US2430353A - Antenna - Google Patents

Description

Nov. 4, 1947. R. w. MASTERS ANTENNA Filed Feb. 21, 1945 ililllllvrlllflvnli,

Patentecl Nov. 4, 1947 ANTENNA noten vv.` Masters, Erima. N. Ji; assigne; to Radio Corporationof Arneri ca,ta.corporation of Delaware Application February 21, 19.45; SerialNo. 5578,9955

8 Claims.

This. invention:relatestoantennas, and more particularly, to broad` band. radiator systems suitable for` the transmission and reception of. ultra high frequency signals .covering a Wide frequency spectrum, as is required for television picture transmission, certain. typesvof radio locator systems, and so on.

The. principalobject ofvrthe present invention is to provide. abroad band antenna structure in whichtheradiator elements are inthe fornrot flat plates or sheets, shapedto provide approxi,- mately constant impedance, throughout a relatively Wide. frequencyband.

Another object is to providean antenna systern. of the, described type. which is. simple. and rugged in ,constructionandtmay he designed rea d-A ily to fulfill typical operatingrequirernents.

These and other. objects. Will loecorneapparent to.. those skilled in the. art upon consideration of the following description with reference to the accompanying,drawing, otwhich Figure 1 is fa schematic perspective diagram of a directive antenna embodying theinstant invention,

Figure. Zisa section showing a'portonoftthe. structure ofFigure l, in detail, and.

Figure 3 is an elevation of a modied form. of radiator elementfor a. system like that otligure l.

Referring to Figure 1, a pair of radiatorele?` ments I- and 3: aredisplosed substantially at the focus of a cylindrical parabolic reflector 5. The radiators I and are supported, as shown more clearly in Figure 2; on insulators i and i at the ends of a pair of coaxial transmssionline sections Sand t", andare connectedtothe inner conducto-rs thereof. The line sections 9 and 9 extend throughthe rear of the reflector 5 to a line balance convertor I I.

The balance convertor Il is of conventional design, and-includes a cylindricalsheath Isur rounding the nal quarter wavelength section of an unbalanced line IE,l and connected to the outer conductor thereof by a disc I'I. The inner conductor of the balanced'linef is connect-calato the outerfconductor oftheiline. I'and the inner conductor of the line 9' is connected to the inner conductor of the line I5. A compensating stub is provided, comprising a quarter wave conductor I9 connected to the sheath I3 by a disc Il" and connected at its other end to the inner conductors of the lines 9 and E5.

r.The radiator elements I and. 3 are in the form of flat sheets of generally triangular or trapezoidal outline, supported with their bases parallinesfitV and"r 91 andare. appliedltlereby, toftlie diators I and 3`.

Thus the radiators are excited as the, elements of dipole,4 Witncurrentl flowing" intot the. radia-y tore. While an qllaflf Current,` flows out of;r the radiator I; anljvice. versa. i

'I'helreflector 5 1 tunctonsto, direct substantially alt of; the radiatedenergy inl a relatively narrow beam. vSince the dimensionsoftherenctorare small,-.in termsooijvvavelength, the action is not closely analogous. to. that ofi a' light' source with an. opticalreflecton Spine ofthe, reflected' en v ergy yinducescurrents in the. radiators, ofjljnagntude and phase depending, unonthe` size and shape of. the; radatorsand`f the focal length. oi the reflector; These Vinclucelzl currents ,materially affect the impedance presented by the radiators tothe feed system.

For ecient broadband" operation of an an: tenne, the impedance must remain relatively QOn-, stanttliroughout the operating It is known that radiators Y having large. suriace areas exhibit this characteristic toI sorneextent.. Howevenit is foundthat. a. closely coupled reflector. Willinf troiuce considerable variation in .the impedance, of( a onventicnel broadband radiatorv- Bfr 'employing Het' Sheet @Citaten- Ofi'eerlerallv triangular, sharia, as described h'jercirr;` the cur-` rents inducedwin the radiatorsloy reilectionare controlled as a. function. otfrequency, so aseto partially compensate thenormalj/ariation of im; penance of the radiators alone,` thus. providing an overall impedance which .is sulo'stantially,A inde-1 pendent ofi frequency@ The exact current..dis-` tfrbutionsin the. .radiators of `the..system,.of Fig; ure.. 1i` are 11,0@ Altncwn. at" present but what been found `experiinentY thattthe optimum, slape ,for one antenna is triangular, with dimensions approximately such that the length of each radiator from apex to base is substantially equal to the width across the base, both being about one quarter wavelength at the mean operating frequency. The focal length of the reflector is approximately 0.35 wavelength.

