US3051951A

US3051951A - Omnidirectional beacon antenna

Info

Publication number: US3051951A
Application number: US683917A
Authority: US
Inventors: Lucanera Constantino
Original assignee: Deutsche ITT Industries GmbH
Current assignee: TDK Micronas GmbH; International Telephone and Telegraph Corp
Priority date: 1957-09-11
Filing date: 1957-09-11
Publication date: 1962-08-28
Anticipated expiration: 1979-08-28
Also published as: GB840149A; CH364536A

Description

Aug. 28, 1962 c. LUCANERA 3,051,951

OMNIDIRECTIONAL BEACON ANTENNA Filed Sept. 11, 1957 In ventor COA/SMn/r/A/o UCM/ERA Attorney United States Patent O rind sept. 11, 1957, ser. No. 683,917 s claims. (ci. 343-106) This invention relates to omnidirectional beacon antennas and more particularly to omnidirectional beacon antennas for use in producing a multilobed radiationpattern having -a fundamental modulation frequency and one or more additional harmonics of the fundamental frequency for use in radio navigation systems such as that commonly known as TACAN.

Omnidirectional beacon systems such as in TACAN have a high order of directional @accuracy which is dependent upon the use of a directive antenna pattern rotated at a fundamental frequency and modulated by a harmonic of fundamental frequency so `as to produce a generally multilobed rotating ldirective radiation pattern. The antennas usually consist of a central omnidirectional radiator surrounded by pat-tern modifying elements .adapted to revolve around the .central radiator. Due to the rotation of the multiple-modulation antenna pattern, a receiver located remotely from the .transmitter receives energy which appears ras an amplitudesmodulated wave `having a fundamental modulation component and a modulation component at a harmonic frequency of the fundamental. Both fundamental and harmonic Ifrequency reference signals are transmitted for comparison with the received components of the rotating pattern so that the receiver may determine its azimuth relative to the beacons lantenna. system.

In beacon systems of this type it is desirable to have the antenna lsystem produce a vertical radiation pattern which provides good coverage at angles above lthe `horizon while having low radiation below the horizon to minimize site errors. Various arrangements have been used to obtain the desired result. `One arrangement uses a central radiator comprising a vertical stack of elements such as cones. However, this arrangement adds considerable height to the antenna Isystem 'and has some additional disadvantages such as producing severe nulls in the pattern at certain vertical angles. Another disadvantage of previous antennas is that they provide coverage over -a relatively narrow band of frequencies.

The principal object of invention is to provide ian improved antenna for a beacon sys-tem having good vertical coverage over ya broad band o-f frequencies.

Another 'object is to prov-ide such an yantenna system having a small vertical height.

According .to one aspect of the invention, a beacon antenna system is provided having the gener-al characteristics of a horn antenna comprising a rst conductive member having a generally horizontal at counterpoise surface, and a .second conductive dish-shaped member which is symmetrical about an axis extending perpendicular to lche counterpoise surface `at the center thereof. rFhe second member is disposed above the rst member with the closest spacing along the axis. A vertically polarized omnidirectional central radiator, such as a quarter-wavelength stub, is placed between the two members along the axis. The counterpoise surface carries the pattern-modulating elements and is rotated about the central radiator.

A further feature of the invention resides in providing the first member with .a second horizontal conductive sur-V face in a plane an odd number, such `as three, of quarter wavelengths below the counterpoise surface to form a radio frequency (R.F.) choke which reduces radiation at negative vertical angles, that is, below the horizon.

3,951,951 Patented Aug. 28, 1952 ICC According to another aspect of the invention, an R.F. choke in the form of an inverted cup having a quarterwavelength llange is placed -about the central feed line to 'the quarter-wavelength stub, the upper surface of the choke being Ian odd number of quarter wavelengths, such as three quarter wavelengths, below the feed point of the central radiator. IA quarter-wavelength hollow conductive sleeve may be placed Iaround the central radiator and feed line, symmetrical of the feed point.

The foregoing and other objects `and features of this invention and the manner of attaining them will become more apparent' and the invention itself will be best understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings comprising FIGS. l and 2, wherein: l

FIG. l is a plan View of a beacon antenna system; and

FIG. 2 is a cross-section View, partly diagrammatic, taken `along lines 2 2 of FIG. l.

