US2287220A - Transmitting antenna - Google Patents

Description

June 23, 1942. A ALFORD 2,287,220

TRANSMITT ING ANTENNA Filed April 9, 1941' 4 sheets-sheet 1 INVENT OR.

June 23, 1942.

A. ALFORD TRANSMITTING ANTENNA Filed April 9, 1941 4 Sheets-Sheet 2 Saz/PCE M FIG] A 70 AEX June 23, 1942.

FREQUENCY SUI/R65 N A. ALI-ORD TRANSMITTING ANTENNA Filed April 9, 1941 4 Sheets-Sheet 5 FEM. @Zaf! FIGB.

r L f- U 6B lNvENTOR June 23, 1942. A, ALFORD i 2,287,220

TRANSMITT ING ANTENNA Filed April 9, 1941 v4 sheets-sheet 4 [Af/Wala y ,f7/v5 Mp/,4 raf? 4R65 pm/115751? Havank Patented June 23, 1942 Andrew Alford, New York, N. Y., assignor to Mackay Radio and Telegraph Company, New York, N. Y., a corporation of Delaware Application April 9, 1941, Serial No. 387,653

(Cl. Z50- 33) 12 Claims.

This invention relates toantennae and more particularly to antenna systems generally useful for transmitting signals.

In transmitting antenna systems heretofore proposed it has generally been found necessary to take special precautions or to resort to special constructions of harmful effects on the transmission characteristics if accumulations such as sleet are to be avoided.A

Moreover, in order to secure the desired distribution, particularly in broadcast antennae it has been considered necessary to have the antenna greater than a half wavelength long, or to insulate the antenna from ground and provide special loading at the upper end, usually in the form of a capacity area and a large choke coil. These are generally undesirable features since they entail additional expense in the mast and/or the insulating means therefor.

It is an object of my invention to provide antenna structures which avoid the above outlined diffculties and in addition furnish further advantages.

One feature of my inventioncomprises an antenna structure of the dipole or mast form, in which energy is supplied to one end of a central conductor, the other end of which is operatively coupled with an outer conductor or conductor system. By this varrangement the desired current distribution in the radiating portion of the antenna may be more readily achieved. Furthermore, the outer conductor need not be insulated from the earth, and no insulators capable of withstanding high potentials are required.

According to a further feature of my invention, a mast or tower antenna may be provided, in which energy is fed to the radiator by means of a conductor located Within the metal tower structure. Thisconductor is terminated at one end in a capacity area, or is coupled to the tower by means of a loop. Additional conductor ele' ments, or a conductor element, are connected at their upper end to the mast either at its top or at some intermediate point, and are held in place at their lower ends in insulated spaced relation with respect to the mast, by simple insulators or by impedance elements or by their own inherent rigidity.

A still further feature of my invention resides in a feeding system for antennae of the type discussed generally above by which a desired distribution of energy, without accentuated trouble from minor lobes may be obtained.

While I have outlined a few of the features above, a better understanding of my invention and the features and objects thereof may be had from the particular description thereof made with reference to the accompanying drawings in which l Figs. l-4 show embodiments of dipole antennae according to my invention;

Figs. 5 and 6 show structural arrangements of dipole antennae supports according to my invention.

Figs. 'T-ll show various vertical mast antennae according to my invention.

Fig. 12 isla diagram used in explaining a further feature of my invention;

Figs. 13 and 14 are dipole antennae incorporating a further feature of my invention, and

Figs. 15 and 16 are mast or tower antennae structures incorporating'the further features of my invention.

Turning to Fig. 1, a dipole unit is shown comprising an outer conductor I0 which may be of a single tubular form, inner conductors Il, I2 extending from a point nearv the center of conductor I Il to points just outside the outer ends of the conductor I0 and capacity areas I3, I4, connected to the outer ends of conductors II, I2, respectively. Energy issupplied to the antenna over a transmission line I5 from a high frequency source I6. Inorder to control the energy fed to the antenna a transmission line section I1 provided with a short circuiting bar i8 is connected to conductors II and I2, and transmission line I5 is coupled at a point intermediate the short circuiting bars and the conductors. It is clear, however, that if the proper tuning and energy transfer is already furnished by the antenna system, this coupling arrangement may be 1 omitted.

