US2229733A

US2229733A - Antenna structure

Info

Publication number: US2229733A
Application number: US207660A
Authority: US
Inventors: Goldmann Joachim
Original assignee: INTERNAT TELEPHONE DEV CO Inc
Current assignee: INTERNAT TELEPHONE DEV CO Inc; INTERNATIONAL TELEPHONE DEVELOPMENT Co Inc
Priority date: 1938-05-13
Filing date: 1938-05-13
Publication date: 1941-01-28
Anticipated expiration: 1958-01-28
Also published as: FR866286A; DE756558C

Description

Jan. 28, 1941. J, GOLDMANN ANTENNA STRUCTURE Filed May 13, .1938 4 Sheets-Sheet 2 IN VEN TOR. lf/M GOLD/VA/V/V A TTORNIL'YZ.

Jan. 28, 1941- ,J. GOLDMANN ANTENNA STRUCTURE Filed May 13, 1938 4 Sheets-Sheet 3 INVENTOR.

A TTORNEYS.

Jan. 28, 1941. J. GOLDMANN ANTENNA STRUCTURE Filed May 13, 1938 4 Sheets-Sheet 4 INVENTOR. JO/ICH/M GOLD/VA/V/V ATTORNEYS.

Patented Jan. 28, 1941 UNITED STATES ANTENNA. STRUCTURE Joachim Goldmann, Berlin-Wilmersdorf, Germany, asslgnor to International Telephone Development Co. Inc., New York, N. Y., a corporation of Delaware Application May 13, 1938, Serial No. 207,660 6 Claims. (Cl. 250-11) The present invention relates to antenna structures and especially antenna structures comprising at least one dipole element and means for feeding such element or deriving energy therefrom. The invention is particularly applicable to transmitting systems of the type generally known as beacons.

It is an object of the present invention to provide a radiating system comprising at least onefed dipole which shall provide a desired radiation pattern free from distortion. More speciiically it isan object to provide such a radiating system comprising a dipole and a lead-in arrangement for said dipole which shall include means to isolate the dipole from the lead-in arrangement to prevent distortions introduced by said lead-in arrangement and at the same time shall be free from distortions introduced by asymmetry of the dipole or of the isolating means used for isolating said dipole.

It is a further object of the invention to provide a dipole and lead-in unit for antenna systems which shall have substantially the radiant pattern of an ideal cylindrical dipole suspended in free space without lead-in lines. -In particular it is an object to provide such a dipole and lead-in structure which shall be readily adjustable. a

It is a further object of the present invention to provide a radiating system for a course beacon including a main radiating dipole fed over a shielded lead-in line disposed along the dipole axis and effectively isolated from this lead-in line except for feeding purposes, wherein the effective electrical shape of the dipole is perfectly symmetrical and asymmetries resulting from the means used to isolate the dipole are eliminated.

It is a further object to provide such a radiating system including in addition to the main radiating dipole, a plurality of parasitic reflector dipoles controlled by relays, wherein the control wires for actuating the relays are so disposed as to introduce no distortions in the radiation diagram. It is a further object of the invention to provide such a radiating system in which one single coaxial line serves both as the lead-in line for the radiating dipole and also for a control line to actuate the relays which control the parasitic reflector dipoles.

According to one feature of the .invention, a radiating dipole is center fed by a line disposed end-on to the dipole along its axis, and extending within the dipole to the center thereof, and the dipole is isolated from such line by resonant circuit structures operating according to the principles set forth in an application filed by Frederick A. Kolster on April 28, 1938, Serial No. 204,735, and assigned to the same assignee as the present application.

According toa further feature of the. present invention, the dipole is so constructed as to form a uniform cylindrical outer surface within which the resonant circuit structure which isolates the dipole from the feed-line is disposed, so that 10 the outer surface of the dipole is substantially free from irregularities, discontinuities and asymmetries. According to still another feature of the present invention, the relays which control the parasitic dipoles are actuated over lines extending perpendicular to these parasitic reflector dipoles and to the main dipole. According to still a further feature of the present invention, such perpendicular extending control lines are connected to the coaxial line which feeds the main dipole and the control currents-for the relays are transmitted over this coaxial line together with the high 'freq'uency'currents for feeding the main dipole.

