US2537191A - Antenna - Google Patents

Description

Jan. 9, 1951 c, c, MOORE 2,537,191

ANTENNA Filed May 8, 1947 I6 l6 a FIG. 1

G d b c/ 213 7 ML F l5 '6 5 J g FIG. 2

FIG. 5

Wave Signal- Device A2 Affomqy Patented Jan. 9, 1951 UNITED:

STATES PATENT OFFICE,

ANTENNA Clarence C; Moore, Elkhart, Ind.

Application. May 8, 1947, SerialNo. 746,740

6' Claims. 1 The present invention relates to an antenna and more particularly to anantenna foruse. with wave signal devices whet-heradapted to radiate primarily upon the voltage of the antenna. For

example; there has been a considerable loss due to corona which takes place at high voltages and due to thepartial ionization of the air about the'antennacausing the air tobecome a partial conductor and carry current; The corona does notbegin to take place'except at a certain definite voltage which varies greatly'in dependence upon the shape and sizeof the antenna: conductors as well as on the condition of the medium surrounding the antenna as, for example, the altitude at which the antenna is disposed. Once the critical voltage for a particular location is exceeded, a large amount of energy loss may take place due to corona. Thisphenomenon'is to a certain extent a limitation upon the amount of power which may be radiated by an antennasince for an antenna of certain dimensions, the greater the power applied thereto: the greater'must be the voltage andhence, the greater the corona loss; Consequentlyior a particular transmitting antenna there-is a limit to the power input beyond which it is inadvisable to go because a large amount of power is wasted due to corona loss and little-is gained asfar aspower radiated is concerned. In certain parts of the world, where elevations above sea level are great, as for example, in many parts of South America, the corona problem: is particularly had even at relatively low valuesof power radiated. It would-bedesirable to provide an antenna wherein the corona prob-- lemwould be subsbtantially eliminated at all altitudes'andalso where large amounts of radio frequency power are to be radiated. It would furthermore be-desirable to provide an antenna in which'thevoltage problem was eliminated so that the expense ofinsulators-for supporting the same could. begreatly reduced and: whereby ice and snow. would have. substantially no deleterious ef;- fect assfa-r as. the. operating characteristicsof 'the antenna are concerned,

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Accordingly, itis an object of the presentinvention to provide a new and improved antenna for wave signal devices.

It is another object of the present invention to provide a loop antenna having a distributed voltage whereby the corona problem is substantially eliminated and, due to the low voltages involved, no expensive insulators are required and no deleterious effect from ice and snow isexperienced.

It-is another object-of the presentinvention to provide anew and improved-antennahaving circular polarization whereby fading efiects are reduced.

It is another object of the present invention to provide an improved antenna having some of the desirable characteristics of rhombic antennas without the loss of power characteristic of. such antennas inthe termination impedance thereof It isanother object of the present invention to provide an antenna for wave signal devicesin which reversal of the conductor in the antenna occurs at the place where phases would normally reverse so that all currents in the antenna flow in the same direction at the same instant whereby the benefits of stubs are obtained-without requiring the provision thereof.

Itis a further: object of the present invention to provide a loop antenna having an even numberof turns of. a length of one or: more wave lengthsaround eachturn in which substantially no voltage components are present and the only voltage existing is that due to the impedance be' tween the adjacent loops.

Further objects and advantages of the present invention will become apparent as the following description proceeds and the features of novelty which characterize this invention-willbe pointed out with. particularity. in the claims annexed to and forminga part of thisspecification.

For abetter understanding of the present in-- vention, reference may be had to the accompanying drawings in which:

Fig. l is a schematic diagram of an antenna embodying the present invention;

Figs: 2, 3 and 4 illustrate other embodimentsof the invention;

Fig. 5- illustrates the antenna in accordance with the'invention so positioned to provide a nondirectional pattern; and

Fig: 6 illustrates an antenna array in accordance with the invention which provides a uni directional pattern. Inaccordance with the invention, I providean' antenna having at least four series portionswhlch are one-half wave length long and so positioned that the instantaneous currents in the various portions are all in the same direction. As the basic antenna will have four portions I have chosen to call this antenna a quad. Tests made of antennas of various configurations which fulfill the above requirements have indicated in every case that the voltage of the antenna is uniformly distributed along the antenna so that there is substantially no voltage difference between any two adjacent portions of the antenna.