It is found that when conductor I0 is made substantially equal to one-half of a wavelength long, a voltage distribution as shown in dotted lines by the curve I9 is obtained. This may be explained in the following manner: Energy fed to unit conductors II, I2 is of opposite phase so that by reason of the capacity areas I3,' Il, traveling wavesof opposite polarity are induced in the outer conductor and travel in opposite directions, as indicated by 'the Aarrows 20, 2|. At the center point of the antenna these units meet and since they are of substantially equal magnitude and opposite phase they cancel one another so that at the mid-point of the conductor the current'is zero. 'I'his condition obtains so long as the two arms Il and I2 are at Substantially the mid-point of conductor I0,

regardless of the length of conductor Il. If conductor I is made greater than a half wavelength long then a distribution of the type shown by the solid curve 22 is obtained. This curve presents a current loop at the center of the antenna and current nodes at points a quarter of a wavelength away from this center point. It may be seen then that this arrangement while achieving the desired distribution will have considerable voltage at the terminal ends thereof. As a consequence a relatively large insulator would be necessary to assure the proper insulation of plates I3, I4 of conductor III.

In the arrangement shown in Fig. 2 the construction is very similar to that shown in Fig. 1,

except that instead of a single continuous cori-- ductor I0, two half conductors IOA, IIIB are provided insulated from one another at the central point by an insulating ring 23. Because of this arrangement wherein the parts IIIA and IDB are insulated one from another, there will not be complete cancellation at this point, but instead a current node will exist at thispoint, as indicated by the curves 22A` and 22B. Accordingly, this arrangement does not necessitate the provision of large insulators for supporting plates I3 and I4 at the end. However, this arrangement requires an insulating arrangement at the middle which must, therefore, contain considerable voltage.

In accordance with the arrangement shown in Fig. 3, the advantage of the distributionof Fig. 2 together with the preferred mechanical construction of Fig. 1 may be achieved. According to this arrangement the antenna structure itself resembles that of Fig. 1 with the addition that to each of the outer ends of central conductor I0 is connected a further outer sheath 24, 25,`

insulators or large insulators for withstanding' high voltage drop is avoided.

If desired, the outer conductors may be made of any desired length and need not extend to a point near the center of the conductor I0, as shown in Fig. 3. For example, conductive arrangement 24, 25 may be arranged to extend only a fraction of the length of the tube III, as shown in Fig. 4. This arrangement provides a distribution substantially as indicated at 22A, 22B in this figure.

Dipole units of the type shown in Figs. l, 3 and 4, lend themselves readily to simple mast construction arrangements such as shown in Fig. 5. In this arrangement the outer conductive means is made in two parts IOC, IOD which are con-- nected at their inner end to a metal supporting mast 30. Energy from the signal source I6 may be supplied over a pair of conductors I which may be connected directly at their upper end to a metal plate terminating mast 30. A short circuiting bar 3| may be properly adjusted so that the transmission line I5 is terminaf ed at this point. The central conductors II, I2, may be energized in the desired degree by means of short connecting lines 32, 33, connecting the transmission line section I1 at the desired point to line I5. Instead of capacitive coupling means at the ends of conductors I I, I2, the arrangement of Fig. 5 provides coils I3A, I4A, connected at one end to conductors II, I2, respectively, and at the other end to conductors IUC, IIID. It is thus shown that a dipole arrangement in which practically no insulating structures are required, is thus provided. In order to protect the arrangement from the elements, insulating covers 34, 35, may be provided over the coupling coils I3A, I4A and the `open ends of conductors IIIC, I 0D. Any number of units of this type may be provided on the mast to secure,the desired array eect.

It has been found that an antenna unit of this general construction as shown in Fig. 5 is not appreciably affected by reason of ice accumulation on the dipole element. In a dipole unit of this type which was constructed and tested, it was found that even encasing the whole outer conductor in a block of ice extending four inches out from the conductor arrangement made no appreciable effect in the transmission characteristics of the antenna.

In Fig. 6 is shown an array system of antenna units similarly constructed to those shown in Fig. 5. However, in this figure the dipoles are arranged with capacitive coupling means I3, I4, at their ends instead of the coils shown in Fig. 5. It can'be clearly seen that with this arrangement the energy may be readily adjusted in different units of the array if desired merely by changing the coupling point of the short coupling lines 32, 33 with respect to sections Il. From the above description it is clear that the dipole transmitting unit as set forth above, possesses very desirable characteristics. No necessity for providing insulation is present in this case. It should be further understood that if a different type of distribution is desired, outer conductor sections, such as 24, 25 of Figs. 3 and 4, may be provided on the dipole unit of Figs. 5 and 6. Furthermore, it should .be understood that these outer conductor elements such as 24, 25, may if desired, be connected to a point intermediate the length of the conductor Ill, it being merely necessary in order to secure the desired distribution that the open `ends of these conductor arrangements be faced toward the center of the unit.