The exact nature of my invention can best'. be understood by reference to the attached' drawings, in which Fig. 1 represents an elevation of a two-beam course beacon constructed in accordance with my invention;

Fig. 2 is a sectional elevation of the structure of Fig. 1, taken at the section plate 2-2, to illustrate the side elevation of one of the parasitic reflector dipoles of the structure of Fig. 1;

Fig. 3 is a sectional elevation of the structure of Fig. 1, taken at the section plane 33, to illustrate the side elevation of the main radiating dipole of the structure of Fig. 1;

Fig. 4 is a detailed front elevation of the main radiating dipole of Fig. 1 with part of the housing structure broken away to illustrate the internal construction:

Fig. 5 is a sectional detail of the lower-limb assembly (generally designated as assembly 5 in Fig. 4) of the main radiating dipole;

Fig. 6 is a sectional detail of the upper-limb assembly (generally designated as assembly '8 iii' Fig. 4) of the main radiating dipole;

Fig. 7 is a sectional detail of the auxiliary wave controlling assembly (generally designated as assembly I in Fig. 4) of'the main radiating dipole; I o

Fig. 8 is a sectional detail of the construction at the central junction of the main radiatin dipole (this central junction being generally designated as 8 in Fi 4).

Referring more particularly to Fig. 1, the main radiating dipole I0 is fed at its central junction 8 over coaxial line H, which comprises inner conductor HA and outer conductor or sheath IIB, from the transmitter station l2, which in the preferred embodiment of my invention is adapted to provide a continuous supply of ultrashort wave power at a wavelength of approximately two and one-half meters and at a power level of several watts. The dipole l0 whose detailed construction is more clearly illustrated in Figs. 4, 5, 6, '7 and 8, is supported upon a pole I3, which in the preferred embodiment has a total height of the order of fifty or a hundred feet. Attached to the pole I3 is a cross arm l4, near the extremities of which the upright arms l5 are adjustably bolted in such manner that their distance from the pole I3 may be varied. Attached to the upright arms II are the parasitic reflector dipoles I5 and II, which are essentially similar but differ in respect of the fact that dipole I6 is normally operative whereas dipole I1 is normally inoperative.

Each of the parasitic reflector dipoles l6 and I1 comprises two limbs I8 having telescopic end portions I9 for adjusting the'length of the limbs to tune the dipole. The two limbs ll of the dipole l6 are jointed at their center through a relay 20 and the two limbs I8 of the dipole H are similarly joined by a relay 2|. The two relays 20 and 2| are preferably of rugged construction and protected by weatherproof housings. Each of these relays is adapted to be actuated by direct current keying signals, the relay 2|] being actuated by signals over the line 22 while the relay 2| is actuated by signals over the line 23. The relay 20 has its contacts arranged so as to normally close the connection between the two limbs ll! of the dipole l6, and is adapted upon energization to open its contacts, thus disconnecting the two limbs of this dipole to render the dipole inoperative. Conversely the relay 2| has its contacts arranged so that normally the .two limbs l8 of the dipole H are disconnected and in response to the energization of the relay 2| its contacts are closed to join the two limbs of this dipole. Preferably the operating characteristics of the two relays 28 and 2| are so related that upon simultaneous energization of the two relays, relay 20 will open its contacts to disable the dipole |.6 before relay 2| closes its contacts to render the dipole effective. Conversely, upon simultaneous cessation of the energization of the two relays relay 2| will preferably open its contacts to disabledipole before relay 28 recloses its contacts to render dipole l6 again effective.

The

lines

22 and 23 extend perpendicularly to. the parasitic reflector dipoles as well as to the main radiating dipole I, so that at all points these lines are transverse to the field of the antenna system. Preferably the

lines

22 and 23 are also provided with chokes which may be housed within the housings of relays 23 and 2|, and if desired other chokes such as 24 may be inserted in these lines adjacent the main radiating dipole l0. At the, central junction 8 of dipole Ill, these

lines

22 and 23 are connected to the two

limbs

5 and 6 of the dipole It, as more clearly shown in Figs. 4 and 8, so that the two lines are connected in parallel and one wire of each line is conductively joined to the inner conductor A of the line H, while the other wire. of each line is con-' ductively joined to the outer conductor or sheath 3 of the line H. The transmitting station I2 is adapted to supply not only ultra-short wave energy for exciting the main radiating dipole Ill, but also direct current control, signals for actuating the relays 23 and 2|, these direct current control signals being transmitted over the same line H which carries the ultra-short wave energy.

