US3000008A

US3000008A - Shielded antenna

Info

Publication number: US3000008A
Application number: US37949A
Authority: US
Inventors: Pickles Sidney
Original assignee: Individual
Current assignee: Individual
Priority date: 1960-06-22
Filing date: 1960-06-22
Publication date: 1961-09-12
Anticipated expiration: 1978-09-12

Description

Sept. 12, 1961 s, c s 3,000,008

SHIELDED ANTENNA Filed June 22, 1960 2 Sheets-Sheet l INVENTOR. flow-y Pumas W PW 9WMW ArraiA I Sept. 12, 1961 s. PICKLES 3,000,008

SHIELDED ANTENNA Filed June 22, 1960 2 Sheets-Sheet 2 FIG'3 W P2144 967mm United States Patent 3,000,008 SHIELDED ANTENNA Sidney Pickles, P.O.. Box 530, Colusa, Calif. Filed June 22, 1960, Ser. No. 37,949 9 Claims. (Cl. 343-492) The present invention relates to an improved antenna structure, and more particularly, to the elimination of interfering radiation from antenna support means.

Directional transmitting antennas find a wide applicability in various fields of broadcasting, and diificulties are often encountered in maintaining the desired direction and intensity of radiation from such antennas. The foregoing is particularly true in connection with high frequency transmission wherein antenna gain is desired. Although various types of antenna-mounting structures may be employed, it is well recognized that metallic masts or support tubes are most desirable in this respect. Much greater structural rigidity may be attained from metallic support members, and various other problems of different types of support structures are entirely overcome by the use of metallic masts, or the like. One serious difficulty encountered in the utilization of metallic support structures is the inadvertent and almost unavoidable energization of such structures from the antenna radiator. It will be appreciated that any metallic member, such as a mast or the like, supporting an antenna structure, will, itself, radiate upon being energized, and consequently, there will be produced an interfering radiationpattern. The result of this circumstance is highly undesirable, inasmuch as a shifting in the direction of major radiation from the antenna may occur, or an actual decrease in directional radiation may result.

Various different approaches have been advanced for overcoming the above-noted difficulties. Masking of the support structures has been suggested, and various physical antenna configurations proposed; however, these approaches to the problem generally introduce added complexity and additional difliculties. The present invention overcomes the problems of radiation from antenna support structures by the intentional energization of such structures in such a manner as to accomplish a complete cancellation of energy therein, so as to fully preclude radiation therefrom. Only by the complete cancellation of energy on the support structures is it possible to prevent interference withthe desired radiated signal. Prior-art devices fail to entirely cancel such energy, inasmuch as the cancellingsignals are never identical in amplitude and opposite in phaseto the signals to be cancelled. The pres ent invention provides a-true and complete cancellation of energy induced in antenna support structures, so that the radiated energy from-a unidirectional or omnidirectional. radiator isunafifected by the antenna support. It is thus possible, in accordance herewith, to provide for true omnidirectional antenna radiation under the conditions wherein the antenna radiator is mounted upon metallic support means. Furthermore, the invention provides for the multiplication of radiators to achieve particular desired radiation patterns, While yet preventing interference from support structure radiation. Substantial antenna gain may be achieved. with the present invention without sacrificing directional properties, and this servesto particularly adapt the invention to high frequency. operations.

The present invention accomplishes the above-noted results by the provision of shield sections in conjunction with antenna radiators, and by the driving of these shield sections in particular relationship to the radiator excitation for establishing complete cancellation of unwanted radiation. More particularly, the present invention provides. end shield structures disposed at opposite ends of ice antenna radiators, and excited in an opposite sense to each other and to adjacent ends of the radiator. The end. shields of the present invention are excited by voltages of. the same amplitude as those employed to excite the radiator itself and, with the opposite phase relationship noted above, there is then produced a true and complete cancellation of energy in the shield and metallic support structure employed to mount the radiator and shields. There remains then only the. desired excitation of the radiator itself, so that there is produced from a single dipole, for example, a radiation pattern which almost exactly duplicates the theoretically calculated radiation pattern from such an antenna.

