US3066295A

US3066295A - Side-fire helical antenna with conductive support

Info

Publication number: US3066295A
Application number: US806838A
Authority: US
Inventors: Lloyd O Krause; Ronald E Fisk
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1959-04-16
Filing date: 1959-04-16
Publication date: 1962-11-27
Anticipated expiration: 1979-11-27
Also published as: GB930382A

Description

Nov. 27, 1962 1.. o. KRAUSE ETAL 3,066,295

SIDE-FIRE HELICAL ANTENNA WITH CONDUCTIVE SUPPORT Filed April 16, 1959 FIG.1

FIG?) INVENTORS Lloyd QKrause [I n BY Ronald E. Fisk TRANSMITTER AT TOR EY 3,85%,295 Patented Nov. 2?, i962 3,066,295 SIDE-F HELICAL ANTENNA WITH CGNDUCTIVE SUPPORT Lloyd 0. Krause, North Syracuse, and Ronald E. Fisk,

Liverpool, N.Y., assignors to General Electric Company, a corporation of New York Filed Apr. 16, 1959, Ser. No. 806,838 21 Claims. (Cl. 343-874) This invention relates to antennas of the kind used for the radiation and reception of electromagnetic energy and more particularly to antennas for radiating and receiving high frequency energy having a broad azimuth directivity and wide bandwidth.

In many communication and television applications, there is a need for radiating electromagnetic energy from a central source to a plurality of fixed or mobile receivers at any azimuth position about the central source. The radiation should be omnidirectional to permit the uniform distribution of the radiant energy to all points in circles concentric with the central source. Such a distllblltzOl'l affords the efiicient utilization of the available electromagnetic energy when the receivers are uniformly distributed over a given area or when the mobile receivers have equal probabilities of being at any position within the area.

Although antenna systems are available which are substantially omnidirectional, their radiation efliciency is limited by the spread in the elevation distribution of the electromagnetic energy. The elevation distribution may be defined as distribution in planes normal to the surface of the earth. When communication antenna systems transmit line of sight range signals, i.e., PM. or television, most of the electromagnetic radiation transmitted in directions above the horizon is incapable of reception and therefore wasted. To minimize the amount of unavailable radiation transmitted by such antenna systems, it is necessary to decrease the angular spread of the radiation elevation distribution.

Many techniques employing complicated arrays and stacks have been employed in obtaining more desirable elevation directivity characteristics. The resultant antenna systems are usually complex and expensive. However, very satisfactory solutions for the problem are obtained by using the side-fire helical antennas described and claimed in the following copending United States applications: Lloyd 0. Krause and Howard G. Smith, Serial No. 732,482, filed May 2, 1958, now Patent No. 2,985,878; Paul M. Pan, Serial No. 646,837, filed March .18, 1957, now Patent No. 3,019,438; and Lloyd 0. Krause, Serial No. 739,748, filed June 4, 1958, now Patent No. 2,953,786; all of which are assigned to the same assignee. Each of the helical antennas disclosed in the cited applications has a cylindrical central conductor with a helical radiating conductor disposed, with a radial separation, about the cylindrical central conductor. A radiating conductor is one which is capable of radiating electromagnetic energy when it is coupled to a source of such energy.

These side-fire helical antennas have stimulated a demand for even better antennas of the same type. In particular, even through the bandwidth of these antennas is unusually broad for their type, it has been found that greater bandwidths are desirable in some applications. For example, the lower channels of VHF television transmission require large percentage bandwidths with channel 2 requiring a twelve percent bandwidth. Furthermore, these antennas may be considered as unterminated radiating transmission lines which because of their length and radiating conductor to central conductor spacing cause controlled radiation and attenuation of the energy propagated along the line. Presently, to provide such bandwidth it is necessary to use a higher rate of attenua tion per turn with fewer turns and resulting lowered vertical directivity. Thus, fewer than the optimum number of turns must be used.

It is accordingly a general object of the invention to provide an improved antenna.

It is a more specific object of the invention to provide an improved helical antenna which has a high radiation etficiency together with a very broad bandwidth.

It is another object of the invention to provide an improved helical antenna of the side-fire type which is more adaptable in certain applications than previous helical antennas.