The construction of the main radiating dipole It can most readily be seen from Figs. 4, 5, 6, 7 and 8. Referring more particularly to Fig. 4, it

can be seen that the main radiating dipole comprises a lower-limb assembly I and an upper-limb assembly 6, these two

assemblies

5 and 5 being suitably joined together and supported at the central junction 3, as well as an auxiliary wave controlling assembly I. The lower-limb assembly 5 and the auxiliary wavecontrolling assembly 1 are adjustably united by the threaded central sleeve 43 to which both the assemblies 5 and I are attached, as more clearly shown in Figs. 5, 7 and 8. The central junction 8 of the main radiating dipole III is protected by a wooden housing 3|, shown in Fig. 4 with the front cover removed. The upper-limb assembly 3 is protected by an insulating tube 32 preferably of fibrous material impregnated with phenol condensate, this housing tube 32 being supported from the housing 3|, as more clearly shown in Fig. 8. A cap 33 protects the top of the housing tube 32 to exclude the entrance of moisture or dirt. A lower housin tube 34 similar to the tube 32 protects the lowerlimb assembly '5 and the auxiliary assembly I, this housing tube 34 being maintained in position by a clamp 35 which bears againsta disc closing the lower end of the tube 34, and the tube also being located by a suitable collar at the bottom of housing 3|, as more clearly shown in Fig. 8.

The structures of

assemblies

5, 6 and 1 embody certain of the important novel features of the present invention, the exact construction of these assemblies being clearly illustrated in Figs. 5, 6, '7 and 8. Referring now more particularly to Fig. 5, it will be seen that the lower-limb assembly 5 illustrated in this figure, comprises a central sleeve 40 slidably disposed over the outer conductor B of line H. To this central sleeve 4|! an enclosing tube 4| is fixed by means of a brass disc 42 soldered to central sleeve 48 and screwed to enclosing tube 4|, and by means of an insulating disc 43 loosely bearing against central sleeve 48 and screwed to enclosing tube 4|. Near the lower end of enclosing tube 4| a tubular skirt 44 is adjustably attached to the outer surface of 4| by means of set screws which pass through a spacer ring 43 fixed to the tubular skirt 44. Cooperating with the tubular skirt and with the end of enclosing tube 4| a condenser cup 43 is threaded on the central sleeve 40 so that it may be axially adjusted along this central sleeve to vary the capacity between the cup 48 and the skirt 44 and enclosing tube 4|. A lock nut 41 is provided to maintain the cup 46 in position after adjustment.

Outside of the upper end of enclosing tube 4| is slidably fitted an exterior tube 49 whose lower end is split and provided with ears 58 through which a screw may be passed to clamp the lower end of the exterior tube 43 against the enclosing tube 4|. At the upper end of the exterior tube 49 is soldered a brass disc 5| which is fixed to the sheath 3 of line H by clamping this disc place.

between fitting 52 and nut 53. The fitting 52 which may be made of brass, is soldered to the sheath MB of line H and is externally threaded at its upper end to receive the nut 53. On the inside or this fitting 52 a plug 54, see Fig. 8, of insulating material such as Isolantite is cemented to form an air-tight and mechanically strong seal with the fitting 52, and a stem 55 extends through the insulating plug 54 and is also sealed thereto with cement. The inner conductor IIA of line H is tubular in form and is soldered over the lower end of stem 55 so that the sheath NB, the fitting 52, the plug 54, the stem 55 and the inner conductor A are integrally joined together and sealed in an air-tight manner.-

It will thus be seen that the lower-limb assembly 5 comprises two'principal portions. One of these portions includes the exterior tube 49, the fitting 52 and nut 53, the insulating plug 54, the stem 55 and the sheath B and inner conductor HA of line H, all of these parts being fixed with respect to one another. The other principal portion of the lower-limb assembly 5 comprises central sleeve 40 and enclosing tube 4| together with the discs 42 and 43 which unite the central sleeve and enclosing tube. The skirt portion 44 with its ring 45 and the condenser cup 46 with its lock nut 41 may also be considered as included in this second portion of the lowerlimb assembly, although these parts are not actually fixed with respect to the enclosing tube and central sleeve since skirt 44 may be adjusted along the outside of the enclosing tube and since condenser 46 may be screwed axially to adjust it along the central sleeve 40. It should be noted that in the completed beacon assembly the exterior tube portion of the lower-limb assembly 5 is fixed and the other portion of this assembly (including the central sleeve 40 and enclosing tube 4|) is held in position by the frictional clamping of the lower end of exterior tube 49 against the enclosing tube 4|. Thus to adjust the overall length of the lower-limb assembly 5, it is merely necessary to loosen the clamping screw extending through ears 56 and then to bodily slide the enclosing tube and central sleeve portion of the lower-limb assembly up or down along the sheath B. When the correct adjustment of the length is attained thescrew extending through clamping ears 50 may again be tightenedto fix the enclosing tube 4| and central sleeve 40 in position.

