US3054107A

US3054107A - Wide band omnidirectional beacon antenna

Info

Publication number: US3054107A
Application number: US836779A
Authority: US
Inventors: James S Engel; Howard M Bellis; Erwin J Huber
Original assignee: Deutsche ITT Industries GmbH
Current assignee: TDK Micronas GmbH; International Telephone and Telegraph Corp
Priority date: 1959-08-28
Filing date: 1959-08-28
Publication date: 1962-09-11
Anticipated expiration: 1979-09-11

Description

Sept. 11, 1962 J. S. ENGEL ETAL 3,054,107

WIDE BAND OMNIDIRECTIONAL BEACON ANTENNA Filed Aug. 28

RF ENERGY 4 5' 45 IN V EN TORS.

ATTORNEY United States Patent 3,054,107 WIDE BAND OMNIDIRECTIONAL BEACON ANTENNA James S. Engel, Tenafly, Howard M. Bellis, Park Ridge, and Erwin J. Huber, Midland Park, N.J., assignors to International Telephone and Telegraph Corporation,

Nutley, N.J., a corporation of Maryland Filed Aug. 28, 1959, Ser. No. 836,779 7 Claims. (Cl. 343761) This invention relates to omnidirectional beacon antennas of the type used in producing a multiple-modulation radiation pattern having a fundamental modulation frequency and one or more additional harmonics of the fundamental modulation frequency for use in radio navigation systems such as that commonly known as TACAN and, more particularly, to means for stabilizing the modulation patten over a wide range of radio frequencies.

Omnidirectional beacon systems such as 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 this fundamental frequency so as to produce a generally multilobed rotating directive radiation pattern. Due to the motion of the multiple-modulation antenna pattern, a receiver located remotely from the transmitter receives energy which appears as an amplitude-modulated wave having a fundamental modulation component and a modulation component at a harmonic frequency of the fundamental. Both fundamental and harmonic frequency reference signals are transmitted omnidirectionally for comparison with the received components of the rotating pattern so that the receiver may determine its azimuth relative to the beacons antenna system.

Basically, the beacon antenna comprises, inter alia, a stationary central radiating array around which are rotated at the same angular speeds two concentric dielectric cylinders. One cylinder carries a conductive parasitic element or elements that produces, in cooperation with the central radiating array, the fundamental modulation. In a similar manner, the other cylinder carries a number of parasitic elements or combination of elements corresponding to the harmonic of the fundamental desired to be produced.

In the past, because of the difficulty in stabilizing the modulation pattern over a wide radio frequency spectrum range, the TACAN system comprised two bands of operation, viz., low band operation in which transmission occurs over a frequency range from approximately 960 to 1024 megacycles per second and receives from 1025 to 1087 megacycles, and high band operation in which reception is from 1088 to 1150 megacycles and transmission is from 1151 to approximately 1215 megacycles. As a result thereof, in the past, two different antennas were required to cover each of the TACAN bands, each band havirn its own dimensioned fundamental and harmonic parasitic elements as well as its own dimensioned fundamental and harmonic cylindrical diameters that difiered from the corresponding members of the other band. Furthermore, in one type of system, in addition to the dimensional dilferences mentioned, corresponding parasitic elements of each band were composed of material of different impedance characteristics. While the above considerations do not limit the usefulness or performance of the TACAN system, the cost of manufacturing two different antennas, as well as the lack of a standardization between corresponding members of each band, was found to be objectionable.

The principal object of this invention is to provide an omnidirectional beacon antenna having a stabilized modulation pattern over a broad radio frequency bandwidth.

3,354,107. Patented Sept. 11, 1962 Another object is to provide an omnidirectional beacon antenna having uniform and standard parasitic corresponding elements as well as uniform and standard fundamental and harmonic corresponding cylinders for use in both low and high band operation.

A further object of the invention is to provide an omnidirectional beacon antenna having an increased bandwidth without substantially deviating from the physical dimensions of prior similar antennas.

Still another feature is to provide a single TACAN antenna beacon covering its entire frequency spectrum range.