It should be understood that the present invention is applicable to antennas for use with wave signal receivers or wave signal transmitters. It is a generally accepted fact that any good transmitting antenna is also a good receiving antenna, especially when receiving the frequency for which it is designed. Accordingly, although in the following description reference is primarily made to transmitting antennas, it should be understood that the invention is equallv applicable to receiving antennas and a transmitting antenna is described by way of example only.

Referring now to Fig. 1 of the drawings, there is illustrated a loop antenna embodying the present invention generally designated at II] which is il ustrated as being connected to a transmission line H which is in turn connected to a wave signal' device l2 as, for example, a transmitter; Essentially. the antenna of the present invention is a loop antenna comprising an even number of conductor turns, namelv, two, four, six or more. As illustrated, the antenna Ill comprises two turns l3 and I4 suitably supported at the corners thereof by insulators l5 and I6, respectively. Since the antenna has substantially no voltage points such as the characteristic volta e antinodes of prior art antennas, the insulators l5 and Hi can be reatively inexpensive and in a particular installation insulators of the ordinary ten cent store variety were found to be very satisfactory even with a transmitting antenna for transmitting large amounts of radio frequency energy.

Although the antenna of the present invention may have various shapes as will become ap arent from the following description, the antenna IU of Fig. 1 is illustrated as comprising conductors 13 and M in the form of a square having an electrical length of approximately one-quarter A wave on each side so as to produce a total length around the loop of one full wave length. The four one-half wave portions required to make up the quad antenna are provided by the sections between a and b, b and c, c and d and irom 11 back to a through the wave signal device. The spacing of the conductors l 3 and M is determined by the surge impedance desired and preferably is such as to have the same surge impedance as the transmission line I! connected thereto. It will be understood thatadditional pairs of conductors such as l3 and [4 may be added in series, thereby increasing the radiation resistance of the antenna and the power generated thereby. For a particular installation for a broadcasting antenna for broadcasting radio frequency signals having a frequency of the order of 28 megacycles, an antenna embodying the square loops formed of conductors l3 and !4 having a length of eight feet on the side was found to be very satisfactory and capable of beaming a powerful signal comparable, if' not superior, to prior art antennas while requiring le'ss'spa'ce and being considerably less expensive than such prior art antennas. i

The currents flowing in the antenna are indicated by the arrows associated with the parallel arms thereof, and it is noted that these currents are in phase due to the fact that the conductor is reversed at the point where the phases of the currents would normally reverse. That is, the current reverses every half wave and, therefore, the current in the portion between D and 0 will be opposite to that between a and b, but as the wires of the two sections are reversed, the currents will be in the same direction. Consequently, all currents fiowing in the conductor at a particular instant are in the same direction. By virtue of the distributed current and voltage in the antenna l9, it is possible for the antenna to be opened and fed at any point which is a desirable characteristic from the standpoint of mounting the same. It is also pointed out that the antenna is re-entrant and does not require a terminating resistor as does the usual rhombic and other loop antennas. This eliminates the energy loss of the'terminating resistor and also reduces the cost of the antenna.

As previously stated, the voltage of the antenna has been found to be substantially uniformly distributed about the antenna. It is believed that the reason for this is that the turns of the antenna are close-spaced and form, in effect, a balanced transmission line, and the currents flowing in thevarious radiating portions thereof at any instant all flow in the same direction. However, in a transmission line the currents in the two conductors are substantially degrees out of phase while in the quad antenna as disclosed the currents are substantially 360 degrees out of phase or in phase. Any difference in the phase relationships'in the adjacent turns of the antenna tend to be corrected by the interrelation between the electromagnetic fields producedby the turns. It is well known that when two electromagnetic fields operate in close proximity with each other with a slight phase diiference between the fields, there is produced a tremendous interaction of power which tends to cause the fields to correct each other. This is generally similar to the action of two generators which are connected to the same line and in which generators rapidly tend to be drawn into phase. It is pointed out that although the currents in the various turns of the antenna are in the same direction, they are out of time phase by one cycle in each successive turn.