Referring now more particularly to Fig. 6, the upper-limb assembly 6 illustrated in this figure comprises a main tube 60 closed at one end by a brass disc 6| soldered to it. Into this brass disc 6| isthreaded the stem 55 which passes through the fitting 52 and is connected to the inner-conductor A of line H as previously mentioned. A spacer 56 is slipped over the stem 55 between disc El and insulating plug 54, so that when the disc BI is screwed onto the stem 55 this spacer 56 will press against the insulating plug 54 and thus further tend to maintain plug 56 in Fig. 8 particularly well illustrates this portion of the structure. As shown in Fig. 6, inside of the upper end of the main tube 60 there is slidably fitted a telescopic extension tube 62 whose upper end is closed by a brass disc 53 soldered thereto. This extension tube 62 serves to adjust the length of the upper limb assembly 6 of the main dipole, and after the proper adjustment has been obtained this extension tube 62 is locked in place by tightening a screw which passes through a pair of clamping ears G5 similar to the clamping ears 50. The upper end of the main tube 60 is slotted so that by means of the clamping ears 65 this main tube 60 is tightly clamped against the extension tube 62.

Referring now more particularly to Fig. 7, the auxiliary wave controlling assembly I illustrated in this figure, comprises an auxiliary enclosing tube 10 somewhat similar to the enclosing tube 4| of assembly 5, this auxiliary enclosing tube 10 being adiustably attached to the same central sleeve 40 to which enclosing tube 4| is fixed as previously mentioned. For the purpose of such adjustable attachment of tube I to the sleeve 40, this sleeve is threaded near its lower end and a brass disc H which is soldered to the lower end of auxiliary enclosing tube 10 is screwed onto this threaded lower end and secured in place after adjustment by lock nut 12. An insulating disc 13 is fixed inside the auxiliary enclosing tube 10 near its upper end, and is adapted to slidably bear against the correspond ing portion of sleeve 40. Since it is preferable that the portion of sleeve 40 against which disc 13 slides should not be threaded and since in any case it is advantageous to be able to remove condenser cup 56 of assembly from the sleeve 60 without having to screw it along the full length of this sleeve, it is preferred to make thesleeve 4t in two parts as shown in Fig. 7, and to unite these parts by means of a coupler 74 which is preferably soldered to the lower portion of sleeve to and into which the upper portion of sleeve 40 is screwed. It will be understood, however, that sleeve 60 may also be made in one integral piece since the construction of this sleeve in two parts is merely a matter of manufacturing convenience and expediency.

Near the upper end of auxiliary enclosing tube a tubular skirt I5 is adjustably attached by set screws which pass. through a brass ring 16 soldered to this skirt. Cooperating with tubular skirt l5 and with the-upper end of auxiliary enclosing tube 10 is the auxiliary condenser cup H which is threaded on sleeve 4|] and locked in position by nut 18. Preferably the total length of the auxiliary enclosing tube 1|] is somewhat longer than the length of enclosing tube 4| between its lower end and the point at which disc 42 is attached. If this is so, the tubular skirt portion and condenser cup 11, or at least one of these, will preferably be somewhat shorter than the corresponding condenser ,cup and

tubular skirt

46 and 44 of assembly 5, since it is ordinarily desired that the chamber enclosed by auxiliary enclosing tube Ill should be resonant to approximately the same frequency as the chamber enclosed by enclosing tube 4| below disc 42.