Another antenna, of the same type but with a somewhat different proportioning of the convertor ll and the line sections 9 and 9', Was found to operate best with radiator elements in the form of trapezoids, or truncated triangles, as illustrated in Figure 3. In this case, the optimum dimensions were found to be approximately those shown in Figure 3. In the absence of a better generic term, the Words generally triangular are used herein and in the appended claims to mean the shape shown in Figure 3 as Well as that of Figure 1, and similar intermediate shapes which are in fact generally or approximately triangular.

In order to operate efciently, not only must the antenna impedance be constant, but it must match that of the feed lines. While coaxial lines may be built to have any reasonable value of characteristic impedance, it is convenient to use a commercially available line, having an impedance of approximately 50 ohms. The structure of Figure 1, with the described dimensions, will match such a line. It should be noted that the line sections 9 and 9 must have a characteristic impedance half that of the remainder of the system, or in the present example, 25 ohms.

The operation of the system for reception is similar to that for transmission, and similar requirements must be met for broad band operation, although in general they are not so critical. The described antenna, if designed for transmission, will provide satisfactory characteristics for reception.

Although the invention has been described as an antenna including only a single pair of radiators and a single parabolic reflector, it will be apparent without further illustration that a plurality of such structures may be used in combination, each acting as one element of an array, without materially affecting the broad-band characteristics secured in accordance with my invention by the combination with a reector of a flat sheet radiator of generally triangular shape.

I claim as my invention:

1. A bro-ad band antenna including at least one pair of radiator elements comprising flat sheets of conductive material, each of approximately triangular form, lying in a common plane With their bases parallel and adjacent each other, and transmission line means connected to said radiator elements respectively at substantially the midpoints of said bases.

2. A broad band antenna including at least one pair of radiator elements comprising flat sheets of conductive material, each of approximately isosceles triangular form, lying in a common plane with their bases parallel and adjacent each other, and transmission line means connected to said radiator elements respectively at substantially the midpoints of said bases.

3. A broad band antenna including a reflector and at least one pair of radiator elements comprising flat sheets of conductive material, each -of generally isosceles triangular form, lying in a common plane with their bases parallel and adjacent each other, and transmission line means at substantially the midpoints of said bases.

4. A broad band antenna comprising a reflector, a line balance convertor lying outside and adjacent the back of said reflector with its longitudinal axis parallel to the focal axis of said reiiector, a pair of balanced lines extending parallel to each other and perpendicular to said axes from said convertor, and a pair of coplanar sheet radiator elements connected to and supported by said balanced lines respectively, said sheet radiator elements being of approximately triangular form, with their bases parallel and adjacent each other at the points of connection to said balanced lines.

5. A broad band antenna comprising a cylindrical parabolic reector, a line balance convertor of generally cylindrical form lying outside and adjacent the back of said reector With its axis parallel to the focal axis of said reflector, a pair of balanced lines extending parallel to each other and radially from said convertor, and a pair of coplanar sheet radiator elements connected to and supported by said balanced lines respectively, said sheet radiator elements being of generally triangular form, with their bases parallel and adjacent each other at the points of connection to said balanced lines.

6. A broad band antenna comprising a line balance convertor of generally cylindrical form, with an unbalanced line extending along the axis of said convertor and a pair of balanced lines extending parallel to each other and radially of said convertor, and a pair of radiator elements connected to and supported by said balanced lines respectively, said radiator elements comprising coplanar sheets of conductive material, each of generally triangular form, with their bases parallel and adjacent each other at the points of connection to said balanced lines.

7. A doublet antenna structure including a pair of coplanar flat sheets of conductive material, each of generally isosceles triangular form, with their bases parallel and adjacent each other, and a pair of transmission lines connected to said sheets respectively at said bases.

8. An antenna structure including at least one pair of coplanar iiat sheets of conductive material, each of approximately isosceles triangular form, with their bases parallel and adjacent each other, at least one reector and a pair of transmission lines connected to said sheets respectively at said bases.

ROBERT W. MASTERS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,158,124 Fessenden Oct. 26, 1915 FOREIGN PATENTS Number Country Date 344,620 Great Britain Mar. l2, 1931

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