The structural arrangements described in connection with the dipole system shown in Figs. 1 to 6, lend themselves readily to application of mast type antennae. This type antennae may be considered as merely a half of one of the dipole units the other portion thereof being the reflected image in the earth. In Fig. '7 is shown one type of mast arrangement in which the high frequency source 40 is connected over a transmission line 4I to a capacity area 42. This conductor 4I is arranged internally of a mast 43, which is mounted directly on the ground and arranged to make further electrical connection therewith. Conductor 4I extends from a point near the bottom of mast 43 to a point just above the mast. The distribution from this arrangement is indicated by the curve 44. It is seen that this curve has the lobe at the ground and for this reason is not generally desirable for broadcast purposes.

A more suitable distribution may be achieved by means of the arrangement shown in Fig. 8 wherein mast 43 is supported from the earth by means of insulators 45. 'Ihis arrangement, however, has the disadvantage that the heavy mast 43 must be supported on grid screen insulators. Such a consruction is relatively expensive and it is desirable to avoid this if possible.

A preferred mast antenna arrangement is shown in Fig. 9 wherein an outer conductor arrangement 4'|, which may be merely a number of conductors arranged around mast 43 is provided, these conductors 41 being connected to the mast and extending toward the earth in spaced relation from the mast. With this arrangement simple strain insulators 48 may be provided and these need not be designed to support *he entire weight of the mast as is required in accordance with the structure of Fig. 8.

Fig. 10 is similar to Fig. 9 except that the outer conductor arrangements Q1 extend only a short distance toward the earth. This gives a higher point of radiation for the system than the arrangement of Fig. 9 and may be desirable in some cases.

In Fig. 11 an arrangement somewhat similar to Figs. 9 and l0 is shown. However, in this arrangement the outer conductors 41 are arranged at a point below the top of mast 43 and may, if desired, be connected to a suitable impedance device such as shown at 50, to the earth. In addition a lightning protector 5l is shown exending above plate 42 and connected directly to the grounded mast 43. This conductor 5| extends through anopening in capacity area 42 and serves to protect the entire system from lightning.

It should be realized that the various features shown in Figs. 7 and 8 may be interchangeably used as desired, these specic examples being shown only by way of illustration. Many variations in the exact structure may be made within the scope of this invention. l

As shown in the discussion above in connection with Figs. l to 1l, the antenna arrangement according to my invention has certain very marked advantages. I have, however, found that still further improvements of operation may be made in accordance with a system of this type. It is found that when a large diameter radiator is used the distribution of the radiation pattern is not all'that may be desired. The reason for this variation in the radiation pattern will be more fully explained with reference to Fig. 12 showing various radiation diagrams. The radiation diagram from a large diameter radiator is found to depart greatly from the theoretical value that it should have considering the length of the unit. Accordingly, while this large diameter radiator has the advantage of greater radiation resistance and less losses, it does not present sharp minimum and nulls as in the case of the iine radiator arrangements.

In considering this phenomenon a dipole radiator consisting of twoarms 5B and 5i will be considered, this arm radiator being such that each of the arms 50 and 5| is slightly greater than one half of a wavelength. The energy producing the pattern in each half of the dipole may be considered as that produced by two traveling waves, one traveling outward and the other one reflected from the ends and traveling back toward the center of the dipole. In an article entitled A Discussion of Methods Employed in Calculations of the Electromagnetic Field of Radiating Conductors by the present inventor, published in Electrical Communication for July 1936, No. l, vol. 15, the method of calculating the electromagnetic ileld from a radiating conductor shown in the upper diagram of Fig. 12, that the radiation pattern f1, fz from the extremely ine radiator having theoretically a substantially zero diameter, and the radiation diagram FI, F2 from the large diameter radiator caused by the forward wave fed to the units 50, 5I, are identical. However, the radiation patterns b1, ba, caused by the back waves in the fine radiators are substantially mirror reilections of f1, f2, while the radiation pattern produced by the back waves in the larger conductors areon a much smaller scale, as shown at Bl, B2. This reduction in the size of the radiation pattern for the larger diameter radiators is due to the decreased radiation resistance, since with the large diameter conductor a considerable amount of the energy is lost by radiation so that the back Wave is much lower in amplitude than the forward wave. Thus the arrows shown in connection with the arrangement of Fig. 12 may indicate the relative signal strength. Y