The general manner in which the

assemblies

5, 6 and I are combined with each other and with other parts to constitute the main radiating dipole I 0 can best be seen from Figs. 4 and'8. As

already explained in connection with the description of Figs. 5 and 7, and as is plainly evident from Fig. 4, the

assemblies

5 and 1 are united by the common central sleeve 40' since both the auxiliary enclosing tube Ill and condenser cup 11 of assembly 1 as well as condenser cup of assembly 5 are adjustabl'y attached to this common central sleeve, and since the enclosing tube 4| of assembly 5 is fixedly attached to this'same sleeve. It will thus be evident that upon adjustment of the length of the lower-limb assembly 5 sliding enclosing tube 4| upward or downward within the exterior tube 49, as previously described, the spacing between the adjacent ends 01. assemblies I and 'I will not be altered and likewise the condenser adjustment of each of these assemblies will not be altered. It will also be apparent that the condenser adjustment of the auxiliary wave controlling assembly I may be varied by screwing the enclosing tube 10 up or down along the central sleeve 46 without varying the separation between the assemblies I and I.

As can best be seen from Fig. 8, the assemblies I and I are fixed with respect to one another by the fitting II, the insulating plug I4 and the spacer II. The adjustment of enclosing tube 4| upward or downward within the exterior tube 46 for adjusting the total length of the lowerlimb assembly I will not in any way vary the separation between assemblies I and I. Similarly the adjustment of telescopic extension tube 62 upward or downward within the main tube 66 to vary the total length of upper-limb assembly 6 will not in anyway alter the spacing between the upper-limb assembly and the lowerlimb assembly. These two

assemblies

6 and 6 are supported by clamp 66 attached to the end of insulators II which are screwed to the housing 3!. This housing 3| is in turn fixed to the cross arm l4 which, as previously explained, is attached to the pole l3.

At the lower end of line II a suitable insulating and air-tight seal is provided preferably similar to the seal at the top of this line, and if desired means may be provided for maintaining the interior of the tube filled with an inert gas or with dry air or some other gas at normal or elevated pressure.

The exact construction of the preferred embodiment of my invention having been fully described, the operation thereof may be briefly set forth. For a further disclosure of the principles of operation of the auxiliary wave controlling assembly I and the lower portion of the lower limb assembly I below disc 42, reference is made to the previously mentioned application filed by Frederick A. Kolster, on or about April 28, 1938', and assigned to the same assignee as the present application.

The toroidal chamber formed by the lower portion of enclosing tube 4| (below the disc 42) and the corresponding portion of central sleeve 46 together with condenser cup 46, tubular skirt 44 and disc 42, constitute a toroidal resonating circuit which may be tuned by varying the capacity between condenser cup 46 and the coop-, crating portions of 44 and 4|. To so vary this capacity it is preferred to effect the coarser adjustment by loosening the set screws which fix skirt 44 to the tube 4|, and then sliding this skirt up or down so as to attain approximately the correct tuning. A slight further adjustment may be conveniently made to obtain exact tuning by loosening the lock nut 41 and screwing the condenser cup 46 up or down by a small fraction of an inch, but it is preferred to effect only the fine tuning in this latter manner since any considerable displacement of condenser cup 46 would substantially vary the spacing between assembly I and assembly I, and such a variation might require retuning of assembly I in case there were any appreciable standing wave intensity along the sleeve 40 between the two assemblies.

Similarly the chamber formed by auxiliary enclosing tube 16 and the corresponding portion of central sleeve 46 together with disc II and at the other end of the chamber condenser cup TI and tubular skirt II constitute a second toroidal resonating circuit which is also tunable. To tune this auxiliary resonating circuit it is preferred to effect the coarse adjustment by loosening-the set screws which fix skirt 'II to the tube II and then moving this skirt up or down along the tube II to obtain approximately the correct adjustment. The finer adjustments are preferably effected by screwing the disc H and tube 16 up or down along the central sleeve 46 since such an adjustment will not vary the spacing between the assembly I and the assembly I.

By adjusting the tuning of the toroidal circuit of assembly I the passage of waves through this circuit may be controlled in almost any desired manner. If this resonant circuit is tuned approximately to resonance, a condition can be obtained in which in spite of the presence of very high voltage waves along skirt 44 and the other external portions of the assembly I which lie above this skirt, a very slight and in fact practically negligible wave intensity will exist on condenser cup 46 and on all the other portions of the structure below the condenser cup. Thus the I surface constituted by exterior tube 46, the exposed portion of enclosing tube 4! between the lower end of exterior tube 46 and the skirt 44. and finally the skirt 44 itself, may be considered as constituting the lower limb of the main radiating dipole, while all the portions of the structure below the lower end of skirt 44 may be considered as practically ineffective so far as radiation is concerned because of the fact that there is only a negligible intensity of waves in these remaining portions.

