US2539433A - Circularly polarized antenna - Google Patents

Description

Patented `1an. O,

2,539,433 CIRCULARLY POLARIZED ANTENNA Armg G. Kandoian, Glen Rock, N. J., assignor to International Standard Electric Corporation, New York, N. Y., a corporation of Delaware Application March 20, 1948, Serial No. 16,117

3 Claims.

This invention relates to antennas and more especially to antennas for producing or responding to circularly or elliptically polarized waves.

The invention is in the nature of an improvement upon the type of antenna disclosed in my prior application, Serial No. 574,879, filed J anuary 27, 1945, now Patent No. 2,465,379 granted March 29, 1949. n

A principal object of the invention is to provide. a high-gain omnidirectional circularly polarized antenna which is particularly suitable for frequency modulation systems, television systems, and indeed any system operating in the high frequency ranges, for example 100 megacycles or more.

Another object is to provide a circularly polarized antenna comprised of an array of antenna units each of which has a loop portion for producing horizontally polarized components and integral vertical portions for producing vertically polarized components, the units. being especially designed so that they can be rigidly supported from a suitable mast or column, Without changing the circular polarization of the waves from the antenna as a whole.

A further object is to provide a high-gain antenna composed of a series of stacked-up loop elements having integral vertical radiating stubs whereby the resultant polarization of the antenna can be either circular or elliptical.

A feature of the invention relates to a highgain omni-directional and circularly polarized antenna which is constituted of a series of superposed units, each unit consisting of a set of radiators for producing a loop current for horizontal polarization, and each radiator having at least one vertical radiating stub symmetrically arranged with respect to the vertical axis of the antenna.

Another feature relates to a high-gain circularly polarized antenna comprises of a series' of superposed horizontal units, each unit consisting of a series of radiators for producing horizontally polarized radiation components, all the units being supported from a central metallic supporting mast or pedestal, and each radiator having at least one radiating stub to produce vertically polarized radiation components.

A further feature relates to a circularly polarized antenna comprised of a series of superposed horizontal units supported from a common central mast, each unit having a series of horizontal elements for producing horizontally polarized radiation, each element having at least one vertical radiating stub, which stubs are llocated symmetrically around the mast and on therespective dipoles at a predetermined point of the voltage distribution therealong. As a result of this construction, the stubs can be dimensioned and located so that the current in each stub can be made to lead or lag in phase the currents in the associated dipole on either side ofthe junction point ofthe stub therewith. l

A further feature relates to a simplied and rugged high-gain antenna for circular or elliptical polarized Waves.

The above-mentioned and other features and objects 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 lfollowing description of an embodiment of the invention taken in conjunction with the accompaying drawings.

In the drawing,

Fig. 1 is a perspective View of an antenna according to the invention.

Fig. 2 is a detailed' view of one of the horizontal antenna sections used in the various horizontal units of Fig. 1, to show the location of one oi the vertical stubs with respect to the voltage distribution curve.

Fie. 3 is a vector diagram explanatory of Fig. 2.

Fig. 4 is a perspective view of a modied structural arrangement of one of the units of Fig. l'.

It has been known heretofore that the combination, in free space, of a loop antenna current anda dipole antenna current in mutually concentric relation, and in phase produces a circularV 'polarization of the radiated waves. Thus, I have disclosed in my prior application Serial No1 574,879,'led January 27, 1945, the combination of a vertical antenna section and a horizontal loop section appropriately connected to a trans'- mission line and relatively phased to produce circularly polarized waves or elliptically polarized waves. When such a combination of horizontally polarized loop and vertically polarized dipole are excited in phase, the resulting polarization will be elliptical. If the power input to the loop and the dipole are equal, then the polarization of radiation will be circular. One of the ways to increase the gain of such an elliptically or circularly polarized composite antenna, is to superpose a series of similar composite units. However, while theoretically this is true, practically it is diiiicult of attainment by reason of the fact that such stacked-up units must be supported by rigid vertical supports, and at high frequencies, for example megacycles or more, these supports for practical `elements 8.

reasons must be metallic. If a single central support or mast is used, it does not appreciably aect the horizontal radiation, since the support is then symmetrically disposed along the common vertical axis of the stacked-up loops, and the opposite sides of each loop induce in the support equal and opposite currents which Acancel each other out.

On the contrary the vertical radiation from the dipole or any equivalent radiator which carries currents in phase with those in the loop, is very seriously aected by the vertical supporting structure even though it is located centrally and symmetrically with respect to the several loops. Such supports primarily affect the phase of the resultant vertically polarized radiation. Thus while the dipole and loop, when considered in free space, may easily have their respective vertical and horizontal polarizations in proper phase quadrature, the presence of the metallic supporting structure changes the phase of the vertical polarization from the proper quadrature relation, so that the resultant polarization is not circular.

,unit I, may comprise four straight rods or metal tubes 5, t, l, 3, arranged end-to-end to any suitable conguration such as square, rectangular, circular, etc. Preferably the horizontal radiator members 5 8 are all of equal length, for 'example one-half wave length at the midfrequency of the operating frequency band of the antenna and are excited in phase by a feedline 9 to form in effect a single and substantially closed radiation loop, and all the units are preferably of the same physical loop dimensions.

