US3019439A - Elliptically polarized spiral antenna - Google Patents

Description

Jan. 30, 1962 H. J. REIS ETAL 3,019,439

ELLIPTICALLY POLARIZED SPIRAL ANTENNA Filed Sept. 19, 1957 4 Sheets-Sheet 2 INVENTOR. HERBERT J. REIS FRANCIS M. KUDO AT TORNEY Jan. 30, 1962 H. J. REIS ETAL 3,019,439

ELLIPTICALLY POLARIZED SPIRAL ANTENNA Filed Sept. 19, 1957 4 SheecS-Sheel'I I5 INVENTOR. HERBERT J. REIS FRANCIS M. KUDO ATTORNEY H. J. REIS ETAL ELLIPTICALLY POLARIZED SPIRAL ANTENNA Jan. 30, 1962 4 Sheets-Sheet 4 Filed Sept. 19, 1957 3,019,439 ELLIITICALLY POLARIZED SPIRAL ANTENNA Herbert J. Reis, Middle River, and Francis M. Kudo, Kenwood, Md., assigncrs to Martin-Marietta Corporation, a corporation of Maryland Filed Sept. 19, 1957, Ser. No. 684,876 19 Claims. (Cl. S45-853) This invention relates to an antenna of generally spiral construction, iiush mounted with the surface of a ground Waves in an eiiicient manner and over a wide range of frequencies.

e past, so-called stub In th with a moderate degree of success for communication and for only of an octave.

drag. Other advantages.

According to the a novel and improved travelling wave antenna which, be

both the horizontal and vertical planes, for use in electronic countermeasures equipment and ground based weapons systems.

The antenna is small,

the radiating elements are in the form of interwound spirals formed about a common axis and located in a substantially common plane, with balanced feed means connected to the radially inner ends of the elements whereby a balin a number of locations in the process of winding across the face of the antenna. As a further modification, the central portion of the face of the antenna may be raised somewhat, this having the result of producing radiation closeito the ground plane rather than in modifications not having the raised central wound spirals formed about portion. Spiral radiating elements may be employed in the modification having the raised central portion, as may radiating elements of essentially square configuration previously described.

Since the mean diameter of the radiating circumferential zone varies with frequency, a broad frequency range of operation is possible with an antenna of suitable diameter. Because of the orientation and distrbiution of field vectors, a null is produced in a direction normal to the plane of the antenna, with consequent radiation extending in a lateral, encircling direction above (or below) the ground plane of the antenna. Due to the many windings of the antenna, a traveling wave exists along the turns to yield omnia'zimuthal radiation along a wide frequency range.

The above and other features in this invention will become apparent upon reference to thefolllowing detailed description and accompanying drawings in which:

FIGURE 1 is a plan View of a first embodiment of a multi-conductor spiral antenna according to this invention;

FIGURE 2 is a side View of the antenna according to FIGURE l, partly in section to reveal internal construction;

FIGURE 3 is a simplified view revealing details of the feed means and the polarities associated with the coaxial conductors employed in the antenna according to this modification;

FIGURE 4 is an exploded lview of the antenna according to FIGURES 1 and 2 revealing inner construction;

FIGURE 5 is a simplified diagram of the .radiating elements of the antenna of FIGURES 1 and 2, revealing direction of current flow through the radiating elements at a given instant and the direction of the generated electric field in the circumferential region from which radiation originates;

FIGURE 6 is a typical conical radiation pattern of the type obtained by the use of an antenna of the type shown in FIGURES l and 2;

FIGURE 7 is a view taken through the radiation pattern of FIGURE 6, revealing the manner in which a given section of the radiation pattern is polarized according to components at one instant;

FIGURE 8 is a plan view of a second embodiment according to this invention in which the radiating elements are of substantially square configuration;

FIGURE 9 is a plan view of a third embodiment of this invention in which the radiating elements are similar to those of the second embodiment, but with the central portion of the antenna raised;

FIGURE 10 is a perspective view of the antenna according to FIGURE 9;

FIGURE 1l is a simplified view similar to FIGURE 3 revealing how the feed means are connected to the radiat ing elements of an antenna in which the central portion is raised;

FIGURE l2 is a conical radiation pattern similar to FIGURE 6, this pattern being obtained from an antenna having a raised central portion; and

FIGURE 13 is a view taken through the antenna pattern of FIGURE 12, revealing the components of po1arization of a given section thereof at a given instant.

