US2153589A - Antenna - Google Patents

Description

April 11, 1939. HQPETERS N 2,153,589

ANTENNA Filed May 19, 1936 RmEcmR CONDUCTOR INVENTOR HAROLD O. ETERSON /IANC ATTO RNEY Patented Apr. 11, 1939 PATENT OFFICE ANTENNA Harold 0. Peterson, Riverhead, N. Y., asalgnor to Radio Corporation of America, a corporation of Delaware Application May 19, 1936, Serial No. 80,498

8 Claims.

The present invention relates to antennas, and particularly to an antenna system for radiating horizontally polarized waves substantially equally in all directions in the horizontal plane.

The vertical antennas commonly used at transmitters for broadcasting purposes have the property of radiating vertically polarized waves substantially equally in all directions along the horizontal plane. It is in some cases found desirable to radiate energy which is horizontally polarized, since a horizontally disposed receiving antenna will in many cases be less susceptible to local interference than one oriented for the reception of vertically polarized waves. It is, however, not possible to broadcast horizontally polarized waves in all directions with the horizontal type of doublet antenna commonly used, inasmuch as these have a directive characteristic whereby they radiate very little energy in a direction parallel to the length of the doublet. The present invention provides an emcient antenna system which radiates horizontally polarized waves substantially equally in all directions.

Referring to the drawing, Figs. 1, 2, 8. 4, 5 and 6 illustrate, diagrammatically, transmitting antennas in accordance with the invention, for producing radiation of horizontal polarization with equal efllciency in all directions. Figs. 4a and 4b are given to illustrate the distribution of current amplitude on the two halves of the system of Fig. 4 at any instant.

Fig. 1 shows an antenna comprising a conductor I arranged in the form of a circle in the horizontal plane and having a diameter equal to where A is the wavelength. In other words, the diameter shown in Fig. 1 is such that the circumference is approximately two wavelengths long. If the circumference is chosen to be an even integer number of wavelengths long, such circumference must be used that will produce a diameter close enough to an odd number of half wavelengths, so as to produce substantially equal radiation in the horizontal plane. Similarly, if the circumference is chosen to be an odd integer number of wavelengths long, such circumference must be used that will produce a diameter close enough to an even number of half wavelengths to achieve the same result. In other words, suitable lengths must be chosen to satisfy the above will vary therefrom, although substantially obeying the laws set forth above. This relationship is required to be such that the radiation fields from current elements in opposite sides of the circumference add up in phase at a distance. In the case of Fig. 1, this condition is satisfied for radiation in directions inclined 38 from the plane of the loop. In other words, optimum radiation for the system of Fig. 1 is at an angle of 38 from the plane of the loop. It should be understood, however, that although optimum radiation is at an angle to the plane of the loop in the system of Fig. 1, that the waves are radiated substantially equally in all directions in the plane of the loop. For optimum radiation in the plane of the loop it would be necessary to modify the dimensions of Fig. 1 so that the diameter is 0.88). 1 This value is derived as follows for optim radiation in the plane of the loop: Let

360.1r.R o 360.2.R A 180 wherein the term through two diametrically opposite points in the loop.

The term represents the phase delay in degrees, of the space wave in traveling across the diameter of the loop.

This equation reduces to R=.44 The energy from the transmitter T, here shown conventionally, is fed through a radiationless type of transmission line TL into this circular shaped conductor at one end, and the other end of the conductor is damped by means of surge resistance R so that flow of energy along the conductor is in one direction only, and consequently no standing waves exist on the conductor. The current waves in the conductor travel in the direction indicated by the arrow. The effect of this travelling current wave on the wire is to produce instantaneously maximum radiation in certain directions and minimum radiations in other directions; However, the direction of maximum and minimum radiation changes as the current wave progresses around the wire, resulting in substantially equal radiation of energy in all directions along the horizontal plane. The broken lines around the antenna I indicates the current amplitude distribution at a given instant.

Fig. 2 illustrates a modification of this type of radiator in which a cylindrical reflector 2 is placed inside of the circle and spaced from the conductor by a suitable amount sufficient to give reflection of proper phase. Fonthis condition, the antenna will be spaced approximately onequarter wavelength from the reflector. Reflector 2 is preferably made of metal, although it may be made of a substance whose dielectric constant is considerably greater than that of air.

Fig. 3 shows, in cross section, a modification of this reflector wherein a circular antenna conductor 3 is placed between two annular reflectors 4, 4' which face one another and are designed, in the manner shown, to give concentration of energy in the vertical plane. This system of this figure, as well as that of Fig. 2, may be energized in the same manner as that of Fig. 1 so as to preclude the formation of standing waves.

Fig. 4 shows a system utilizing two parallel circles of conductors 5, 5' fed from a symmetrical and closely spaced transmission line T11 and spaced apart by approximately one-half the length of the communication wave. The ends of transmission line TL are normally in phase opposition. Since both of the parallel conductors extend in the same drection, it is therefore necessary to interpose a one-half wave section of line S in series with one side of the transmission line so that the currents in the two circular antennas will be cophasal. Another one-half wave section of line S is also applied at the far end of the system connecting the two halves together through surge resistor R. It should be understood that the total length of section S including the length of damping resistance R is onehalf wavelength.