According to one aspect of the invention, in an antenna system in which a group of parasitic conductive elements of a given impedance characteristic are disposed for rotation about a central radiator good modulation over a wide range of radio frequencies is obtained by including a second group of parasitic conductive elements having a relatively different impedance characteristic disposed alternately between the parasitic elements of the first group.

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 the invention taken in conjunction with the accompanying drawings comprising FIGS. 1 to 4 wherein:

FIG. 1 is a view in perspective of the preferred embodiment of the omnidirectional beacon system of this invention;

FIG. 2 is a sectional view of the embodiment of the antenna system taken along the lines 22 of FIG. 1; 7

FIG. 3 is a view of one of the groups of parasites of the preferred embodiment for harmonic modulation, and one of the groups of parasites for stabilizing the depth of modulation; and v i 7 FIG. 4 is a partial perspective view of another embodiment of the omnidirectional beacon system of this invention.

In the preferred embodiment of the invention, the parasitic elements are disposed above a counterpoise, and the radiator is a monopole disposed centrally over the counterpoise. Further, in the preferred embodiment the parasitic elements are placed on dielectric cylinders, with one group of parasites on an inner cylinder for fundamental modulation and a plurality of groups of parasites on an outer cylinder for harmonic modulation.

Referring to FIGS. 1 and 2 of the drawing, an antenna system for producing a rotating multilobed shaped azimuth directivity pattern comprises a central radiator 1 supported at the center of a counterpoise 2. A harmonic frequency series of parasites composed of V- shaped groups of conductive

parasitic elements

3, 3a spaced at regular angular intervals are affixed to the surface of an outer rotating fiberglass housing'4 while a fundamental frequency group of parasitic elements '5 is attached to an inner fiberglass housing 6.

Referring more specifically to FIG. 2 of the drawing, a variable source 23 of radio-frequency (-R-F) energy is coupled to a coaxial transmission line 7. The inner conductor is coupled to a central radiator 1 which essentially comprises a quarter wavelength vertical stub antenna. A counterpoise 2 which includes an inner stationary disk 8 and an outer rotating disk 9 surrounds the central radiator assembly. The outer conductor of transmission line 7 is coupled to disk 8. A quarter wavelength choke generally indicated at 10 is provided by overlapping disks 8 and 9 so that there is no leakage of energy as the meta-1 disk 9 rotates. The outer edge of disk 9 has a flange 1-1 which acts as a radio-frequency choke to prevent undesired radiation. Surrounding the central radiator assembly 1 is an inner fiberglass housing 6,

tal flange 13 attached to disk 9.

. acteristic.

. 3 which includes a generally horizontal portion 12 which extends over the outer edge of disk 8 and is attached to disk 9, as for example, by means of mounting screws 15 located in equidistant slots 16 on flange 20. The fundamental frequency parasitic group of elements is carried by the inner fiberglass housing 6 which rotates about the central radiator -1. Also rotating with the metal disk counterpoise 2 is an outer fiberglass housing 4 on which a plurality of

parasitic element groups

3, 3a are carried for the harmonic modulation. Housing 4 has a horizon- The metal disk 9 and the attached housings 4 and 6 are rotated by means of a 'motor 14.

radiator at which the desired radiation component of each is near a maximum, as determined by the Bessel Function expansion; and each is designed in length, resistance, and position to produce the desired radiation char- Further information on TACAN may be found in Electrical Communications, published by In- .ternational Telephone and Telegraph Corporation, New ,York, N.Y., volume 33, No. 1, March 1956, with the principles of antena design on pages 35 to 59.

In the embodiment shown here, the parasites and counterpoise disk 9 are rotated at 15 cycles per second, which ..is the fundamental modulation frequency produced by .the single group of parasites 5 on housing 6.

parasites

3, 3a produce the ninth harmonic of modula- The tion at 135 cycles per second, and there are nine groups .of these

parasites

3, 3a spaced at 40 intervals on housing 4.