Briefly, in accordance with a general aspect of the invention, an antenna is provided comprising a central conductor and a radiating conductor. The central conducior has a polygonal cross-section. The radiating conductor is developed about the central conductor as a series of axially progressive turns which are radially spaced from the central conductor. A first energization terminal is coupled to the cenlral conductor and a second energize.- tion terminal is coupled to the radiating conductor. The energization terminals are adapted to receive signal energy for radiation by the radiating conductor.

It should be noted that there is a discontinuity in the spacing between the radiating conductor and the central conductor at each vertex of the polygon. This discontinuity is electrically equivalent to a lumped reactance across the equivalent transmission line. Thus, at each vertex there is a discontinuity loading effect. Furthermore, it should be noted that when each turn of the radiating conductor is substantially an integral number of operating wavelengths and the polygon is regular the loading is periodic. This periodic loading causes a dispersive phase velocity with a frequency characteristic having a positive slope. Hence, the turn to turn phase remains in substantial equality over a wider frequency range, thus giving increased operating bandwidth for a given number of turns and atienuation per turn. Hence, a more optimum number of turns for a given application may be used. In some cases, it may be desirable to add additional periodic loading by the addition of metallic or insulative discontinuities.

The major mode of energy transmission of a side-fire helical antenna follows the path traced out by the radiating conductor. It is this major mode which causes the antennas to side-fire radiate in azimuthally distributed patterns with a minimum of elevation distribution. However, these antennas may also be considered to be degenerate forms of coaxial transmission lines with the central conductor of the antenna serving as the central conductor of the coaxial transmission line and the radiating conductor serving as a discontinuous outer conductor of the coaxial transmission line. Thus, there is a minor mode of energy propagation which coaxially travels along the antenna. This minor mode does not radiate and attenuate. Therefore, it determines the limit of isolation between the feed and other end of the helix. Thus it limits the ease and degree of self-diplexing or dual-feeding of the antenna.

It is accordingly an object of another aspect of the invention to enhance the performance of helical antennas of the side-fire type when used in self-diplexed applications.

It is another object of this aspect of the invention to provide a side-fire helical antenna which has. a minimum of coaxially propagated energy.

Briefly, in accordance with this aspect of the invention, an antenna is provided comprising a ribbonlike conductor extending along the axis of the antenna as a plurality of axially progressive turns. A radiating conductor is further provided which extends along the axis of the antenna as a plurality of axially progressive turns. The radiating conductor is radially displaced from the ribbonlike conductor with each element of the radiating conductor radially projectable on the ribbonlike conductor. First and second energization terminals are respectively coupled to the ribbonlike conductor and the radiating conductor, and adapted to receive signal energy for'radiation by the radiating conductor.

A feature of this aspect of the invention is the construction of the ribbonlike conductor from a substantially flat mesh of conductors.

It should be noted that the use of a ribbonlike mesh of conductors further limits the propagation of the minor coaxial mode to further increase the isolation between the energization terminals and the ends of the antenna. Therefore, such an antenna can more easily be of the self-diplexing type. That is, two separate signals can be simultaneously fed to the same radiatable conductor for radiation. One signal is fed to one end of the radiating conductor and the other signal is fed to the other end of the radiating conductor. Such a system is highly advantageous in television transmission where the auralsignal and the video signal are simultaneously transmitted. The two signals remain essentially isolated from each other.

In addition to the electromagnetic advantages gained, there are also many mechanical advantages. In the lower frequency channels of television transmission the required size of the antennas is quite large. Since the antennas must be elevated to insure uniform signal reception, it is necessary to support these antennas on very tall masts. However, when the antennas of the invention are employed the mechanical load borne by the mast is much less and, in fact, the mast may be considered as part of the antenna. Furthermore, since the antennas of the invention are skeletal in nature, i.e. there is a min imum of continuous plane surface per unit volume, they oifer a minimum of resistance to the Wind. Consequently the supporting masts require a minimum of bracing. In many uses, standard structural shapes are easily adaptable.

