US2126531A - Antenna - Google Patents

Description

Aug. 9, 1938. P. s. CARTER- 2,126,531

ANTENNA Filed hfl rch 9, 1956 2 Sheets-Sheet l INVENTOR/ B PHILIP S.CARFER ATTORNEY.

9, 1938. P. ,s. CARTER 2,126,531

ANTENNA Filed March 9, 1936 2 Sheets-Sheet 2 7'0 TRANSMITTER INVENTOR. PHILIP 5. CARTER ATTORNEY.

from a central point. .may either be dipoles or grounded vertical an- Patented Aug. 9, 1938 UNITED STATES PATENT =1 OFFICE 7 2,126,531 d f ANTENNA -Philip .s -Carter lort Jefi'erson, N. Y; assignor to Radio Corporation of America, a corporation of Delaware Application March '9, 6 Claims.

This invention relates to an antenna system for broadcasting vertically polarized waves.

Heretoforein order to obtain a high latitudinal concentration of radiation, it has been usual to employ an array of tall radiators which reach considerable heights. An arrangement of this sort is very costly, and in most cases it is not possible to obtain equal radiation in all horizontal directions.

The present invention provides an improved antenna system wherein there is obtained substantially equal radiation in all horizontal directions and a great reduction in undesirable high -angle radiation. In brief, the invention consists of concentric circular arrays of vertical radiators spaced apart according to a definite mathematical law, all of the vertical radiators in each circular array being of substantially equal length and energized cophasally with equal currents while adjacent circular arrays are fed either cophasally or in opposition, depending upon the lengths of the radii of the arrays as measured These vertical radiators tennas.

I have found that for a given total current the field strength of the radiated wave in the .horizontal direction from .a circular array of a number of vertical radiators is proportional to Jn(2wa/ where a is the radius of the circle and J(27rCL/7\) is the zero order Bessel function of the first kind with the argument. (ZTra/X). It is thus apparent that for maximum radiation horizontally, the radius must be such as to result in the function Jo(21ra/)\) being a maximum or minimum. For this condition, J1 of (21ra/i) =0, where J1 is the corresponding first order Bessel function of the first kind. Hence the radii should be roots of the function J1(21ra/)\) This results in values approximately equal to 0.61, 1.12, 1.62,

2.12, 2.62 etc. wavelengths, wherein all radiators in each circular array are fed cophasally, but

adjacent circular arrays are fed in phase opposition.

The invention is not limited to the arrangement already discussed. It is not necessary in an array of circles to have radii corresponding to all successive roots of the Bessel function mentioned. For instance, it might be desirable to use an array having radii of 0, 1.12, 2.12 etc.

wavelengths or 0.61, 1.62, 262 etc. wavelengths, :111 radiators in the circles in either of these combinations being fed cophasally. Another combination might be with circles of radii .0, 1.62, 3.12

etc. wavelengths, where the radiators in adjacent circles are fed in phase opposition. 1

A' brief mathematical analysis of the theory underlying the present invention will now be given with particular reference to Fig. 10. Let us assume that there are a large number of 1936, .Serial No. 67,785

radiators-nina circle of radius a, as shown in this figure of the drawings; then, if I is the total current in all the radiators the current in one radiator is The number of radiators within an angle d9 is and the total current in these radiators is:

Now consider that the field Waves arrive.at

point P in this sketch, which point is at a sufiicient distance from the circle for all paths to be parallel. Let us now take as reference phase the phase of a wave arriving from an element on the reference axis 9:0. This wave has travelled a distance R. The Wave from the element 110 has travelled a distance r=R-a sin 9. The difierence in distance is asin 9, to which corresponds a distance in time where is the zero order Bessel function of the first kind.

Now, for a given current the magnitude of the field will be a maximum when .is a maximum or a minimum.

JrT

is the first order Bessel function of the first kind. From the roots of this function we obtain the relations given in the docket.

No radiation horizontally takes place when the radius a is such that or when a=0.382 0.8801, etc.

A better understanding of the invention may be had by referring to the following description in conjunction with drawings wherein:

Figs. 1-4, inclusive, illustrate plan views of antennas in accordance with the invention;

Figs. -8, inclusive, illustrate polar diagrams of the field distribution in any vertical plane of various combinations of individual circular arrays shown in Fig. 1;

Fig. 9 shows, by Way of example only, one way of feeding the antenna arrays; and

Fig. is a drawing given merely for the purpose of the theoretical explanation advanced above.