It has been found that with the harmonic parasites 3,

3a adjusted to produce maximum modulation at some predetermined operating radio frequency, that the depth of modulation decreases for the lower frequencies and increases for the higher frequencies. According to the invention, in order to stabilize the depth of modulation over a substantial range of operating frequencies, a

, second series of modulation controlling parasites with a relatively different impedance characteristic from the former series is disposed for rotation about the central radiator 1. The effect is that the first series continues to provide the majority of the modulation while the second series reduces the modulation at the upper frequencies and increases the modulation at the lower frequencies.

In the embodiment shown in FIG. 1, the

parasitic elements

17 and 17a comprise a group of the second series. The number of groups of the second series corresponds to the harmonic selected, which in this case would be nine. For the sake of simplicity, the

groups

17, 17a of the second series are mounted on the same fiberglass housing 4 as the first series, it being obvious, however,

that they may be mounted on their own housing as long i as they rotate at the same angular speed as their associated group in the first series.

Referring to FIG. 3, the harmonic modulation group of the first series comprises the two

elements

3, 3a that are symmetrically disposed about a center line 18 and slant upward and away from the center line 18 at equal angles therewith. As explained in the copending United States Patent Application Serial No. 672,543, of C. Lucanera and H. Avery, entitled Omnidirectional Beacon Antena filed July 15, 1957, now Patent No. 2,912,693, the purpose of the V-

shaped elements

3, 3a

is to provide sufiicient modulation up to high vertical angles. The modulation controlling group of the second series, as shown in FIG. 3, comprises the slanted inverted V-

shaped elements

17, 17a that are symmetrically disposed about the center line .18 of the group of the first series and form equal angles therewith with the

elements

17, 17a slanting downward and away from center line 18.

When the changes in modulation are negligible for changes in vertical angle, an arrangement of vertical parasites may be employed as illustrated in FIG. 4 in which the corresponding parts of FIG. 1 are generally indicated by like reference numerals. The vertical parasites 3b provide the majority of modulation while the other parasites 17b control the modulation for changes in radio frequency as explained above by having relatively ditferent impedance characteristics. In the embodiment shown in FIG. 4 the vertical parasites 3b are symmetrically spaced 40 from each other about the fiberglass housing .4. The controlling modulation parasites 17b are also spaced symmetrically about the fiberglass housing 4 with each parasite 17b placed midway between two consecutive parasites 3b.

While specific configuration and combination of the groups of the first or second series of the embodiment are shown in FIGS. 1 and 4, it is understood that there are other possible configuration and combinations that will produce the desired effects, as for example, the inverted V-shaped

groups

17, 17a of the second series in FIG. 1 may be combined with the vertical parasite 3b in FIG. 4. Furthermore, it is obvious that the modulation control over a substantial frequency range may be eifected even on a fundamental frequency group, as for example, the fundamental frequency group of parasitic elements 5, in a similar manner as was done for the

harmonic groups

3, 3a or 3b.

In order to provide correct bearing information, it is important that the fundamental and harmonic modulation waves be maintained at a predetermined phase relationship with each other. It has been found that with the antenna designed to maintain the desired phase relationship over a maximum bandwidth of operating frequencies, that a phase reversal occurs when the antenna operates outside this bandwidth. According to the invention, in order to maintain the desired phase relationship, means are included to orient relatively the fundamental parasites with respect to the harmonic parasites. One such means includes, a pair of positioning holes 19, spaced 180 apart which are provided on the flange 20 of the fundamental fiberglass housing 6 at an optimum position for producing the desired phase relationship. A corresponding pair of matched positioning holes 21 are similarly located on the rotatable disc 9. The fundamental housing 6, by means of the positioning pins 22 and screws 15, is thus oriented with the harmonic housing 4 at the desired phase relationship. When a phase reversal occurs, the housing 6 is shifted 180 to maintain the phase relationship. In a similar manner, to provide for phase shifts of other than "180 a plurality of positioning holes, not shown, may be located about the periphery of the flange 20* at regular or other desired spaced intervals.