It is an object of the present invention to provide an improved antenna structure fully cancelling all radiation. from antenna support means.

it is another object of the present invention toprovide. an improved transmitting antenna having driven end shields for completely suppressing all radiation from both. the end shields and antenna support structure.

It is a further object of the present invention to pro.- vide an improved antenna having multiple radiators. mounted upon metallic support means, and electrically driven shielding means fully suppressing all radiation from the support means and shield means.

It is yet another object of the present invention to provide single or multiple dipole antennas actually producing theoretical omnidirectional radiation patterns therefrom.

Various other possible objects and advantages of the.

present invention will become apparent to those skilled in the art from the following description of particular preferred embodiments of the present invention; however, no limitation is intended by the terms of this de.- scription, and instead, reference is made to the appended. claims for a precise delineation of the true scope of the present invention.

The invention is illustrated in the accompanying drawings, wherein:

FIG. 1 is a partially cut away view of an improved antenna, in accordance with the present invention;

FIG. 2 is a plot of radiation intensity about the an.- tenna of FIG. 1, superimposed uponthe theoretically calculated radiation plot of a dipole antenna and also showing in. phantom the radiation pattern about an unshielded concentric antenna;

FIG. 3 is an illustration of a multiple radiator antenna, in accordance with the present invention;

FIG. 4 is a plot of radiation intensity about the antenna of FIG. 3; and

FIG. 5 is a partially cut away view of an alternative. embodiment of the improved antenna. of this invention.

Considering now particular preferred embodiments of the present invention in some detail, and referring first to FIGS; 1 and 2, it will be appreciated that a conventional dipole antenna radiator, when properly excited, produces a radiation pattern which is substantially omni directional in that the great majority of energy is radiated in a plane passing through the center of the dipole. When such a dipole radiator is mounted upon a metallic. support structure in order todispose the antenna radiator in desired position for. operation, it willbe. appreciated. that the dipole also excites the support. structure so that. energy passingtherethrough. will also. produce radiation... This, radiated energy from support. structures serves; to. modify the overall radiation pattern of the antenna in an, undesirable fashion. Numerous possible. radiation; pat terns may result from, the foregoing situation, and there normally at. least results a change in the directionjofi maximum radiation. The present. invention overcomes; this difliculty of radiation from antenna support means;

n a by the provision of intentionally excited end shields to the end of establishing a cancellation of undesired energy flow, so that radiation occurs only from the dipole itself. As shown in FIG. 1, there may be provided a central support tube or mast 11. This support tube 11 is preferably formed of metal for structural strength, and is made with a hollow configuration so that a coaxial cable 12 may be extended therethrough from a source of antennaexcitation, not shown. Upon the support tube 11, there is coaxially mounted a hollow cylindrical radiator 13, formed of metal, and secured thereto by a central diaphragm 14. This diaphragm '14 is also made of metal and is disposed transversely of the support tube 11 at the center of the radiator 13. The ends of the cylindrical radiator 13 are open, and are unattached to the support tube 11. The radiator 13 is formed with a total length of one-half wavelength of the exciting energy, so as to thereby form a dipole radiator. With the diaphragm 14 disposed at the center of this radiator, there will thus be seen to be formed by the radiator 13 and diaphragm 14 a pair of back-to-back quarter-wave cavities, having open ends extending away from each other. Excitation of this dipole structure would result in the energization of the support tube 11, so that radiation would occur therefrom to interfere with the desired radiation from the antenna radiator.