Additional objects, features and advantages of the invention will be apparent from the following detailed description when read with the accompanying drawings wherein:

FIGURE 1 is an elevational view of an antenna structure, in accordance with a preferred embodiment of the invention, which permits the radiation of electromagnetic energy having a very large bandwidth;

FIGURE 2 is a cross-sectional view of the antenna structure taken along the line 2-2 of FIGURE 1 showing the central conductor as triangular in cross-section;

FIGURE 3 is a cross-sectional view of another embodiment of the invention in which the radiating conductor and the central conductor project as squares on a plane perpendicular to the axis of the antenna; and

FIGURE 4 is an elevational view of a portion of an antenna structure in accordance with another embodiment of the invention in which the ribbonlike central conductor is a continuous sheet conductor rather than a mesh of conductors as shown in the embodiment of FIGURE 1.

Helical antenna systems may be grouped into two characteristic types. side-fire and end-fire.

In the side-fire type with which the subiect invention is concerned, the antenna system is vertically mounted with respect to the earth, and the radiation pattern may be either linearly or circularly polarized. More exactly, the volumetric radiation pattern of the side-fire type is a solid of revolution about the antenna axis of a directive lobe normal to the axis. The radiation from an endfire helical antenna system is concentrated along the axis of the helical antennas. The radiation may also be either circularly or linearly polarized.

The side-fire type is particularly useful in television broadcasting and in communication systems where receiving locations are in various directions. The end-fire 4; type is particularly useful for directed communications and in radar systems. i i

Side-fire types may be arrayed; that is, a number of helical antennas may be supported end to end along a common axis. The side-fire types when arrayed (stacked) produce a more concentrated radiation pattern in directions normal to the common axis.

Each helical antenna comprises a series of single turns or helices. When the helical circumference is approximately some integral number of operating wavelengths, for example, two or four. wavelengths, and is driven between a point on the helix and a concentric conducting mast, the major mode of radiation dominates; that is, the helical antenna is of the side-fire type. This follows because when the helical turns are substantially an integral number of operating wavelengths in circumference, the radiative currents of each turn are in phase at any discrete azimuth. Hence theyact in concert to cause side-fire radiation, somewhat similar to an in-phase fed echelon array of radiators.

A single bay antenna system for radiating electromagnetic energy in which two radiating conductors are disposed about a central conductor of polygonal cross-section, in accordance with the preferred embodiment of the invention, is shown in FIGURES 1 and 2. The antenna system generally comprises a mast 20 carrying central conductors or

ribbonlike elements

22 and 24. The

ribbonlike elements

22 and 24 are meshes of conductors. As shown in FIGURE 2, the cross-section of the most 20 is triangular and the projection of the

ribbonlike elements

22 and 24 on a plane perpendicular to the axis of mast 20 is a triangle. Insulatively supported bythe mast 20 are radiating

helical conductors

26 and 28. A first energization terminal 30 is coupled to the junction of the ends of the

ribbonlike elements

22 and 24 at approximately the mid-point of the mast 20. A second energization terminal 31 is coupled to the junction of the

helical conductors

26 and 28 adjacent this mid-point. The first and

second energization terminals

34 and 31 are respectively connected to the outer and inner conductors of a coaxial line 36 which is connected to one output stage of a transmitter 38. The antenna system will radiate signal energy of a first kind; for example, the video signals of a television transmitter. However, the antenna system is self-diplexing and can simultaneously radiate, for example, both the audio and video signals of a television transmitter. To perform this self-diplexing, third and fourth energization terminals 32 and 34 (FIG. 1) are respectively connected to the ends of the

helical conductors

26 and 28 near the ends of the mast 20. The third and

fourth energization terminals

32 and 34" are con nected in parallel to the central conductor of the coaxial line 44) which is also connected to another output stage of the transmitter 38. Thus, if the transmitter 38 is a television transmitter, the coaxial line would be coupled to the audio output stage. It should be noted that although the third and fourth energization terminals are shown near both ends of the mast 20, the mast may extend beyond these points. More particularly, the third and fourth energization terminals are near the electrical ends of the antenna.

