US2745102A

US2745102A - Antenna

Info

Publication number: US2745102A
Application number: US635117A
Authority: US
Inventors: Norgorden Oscar
Original assignee: Individual
Current assignee: Individual
Priority date: 1945-12-14
Filing date: 1945-12-14
Publication date: 1956-05-08
Anticipated expiration: 1973-05-08

Description

May 8, 1956 o. NORGORDEN ANTENNA Filed Dec. 14, 1945 Illll POWER CIRCUIT LII-51 gwuam too OSCAR NORGORDEN IOI United States Patent O ANTENNA Oscar Norgorden, Washington, D. C.

Application December 14, 1945, Serial No. 635,117

7 Claims. (Cl. 343-834) (Granted under Title 35, U. s. Code 1952' sec. 266) This invention relates to'antennas, and is particularly directed to providing an antenna whose input impedance can be adjusted to match the surge impedance of the transmission line to which it is connected.

Because radio apparatus can seldom be installed imrnediately adjacent the input terminals of its associated antenna, almost every radio installation involves the use of a transmission line to interchange energy between the radio apparatus and the antenna. The termination of such a line has a significant bearing on successful system operation.

Important advantages result from terminating a line in its surge impedance. When such a termination is effected, no standing waves are present on the line, and the input impedancetolthe line is a constant, equal to the surge impedance, regardless of the length of the line. The power transfer achieved by the line is, moreover, not sensitive to small changes in transmitter frequency, and the line operates with maximum efliciency and minimum losses. In view. of these advantages, termination of. R. F. (radio frequency) lines in their surge impedances is, an almost universal practice. a

Practical R..'F. lines have as surge impedance aresistance, ranging from perhaps fifty'ohms for coaxial lines to severalhun'dred ohms' for open-wire lines, The impedance presentedby the input terminals of an antenna depends upon the physical conformation of. the antenna and upon the character and location of .nearby objects. It is not necessarily a'pure resistance. 'Both the resistive and reactive components of input impedance for practical antennas may be anywhere within wide limits. In consequence, some type of impedance transformation apparatus has heretofore been employed inradio 'systemsas a n'ieans of coupling an antenna to the line which is expected to transfer energy to or from it.

This invention eliminates the necessity for sneh coupling apparatusfit provides an antenna whose input impedance may be adjusted within wide limitswithout materially affecting the, directional or radiating properties of' the antene na. Thus such an antenna may be adjusted toaiford a surgeimpedance termination for the line without need for pedance transforming apparatus to couple the antenna to the line. This is accomplished by employing in combination a'driyen antenna and a parasitically excited antenna placed parallel andclosely adjacent the drivenantenna'.

The separation between the antennas is very small in terms of wave length; it may be of the order of one-fortieth wave length. By reason of its proximity .to thedriven component, the parasitic component of the antenna does not appreciably alter the directive pattern possessed by the principal component alone. By appropriate choice of lengths for such an antenna, its input impedance may be madea resistance equal to any'desired value'within a wide range.

One of the objects of this invention to provide an antenna which may be adjusted to match the surge impeda ance of a transmission line without any impedance transformer.

2,745,102 firs May 8,

Another object of this invention is to provide an antenna comprising a driven component anda parasitically excited component in proximity thereto, having in combination a directional pattern similar to that of the driven component alone and having input impedance equal to the surge impedance of its associated transmission'line.

Detailed description of the invention will be with reference to the appended drawings, of which:

Figure l is a view, principally in cross section, of one embodiment of the invention comprising a vertical radiator and an artificial'ground plane, mounted at the top of a mast;

"Figure 2 is a perspective view of another embodiment of the invention wherein a vertical radiator is associated with a reflector to effect directional radiation;

Figure 3 is a diagrammatic showing of an embodiment of the invention utilizing a balanced center-fed dipole in conjunction with a closely-spaced, parallel, parasitic antenna, designed to be operative in free space without a ground plane; and

Figure 4 is a diagrammatic representation of an embodiment of the invention as it might be designed for low frequency applications. a

Figure 1 shows, primarily in cross section, the constructional details of an antenna mounted atop a hollow cylindrical mast, the antenna having non-directional characteristics in'the horizontal plane such as might be appropriate for beacon service or broadcasting. The radiating elements c'onsistof vertical driven component 5 and parasitically excited component '6, parallel and closely adjacent. Both components work in conjunction with an artificial ground plane made of a plurality of conducting rods 31, extending radially outward immediately beneath and in a plane perpendicular'to the axes of antenna compone'nts 5 and 6. Components 5 and 6 are cylindrical in shape and formed of conducting-material.

v The supporting structure for the antenna assembly is hollow mast 7. A heavy conducting sleeve 8, having an inwardly extending shoulder 9 integrally formed with its upper portion, fits snugly over the top of mast 7, the lower side of shoulder 9 resting, as shown, on the upper end of'the mast. A cap 10, fashioned of insulating material; is rigidly afiixed to the upper end'of sleeve 8 by bolts 11 which extend through a plurality of formed open- .ings 12 circularly disposed in cap 10. These bolts are threaded into the upper part of sleeve 8. A gasket 23" being identical to'the axis of bolt 46. Hexagonal portion 14 affords a means of tightening bolt 46, and it also serves as'a base for the lowerend of antenna component 6,

which'snugly'engages' extension 13 when fitted thereon.