Referring to the drawing, the disclosed embodiment of the antenna `system includes a conductive counter-poise surface 1 and a cone-shaped conductive member 2 disposed above the counterpoise surface with its apex at its lower point along the axis perpendicular to the center of the counterpoise surface. A stationary central radiator comprising a quarter-wavelength stub 3 is placed between the counterpoise and the conical member and is vertically disposed along the axis. The central radiator is fed by a transmission line 4, which consists of a length of ilexible coaxial cable 5 with the copper sheath removed and enclosed in a 34E-inch rigid hollow tubular conductor 6 which supports it. This forms a characteristic impedance of 50 ohms. The central coductor 7 of this transmission -li-ne is connected to 'a feed point :at the lower end of the stub radiator 3. The transmission line 4 is coupled to a source of R.F. energy, not shown.

To reduce the R.F. current owing on the outside of Ithe transmission line and to prevent it from acting as a radiator, an R.F. choke in the form of an inverted cup 8 is placed around the transmission line approximately three quarter wavelengths from the feed point to the stub 3. The flange 9 of the choke is approximately one quarter wavelength long. 'Ilhe cup Sis connected to the outer con- .ductos` 6 of the transmission line 4. A length of hollow conductive tubing 1t) one quarter wavelength long is placed `around the stub 3 and transmission line 4, symmetrically and concentrically in respect to the feed point, 4t-o further 'aid in reducing the R.F. current on the line 4. This sleeve 10 is supported by an insulating tube 11.

The central stationary elements includ-ing the radiator 3, transmission line 4, inverted cup `8, and sleeve 10` are enclosed within a dielectric cylinder 12.

The rotating elements, including the counterpoise surface 1, are supported by a dielectric cylinder 13, which is rotated at l5 lcycles per second by an arrangement shown diagrammatically by a motor 14 and a gear arrangement 1S.

To reduce the radiation at negative angles below the horizon and improve the vertical pattern, a second horizontal conductive surface 16 is placed three quarter wavelengths below the counterpoise surface 1. The surface 16 and the counter-poise surface 1 are electrically connected at their inner edges by a tubular conductive cylindrical portion 17, which is attached to the dielectric cylinder 13.

To provide the multilobed horizontal pattern, a parasitic element 18 is attached to cylinder 13 to provide a fundamental modulation, and nine parasitic elements 19 are equally spaced around the outer edge of the counter' poise surface 1 to provide the ninth-harmonic modulation.

length long and insulated from counterpoise surface 1. However, if desired, they may be a quarter wavelength long and electrically connected to the counterpoise surface y1. A description of TACAN antennas and the design considerations involved in determining the characteristics and location of the parasitic elements may be found in Electrical Communications, published by International Telephone and Telegraph Corporation, New York, New York, vol. 33, No. 1, March, 1956, pages 35-59. It has been found that one satisfactory type of parasitic elements may comprise 3z-inch hollow aluminum tubing. In some arrangements it may be desirable to slant the outer parasitic elements toward the center and support them by means of insulators attached to cone 2. With such arrangement it would be necessary to rotate the cone 2 and, therefore, it may be supported by the rotating dielectric cylinder 13 as shown. However, with the parasitic elements vertically disposed as shown, the cone 2 should preferably be supported by the stationary dielectric cylinder 12 to reduce the weight of the rotating structure.

An antenna system comprising the above described new combination of elements produces a `carrier radiation pattern which is omnidirectional in the horizontal plane, and in vertical planes has a relatively high strength from the horizon up to positive vertical angles of about 50, while having a relatively low strength at angles below the horizon. This combination does not produce any appreciable nulls in the vertical pattern within the useful range, such as are characteristic of other arrays.

The rotating parasitic modulating elements 18 and 19 produce a space modulation of the carrier pattern in the horizontal planes to give azimuth bearing information. The arrangement according to this invention produces useful modulation from the horizon up .to fairly high vertical angles.