The members 5 8 are supported from a com- 'mon vertical metal mast I which is co-axial` with respect to the several units. If desired, the various radiator elements 5, 6, 'I and 8 of each unit can be so excited that the mid-points between the end of each lelement is at a voltage node. In that case, the elements can be attached by respective arms II, I2, I3, I4, extending from the mast l to the mid-point of the respective In order to facilitate the supporting and connection of the respective units I--4 to the mast Il] and to the feeder line, the mast IIl may take the form of a metal pipe I5 (Fig. 4) having centrally thereof a conductor I6, thus forming a coaxial transmission line. Likewise, the radiator arms 5 8 may each be in the form of a tubular metal member and the supporting arms II-l may likewise be tubular metal members. The radiators 5 8 and the arms Il I are in communication with each other at their respective junction points. The central conductor I6 is provided, adjacent each unit, with four branches I'I, I8, I9, 20. The branch El extends centrally through one-half the length of element 5 and then connects to a metal plug 2I fitted in the adjacent end of element 8. Likewise the branch I8 extends centrally through one-half of element 6 and connects to a metal plug 22 tted within the end of element 5. Likewise the branch I9 passes centrally through one-half of element I and conto mast i5.

4 nects to the metal plug 23 in element 5. The branch 28 passes centrally through one-half of element 8 and connects to the metal plug 24. The member I5 which forms the central mast can be connected to a suitable junction box 25 to which the arms Il 2l can be attached. Thus the elements 5, 6, 'I and 8 of each unit provide a substantially closed planar periphery around a substantially symmetrical area with respect Since the radiator elements 5 8 are preferably of a length corresponding substantially to one-half the wave length of the mid-frequency of the operating frequency band, the impedance relations between the transmission line I5, I6 and the various antenna units can be appropriately proportioned. When such an antenna is excited, it produces substantially horizontally polarized radiation components. In order to produce the desired vertically polarized radiation components, each of the elements l5 8 of each unit has attached thereto a vertically-extending metal stub 25, 2l, 28, 29, each of which acts as a vertically polarizing radiator. The length of each stub and its physical position on its associated radiator element are chosen so as to maintain .vertically polarized radiation symmetrical around the vertical axis, notwithstanding the presence of metallic mast i3.

There is shown in Fig. 2 for example the radiator element 5 and its attached stub 2l. If the stub 2l is mounted perpendicular to the element 6, current will flow along the stub 2. The magnitude of this current will be a function of two major factors, namely the driving voltage and the impedance of the stub itself which can be made inductive, capacitive, or resistive. If we assume the driving voltage for the antenna to be fixed with respect to the current I1 through each of the radiator elements, it is possible to control the relative amplitude and phase of the stub current I3 by adjusting the length, and crosssection of this stub. It is also possible to adjust the amplitude primarily and the phase secondarily of the current in each of the stubs by varying its relative position along the length of its corresponding horizontal radiator 6. In other words, when the individual loop units I, 2, 4, are horizontal, the current in the stubs is vertical and can be made any relative amplitude and either in phase, or lagging or leading with respect to the loop current by simply adjusting the stub position and dimensions.

In the absence of the central supporting mast I8, the stub current could be brought into phase with the loop current to produce circular polarization. However the presence of mast I8 renders the attainment of circular polarization difficult where a series of units are to be vertically .superposed. Therefore, by employing the stubs and by adjusting the physical dimensions of each of the stubs, the stub current may be made to lag or lead the loop current, depending on the size of the loop and the dimensions of the mast iii. The vectoral relation between the currents l1, I2 and I3, flowing in each of the radiator sections and the associated stub, are indicated in Fig. 3. In Fig. 2 the curve 38 represents the voltage distribution curve along the length of one of the loop radiator elements, and the curve SI represents the current distribution curve. From this it will be seen that by varying the position of the stub 21 along the length of element 6, for example, it is also possible to control the amount and phase ofthe stub current. The invention therefore contemplates an arrangement wherein the proper relation between the vertical current in the stubs and the horizontal current in the associated radiator elements is effected by choosing the proper physical dimensions of each stub or by choosing its location on the respective radiator element, or by a combination of both.

I have found that with the construction as described, it is possible to produce a high-gain omni-directional circularly polarized antenna which is rigid in construction, and employing any desired number of stacked-up radiator units supported from a common central metal mast.

While the drawing shows an antenna consisting of four such units, it will be understood that a greater or less number may be employed, depending upon the desired gain,

While I have described above the principles of my invention in connection with specic 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.

What is claimed is:

1. An antenna system for circularly polarized energy, comprising a plurality of radiant acting members forming a substantially symmetrical closed radiation loop in a given plane, means to excite said members to produce similar voltage distribution curves therealong, a conductive mast on which said members are structurally fastened, and an individual radiator stub attached to each member and extending substantially perpendicular therewith, each stub being spaced along the length of said member and dmensionally proportioned to produce a predetermined phase shift between the current in the stub and that in the closed radiation loop in a given plane, means to excite the members of each unit to produce similar voltage distribution curves therealong, a common conductive mast along which all said units are structurally fastened in spaced relation, and an individual radiator stub attached to each member and extending substantially perpendicular therewith, each stub being located along the length of each member to produce a predetermined phase shift between the current in the stub and that in the associated loop to maintain the circular polarization of the system.

3. An antenna system for circularly polarized energy, comprising a plurality of antenna units each composed of a plurality of radiant acting members forming a substantially symmetrical closed radiation loop in a given plane, means to excite the members of each unit to produce similar voltage distribution curves therealong, a common conductive mast along which all said units are structurally fastened in spaced relation, and an individual radiator stub attached to each member and extending substantially perpendicular therewith, each stub being dimensionally proportioned and located along the length of the member to which it is attached to produceV a phase shift between the current in the stub and that in the associated loop to maintain the circular polarization of the system.

ARMIG G. KANDOIAN.

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

UNITED STATES PATENTS Number Name Date 2,383,490 Kandoian Aug. 28, 1945 2,391,026 McG-uigan Dec. 18, 1945 2,426,632 Marchand Sept. 2, 1947 2,465,379 Kandoian Mar. 29, 1949

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