar reflector disposed on one side of the spiral antenna element ma plane substantially parallel to the plane of said element, and a grating having a plurality of closely spaced parallel wires disposed between said element and said reflector in a'plane parallel to said reflector and a quarter wavelength therefrom. p
3. An antenna sys'tem comprising, a spiral'antenna element, a planar 'reflector*di'sp6sed"on one side ofthe' spiral antenna element in a plane substantially parallel to the plane of said element, and a grating having a plurality of parallel conductors with relative spacing substantially less than a half wavelengthand greater than the conductor thickness disposed between said element and said reflector and a quarter wavelength from said reflector.
I References Cited in the file of this patent Y UNITED STATES PATENTS 2,790,169 v Sichak Apr. 23, 1957 2,863,145 Turner Dec. 2, 1958 2,930,039 Ruze Mar. 22, 1960 2,935,746 Marston May 3, 1960 OTHER" REFERENCES 'Kaiscr z' Scanning Arrays Using the Flat Spiral Antenna, NavalResearch"Laboratory Report 5103, Mar. 14, 1958, p. 4.