I have found, however, that the adjustment of the resonant circuit of assembly 5 affects not only the degree of wave blocking or the amount of attenuation of waves in passing from the effective radiation portion of the lower dipole limb to the portions of the structure therebelow, but also at the same time influences the coefllcient of reflection of waves from the lower end 01' the effective radiation portion of the lower dipole limb. Since it is desired for symmetrical radiation to adjust the resonant circuit oi assembly I in such manner that the reflection coefiicient from the lower end of skirt 44 will closely simulate the reflection coeflicient from the upper end of the upper limb of the dipole (i. e. from the upper end of telescopic extension tube 62) I have in accordance with one feature of my invention provided the further auxiliary wave controlling assembly l disposed immediately below the assembly 6 and adapted to be independently adjusted for further controlling any waves which may pass down below the lower end of skirt 44.

According to the preferred method of adjusting the structure above described, the resonant circuit of assembly 5 is first tuned so as to provide as high an attenuation of waves of the desired frequency as possible. Then the two limbs of the dipole are adjusted to the desired-preferably equal-lengths and the distribution of standing waves along the efi'ective radiation portion of assembly I which constitutes the lower limb of the dipole is compared with the corresponding distribution along the upper limb of the dipole constituted by assembly I. The resonant circuit of assembly I is then finely adjusted so as to make the two distributions as nearly symmetrical as possible. When this is done, it may be found that the attenuation of the waves passing below the lower end of skirt 44 is not sufficient to render the waves below this point completely negligible. The resonant circuit of assembly I is then adjusted so as to more completely extinguish the waves so as to prevent their passing down over the line H. In some cases such adjustment of assembly 1 will slightly alter the distribution of waves along the lower limb of the dipole and in such case assembly 5 should again be readjusted.

Ordinarily no more adjustment than this will be necessary, but in certain cases where a very accurate symmetry between the two halves of the dipole is required and at the same time a very complete extinction of the waves passing down over the line I I is necessary, the distance between the assemblies 5 and I may be varied by screwing disc 1| down along the central sleeve 40 and then screwing condenser cup 11 down along this central sleeve 40 by a corresponding amount. A fine adjustment of the separation between the two assemblies 5 and I is not necessary, and

EDI

therefore it is in all cases sumcient to try a very few difierent spacings, readjusting the assemblies Sand 1 each time to obtain the required distribution on the lower limb of the dipole and at the same time to obtain the maximum attenuation of waves passing down over the two

assemblies

5 and 1.

It will be noted that the effective outer surface. of the lower limb of the dipole is very nearly a continuous smooth cylinder with no discontinuity except the very slight increase of diameter at ring 45. Furthermore, the diameters of the upper and lower limbs of the dipole are substantially the same. These factors when combined with the possibility of obtaining exactly the same reflection coeflicient at the ends of the two limbs of the dipole, and at the same time of obtaining a substantially complete extinguishment of waves passing down over the line H, enable a' very symmetrical radiation to be obtained. At the same time, distortions of the radiation pattern with respect to any horizontal diagram taken in a plane perpendicular to the axis of the dipole, are eliminated'by the concentric arrangement of the feed-line with respect to the.

dipole.

It should furthermore be noted that the small amount of waves which do pass down beyond the end of skirt 44 and are finally extinguished by assembly 1 are insuilicient to cause any significant distortion of the pattern since these waves are only effective over a distance of a few inches. The positioning of assembly I with the condenser cup uppermost aids in reducing the effect of such weak attenuated waves which may exist below the .lower edge of skirt 44 and above the lower edge of condenser cup 11. It should furthermore be noted that if it is desired to take account of even these weak waves occurring in a very limited region, this can be done by suitably adjust.- ing the length of the upper dipole limb so as to slightly differ from the length of the lower dipole limb, and then correspondingly adjusting the distribution of waves along the two limbs. Ordinarily, however, such adjustments are not at all necessary since the structure is inherently highly symmetrical and can be made to give an almost perfectly symmetrical radiation diagram merely by tuning the two assemblies 5 and I and adjusting the lengths of the two limbs of the dipole so as to be equal.