Referring initially to FIGURE 1, there is illustrated an antenna 10 constituting a first embodiment of this invention wherein the radiating portion or face 11 consists of radiating elements 12, 13, 14 and 15 in the form of intera central axis and disposed in a common plane. The inner ends of these elements terminate in a common central area at feed points 12', 13', 14 and 15 respectively. The outer ends of these elements may terminate adjacent the outer edge of the` antenna in any convenient manner such as the 90 relationships shown.

The radiating elements are electrically isolated from each other, and accordingly printed circuitry techniques may be employed in the illustrated embodiment for the creation of radiating elements upon a dielectric sheet 16. The sheet 16 may be structurally mounted by suitable screws or the like upon a mounting plate 17, which in turn may be provided with mounting holes 13 to enable the. antenna to be, secured in the desired operating position, such as to the underside of an aircraft. Radiating elements of other construction may of course be employed if desired.

In FIGURE 2 a cavity 21 is defined on the side of the dielectric sheet that is remote from the radiatingI elements, and to this end, a cavity plate 19 is secured to the underside of mounting plate 17 in the illustrated manner. The cavity plate is provided with circumferential edge portions 2'2 located radially outwardly of the radial portion of the antenna so as to define a closed cavity and to properly support plate 19 with respect to mounting plate 17. If desired, members 17, 19 and 22 can be of integral construction, such as by the employment of metal stamping techniques.

Although there is no definite size for cavity 21, the best results have been. obtained when the depth of this cavity is slightly less than a quarter wave length at the high frequency end of the band of operation. The cavity 21 acts as a reector to direct radiation outwardly from the face of the dielectric sheet in which the radiating elements are disposed, for without the presence of the cavity, an antenna of this type would tend to radiate energy both below and above the ground plane, thereby dissipating its power in an undesirable direction and decreasing its range and overall efficiency. Other details of this construction may be observed by referring to FIG- URE 4.

Centrally mounted on the lower side of cavity plate 19 is a connector 38 through the interior of which are located a plurality of coaxial lines for supplying energy to the radiating elements. Inasmuch as four radiating elements 12 through 15 are employed in this embodiment, the lines 32 through 35 are connected to these elements, respectively, at feed points 12', 13', 14 and 15 aspreviously mentioned.

Since coaxial lines 32 -through 35 are to be connected to coaxial feed cable 23 in a balanced arrangement, a broad band balun 31 is preferably secured to the lower end of connector 38. This type of balun is described at some length by Nathan Marchand in his article entitled, f

Transmission-Line Conversion, in Electronics December 1944 issue, pages 142 through 145. As brought out in the article, whenever it is necessary to use a balanced two wire line over one part of a system and a coaxial transmission line over another part of the system, a conversion transformer is often necessary at the juncture of the two types of lines in order to maintain currents on the two types of lines in their proper relations.

In FIGURE 2, the balun 31 is generally of the type shown in Figure 6 of the Marchand article and employs a solid stub 29 centrally disposed in one end of the balun, and extending for approximately one half the length thereof. Coaxial feed line 23 is attached to the opposite end of the balun, with outer conductor 25 being secured to the continuous shield forming the exterior of the balun, and the inner conductor 24 being tapered to a size commensurate with the size of coaxial line 26 located in the balun in aligned relationship with solid stub 29. The inner'conductor 24 is connected to inner conductor 27 of line 26, and conductor 27 in turn is connected to solid stub 29 by a suitable electrical connection. Outer conductor 28 of line 26 terminates approximately at the midpoint of the balun but spaced somewhat from the stub 29. Dielectric portion 36 of line 26 separates conductors 27 and 28, continues past the termination of outer conductor 23 into contact with stub 29, although dielectric 36 is apertured to receive a small block of dielectric 37 on its upper side. The dielectric 37 is inserted in this gap between conductor 2S and stub 29 so as to increase the dielectric strength of the medium in the gap, thereby increasing the power handling capabilities of the balun.