In a specific embodiment of the invention for use in the band of 960 to `1025 megacycles, the vertical spacing between the outer edge of cone 2 and surface 1 is 12 inches, surface 16 is 10 inches below surface 1, the upper surface of the inverted cup 8 is 7 inches below the lower edge of the sleeve 10 and `61/4 inches below surface 1, the inner dielectric cylinder 12 has a diameter of 4 inches and the outer dielectric cylinder 13 has a diameter of 51A; inches. The surfaces 1 and 16 have a diameter of 41 inches, and the dimension of the cone from the apex to the outer edge is ll inches.

While for optimum performance it is desirable that the combination include all of the elements as described, satisfactory performance for some purposes may be obtained with various subcombinations and these are considered as being within the scope of the invention.

While I have described above the principles of my invention in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of my invention as set forth in the objects thereof and in the accompanying claims.

I claim:

l. An omnirange beacon antenna comprising a first conductive planar counterpoise member, a conductive conical member disposed coaxially about a common axis of said antenna and above said rst member with the apex of said conical member directed toward said first member, a vertically polarized central radiator disposed along said axis and located between said counterpoise member and said conical member, dielectric supporting means connected to both said members and mounted for rotation about said common axis, a transmission line disposed along said common axis and connected to said central radiator, a plurality of parasitic elements mounted on said rst member and disposed parallel to said axis, means to rotate said supporting means about said axis to cause said parasitic elements to rotate about said axis whereby the rotation of said parasitic elements about said central radiator produces a multilobed rotating antenna pattern.

2. An omnirange beacon antenna comprising a iirst conductive planar counterpoise member, a conductive conical mem-ber disposed coaxially with said counterpoise member about a common axis of said antenna and above said counterpoise member with the apex of said conical member directed toward said counterpoise member, a vertically polarized central radiator disposed along said axis and located between said counterpoise member and said conical member and spaced apart from the apex of said conical member, a second conductive planar counterpoise member disposed about said common axis and located on the opposite side of said lfirst counterpoise member from said lcentral radiator, dielectric supporting means -connected to said first and second counterpoise members and said conical member and mounted for rotation about said common axis, a plurality of parasitic elements insulated from and mounted on said iirst counterpoise member and disposed parallel to said axis, means to rotate said dielectric supporting means about said axis to cause said parasitic elements to rotate about said axis whereby the rotation of said parasitic elements produces a multilobed rotating antenna pattern.

3. An omnirange beacon antenna comprising a rst conductive planar counterpoise member disposed about a common axis of said antenna, a second conductive planar counterpoise mem-ber disposed about said axis and spaced apart along said axis from said first counterpoise member, a conductive conical member disposed about said axis on the opposite side of said second counterpoise member from said iirst counterpoise member with the apex of said conical member directed toward said second counterpoise member, a vertically polarized central radiatior disposed along said axis between said second counterpoise member and said conical member and spaced apart from said conical member and said second counterpoise mem-ber, dielectric supporting means connected to both said counterpoise member and said conical member and mounted for rotation about said axis and said central radiator, a plurality of conductive parasitic elements disposed on said second counterpoise member on the same side of said second counterpoise member as said central radiator and disposed parallel to said axis, means to rotate said dielectric support means whereby the rotation of said parasitic elements about said central radiator creates a multilobed rotating antenna pattern having considerably greater radiation strength at points located on the same side of said axis as said conical member as compared to points located on the opposite side of said axis.

4. An omnirange beacon antenna according to claim 3 wherein each of said parasitic elements is one-quarter wavelength long and is electricall connected to said counterpoise member.

5. An omnirange beacon antenna for producing a rotating multilobed antenna pattern comprising a first conductive planar counterpoise member disposed about a common axis of said antenna, a second conductive planar counterpoise member disposed substantially parallel to said rst surface and spaced apart from said first member along said common axis, a conductive conical member disposed about said axis on the opposite side of said second counterpoise member from said iirst counterpoise member with the `apex of said conical member directed toward said second counterpoise member, a vertically polarized central radiator disposed along said axis between said second counterpoise member and said conical member and spaced apart therefrom, a fundamental parasitic element insulated from and mounted on said second counterpoise member and disposed parallel to said axis and between said conical member and said second counterpoise member, a plurality of parasitic elements insulated from and mounted on ysaid second counterpoise member on the opposite side of said member from said first counterpoise member and disposed parallel to said axis, dielectric support means connected to both said counterpoise members and said conical member and mounted for rotation about said axis, means to rotate said support means connected to said support means whereby the rotation of said parasitic elements about said central radiator creates a rotating multilobed antenna pattern.