The present invention provides end shields which are purposely excited in order to prevent this undesired radiation noted above. As illustrated in FIG. 1, there may be provided a pair of quarter-wave cylinders 16 and 17, disposed at opposite ends of the radiator 13. These end shields 16 and 17 are formed as hollow, metallic cylinders, disposed coaxially about the support tube 11 at opposite ends of the radiator 13, with open ends facing the radiator and solid transverse end walls at the outer ends of the shields. The end shields are thus mounted upon the support tube 11 by these end walls, and will be seen to each comprise quarter-wave cavities, disposed in facing relationship to the quarter-wave cavities of the radiator. Furthermore, the cavities of the end shields will be seen to be shorted to the support tube 11, at the outer ends of the shields, so as to provide an infinite impedance to voltage applied to the shields.

With regard to the excitation of the antenna radiator 13 and associated end shields 16 and 17, there is provided an opening 18 in the support tube 11 intermediate the end shield 16 and radiator 13. Through this opening there is extended a jumper connection 19, which is electrically joined to the central conductor of the coaxial feed line 12 within the support tube 11. At this point the sheath of the coaxial feed line 12 is electrically and structurally connected to the support tube 11. The jumper 19 is electrically connected to the central conductors of a pair of coaxial feed cables 21 and 22. These cables 21 and 22 are of equal electrical length, and the firstthereof extends from the point of emergence of the jumper wire 19 from the central support tube 11, along the support tube through the end shield 16, and thence radially outward thereof to the outer surface of same, and back. along the end shield to the open end thereof adjacent the radiator 13. At this point the sheath of the cable 21 is electrically connected to the end shield 16, and the central conductor is extended across the gap into electrical connection with the radiator 13. The other coaxial feed cable 22 extends from the opening 18 in the central support tube 11, along the tube to the radiator diaphragm 14, and thence radially outward of the radiator and along the outer edge thereof to the far end of the radiator. At this point the sheath of the cable is electrically connected to the radiator 13, and the central conductor of the cable extends across the gap between the radiator and end shield into contact wtih the adjacent surface of the end shield 17. It will be seen that each of the feed cables 21 and 22 has identical lengths, and furthermore, that opposite ends of the radiator 13 are ener- 4 gized with excitation voltages of equal amplitudes and opposite phase. Inasmuch as the central conductor of the cable 21 contacts one end of the radiator 13, and the sheath of the other cable 22 contacts the other end of the radiator 13, the foregoing voltage relationship is herein attained. It will also be appreciated that the end shields 16 and 17 are electrically driven from the cables 21 and 22 which, in turn, of course attach to the main coaxial cable 12 extending through the support tube to the source of excitation voltage. It will be appreciated further that the end shields are oppositely energized from the adjacent ends of the radiator 13. Suitable impedance matching of the cables 12, 21 and 22 may be employed.

As above noted, the end shields 16 and 17 are closely spaced from the ends of the radiator 13 so as to thereby define

gaps

26 and 27 between the ends of the radiator 13 and the end shields 16 and 17, respectively. Excitation voltage is applied across these gaps, with the voltage across the gap being in phase but in an opposite sense relative to the radiator 13.

Operation of the present invention may be best understood by considering the application of excitation voltages thereto, and following the energization of the radiator and end shields during one complete cycle of applied voltage. With the main cable 12 energized, there will at one particular point in time be applied a positive voltage to the left end of the radiator 13, and a negative voltage to the right end of the adjacent shield 16. This follows from the connection of the cable 21, with the central conductor thereof connected to the radiator 13, and the sheath thereof connected to the end shield 16. At this same time, the cable 22 will apply a negative voltage to the right end of the radiator 13 at the sheath of this cable, and a positive voltage to the adjacent or left end of shield 17 at the connection of the central conductor of the cable 22. It will be seen that the voltages at the ends of the cables 21 and 22 are identical, inasmuch as both cables have equal electrical lengths extending from the cable 12. The above-noted voltages may be considered to proceed as voltage waves along the elements upon which same are impressed. Consequently, there will result a positive voltage wave progressing to the right of radiator 13 from the left end thereof, and a negative voltage wave progressing to the left along the radiator 13 from the right end thereof. Likewise, there will be found a negative voltage wave progressing to the left along the end shield 16, and a positive voltage wave progressing to the right along the end shield 17. Inasmuch as the radiator 13 is one-half wavelength long and each of the end shields 16 and 17 is one-quarter wavelength long, it will be appreciated that ninety electrical degrees fol lowing the impression of the above-noted exciting volt age, the positive and negative Waves launched at opposite ends of the radiator 13 will pass each other at the center of the radiator, while the positive and negative waves launched along the end shields 17 and 16, respectively, will have reached the outer ends of the end shields.