The four coaxial lines 32 through 35 are connected in a particular arrangement as illustrated in FIGURES 2 and 3 so as to achieve a balanced arrangement. The center conductor of each lines 32 and 33 is connected to the outer conductor 2% of coaxial line 26, and the center conductors of lines 34 and 35 are connected to the solid stub 29. Balance is achieved by crossing over two of the lines as shown in FIGURES 2 and 3 so that polarities are attained for the antenna feed terminals as shown in FiGURES l and 3. In other words, when terminals 12 and 14 are positive, terminals 13 and 15' will be negative and vice versa. Freferably the top and bottom ends of the outer conductors of lines 32 through 35 are connected to ground for shielding purposes, this also causing the capacity from center conductors to ground for all four lines to be equal.

FIGURE 5 is illustrative associated with this antenna. 42 through. 45 correspond with radiating elements 12 through 15 of FIGURE l.. When these elements are energized in the manner indicated by the inner arrows I, the current vectors I indicated by dotted lines will be established at radially outer locations on the radiating elements. Since each radiating element is typically many wave lengths long and radiation originates in a mean circumferential region equaling two wave lengths, the direction of the arrows representing current in the radiating region is approximately as shown. Electric field vectors E are produced in a circumferential zone with orientation similar to that shown in this figure, lying substantially at right angles to the current vectors I. Also, since the mean diameter of the radiating circumferential zone varies with frequency, a broad range of operation is achieved by the use of an antenna of suitable diameter. Because of the orientation and distribution of the eld vectors, a null is produced in a direction normal to the plane of the spiral, with energy being radiated toward all sides.

FIGURE 6 is illustrative of the type of radiation pattern produced by an antenna as described. Elliptically polarized energy is radiated or received in all directions on the side of the ground plane upon which the antenna is mounted. FIGURE 7, which is a typical section taken through the radiation pattern of FIGURE 6, reveals the polarization of two components of the radiated electric field at any one instant. More particularly, due to the current distribution at the antenna in the horizontal plane as shown in FIGURE 5, horizontally polarized components of the radiating electric field are achieved in space. Two of these components are shown in FIGURE 7 by the vectors E, where the vector in the left lobe is entering the plane of the page, whereas the other vector is coming out of the page in the right lobe, this corresponding with the phasing of diametrically opposite current vectors at the antenna.

Due to the radial electric field distribution at the antenna as `shown in FIGURE 5, electric field radiation po, larized in the G-direction is also achieved. In FIGURE 7, two 0 components of the electric field are shown by vectors E, which point downwardly at a slant angle corresponding to the 0-direction, this also corresponding with the electric field vectors pointing outwardly in FIGURE 5. This polarization bears a resemblance to that obtained from radiation by an annular slot antenna in a finite ground plane where the electric field at the antenna is also radial. As a result of the radial electric field at the antenna, the polarization of the radiated field from the annular slot antenna is also in the 0-direction.

A spiral type antenna as described herein differs from of the theory of operation The four radiating elements the annular slot, loop, and other resonant antennas wherein standing waves exist, for the spiral type antenna contains traveling waves along the radiating elements. Because of the configuration of the antenna, and more speciiically the four conductors, spacing between conductors, many turns, and polarities of the feed terminals, the current and electric field distributions shown in FIGURE are achieved in a region corresponding to a mean circumference of two wave lengths, this accounting for the orientations of the current and electric field vectors illustrated in the latter figure. Since traveling waves exist in the antenna, nearly equal radiation is achieved along circles parallel to the face of the spiral with centers along the perpendicular axis of the spiral. Elliptical polarization is obtained because the Eg, and E, components are about 90 out of time phase.

Referring to FIGURE 8, another embodiment according to this invention is shown, with the radiating elements through 55 corresponding to elements 12 through 15 and 42 through 45 of earlier figures, and preferably being 8 form 'an figuration, `with each element being bent approximately 90 D ata number of locations in the process of winding across the face of the antenna. Feed points 52 and 54 of elements 52 and 54 are connected to the outer conductor of a coaxial line, and feed point 53 is connected to the center conductor. Although a balun is not used in the illustrated embodiment, a shallow cavity (not shown) is mounted on the underside of the antenna in a manner similar to that shown in FlGURE 2. The cavity is square to conform to the square configuration of the radiator, but it `can be circular if desired. A feed arrangement can consist olf a single coaxial line passed through the bottom center of the cavity and electrically connected to the radiating elements in the aforementioned manner.