In Fig. l is shown a plan View of one antenna arrangement in accordance with the invention, comprising four concentric circular arrays 2, 3, 4, 5 of vertical radiators with a single radiator I at the center. This system may be considered as consisting of five circular arrays, the innermost array consisting of single radiator I which is of zero radius. The radii from the central radiator l to successive arrays are, as indicated, equal to 0.61, 1.12, 1.62 and 2.12 wavelengths, which are successive roots of the Bessel function mentioned above. All the radiators in any one circle are of equal length and energized cophasally in any suitable manner and with equal currents, while radiators in adjacent circles are fed in phase opposition. The radiators in each circle are of sufficient number to produce an effect approximating a current sheath. If desired, the circular arrays may have currents of different magnitude with respect to one another.

Figs. 2 and 3 show plan views of an antenna system wherein the radii of successive arrays correspond to alternate roots of the Bessel function named. In both of these figures the adjacent circular arrays are fed cophasally.

Fig. 4 shows, by way of example, another combination of circular arrays which may be used, and wherein the radiators in adjacent circular arrays are energized in phase opposition.

Fig. 5 is a polar diagram of the field distribution in any vertical plane for a single radiator.

Fig. 6 is a similar diagram for a circle of radiators having a radius of 0.61 wavelength.

Fig. '7 is a diagram resulting from the combination of a circle of radiators having a radius of 0.61 wavelength from a central point and a single radiator at said central point.

Fig. 3 is a similar diagram for the system of Fig. 1.

Fig. 9 shows one way of feeding all the radiators in any one circle by means of equal length lines connecting with a main feeder. If the radiators are dipoles, each line would comprise a pair of wires. Similarly, other circular arrays are also fed from the center. To obtain phase opposition or cophasal relation between any two circular arrays, the central connection points of the lines extending to the individual radiators would be joined together by a proper length of line to give the desired phase relation.

From the foregoing it will be understood that the invention is not limited to the precise antenna systems shown, since other circular arrays may be used which are suitably energized and have as radii roots of the Bessel function named, without departing from the spirit and scope of the invention.

What is claimed is:

1. An antenna comprising a plurality of concentric circular antenna arrays each composed of vertical radiators, the radius of each circular array being such that the zero order Bessel function of the first kind, namely J 0(21ra/1) with the argument (21ra/A) is a maximum or a minimum, where a is the radius of the circular array, A the wavelength, and high frequency apparatus for energizing the radiators in each circular array cophasally.

2. An antenna comprising a. plurality of concentric circular antenna arrays each composed of vertical radiators, the radii of successive circular arrays multiplied by being successive roots of the Bessel function of the first kind, J1(21ra/ with the argument (21ra/A), where a is the radius and A the wavelength, and high frequency apparatus for energizing the radiators in each circular array cophasally but out of phase with respect to the radiators in the adjacent array.

3. An antenna comprising a plurality of concentric circular antenna arrays each composed of vertical radiators, the radii of successive circular arrays multiplied by A being alternate roots of the Bessel function of the first kind, J1(21ra/7\), with the argument (21ra/A), where a is the radius, and 1 the wavelength, and high frequency apparatus for energizing the radiators in all circular arrays cophasally.

4. An antenna comprising a plurality of concentric circular arrays each composed of vertical radiators, a single vertical radiator at the center of said arrays, the radius of said first circular array as measured from said center being approximately .6121, the radius of the second circular array being approximately 1.121 and that of the third array approximately 1.621, where A is the wavelength, and high frequency apparatus for energizing the radiators in each array cophasally, but adjacent arrays out of phase.

5. An antenna comprising a plurality of concentric circular arrays each composed of vertical radiators, a single vertical radiator at the center of said arrays, the radius of the first of said first circular arrays as measured from said center being approximately 1.121, the radius of said second circular array being approximately 2.121, where A is the wavelength, and high frequency apparatus for energizing the radiators in all arrays cophasally.

6. An antenna comprising a plurality of concentric circular arrays each composed of vertical radiators, the radius of the first of said arrays as measured from the center being approximately .611, and the radius of the second array being approximately 1.621, where is the wavelength, and means for energizing all the radiators of all arrays cophasally.

PHILIP S. CARTER.

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