The ribbonlike element 22 starts near the mid-point of the mast 2t) and extends as a plurality of axially progressive turns toward the top end of the mast 29. Similarly, the ribbonlike element 24 starts atthis mid-point and extends as a plurality of axially progressive turns toward the bottom of the mast 29. The

ribbonlike elements

22 and 24 are preferably joined at the mid-point. It should be noted that the turns are spaced from each other to provide axial discontinuities which suppress the minor or coaxial mode of propagation, The helical conductor 26 extends from the energization terminal 31 as a plurality of axially progressive turns toward the top end of the mast 2t) and the helical conductor 28 similarly extends to the bottom end of the mast 20. Each of the axially progressive turns is, preferably, substantially an integral number of operating wavelengths. The ribbonlike element 22 is in the radial shadow of the helical conductor 26. In other words, each element of the helical conductor 26 is radially projectable on the ribbonlike element 22. The ribbonlike element 24 is similarly in the radial shadow of the helical conductor 28. Accordingly, the system may be considered as a radiating transmission line system, the

helical conductors

26 and 28 being the radiating transmission lines and the

ribbonlike elements

22 and 24 the ground planes.

The mast 20 is fixed to a tower 54 braced by guy wires such as guy wire '56. In addition, a beacon light 58 and lightning rods 62 and 64 are preferably provided at the top of mast 20'.

By referring to FIGURE 2, a more detailed understanding of the various elements of the antenna system may be obtained. In particular, the mast 28 includes three parallel

upright members

42, 43 and 44 axially extending along the entire length. Bracing is provided by the struts or

lateral support members

45, 46 and 47. It should be noted that the

lateral support members

45, 46 and 47 form the sides of a triangle with the

upright members

42, 43 and 44 at the vertices. The ribbonlike element 24 which is identical to the ribbonlike element 22 is comprised of a mesh of longitudinal conductors such as conductor 4'8 and transverse conductors such as conductor 50. The portions of the ribbonlike element 24 between adjacent

upright members

42, 43 and 44 are substantially fiat.

The helical conductor 28 which is identical to the helical conductor 26 is supported by insulative standofls such as standoff 52. Except for the portion near the energization terminal 31, the helical conductor 28 projects as a circle on a plane perpendicular to the axis of ti e mast 20. It is seen that the spacing between the helical conductor 28 and the ribbonlike element 24 periodically varies between a maximum and a minimum. At the minimums there is a capacitive loading of the antenna. However, it should be noted that when particular non-azimuthally uniform radiation patterns are desired, this projection will be a closed curve having a variable radius of curvature such as an ellipse.

It should be noted that the rate of attenuation and the relative percentages of modes of propagation are controlled by the effective radii of curvature of the antenna. In other words, when a conventional helical conductor is disposed around a cylindrical central conductor, the effective radii of curvature are the radius of the helix and the radius of the central cylindrical conductor. On the other hand, when a helical conductor is developed about a conductor of polygonal cross-section, the effective radii of curvature are the radius of curvature of the helix and the radius of curvature of a circle having approximately the same area as the polygon. Similarly, if a helix of noncircular turns is employed as the radiatable conductor, its efiective radius of curvature would be approximately equal to the radius of a circle having an area equal to the projected area of the noncircular turn.

In any event, it has been found that the effective radius of the central conductor should be greater than sixty percent of the effective radius of the radiating conductor.

During operation as a television transmission antenna system the video signal is fed from the transmitter 38 via the coaxial line 36 to the energization terminals 3% and 31 where a first pair of waves of electromagnetic energy related to the video signal is launched on the antenna. One wave of electromagnetic energy travels between the helical conductor 26 and the ribbonlike element 22 toward the top end of the mast 20. Another wave of electromagnetic energy travels between the helical conductor 28 and the ribbonlike element 24 toward the bottom end of the mast 2d. The major mode of propagation follows the axially progressive turns of the

helical conductors

26 and 28. As the electromagnetic waves progress along these paths of travel there is a progressive radiation into space W1 ich causes an attenuation of the energy content of the waves. When each turn of the

helical conductors

26 and 28 is an integral number of operating wavelengths, the radiated energy is in phase at each azimuth position causing a reinforcement of the radiating energy.

At the same time, the audio signals are fed from the transmitter 38 via the coaxial line 46} respectively to the

energization terminals

32 and 34. A second pair of electromagnetic waves related to the audio signal is launched on the antenna. One of these Waves travels between the helical conductor 26 and the ribbonlike element 22 toward the center of the mast 20 and the other electromagnetic wave similarly travels between the helical conductor 23 and the ribbonlike element 24 toward the center of the mast 2%. Both waves progressively radiate.