A study of feed points shows that current distribution at the center of this antenna embodiment is similar to that shown in FiGURE 5 since, when current is lowing toward 53' in conductors 53 and 55, current will ow away from 5,2 and 54 because these points are of opposite polarity with respect to that of feed point 53. Current and electric field distributions in the circumferential radiating zones are similar to that achieved in the embodiment shown in FIGURE l, because of the similar current distribution at the center and the generally spiral type configuration of the radiator. However, due to the unbalanced feed arrangement sbown in FIGURE 8, radiation in yazimuth is notas symmetrical as that obtained from the antenna shown in FIGURE l, wherein a balun was employed. If the balanced feed arrangement be indicated, a balun may of course be employed with the antenna illustrated in FIGURE 8.

Referring now to FIGURES 9 and l0, an embodiment is illustrated in which the central portion of the face of the antenna is raised to form a somewhat pyramidal configuration. However, as an example, the central portion of the face of the antenna may be raised in the order of magnitude of 5/8, so that the radiating elements 62 through 65 of this embodiment are still disposed in a substantially common plane upon dielectric sheet 66. Therefore the increase, if any, in aerodynamic drag of this embodiment when employed in an aircraft is small. Although the desired type of feeding arrangement may off course be employed with this embodiment as with the earlier embodiments, a balun is preferably used, With the feed lines preferably being crossed as shown in FIGURE ll in order that balance will be achieved. In the latter figure, cavity 71 is defined by a tapered bottom surface that agrees fairly closely with the configuration of the radiating surface of the antenna.

Since the mean diameter of the radiating circumferential zone varies inversely with frequency, radiation at the high frequency end of the operating band originates near the apex of the pyramid to produce radiation closer to the ground plane than radiation from a fiat spiral antenna. However, the reduction in angle of radiation at the low frequency end of the operating band is not as significant because radiation originates near the base of the pyramid where the diameter of the pyramid is greater.

The radiation patterns obtained by the use of the embodiment according to FIGURES 9 and l() are shown in EIGURES 12 and 13, which correspond comparatively closely with the radiation pattern illustrated in FIGURES 6 and 7 but with the radiation being somewhat closer to the ground plane because of the raised central portion of the antenna.

The described embodiments of an antenna according to this invention are merely exemplary, and other configurations and other feeding arrangements are possible within the orbit of this invention. As an example, the balun could be eliminated and a balanced arrangement nevertheless obtained if separate generators are used to energize Ithe radiating elements, the generators being phased so as to present appropriate polarities. By the selection of the desired configuration, various radiation patterns may be obtained which advantageously are elliptically polarized and designed vfor operation over a wide frequency range.

We claim:

l. A flush mounted elliptically polarized omniazimuthal antenna having a face, and a plurality of at least four conducting elements electrically isolated from each other and interwound in a common direction across said face so that the introduction of electromagnetic energy to said antenna will produce apparent current vectors at quadratic points around the means circumferential region of said elements, the apparent current vector at any one quadratic point being circumferentially opposed to the apparent current vectors at the adjacent quadratic points, whereby said antenna will have an elliptically polarized omniazimuthal pattern.

2. A iiush mounted elliptically polarized omniazimuthal antenna having a face and an underside, a plurality of at least four conducting elements electrically isolated from each other and interwound in a common direction across said face so that introduction of electromagnetic energy to said antenna Will produce apparent current vectors at quadratic points around the mean circumferential region of said elements, the apparent current vector at any one quadratic point being circumferentially opposed to the apparent current vector of the adjacent quadratic points, balanced coupling means mounted on said underside, with the radially inner ends of said radiating elements connected to said coupling means, whereby a balanced and symmetrical wave pattern may be transmitted.

3. The antenna as defined in claim 2 in which mounting means for said antenna are provided, said mounting means deiining a cavity on the underside of said antenna of a depth approximately 1A wave length, whereby a radiation pattern is principally formed on the face side of said antenna.