Accordingly, when Vthe front and back radiation patterns are combined, as shown at C, Fig. 12, those from the ne radiator will be symmetrical, as shown at c1, cz, whereas the combined patterns for the large diameter radiator will be inclined one to another, as shown at CI, C2. These two patterns CI, C2, add together to produce the overall radiation pattern of the dipole, as shown at d1. As a consequence the length of an, y1, zz, yz, are equal and the radiation di, therefore, produces a cancellation at this point, so that one large lobe and two small lobes are provided with a complete null at a point between these lobes. However, in the case of the large diameter conductor, points Xl, YI, and X2, Y2, are not equal in length and consequently complete cancellation does not take place at this angle. The total pattern Di, therefore, has a radiation pattern which is somewhat lower in the principal direction than for the fine radiator and does not have any null. Furthermore, because Xl, YI are predominantly large, the minor lobes of this pattern are considerably larger than in the case of the ne conductor arrangements.

It can be seen that because of this phenomenon it was previously found to be not possible to secure the desired radiation distribution for mast antenna for example, which were greater than a half wavelengthlong. In this arrangement when the relatively large masts were used, it was found that the sky-wave was greatly exaggerated and it was not possible or practical to eliminate this skywave or to reduce its magnitude to the desired extent.

IIn accordance with my invention I provide an arrangement whereby the harmful eiect of the large diameter radiator may be modied or completely overcome. An explanation of the circuit arrangement for securing this adjustment will be made in connection with Fig. 13. In this gure a high frequency source 60 is provided, and an antenna consisting of central4 conductors H, l2, having coupling arrangements I3, I4, whereby the vinner conductor is coupled to an outer conductor such as IBA, 10B is shown. It is clear from the explanation previously given, that energy supplied to conductors Il, l2, will cause a wave to travel along outer conductors IDA, 10B, toward the center of the dipole arrangement. If, then, energy isA supplied from source 60 directly to the outer conductors, the energy supplied from the inner conductors over the coupling capacities may be adjustably controlled so as to produce a compensation for the loss of energy in the back waves. By this arrangement the adjustment of the radiation pattern to any desired form may be accomplished. Upon investigating this property it was foundl that an arrangement such as shown in Fig. 14, produced essentially complete compensation for the attenuation of the wave in the outer conductor of the system. In this arrangement the system shown is substantially the same as that shown in Fig. 13. However, in this case no connection whatsoever is made to the section I1 connected to conductors il and l2 of the arrangement. It appears, accordingly, that substantially complete compensation may be achieved merely by arranging the central conductors together with a suitable tuning arrangement such as represented by I1 in a mast antenna structure of this type, or in a dipole arrangement as shown in Fig. 14. It is also clear that with this arrangement the outer conductor system described in connection with the previous ilgures may be also used so as to secure the reversal of the current in the radiating conductor, if this is also desired.

The arrangement of Fig. 14 lends itself readily to mast antenna construction. In Fig. 15 is shown a mast antenna comprising a central mast portion 43 provided with an outer conductor arrangement 41. Within mast 443 is arranged the central conductor 4I connected'to the high frequency source 60. Mast 43 is mounted directly on the earth and is electrically connected thereto. An impedance adjusting arrangement exemplified by condenser 63 is provided connecting the lower ends of conductor 4| to ground. The capacity area 42 connected at the upper end of central conductor 4| is separated from mast 43 by suitable small insulators 65. With this arrangement suitable adjustment of condenser 63 may be made so that the desired horizontal distribution of energy may be readily achieved.