Although the antenna disclosed in Fig. l is illustrated as having a square loop configuration with a'length on each side of one-quarter wave length, it should be understood that other configurations thereof may be employed. For xample, in Fig. 2 of the drawings there is discloseda similar loop antenna in which the top and bot:- tom conductors of Fig. 1 are squeezed together. In other respects the antenna 20 of Fig. 2 is identical with the antenna l 0 of Fig. 1 and includes at least two turns comprising conductors such as '2! and 22. It is noted that this antenna. also fulfills the requirement stated for a quad antenna, that is, four radiating portions each onehalf wave long and arranged so that the cur rents in all portions are in the sam direction.

Very satisfactory results may be obtained for other configurations of the loop such as the circular loop ant'enna'25 of Fig. 3 of the drawings. It should be understood that various other-configuratio'ris are possible as long as the basi'c 'r' quirments set forth are adhered to.' The prin ciples involved in these various configurations are substantially identical and no" further discussion thereof is included herein.

In Fig. 4' of the drawings there is i-llustrated'an antenna 26 similar to theantenn-a ii! of'Fig'. 1 ex-' cept that the turns ofthe loop antenna are defined by coaxial cables 21 and 25; Such-an antenna issuitable for underground use. Due-to the absence of high voltage points on the antenna; the quad'antenna in accordance with the in vention is particularly adapted fonund'erground' or underwater use;

It will be understood that although'a: loopantenna with the plane of the loop disposed in a vertical plane is illustrated in Figs. 1 to 4 of the drawings, antennas in accordance with the invention: may: equally well be; employed. with the plane of the loop disposed in some other plane than the vertical plane. This will, of course, change the radiation pattern of the antenna. It should also be understood that when the antenna comprises fouror-six ormore loop conductors that an integral number of wavelengths per loop is required so that the currents in theadjacent loop portions are in phase. In a single loop; it may be desirable to have an integral number of wave lengths greater than one.

In the antennas described thus far the bi-directional" characteristics of'loop antennas are obtained; In the eventthatit is desired to provide a non-directional antenna embodying the present invention, configurations such as illustrated in Fig. 5 of the drawings may be employed, Fig. 5 showing a pair of square loop antennas such as iii of Fig. 1 connected in parallel but displaced from each other by 90 electrical degrees so that the lobes of the two antenna patterns will be displaced by 90 degrees and the over-all antenna pattern will be substantially non-directional. It is apparent that various other arrangements can be provided in which a plurality of antennas are used to provide a non-directional pattern.

The quad antenna in accordance with the invention may be used in various well known antenna arrays. In Fig. 6 there is illustrated an arrangement in which an antenna as which is on the left side of the antenna 3!] in Fig. 6 to provide a uni-directional pattern in the direction indicated by the arrow in the figure. Satisfactory results have been obtained by spacing the reflector a distance corresponding to one-quarter /4) of a wave length from the antenna 38. The reflector can be positioned closer to the antenna if desired, spacings of, from .1 to .15 of a wave length having been found satisfactory. It is obvious that more complicated arrays using a plurality of reflectors and directors can be used in accordance with well known principles.

The theory underlying the present invent on is not too well understood but extensive tests have demonstrated that an antenna is provided having substantially no high voltage points culty-recently with antennas employed'in con nection with frequency modulation andtelevislon,

is substantially eliminated due to the fact of the distributed voltage around the antenna with substantially-no voltage points thereon.

While there have been shown and described particular embodiments of the present invention, it is not desired for'the invention to be. limited to the exact arrangement shown but it is intended in the appended claims to cover all those modifications which fall within the'true spirit and scope of the present invention.