One-quarter cycle later, at the degree point, the negative charge launched at the gap 27 to the left along the radiator 13 will have progressed one-half wavelength to the left end of the radiator 13, and similarly, the positive voltage wave launched at the left end of the radiator will have progressed to the right end. At this time the excitation voltage has reversed phase so that the cable 21 is thus launching a negative voltage wave to the right along the radiator 13, and a positive voltage wave to the left along the end shield 16. Likewise,.the cable 22 is launching a negative voltage wave to the right along the end shield 17, and a positive voltage wave to the left along the radiator 13. As a consequence, there will be seen to be both a positive and negative wave traveling to the right along the end shield 17 from the left end thereof, and this concurrent positive and negative wave traveling in the same direction is the equivalent of zero current flow.

waves reach the outer ends of the end shields to. then in,

part travel along the support tube 11. The original waves launched along the end shields will be seen to travel down the support tube 11 without cancellation, and this. corresponds to an initial transient condition; however, subsequent waves will be seen to be cancelled so that there is no net current flow in the end shields or support tube. At the 270 degree position, the negative wave launched at the left end of the radiator 13 will have progressed to the center of the radiator, traveling to the right therealong, and the positive wave launched at the right end of the radiator 13 will have reached the center of the radiator, traveling toward the left end thereof. At the 360 degree position, or one full cycle after the point in time herein considered for purposes of explanation, there will be seen to be concurrent positive and negative waves traveling outwardly along the support tube 11 from the endshields 16, and 17, so as to thereby establish a condition of zero net current flow in the support tubes. Likewise, the end shields 16 and 17 will be seen to have both positive and negative waves traveling outwardly thereof from the radiator 13, and new positive and negative waves being launched inwardly from the radiator from the ends thereof at the cable connections.

From the foregoing, it is believed apparent that the half-wave radiator 13 is energized as a dipole at the

gaps

26 and 27 at the ends thereof, and furthermore, that the end shields 16 and 17 are energized so as to establish a condition of zero net current flow therein during excitation of the antenna. Furthermore, the support tube 11, connected to the end shield, will be seen to be likewise energized to establish conditions of zero net current flow therein. As a consequence of the foregoing, there will be produced substantially no radiation from the end shields or metallic support structure 11. The foregoing has been clearly established by measuring the radiation about an antenna constructed as that illustrated in FIG. 1 and comparing a plot of this radiation with the theoretically calculated radiation pattern about a simple dipole antenna radiator. This is illustrated in FIG. 2, wherein there is shown by the dotted line 31, the calculated radiation pattern about a simple dipole radiator. The solid curve 32 in FIG. 2 is a plot of the measured radiation pattern about the improved antenna of the present invention, as illustrated in FIG. 1. The phantom line 33 in FIG. 2 is a plot of the measured radiation pattern about a concen-.

tric dipole antenna without end shields. It will be seen from a comparison of these three patterns that the antenna of the present invention does, indeed, provide dipole radiation without interference from the end shields or metallic support structure. It is further noted that a very material improvement is attained with this invention.