Ordinarily, with side-fire helical antennas, there is a minor coaxial mode of propagation. However, because of the axial discontinuity of the ribbonlike elements along any line parallel to the axis of the mast 2%, this coaxial mode is greatly suppressed so that a negligible amount of the available energy propagates in this mode. This results in a high degree of isolation between the energization terminal 31 and the

energization terminals

32 and 34. This isolation is determined by the total radiative attenuation of the predominant helical mode.

Furthermore, because of the abrupt periodic discontinuities in the radial spacing between the helical conductors 26 and 2S and the

ribbonlike elements

22 and 24, there is a reactive loading etfect which dispersively increases the phase-velocity versus frequency along the helix to yield a broader bandwidth system.

Although for the low VHF television channels it is preferable to utilize a truly circular helical conductor, it has been found that with the high VHF television channels and with UHF television channels radiating conductors having noncircular and even polygonal turns produce desirable radiation patterns. Accordingly, FIGURE 3 shows the cross-sectional view of an antenna which is similar to the antenna of FIGURES 1 and 2 except that the radiating conductor 28' and the ribbonlike element 24' each has a projection of a square on a plane perpendicular to the supporting mast. It should be noted that other polygonal projections are equally suitable. The use of other polygonal projections has certain advantages when chosen for certain applications. For example, in some cases a preferred directional horizontal pattern may be obtained more easily by using any pattern distortion caused by the shape in complementary fashion with other means for directionalizing, such as short stubs attached directly to the helix. Another advantage accrues when it is desired to place the helix around a structural mast or tower which is already in existence, and modifications to which are difiicult to make.

FIGURE 4 shows a portion of an antenna which is similar to the antenna of FIGURES 1 and 2 except that the ribbonlike element 24" is a continuous sheet conductor instead of a mesh of conductors.

There has thus been shown improved antennas which have very broad bandwidth along with high operating efficiency. In particular, one feature of the invention, by providing a discontinuously variable spacing between the radiating conductor and the central conductor, introduces periodic reactive loading which efiects a dispersive increase in phase velocity with frequency and accordingly enhances the frequency response. The combination of this enhancement with proper radiation attenuation per turn permits construction of the antenna with a more optimum number of turns. Furthermore, according to another aspect of the invention, the use of ribbonlike elements for the central conductors greatly suppresses the minor coaxial mode of propagation in the antenna thus leading to higher isolation between the energization terminal and the other end of the helix.

While a number of specific embodiments of the invention have been described in detail, it should be apparent that many modifications and changes may readily be made without departing from the spirit and scope of the invention.

What is claimed is:

1. An antenna comprising a central conductor extending along the axis of said antenna, the projection of said central conductor on a plane perpendicular to said axis being a polygon, said polygon having substantially equal sides, a radiating conductor developed about said central conductor as a plurality of axially progressive turns, a first energization means coupled to said central conductor, a second energization means coupled to said radiating conductor, and means for feeding signal energy to said first and second energization means for radiation by said radiating conductor.

2. The antenna of claim 1 wherein said polygonal crosssection is a-triangle.

3. The antenna of claim 1 wherein said polvgonal crosssection is a square.

4. An antenna comprising a central conductor extending along the axis of said antenna, the projection of said central conductor on a plane perpendicular to said axis having a triangular cross-section, a radiating conductor developed about said central conductor in the form of a helix, a first energization means coupled to said central conductor, a second energization means coupled to said radiating conductor, and means for feeding signal energy to said first and second energization means for radiation by said radiating conductor.

5. An antenna comprising a central conductor extending along the axis of said antenna, the projection of said central conductor on a plane perpendicular to said axis being a polygon, said polygon having substantially equal sides, a radiating conductor developed about said central conductor, said radiating conductor having a plurality of axially progressive turns of varying radius of curvature, a first energization means coupled to said central conductor, a second energization means coupled to said radiating conductor, and means for feeding signal energy to said first and second energization means for radiation by said radiating conductor.