I'claim:

1. A loop antenna system for a wave signal device operating at a predetermined frequency compr sing, an even number of conductor'turns each having an electrical length substantially equal to a wave length at said predetermined frequency, and a conductor having low impedance connecting said conductor turns in series, saidturns being spaced with respect to each other atadistance very small as compared with said wave length and being spaced to provide a predetermined impedance, whereby the instantane ouscurrents in all corresponding close-spaced portions of said turns are substantially in phase and a substantially uniformly distributed voltage exists around said loop, and the maximum efiectiveness of said antenna is in the directions perpendicular to the plane of said loop.

' 2. An antenna for a wavesignal device oper-- ating at a predetermined frequency comprising, elongated conductor means having substantially uniform impedance per unit length thereof, said conductor means being formed to provide a loop having two'series connected turns, each of said turns having an electrical length substantially equal to a wave length at said predetermined frequency, said turns being spaced with respect to each other at a distance very small as compared with said wave length, whereby the instantaneous currents in all corresponding closespaced portions of said turns are substantially in phase and a substantially uniformly distributed voltage exists around sa d loop, and a transmission line connected to said loop for coupling said loop to the wave signal device, the spacing of said turns being such that the impedance of said loop is substantially equal to the impedance of said transmission line.

3. An antenna for a wave signal device operating at a predetermined frequency comprising, a loop having two complete turns connected in series, each of said turns being in th form of a square each side of which has an electrical length substantially equal to a quarter wave length at said predetermined frequency, the spacing between said turns being small as compared with the length of said sides of said turns, whereby the instantaneous currents in all corresponding close-spaced portions of said turns are in phase and a distributed voltage exists around said loop, and a transmission line connected to said loop for coupling said loop to the wave signal device, the spacing of said turns being such that the impedance of said loop is substantially equal to the impedance of said transmission line.

4. A loop antenna system for a wave signal device operating at a predetermined frequency comprising, an even number of conductor turns connected in series, each of said turns having an electrical length substantially equal to a whole number of wave lengths at said predetermined frequency, said turns being spaced with respect to each other at a distance very small as compared ;with said wave lengths, whereby the instantaneous currents in all corresponding closespaced portions of saidturns are in phase and a distributed voltage exists around said loop, and a transmission line connected to said loop for coupling said loop to the wave signal device, the spacing of said turns being such that the impedance of said loop is substantially equal to the impedance of said transmission line.

5. An antenna system for a Wave signal device operating at a predetermined frequency comprising, a'rpair of loop antennas positioned at right angles with respect to each other and connected in parallel, each of said loop antennas including a continuous conductor formed to providean even number of close-spaced turns connected in series, each of said turns having an electrical length substantially equal to a wave length at said predetermined frequency, said turns of each antenna being spaced with respect to each other at a distance very small compared with said wave length, whereby the instantaneous currents in all corresponding close-spaced portions of said turns of each loop are substantially in phase and a substantially uniformly distributed voltage exists around each of said lo ps- 6.' A loop antenna system for a wave signal device operating at a predetermined frequency comprising, a first loop including an even number of conductor turns connected in series, each of said turns having an electrical length substantially equal to a Whole number of wave lengths at said predetermined frequency, said turns being spaced with respect to each other at a distance small compared with said wave length, and a second closed loop having the same axis as said first loop and including an even number of conductor turns having substantially the same configuration and spacing as said conductor turns of said first loop, said second closed loop being spaced from said first loop by a distance substantially equal to a quarter of said wave length.

CLARENCE C. MOORE.

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

UNITED STATES PATENTS Number Name Date 1,597,379 Kolster Aug. 24, 1926 1,747,008 Jacobson Feb. 11, 1930 2,207,781 Brown July 16, 1940 2,235,163 Peterson Mar. 18, 1941 2,323,641 Bailey July 6, 1943 FOREIGN PATENTS Number Country Date 149,532 Great Britain Aug. 19, 1920 299,731 Great Britain Jan. 23, 1930 519,350 Great Britain Mar. 21, 1940

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