In Fig. 16 a still further embodiment of a mast antenna arrangement using this principle, is disclosed. This system differs from that of Fig. 15 primarily in that a central conductor instead of being a single conductor is made as a two conductor transmission line 4|. This transmission line may then be connected directly to earth at its lower end and a condenser may be provided at some point to secure the desired adjustment as indicated at 63. 'I'he radiation of energy from source 6|! by means of kthe mast may take place in the same manner as previously outlined. Since the central conductor line 4|A is not electrically connected to receive energy directly from source 60, it is immaterial how many conductor arrangements are brought down. This transmission line 4|A may accordingly, then be used as a transmission line for supplying energy from a further source 10 which may, if desired, be of higher frequency than source 60. By suitable choice of the connection point of source 'l0 to line 4IA with respect to the short circuited end at the ground, the proper impedance relation for feeding energy along line 4IA` may be provided. A short wave radiator 12 may then be provided mounted on top of condenser area 42. In addition a lightning protection rod 5I is arranged connected to the top of mast 43 and extending above radiators 12.

It is clear that the outer conductor element 4'! may be omitted if desired and the antenna tower may be operated in an arrangement similar to Fig. 7. Similarly, if desired, any oi the forms shown in Figs. 7 to 11 may be utilized in place of the particular arrangement shown in Fig. 16.v

While I have described a new specic example of my invention, it should be distinctly understood that these are submitted merely as illustrations of the invention and not as limitations on the scope thereof. Any modifications and changes may be made within the teachings o1' my invention, it being only necessary to embody therein the principles of the invention as described above. While tower structures are practical from a mechanical standpoint. it is also clear that the principles of my invention apply to antenna arrangements which are supported on independent supporting structures as well.

What I claim is: i

1. A radio antenna comprising a hollow conductor means extending from a position adjacent to a feeding point to a more distant point, an inner conductor means arranged within the hollow of said hollow conductor means, extending throughout the length and slightly beyond the distant end thereof, means for coupling the distant ends of said hollow conductor means and said inner conductor means with one another, and means for supplying energy to at least one of said conductor means at said feeding point.

2. A radio antenna according to claim 1, wherein said antenna comprises two `hollow conductor means and two inner conductor means, extending in opposite directions.

3. A radio antenna according to claim 1, wherein said hollow conductor means consists of a plurality of wires arranged to define a hollow periphery.

4. A radio antenna system according to claim 1, wherein said hollow conductor means is greater than one quarter wavelength at the operating frequency long.

5. A radio antenna according to claim 1, wherein said hollow conductor means is between a quarter wavelength and a half wavelength long.

6. A radio antenna according to claim 1, wherein said hollow conductor comprises a radiating mast structure mounted directly on the earth to produce a direct ground, and outer conductive means galvanically connected to the upper end of said mast structure and extending downwardly therefrom in spaced relation from said mast and said earth, and said means for coupling comprises a capacity area mounted on insulators on the top of said mast structure.

'7. A radio antenna according to claim 1, wherein said hollow conductor means comprises a central hollow conductor member and an outer conductive means galvanically coupled to the outer end of said hollow conductive means and extending back toward said feeding point in spaced relation with respect to said hollow conductive means.

8. A radio antenna according to claim l, wherein said hollow conductor comprises a radiating mast structure mounted directly on the earth to produce a direct ground, and outer conductive means galvanically connected to the upper end of said mast structure and extending downwardly therefrom in spaced relation from said mast and said earth, and said inner conductor means comprises a transmission line, further comprising means for supplying high frequency energy to outer conductor at a point near said ground, and phase adjusting means interconnecting said inner conductor means and ground.

9. A radio antenna according to claim 1,

wherein said hollow conductor comprises a radiating mast structure mounted directly on the earth to produce a direct ground, and outer conductive means galvanically connected to the upper end of said mast structure and extending downwardly therefrom in spaced relation from said mast and said earth, and said inner conductor means comprises a transmission line, further comprising means for supplying high frequency energy to outer conductor at a point near said ground, other radiating means mounted on said capacity area, means for coupling the transmission line forming said inner conductor to said other radiating means, and a separate source of energyfcoupled to the end of said transmission line near said ground for supplying energy to said other radiating means.

10. A radio antenna according to claim 1, further comprising an energy source for supplying energy to said outer conductor means at said feeding point, and connections to said source for supplying energy from saidsource of the desired amplitude and phase to said central conductor means.

11. A radio antenna comprising a hollow conductive 4element of relatively large diameter, means for supplying energy to one end of said hollow conductive element, and means for reducing the effects of attenuation of energy in said hollow conductor comprising an inner conductive means arranged Within said hollow conductive element extending substantially throughout the length thereof and slightly beyond the end of said hollow conductive element remote ANDREW ALFORD.

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