6. An antenna comprising a central conductor extending along the axis of said antenna, the projection of said central conductor on a plane perpendicular to said axis being a polygon, a radiating conductor developed about said central conductor as a plurality of axially progressive turns, a first energization means coupled to said central conductor, a second energization means coupled to one end of said radiating conductor, a third energization means coupled to the other end of said radiating conductor and means for feeding signal energy of a first type to said first and second energization means for radiation by said radiating conductor and signal energy of a second type to said first and third energization means for radiation by said radiating conductor.

7. An antenna comprising a central conductor extending along the axis of said antenna, the projection of said central conductor on a plane perpendicular to said axis being a polygon, a first radiating conductor developed about said central conductor as a plurality of axially progressive turns extending toward one end of said central conductor, a second radiating conductor developed about said central conductor as a plurality of axially progressive turns extending toward the other end of said central conductor, a first energization means coupled to said central conductor, a second energization means coupled to said first and second radiating conductors, and means for feeding signal energy to said first and second energization means for radiation by said first and second radiating conductors.

8. An antenna comprising a central conductor extending along the axis of said antenna, the projection of said central conductor on a plane perpendicular to said axis being a polygon, a first radiating conductor developed about said central conductor as a plurality of axially progressive turns extending toward one end of said central conductor, a second radiating conductor developed about said central conductor as a plurality of axially progressive turns extending toward the other end of said central conductor, a first energization terminal coupled to said central conductor, a second energization terminal coupled to the ends of said radiating conductors remote from the ends of said central conductor, third and fourth energization terminals respectively connected to the ends of said radiating conductors adjacent the ends of said central conductor, and means for feeding signal energy of a first type to said first and second energization terminals for radiation by said radiating conductors and signal energy of a second type to said first, third and fourth energization terminals for radiation by said radiating conductors.

9. An antenna comprising a central conductor extending alorn the axis of said antenna, the projection of said central conductor on a plane perpendicular to said axis having a triangular cross-section, a first helical conductor developed in spaced relation about said central conductor, said first helical conductor starting near the mid-point of said central conductor and ending near one end of said central conductor, a second helical conductor developed in spaced relation about said central conductor, said second helical conductor starting near the midpoint and ending near the other end of said central conductor, a first energization terminal coupled to said central conductor, a second energization terminal coupled to the ends of said helical conductors near the mid-point of said central conductor, third and fourth energization terminals respectively coupled to the ends of said helical conductors near the ends of said central conductor and means for feeding signal energy of a first frequency to said first and second energization terminals for radiation by said helical conductors, and means for feeding signal energy of a second frequency to said first, third and fourth energization terminals for radiation by said helical conductors.

10. An antenna comprising a ribbonlike conductor extending along the axis of said antenna as a plurality of axially progressive turns, the projection of said ribbonlike conductor on a plane perpendicular to said axis being a polygon, a radiating conductor extending along the axis of said antenna as a plurality of axially progressive turns radially displaced from said ribbonlike conductor with each portion of said radiating conductor radially projectable on a portion of said ribbonlike conductor, a first energization means coupled to said ribbonlike conductor, a second energization means coupled to said radiating conductor and means for feeding signal energy to said first and second energization means for radiation by said radiating conductor.

11. The antenna of claim 10 wherein said polygon is a triangle.

12. The antenna of claim 10 wherein said polygon is a square.

13. An antenna comprising a ribbonlike element of a substantially flat mesh of conductors extending along the axis of said antenna as a plurality of axially progressive turns, the projection of said ribbonlike element on a plane perpendicular to said axis being a polygon, a radiating conductor extending along the axis of said antenna as a plurality of axially progressive turns, said radiating conductor being radially displaced from said ribbonlike element with each portion of said radiating conductor being radially projectable on a portion of said ribbonlike element, a first energization terminal coupled to said ribbonlike element, a second energization terminal coupled to said radiating conductor and means for feeding signal energy to said first and second energization terminals for radiation by said radiating conductor.

14. An antenna comprising a ribbonlike element extending along the axis of said antenna as a plurality of axially progressive turns, the projection of said ribbonlike element on a plane perpendicular to said axis being a polygon, a helical conductor extending along the axis of said antenna radially displaced from said ribbonlilte element with each portion of said helical conductor radially projectable on a portion of said ribbonlike element, the projection of said helical conductor on a plane perpendicular to said axis being a similar polygon, a first energization terminal coupled to said ribbonlike element, a second energization terminal coupled to said helical conductor and means for feeding signal energy to said first and second energization terminals for radiation by said helical conductor.