For the radio frequency range of 960 to 1215 megacycles, the

harmonic parasite groups

3, 3a may be on a housing 4, thirty-seven inches in diameter. The V- shaped

elements

3 and 3a may each be four inches long and the inverted V-shaped

elements

17 and 17a may each be seven inches long. The

elements

3 and 3a of the harmonic group may be at an angle of 90 to each other, and the

elements

17 and 17a of the modulation control groups may also be at an angle of 90 to each other. The

parasitic elements

3 and 3a may be made of a resistance wire having a resistivity of 700 ohms per foot, depending upon the amount of modulation desired. The

parasitic elements

17 and 17a may be made of wire having a resistivity of approximately 400 ohms per foot depending on the amount of control desired. With these values an impedance ratio of about 2:1 is established between the

parasitic elements

3, 3a and the

parasitic elements

17, 17a. An antenna having the dimensions and characteristics given above will produce harmonic modulation over the range which is within the acceptable limits of 12 to 30 percent at vertical angles from zero to 50 or more. With this diameter, transmission occurs from 960 to 1025 megacycles and is achieved without phase shift. For the higher transmission frequencies,

viz., 1150 to 1215 megacycles; a reversal of the fundamental modulation parasite is required as explained above.

While we have described above the principles of our 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 our invention as set forth in the objects thereof and in the accompanying claims.

We claim:

1. An antenna system of a predetermined continuous range of frequencies comprising a vertically disposed elongated radiator, a variable source of radio frequency energy coupled to said radiator .and including said range, a first dielectric rotatable cylinder disposed concentrically about said radiator, at least one conductive parasite carried by said first cylinder to produce a fundamental modulation of said radio frequency energy, a second dielectric rotatable cylinder disposed concentrically about said radiator, a predetermined number of first groups of conductive parasites having predetermined impedance characteristics carried by said second cylinder to superimpose a harmonic modulation of said fundamental modulated radio frequency energy, said harmonic corresponding to said predetermined number, a said predetermined number of second groups of conductive parasites having relatively difierent impedance characteristics from said first group and carried by said second cylinder in a predetermined spatial relationship to said first groups to stabilize the depth of modulation of said radio frequency energy over the said range, said range further including therein .at least one band of frequencies at which said harmonic and fundamental modulation will undergo a phase shift from some predetermined phase relationship established between said fundamental and harmonic, means to orient relatively said group of conductive parasites on said first cylinder with respect to said first and second groups of conductive parasites on said second cylinder to maintain said predetermined phase relationship.

2. An antenna system of a predetermined continuous range of frequencies comprising .a vertically disposed elongated radiator, a variable source of radio frequency energy coupled to said radiator and including said range, a first dielectric rotatable cylinder having a first predetermined diameter disposed concentrically about said radiator, parasites carried by said first cylinder to produce a fundamental modulation of said radio frequency energy, a second dielectric rotatable cylinder having a second predetermined diameter relatively different from said first predetermined diameter, a predetermined number of first groups of conductive parasites having predetermined impedance characteristics carried by said second cylinder to superimpose a harmonic modulation of said fundamental modulated radio frequency energy, said harmonic corresponding to said predetermined number, a said predetermined number of second groups of conductive parasites having a relatively different impedance characteristic from said first group and carried by said second cylinder in predetermined spatial relationship to said first groups to stabilize the depth of modulation of said radio frequency energy over said range, a rotatable member connecting said first .and second cylinders including first coupling means to maintain said first and second cylinders in a first predetermined relationship, said range further including therein at least one band of frequencies at which said harmonic and fundamental modulation will undergo a phase shift from some predetermined phase relationship established between said fundamental and harmonic, means to orient relatively said parasites on said first cylinder with said groups of conductive parasites on said second cylinder to maintain said predetermined phase relationship when said antenna operates within said band, said latter means including said rotatable member having a second coupling means to maintain said first 6 and second cylinder in a second predetermined relationship to maintain said phase relationship.