Figs. 4a and 4b illustrate, respectively, the instantaneous current distribution by means of dotted lines along the upper and lower halves of the system of Fig. 4. It will be seen that the two circles 5 and 5' are excited cophasally and therefore aid each other in radiation along the horizontal plane. It will be understood, of course, that if desired any number of these sections may be stacked one above the other, to obtain concentration of energy in the vertical plane.

Fig. 5 shows a modification in which energy is fed from a transmitter T, through a radiationless concentric type of transmission line TL' into a spiral shaped conductor 6, thus obtaining the effect of several circular radiators stacked one above the other to obtain concentration of radiation in the vertical plane. It is preferred that the turns of the spiral be spaced at least onequarter wavelength apart to minimize mutual interaction between turns. Since each turn of the spiral is two wavelengths long, the currents in the various turns will be cophasal, and the radiation effects will be cumulative in a plane perpendicular to the axis of the spiral. The vertical portion of the system of this figure is generally located within the spirals of the conductor 6 Fig. 6 illustrates an arrangement in which the circular radiator is located at such distance above a reflecting earth as to produce substantial concentration of radiation at an angle a inclined considerably above the horizontal. The distance above ground should be such that at a distance, the direct ray radiated from the antenna will be cophasal to the indirect ray which is reflected from the ground. For the geometry of Fig. 6, this condition is satisfied when the distance A, B, C is a half wevelength different from an integer number of wavelengths. It is thus possible to produce a hollow cone-shaped directive diagram which is very desirable for some types of work as, for example, beacons for aiding the navigation of aircraft.

While the current distribution diagrams shown in dotted lines in Figs. 1, 4a and 4b suggest a circle having a circumference of two wavelengths, the system may obviously be constructed with parallel conductors of other lengths, chosen with discretion so as to have the proper radiation characteristics. For instance, the influence which the various circles have upon each other in the stacked antennas shown in Figs. 4 and 5 may be such as to alter the phase velocity of the conductors, in which case the diameter will have to be so changed as to make one circumference have an electrical length of two wavelengths.

It will be obvious, of course, that the antenna of the invention may be used to radiate vertically polarized waves if the system is oriented such that the axis of the circular conductors is horizontal. If this were done, then maximum radiation would ordinarily be along a direction perpendicular to the axis of the circular conductor.

What is claimed is:

1. An antenna system for transmitting horizontally polarized waves comprising a radiating conductor in the form of a circle whose diameter is equal to i where A is the length of the communication wave, said conductor having uniformly distributed inductance and capacitance and being located in the horizontal plane, and means for energizing said conductor and preventing the formation of standing waves thereon.

2. An antenna system for transmitting horizontally polarized waves comprising a conductor in the horizontal plane in the form of a circle and having two terminals, another similarly located conductor spaced from said first conductor in the vertical plane, means for serially connecting said conductors together for cophasal ener gization thereof including a damping impedance coupling together one terminal of one conductor with the correspondingly located terminal of the other conductor, and a two-wire substantially radiationless transmission line one of whose wires is connected to the other terminal of said one conductor and the other wire of which line is connected through a radiationless loop to the other terminal of said other conductor, the length of one side of said radiationless loop being a half wavelength.

3. An antenna system fortransmitting horizontally polarized waves comprising a radiating conductor in the horizontal plane substantially in the form of a circle, said conductor having uniformly distributed inductance and capacitance, and means for energizing said conductor and preventing the formation of standing waves thereon, the length of the circumference of said circle being substantially an even integer number of wavelengths, so chosen that the diameter is approximately an odd number of half wavelengths, whereby radiation is substantially limited to the horizontal.

4. An antenna system for transmitting horizontally polarized waves comprising a radiating conductor in the horizontal plane substantially in the form of a circle, said conductor having uniformly distributed inductance and capacitance, and means for energizing said conductor and preventing the formation of standing waves thereon, the length of the circumference of said circle being substantially an odd integer number of wavelengths long, so chosen that the diameter is approximately an even number of half wavelengths, whereby radiation is substantially limited to the horizontal.

5. An antenna system comprising a plurality of substantially parallel radiating loops located substantially along an axis perpendicular to the planes of said loops, each of said loops having uniformly distributed inductance and capacitance and having a length substantially equal to an integer times the length of the communication Wave, means for connecting said loops in electrically series relation with respect to one another, whereby the energy conductively flows through one loop to the next adjacent loop, and means for preventing the formation of standing waves in said loops.

6. An antenna system comprising a plurality of substantially parallel radiating loops located substantially along an axis perpendicular to the planes of said loops, each of said loops having uniformly distributed inductance and capacitance and having a length substantially equal to an integer times the length of the communication wave, said radiating loops being spaced apart from one another a distance equal at least to one-quarter the length of the communication wave, means for connecting said loops in electrical series relation with respect to one another, whereby the energy conductively flows through one loop to the next adjacent loop, and means for preventing the formation of standing waves in said loops.

7. An antenna system in accordance with claim 2, characterized in this that said two conductors are spaced approximately one-half wavelength apart.

8. An antenna system for radiating substantially horizontally polarized waves, comprising a plurality of radiating loops located above one another and symmetrically with respect to an axis therethrough, each of said loops having uniformly distributed inductance and capacitance and having a length substantially equal to an integer times the length of the communication wave, means for connecting said loops in electrically series relation with respect to one another, whereby the energy conductively. flows through one loop to the next adjacent loop, and means for preventing the formation of standing waves in said loops.

HAROLD 0. PETERSON.

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