The present invention is particularly adapted to those applications wherein antenna gain is desired. In order to maximize directional radiation from an antenna, it is conventional to multiply the number of radiating elements, with such elements being so positioned that the radiation therefrom is additive. In such instances, particular difliculties are encountered by interference by radiation from support structure. In accordance with the present invention, the number of radiating elements may be increased Without interference problems. In FIG. 3 there is illustrated a two-element antenna having coaxially alined halfwave radiators 41 and 43. These radiator are mounted upon a hollow, metallic central support tube 44, with back-to-back end shields 42a and 42b provided between adjacent radiating elements. End shields 46 and 47 likewise formed as shorted quarter-wave cavities, are disposed in facing relation to the outer ends of the radiating elements 41 and 43, respectively. The embodiment of the invention illustrated in FIG. 3 merely includes the multiplication of radiating elements with the same end shielding means being provided, all of same being energized through cables of equal length so as to establish cancelling voltages which produce a net zero current flow in the end shields and in the metallic support structure 44.

The embodiment of the invention illustrated in FIG. 3 and briefly described above, operates along the same principles as are discussed in connection with FIG. 1. By the intentional energization of the end shields in desired phase relation to energized radiators, it is possible in this. embodiment of the invention, as well as that of FIG. 1, to provide for a net zero current flow in the end shields, as well as in the metallic support structure. In this manner, a full and complete cancellation of energy'in the end shields and support structure is accomplished, so that only desired directional radiation from the antenna elements results. A radiation pattern attained from the embodiment of the present invention illustrated in FIG. 3- is shown plotted in FIG. 4, and it will be seen by reference thereto that the radiation pattern is highly directional. Th radiation field pattern i mainly concentrated in two

lobes

51 and 52 of the plot, and it will be seen that these lobes are oriented perpendicularly to the center of the antenna to thereby achieve a close agreement between theoretical radiation and the radiation pattern actually achieved. The minor radiation lobes of the pattern illustrated in FIG. ,4 are quite conventional in multiple-antenna arrays of the type illustrated in FIG. 3, and do not seriously interfere with the directional properties or utilization of this type of antenna. The antenna will thus be seen to provide for a desired addition of energy radiated from the separate dipoles of the antenna, so as to consequently achieve the, highly directional overall radiation with a substantial gain or amplification in the antenna over that available from a single dipole.

A' further embodiment of the present invention is illustrated in FIG. 5, wherein there-is shown a single halfwave antenna radiator 61, having a transverse diaphragm 62 at the center thereof and mounting the radiator upon an elongated coaxial metal tube 63. The radiating element 61, as well as the diaphragm 62 and support tube 63, are all formed of metal and thus energy flowing upon the surface of the radiator 61 will be radiated outwardly there from. At the ends of the radiator 61 there are provided a pair of

shield plates

66 and 67, disposed in facing relation to the open ends of the radiator and spaced therefrom to define

gaps

68 and 69 between the shields and the radiator. These

end shield plates

66 and 67 are formed of a metal, and are mounted upon the central support tube 63 in much the same manner as the radiator diaphragm 62.

Energization of the radiator may be accomplished by the provision of a coaxial transmission line 71 extending through the hollow support tube 63 from a suitable source of energizing voltage. Connection of the coaxial cable 71 to the radiator end shields is preferably accomplished by the provision of a pair of

coaxial feed cables

72 and 73 of equal lengths. The central conductors of each of the

cables

72 and 73 are connected to the central conductor of the cable 71, and the sheaths thereof are electrically connected to the sheath of the cable 71. One of these feed cables 72 extends through the central support tube 63 to the center of the radiator 61 and radially outward through an opening in such tube thereat. This cable 72 further extends, to the far end of the radiator. At this point, the sheath of feed cable 72 is electrically connected to the radiator, and the central conductor thereof extends across the gap 68 into electrical contact with the end shield 66. The other cable 73 extends, radially outward through the central support tube 63 along the other end shield 67 with the cable sheath electrically connected to the end shield and the central conductor of this cable extending across the gap 69 into electrical contact with the adjacent end of the antenna radiator 61. It is herein desired, as in FIG. 1, to apply energization of like amplitude and opposite phase to. opposite ends of the half-wave radiator of the antenna,