15. The antenna of claim 14 Wherein said polygons are triangles.

16. The antenna of claim 14 wherein said polygons are squares,

17. An antenna comprising a first ribbonlike element extending from a point on the axis of said antenna in one direction as a plurality of axially progressive turns,

a second ribbonlilre element of a substantially flat mesh of conductors, said second ribbonlike element extending from said point in the opposite direction as a plurality of axially progressive turns, the projection of said first and second ribbonlike elements on a plane perpendicular to said axis being a polygon, a first helical conductor developed about said axis, said first helical conductor being radially displaced from said first ribbonlike element with each portion of said first helical conductor being radially projectable on a portion of said first ribbonlike element, a second helical conductor developed about said axis, said second helical conductor being radially displaced from said second ribbonlike element with each portion of said second helical conductor being radially projectable on a portion of said second ribboniike element, a first energization means coupled to said first and second ribbonlike elements, a second energization means coupled to said first and second helical conductors, and means for feeding signal energy to said first and second energization means for radiation by said first and second helical conductors.

18. An antenna comprising first and second ribbonlike elements, one end of each of said ribbonlike elements being joined at a point on the axis of said antenna, said ribbonlike elements extending from said point in opposite directions along said axis as axially progressive turns, the projection of said first and second ribbonlike elements on a plane perpendicular to said axis being a polygon, first and second helical conductors disposed about said axis, one end of each of said helical conductors being joined at said point and extending in opposite directions along said axis, said first helical conductor being radially displaced from said first ribbonlike element with each element of said first helical conductor being radially projectable on said first ribbonlike element, said second helical conductor being radially displaced from said second ribbonlike element with each element of said second helical conductor being radially projectable on said second ribbonlike element, a first energization terminal coupled to said first and second ribbonlike elements, a second energization terminal coupled to the junction of said helical conductors, and means for feeding signal energy to said first and second energization terminals for radiation by said helical conductors.

19. The antenna of claim 18 including third and fourth energization terminals respectively coupled to the ends of said helical conductors remote from said point, and means for feeding signal energy of a second kind to said first, third and fourth energization terminals for radiation by said helical conductors.

20. An antenna comprising a mast, said mast including a plurality of upright members with lateral support members, said upright members defining in a cross-sectional plane of said mast the vertices of a polygon, first and second ribbonlike elements of a substantially flat mesh of conductors disposed on said upright members, each of said ribbonlike elements starting near the mid-point of said mast and extending in opposite axial directions to- Ward the respective ends of said mast, the portions of each of said ribbonlike elements between adjacent upright members defining a substantially straight line, first and second helical conductors disposed about said mast, one end of each of said helical conductors being joined together at said mid-point with said helical conductors extending from the junction toward opposite ends of said mast, said first helical conductor being radially displaced from said first ribbonlike element with each element of said first helical conductor being radially projectable on an element of said first ribbonlike element, said second helical conductor being radially displaced from said second ribbonlike element with each element of said second helical conductor being radially projectable on an element of said second ribbonlike element, a first energization terminal coupled to said ribbonlike conductors, and a second energization terminal coupled to the junction of said helical conductors, and means for feeding signal energy to said first and second energization terminals for radiation by said helical conductors.

21. The antenna of claim 20 including third and fourth energization terminals respectively coupled to the ends of said helical conductors remote from said junction, and means for feeding signal energy of a second kind to said first, third and fourth energization terminals for radiation by said helical conductors.

References Cited in the tile of this patent UNITED STATES PATENTS 2,871,478 Lander Jan. 27, 1959 2,945,227 Broussaud July 12, 1960 FOREIGN PATENTS 430,548 Great Britain Jan. 20, 1935 724,795 Great Britain Feb. 23, 1955 1,160,874 France Mar. 10, 1958 OTHER REFERENCES The T.V. Helical Antenna Adapted to Structural Tower Shapes, by Fisk, IRE Transactions on Broadcast Transmission Systems, PGBTS-l 1, September 1958, pages 4 to 10,