4. A liush mounted elliptically polarized omniazimuthal antenna of generally spiral construction having a face, a plurality of at least four conducting elements interwound about a common axis in the same direction across a portion of said face, said conducting elements being electrically isolated from each other and disposed substantially in a common plane, and balanced feed means connected to the radially inner ends of said elements so that when energy is coupled into said antenna through introduction of electromagnetic energy apparent current vectors will be produced at quadratic points around the mean circumferential region of said elements, the apparent current vector at any one quadratic point being circumferentially opposed to the apparent current vector at the quadratic points adjacent thereto, whereby a balanced land symmetrical wave pattern may be transmitted by said antenna.

5. The antenna as defined in claim 4 in which said conducting elements are in the form of interwound spirals.

ama/teo 6. The antenna as defined in claim 4 in which said conducting elements form an essentially square contiguration, with each element being bent approximately 90 in a number of locations on the face of the antenna.

7. The antenna as defined in claim 4 in which a central portion of said face is slightly raised, with said fee-d means connected at said raised portion to the inner ends of said eiements.

8. The antenna as defined in claim 4 in which said conducting elements are disposed upon dielectric material, and said feed means includes a halun connected to said elements by means of a plurality of balanced output conductors connected in an electrically symmetrical arrangement.

9. An elliptically polarized omniazimuthal antenna adapted to be flush mounted on the surface of an aircraft or the like comprising a plurality of at least four interwound conducting elements disposed in a generally spiral arrangement upon dielectric material, mounting means for said antenna including means deiining a cavity of a depth of approximately 1A of a wave length on the side of the antenna opposite the surface of said elements, and feed means including a balun for energizing said elements so that the introduction of electromagnetic energy to said antenna will produce apparent current vectors at quadratic points around the mean circumferential region of said elements, the apparent current vector at any one quadratic point being opposed in a circumferential direction to the apparent current vectors at the quadratic points adjacent thereto, and a plurality of balanced output conductors connecting said elements with said balun in an electrically symmetrical arrangement.

10. The antenna as deiined in claim 9 in which said conducting elements each are formed with a number of 90 bends so that said elements define a substantially square configuration on the face of said antenna.

11. The antenna as defined in claim 9 in which the central portion of said antenna is raised somewhat so as to cause the radiation pattern of the antenna to occur closer to :the ground plane of the antenna.

12. An antenna mounted flush with the surface of a ground plane for transmitting and receiving electromagnetic energy in an elliptica/lly polarized pattern comprising ya face, and four radiating elements interwound about a common axis in the same direction across a portion of said face,y said radiating elements being electrically isolated from each other and disposed substantially in a common plane, and coupling means connected to the first and third of said four conducting elements in afirst phase relation and connected to the second and fourth of said elements in a second phase relation displaced substantially 180 electrical degrees from said first phase relation, whereby inunder for concentrating S troduction of electromagnetic energy to said antenna will produce apparent current vectors at quadratic points around the mean circumferential region of said elements, the apparent current vector at any one quadratic point being circumferentially opposed to the apparent current vectors at the quadratic points adjacent thereto.

13. The antenna as deiined in claim 12 in which said radiating elements are disposed upon dielectric material.

14. The antenna as defined in claim 12 in which said radiating elements are in the form of intertvound spirals.

15. The antenna 'as defined in claim 12- in which said radiating elements -torm an essentially square coniiguration, with each element being bent approximately 90 in a number of locations on the face of the antenna.

16. The antenna as defined in claim 12 in which a eentral portion of said face is slightly raised, with said feed means connected at said raised portion to the inner ends of said elements.

17. An antenna in accordance With claim 12 in which I said coupling means is a two-wire transmission line.

1S. An antenna in accordance with claim 12 which includes means for matching impedances between said coupling means and the ultization circuitry, and mounting means on the underside of said face defining a cavity therethe radiation pattern of said antenna on the other sideof said face.

19. An antenna in accordance with claim 18 in which said means for matchingr impedances is a` balun, and the said first and third elements are electrically shorted, and the said second and fourth elements are electrically snorted together, said coupling means being connected to said elements at the radially inner ends thereof.

References Cited in the tile of this patent tronics, December 1944, pages 142-145.

Antenna Systems, AF Manual 52-19, 1953, pages 227,

Klass: Airborne Spiral Antennas Minimize Drag, Aviation Week, July 14, 1958 pages -82.

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