In order to accomplish this energization in the embodi ment of FIG. 5, it is necessary to extend the length of the feed cable 73 in order that both of the

feed cables

72 and 73 shall have the same electrical lengths. With the central conductor of one cable connected to one end of the radiator and the sheath of the other connected to the other end of the radiator, it will be appreciated that a 180 degree phase diiference will exist between excitation voltages applied to the opposite ends of the radiator, if the feed cables have the same length. This particular provision is diagrammatically illustrated in FIG. by the loop shown in the cable 73; however, it will be appreciated that the break in the antenna support tube 63 is only shown in FIG. 5 for convenience of illustration, in order to properly identify the electrical connections between the cables of this embodiment. In actual practice, the

feed cables

72 and 73 may be entirely contained within the support tube.

With regard to the operation of the embodiment of the present invention illustrated in FIG. 5, it will be seen that there are applied to opposite ends of the radiator 61, excitation voltages of equal amplitude and opposite phase. Likewise, there are applied across the

gaps

68 and 69 at the radiator ends, equal and opposite voltages so that there is attained a radiator energization which produces a true dipole action of the radiator itself. With regard to the cancellation of energy in the support structure 63 and end shield 66, it will be seen that aside from an initial transient condition there is also herein achieved a somewhat similar situation to that illustrated and described above in connection with FIG. 1, wherein voltage waves of opposite polarity simultaneously travel along a conductor to thereby approach the condition of zero current flow wherein substantially no radiation exists. The quarter-wave cavities formed by the radiator 61 will also be seen to have applied at the end thereof, the full voltage between the center conductor and sheath of the feed cable, and it will be seen that this particular configuration allows a substantial reduction in the overall length in the antenna system as compared to the embodiment of the invention illustrated in FIG. 1. Although the antenna structure illustrated in FIG. 5 may not provide the complete cancellation of energy in the support structure that is achieved with the other embodiments of the present invention, it is desirable in that a substantial reduction in current flow in the support structure is achieved, together'with a minimization of overall antenna length.

From the foregoing description of illustrative examples of the present invention, it will be seen that dipole antenna energization is attained by the application of voltages of equal amplitude and opposite phase across gaps formed at the radiator ends between such ends and adjacent metallic shields herein provided. Full electrical connection between the radiator itself and the support means therefor, as well as between the end shields and these same support means, provide for the flow of charges or voltage waves from the excitation source in such a manner that a cancellation thereof occurs in the end shields and support structure, while at the same time providing for a desired dipole energization of the radiating element. Aside from the theoretical considerations, the present invention has been found in practice to produce the desired results, and to accomplish substantially complete cancellation of radiation from metallic members associated with antenna radiators, so as to thereby preclude interference and disruption of the desired radiation pattern. Experimental verification of the foregoing is provided in the plot of FIG. Q, for example, wherein it will be seen that the radiation pattern about a half-wave dipole mounted upon a metal support tube with quarterwave end shields is almost identical to ,the theoretically calculated radiation pattern about an ideally energized dipole antenna without metallic support means. The present invention will thus be seen to provide a material 'physical support thereof.

What is claimed is: I

1. An improved antenna comprising a support tube, a half-wave cylindrical radiator disposed coaxially about said tube and mounted thereon by a radial wall at the center of said radiator, a pair of end shields disposed across the ends of said radiator and mounted on said support tube, and means applying opposite exciting voltage to opposite ends of said radiator and in reverse phase to said end shields.

2. An improved antenna comprising a cylindrical radiator, a metallic support tube disposed axially of said radiator, a metallic diaphragm within said radiator dividing same into two open-ended quarter-wave cavities and mounting the radiator on the tube, a pair of metallic end shields mounted upon said support tube in close proximity to the open ends of said cavities and spaced therefrom, and means applying excitation voltages of like amplitudes between said radiator and shields with said voltages being of opposite sense in relation to said radiator and having return paths of equal lengths.