3. An antenna system of .a predetermined continuous range of frequencies comprising a vertically disposed elongated radiator, a variable source of radio frequency energy coupled to said radiator and including said'range, a first dielectric rotatable cylinder having a first predetermined diameter disposed concentrically about said radiator, parasites carried by said first cylinder to produce a fundamental modulation of said radio frequency energy, a second dielectric rotatable cylinder having a second predetermined diameter relatively dii ferent from said first predetermined diameter, a predetermined number of first groups of conductive parasites having predetermined impedance characteristics carried-by said second cylinder to superimpose a harmonic modulation of said fundamental modulated radio frequency energy, said harmonic corresponding to said predetermined number, a said predetermined number of second groups of conductive parasites having a relatively different impedance characteristic from said first group and carried by said second cylinder in predetermined spatial relationship to said first groups to stabilize the depth of modulation of said radio frequency energy over said range, a rotatable member connecting said first and second cylinders including first coupling means to maintain said first and second cylinders in .a first predetermined relationship, said range further including therein at least one band of frequencies at which said harmonic and fundamental modulation will undergo a phase shift from some predetermined phase relationship established between said fundamental and harmonic, means to orient relatively said parasites on said first cylinder with said groups of conductive parasites on said second cylinder to maintain said predetermined phase relationship when said antenna operates Within said band, said latter means including said rotatable member having a second coupling means to maintain said first and second cylinder in a second predetermined relationship to maintain said phase relationship, each of said first groups further comprising a pair of parasitic elements symmetrically disposed about a vertical center line of the said pair at an angle of 45 thereto, said elements of said first group being closest together at their lowest point and slanting away from each other and the said center line at their highest point, and each of said second groups further comprising a pair of parasitic elements symmetrically disposed about the said vertical center line at an angle of 45 thereto, each of said elements of said second group being closest together at their highest point and slanting away from each other and the said center line at their lowest point the said elements of said second group being further disposed about the said elements of said first group.

4. An antenna system of a predetermined continuous range of frequencies comprising a vertically disposed elongated radiator, a variable source of radio frequency energy coupled to said radiator and including said range, a dielectric rotatable cylinder disposed concentrically about said radiator, a first plurality of groups of conductive parasites carried by said cylinder to modulate said radio frequency energy, each group of said first plurality of groups including a pair of conductive parasites having a predetermined impedance characteristic, and means to stabilize the depth of said modulation over said range including a second plurality of groups of conductive parasites carried by said cylinder in a predetermined spatial relationship to the groups of said first plurality of groups, each group of said second plurality of groups including a pair of conductive parasites having an impedance characteristic different than said predetermined impedance characteristic.

5. An antenna system of a predetermined continuous range of frequencies comprising a vertically disposed elongated radiator, a variable source of radio frequency energy coupled to said radiator and including said range,

a dielectric rotatable cylinder disposed concentrically about said radiator, at least a first pair of conductive parasites carried by said cylinder to modulate said radio vfirequency energy, each conductive parasite of said first pair of conductive parasites having a predetermined impedance characteristic, and means to stabilize the depth of said modulation over said range including at least a second pair of conductive parasites carried by said cylinder in a predetermined spatial relationship to said first pair of conductive parasites, the conductive parasites of said second pair of conductive parasites having an impedance characteristic different than said predetermined impedance characteristic.

6. An antenna system of a predetermined continuous range of frequencies comprising a vertically disposed elongated radiator, a variable source of radio frequency energy coupled to said radiator and including said range, a dielectric rotatable cylinder disposed concentrically about said radiator, a first plurality of groups of conductive parasites carried by said cylinder to modulate said radio frequency energy, each group of said first groups of conductive parasites including a pair of conductive para- ,sites having a predetermined impedance characteristic,

and means to stabilize the depth of said modulation over said range including a second plurality of groups of conductive parasites carried by said cylinder, the groups of said second plurality of groups being disposed in an alternate relationship with the groups of said first plurality energy, each parasite of said first pair having a predetermined impedance characteristic and being disposed symmetrically on opposite sides of a vertical center line with the parasites of said first pair being closest together at their lowest point and slanting away from each other and said center line to form equal angles therewith, and means to stabilize the depth of said modulation over said range including at least a second pair of conductive parasites carried by said cylinder, each parasite of said second pair having an impedance characteristic different than said predterrnined impedance characteristic and being disposed symmetrically on opposite sides of said center line with the parasites of said second pair being closest together at their highest point and slanting away from each other and said center line toform equal angles therewith.

References (lited in the file of this patent UNITED STATES PATENTS Lucanera et al. Nov. 10, 1959