6. An omnirange beacon 'antenna -for producing a rotating multilobed antenna pattern comprising a first conductive planar counterpoise member disposed about a common axis of said antenna, a second conductive planar counterpoise member disposed about said axis and spaced apart along said axis from said iirst counterpoise member, a conductive conical member disposed -about said axis on the opposite side of said second counterpoise member from said first counterpoise member with the apex of said conical member directed toward said second counterpoise member, a vertically polarized central radiator disposed along said axis between said conical member and said second counterpoise member and spaced apart from both, dielectric support means connected to both said counterpoise members and said conical member and disposed for rotation about said common axis, a fundamental parasitic element one-half wavelength long insulated from and mounted on said second counterpoise member and disposed parallel to said common axis and located between said conical member and said second counterpoise member, a plurality of harmonic parasitic elements one-half wavelength long insu-lated from and mounted on said conical member and said second counterpoise member, said parasitic members being disposed along lines directed toward said common axis, means to rotate connected to said dielectric support means whereby the rotation of said parasitic elements about said central radiator produces a rotating multilobed antenna pattern.

7. An omnirange beacon antenna for producing a rotating multilobed antenna pattern comprising a first conductive planar counterpoise member disposed about a common axis of said antenna, a second conductive planar counterpoise member disposed substantially parallel to said rst member and spaced apart therefrom along said axis, a conductive conical member disposed about said axis on the opposite side of said second member from said irst member with the apex of said conical member directed toward said `second counterpoise member, a vertically polarized central radiator disposed along said axis between said conical member and said second counterpoise member and spaced apart from both said conical member and said second counterpoise member, a stationary transmission line disposed along said axis and connected to said central radiator, a radio frequency choke mounted on said transmission line and disposed along said -axis between said first and second counterpoise members, a fundamental conductive parasitic element one-half wavelength long insulated from and mounted on said second counter-poise member and disposed between said conical member and said second counterpoise member, a plurality of conductive parasitic elements insulated from and mounted on said second counterpoise member and disposed parallel to said common axis and located at radii larger than the radius of the base of said conical member, dielectric support means connected to both said counterpoise members and said conical member and mounted for rotation about said common axis, drive means connected to said dielectric support means to rotate said parasitic elements about said central radiator whereby the rotation of said parasitic elements creates a rotating multilobed antenna pattern.

8. An omnirange beacon antenna for producing a rotating multilobed -antenna pattern comprising a first conductive planar counterpoise member disposed about a common axis of said antenna, a second conductive planar counterpoise member disposed substantially parallel to said iirst member and spaced apart therefrom an odd number of half Wavelength along said axis, a conductive conical member disposed about said axis on the opposite side of said second member from said tir-st member with the apex of said conical member directed toward Said second counterpoise member, a vertically polarized central radiator disposed along said axis between said conical member and said second counterpoise member and spaced apart from both said conical member and both said counterpoise members, a stationary transmission line disposed along said axis and connected to said central radiator and spaced apart from both said counterpoise members, a radio `frequency choke mounted on said transmission line and disposed along said axis between said rst and second counterpoise members, a fundamental conductive parasitic element one-half Wavelength long insulated from and mounted on said second counterpoise member and disposed between said conical member and said second counterpoise member at a first radius from said axis, a plurality of harmonic conductive parasitic elements one-half wavelength long insulated from and mounted on said second counterpoise member and disposed parallel to said common axis and located at radii larger than the radius of the base of said conical member, said conical member having a base whose radius is greater than said first radius of said fundamental parasitic element, dielectric support means connected to both said counterpoise members and said conical member 4and mounted for rotation about said common axis, drive means connected to said dielectric support means to rotate and parasitic elements about said central radiator whereby the rotation of said parasitic elements creates a rotating multilobed antenna pattern.

References Cited in the iile of this patent UNITED STATES PATENTS 2,565,506 Litchford Aug. 28, 1951 2,928,087 Parker Mar. 8, 1960 FOREIGN PATENTS 495,977 Great Britain Nov. 23, 1938 114,368 Australia Dec. 9, 1941