3. An improved antenna as set forth in claim 2, further defined by said end shields comprising quarter-wave cavities having open ends facing respective radiator cavities and mounted upon said support tube at the opposite ends of said radiator.

4. An improved antenna as set forth in claim 2, further defined by said end shields comprising flat metallic plates disposed across the open ends of the radiator cavities out of direct electrical contact therewith.

5. An improved antenna comprising a half-wave radiator divided into two open-ended quarter-wave cavities by a central transverse metallic diaphragm, a metallic support tube disposed axially through said radiator and mounting the latter by connection to said diaphragm, a pair of metallic end shields mounted upon said support tube in closely spaced relation to the open ends of said radiator cavities to define gaps thereat, and energizing means including two coaxial feed cables of equal length extending through said support tube and therefrom to apply excitation voltages of like amplitude and phase across said gaps for exciting said radiator to radiate and exciting said end shields to cancel radiation from the end shields and support tube.

6. An improved antenna as set forth in claim 5, further defined by said pair of coaxial feed cables being connected in parallel to a coaxial cable through said tube and extending equal electrical distances to the gaps between said end shields and adjacent radiator ends, means connecting the central conductor of one feed cable to one end of the radiator and the sheath to the adjacent shield, and means connecting the sheath of the other feed cable to the opposite end of the radiator and the central conductor thereof to the adjacent shield for impressing equal voltages of opposite sense relative to said radiator across said gaps at opposite ends of the radiator whereby the latter radiates in the directional pattern of a dipole.

7. An improved antenna as set forth in claim 5, further defined by said end shields each comprising quarter-wave cavities having open ends facing an open end of said radiator, excitation means extending through said support tube, means connecting said pair of coaxial cables to said feed means at a first end of said radiator, a first of said coaxial cables extending along said support tube to the closed shield end then back along the shield to the open end thereof with the central cable conductor extending into connection with the adjacent radiator end,

and a second of said coaxial cables extending through said radiator to said diaphragm and thence outwardly to the radiator and along same to a second end of said radiator end with the central conductor extending into electrical connection with the shield at such end of the radiator for exciting the radiator at opposite ends thereof with balanced voltages of equal amplitude and opposite phase while at the same time oppositely exciting the end shields to cancel energization of same and of said support tube.

8. An improved antenna as set forth in claim 5, further defined by said end shields comprising plates disposed across the open radiator ends in spaced relation thereto, a pair of coaxial cables disposed within said support tube for like connection to a supply cable from an excitation source remote from the antenna, a first of said cables extending from said tube, at a first of said shields and along same to an outer edge thereof whereat the cable sheath terminates and the central conductor extends into electrical contact with the adjacent radiator end, and a second of said cables extending from said tube at the radiator diaphragm and radially outward thereof to the radiator, said second cable further extending along said radiator from said diaphragm to the end thereof adjacent the sec- 0nd of said shields whereat the cable sheath terminates and the central cable conductor extends into contact with said second shield for establishing the radiation pattern of a dipole for said antenna.

9. An improved antenna comprising an elongated metallic support mast, a coaxial cable extending through said mast for connection to antenna excitation means, a plurality of half-wave radiators disposed concentrically about said mast with each having a transverse metal wall at the center thereof afiixing the radiators to the mast, a plurality of metal cylinders of quarter-wave length disposed one adjacent each end of each radiator to define gaps therebetween and afiixed to said mast by transverse metal walls at the opposite cylinder end from the closest radiator, and a plurality of coaxial cables of equal electrical length extending from a common connection with the aforesaid coaxial cable to separate ones of said gaps and impressing voltages of equal amplitude and opposite phase to opposite ends of each radiator and like voltages of like phase across each of said gaps to thereby excite said radiators to radiate while preventing radiation from said cylinders and mast.

No references cited.