It should be noted that if the slight discontinuity intoduced by ring 45 is deemed objectionable, the condenser cup 46 may be arranged to cooperate with the inside surface of enclosing tube 4| rather than with the outside surface thereof and the tubular skirt 44, if required at all, may then be located'inside of tube 4| instead of outside of it, so that the outside surface of the lower dipole limb will be perfectly cylindrical. In practice, however, it is found that the very slight variation in diameter introduced by the presence of spacing ring 45 and skirt 44 can. be neglected.

It should be noted that the positions of

wires constituting lines

22 and 23 are such that even without the presence of chokes 24 these wires would introduce. substantially no distortions in the radiation pattern since they are at all points transverse to the field of the dipole. It is preferred, however, to add the chokes 24 and the further chokes within the relay housings of relays and 2|, in order to prevent any possible influence of the

lines

22 and 23 upon the pattern if these lines are not at all points perfectly perpendicular to the field of the radiating system. Furthermore, at least one set of chokes in each line is desirable in order to prevent the passage of the ultra-short waves directly from the line I I over the

lines

22 and 23, thus causing unnecessary losses and possible injury to the relays as well as perhaps a very slight radiation due to the physical separation of the two wires of each of the

lines

22 and 23. e

Although in the preferred embodiment of my invention above described and shown, the transmission line I l is of the coaxial type, this line may also be shielded two-wire line of a high frequency type. It may be preferred to employ such a two-wire line with a'conducting sheath if the transmitter station 12 has a balanced output, If such a shielded two-wire line is employed, one wire may be connected to the limb B and the other wire may be connected to the limb 5.

Although I have shown and described certain particular embodiments of my invention for the purposes of illustration, it will be understood that adaptations, modifications and alterations thereof occurring to one skilled in the art may be made without departing from the scope of the invention as defined in the appended claims.

What is claimed is:

1. A dipole antenna structure for producing symmetrical radiant action comprising a multiconductor transmission line having a conducting shield conductor and at least one inner conductor, an elongated hollow radiator encircling said shield conductor adjacent one end thereof, a second radiator of similar external configuration extending coaxially with said first radiator beyond the end of said shield conductor, the space between the adjacent ends of said radiators being relatively small, a connection between said shield conductor and one of said radiators and additional connections between the adjacent ends of said radiators and the conductors of said line.

2. A dipole antenna structure for producing symmetrical radiant action comprising a coaxial transmission line having a center conductor and the sheath thereof and forming a sleeve encircling said sheath, a second radiator of similar external configurationattached to said center conductor and extending in the opposite direction to said radiator first mentioned, the space between the adjacent ends of said radiators being relatively small and an additional connection from said sheath to a point intermediate the ends of said first mentioned radiator.

4. A dipole antenna array comprising a coaxial tr as on line having a center conductor and an outer conducting sheath, an elongated hollow radiator connected to the end of said sheath and forming a sleeve encirclingsaid sheath, a second radiator attached to said center conductor and extending beyond the end of said sheath coaxially with said first radiator, a second dipole including two conductor members disposed end to end parallel to said first dipole and spaced therefrom to influence the radiation pattern of said dipole, a keying relay positioned adjacent the inner ends of the conductor members forming said second dipole for altering the eflect of said second dipole, and connections from the sheath and inner conductor of said linefirstmentionedtosaidkeyingrelamsdd connections extending at ri ht angles to the axis of said first dipole and from a point adjacent said end of said sheath.

5. A dipole antenna structure for producing symmetrical radiant action, comprising a coaxial transmission line having a center conductor and an outer conducting sheath, a first radiator including a resonant circuit comprising a sleeve encircling said sheath adjacent the end thereof, said sleeve and sheath extending in overlapping, spaced, concentric relation, anda second radiator connected to said center conductor and having substantially the same external configuration as said sleeve. 1

8. A dipole antenna structure for producing symmetrical radiant action, comprising a multiconductor tron line having a conductive shield, a resonant circuit comprising a sleeve encircling said shield adjacent one end thereof and a member in capacitive relation therewith, said sleeve and member forming a first radiator, a second radiator of an external configuration similar to that of said sleeve extending beyond said shield coaxiallywith said sleeve and connections from each of said radiators to separate conductors of said transmission line.

JOACHIM GOLDMANN.