The inner side of the upper end of sleeve 8 is recessed to forma ledge 15, which serves as a seat for the flanged upper end 16 of a chambered stufiing box 17. Snufiing box 17 has formed within its flanged end a cylindrical apertur'e ls of diameter such as to engage closely a coaxial transmission line 19, which runs to the-antenna assembly through the hollow interior of mast 7. Thelower portion the cap10,- and ahollow member 26'is fittedtherein.

The lower end of member 26 has a head substantially largerthan the aperture 25, and the upper end of member 26 is threaded to engage a nut 27 which holds it firmly in. place. Central conductor 28 of coaxialline 19 is inserted in hollow member 26 and is soldered-thereto. The upper end of member 26, as shown in the drawing, extends beyond the nut 27, providing a conductive support for the enlarged end of a machin'ed'plug 29'having internal threads adapted to engage tightly the threaded end of member 26. The upper end portion 30 of plug 29is cylindrical and is machined to effect a tight friction lit with antenna component 5.

Extending perpendicularly from the vertical edgeof sleeve 8 area plurality of radially disposed rods 31 in-. serted and welded into suitable openings 'in sleeve 3'. The' rods 31 provide an effective artificial ground plane for the antenna system.

Line 19 may be led, as shown-, from base 1 of mast 7 to a power circuit 2, which may bea radio transmitter or receiver.

Initial determination of the proper lengths for antenna components 5 and 6 in a particular application, may best be determined empirically by using a transmitter and a section of slotted'coaxial line. Various lengths for components 5 and 6 may then .be tried successively, the standing wave ratio on the line being measured-for each set of conditions. Correct adjustment will be indicated by unity standing wave ratio on the transmission line. It will normally be found that for matching to a coaxial line the correct length for the driven component will be near a quarter, wave length-in some cases more and in some cases less--while the correct length for the parasiticallyexcited component is normally somewhat less than a quarter wavelength.

In one specific construction. designed for operation at a frequency of 246 me, a wavelength of 122 centimeters, 29 centimeters for the driven component and 23 centimeters for the parasitic component were found to be correct lengths for matchingto a line having surge impedance of 52 ohms. In that embodiment rod of quarterinch diameter was used for the antenna components and the spacing, center to center, between the componentswas one inch, or 2.54 centimeters.

In another construction for use at 143 mc., a wavelength of 210 centimeters, the lengths found to yield correct matching to a 52 ohm line Were 59 centimeters for the driven component and 47.3 cm. for the: parasitically excited component. used for the driven element and rod for-the parasite. The spacing was one inch, center to-center. It has been found that the spacing between. the components is not critical, solong as it is kept to a small fraction of a-wavelength-perhaps one fortieth wavelength or less. The. presence of the-parasitic: component does not appreciablyafiect the directional pattern under such circumstances.-

Determinationof proper lengths for the components need not be made with the system on. ahigh mast; if the antenna is matched to the line when the system is areasonable distance off the ground, the match will not be affected by raising. the system to its normal opera-ting: position.

Figure 2 shows an embodiment of the invention as employed in a directional antenna system. In this embodiment the system is mounted on. a verticalmast32 and is fed by a coaxial transmission line 36. Theradiat ing components of the system comprise adriven element 34 and a parasitically excited element 35-,mounted parallel and closely adjacent, as in the embodiment of Figure 1. They are mounted on head. 33 at the top of mast 32. The details of the mounting and feed arrangements are. not shown in Figure 2; they. may be of the same general characteras in the embodiment ofi Figure 1; A ground plane is formed by the plurality of conduetingrods 41' which ex-tendradially outward from head 33.

In this embodimentdirective characteristicsare-imparted by a reflector screen 37, disposed in back of the dipoles and above the ground plane, consisting of a rigid conducting framework on which is mounted a plurality of vertical rods or wires 38. These vertical conductors 38 are spaced a small fraction of a wavelength apart and as a result function as effectively as a closed screen to reflect radiation from dipoles .34 and 35, while being lighter and OlTering less wind resistance than a solid refiector. The reflector assembly and the ground plane are mechanically reinforced by rigidbraces- 40 which converge to supporting ring 39 on mast 32 below the antenna head 33. In the specific embodiment of Figure 2 the reflector is shown as a corner reflector.

Figure 3 shows diagrammatically an embodiment of the invention in which the driven and parasitic antenna components are designed to radiate independently rather than in cooperation with ground or an artificial ground plane. Transmission line 89, which may be of the open wire or coaxial type, is connected to driven component 88; parasitically excited component 90 is placed parallel to' and closely adjacent component 88. As in the previously described embodiments, the lengths of components 88 and- 90 are proportioned to effect an impedance match between line 89' and the input terminals to driven component 88.

If it were desired to employ the invention in a low frequency application, adjustment by varyingthe lengths of the driven element and parasitic element might not be convenient, because of the physical size of the system. Accordingly for low frequencies an embodiment such as that of Figure 4 would be appropriate. In Figure 4 transmission line 101 feeds radiator 102, which is represented as a vertical radiator working against ground and having a top loading system 106, which might consist of a network of horizontal wires. In series with radiator 102 at its input terminal is variable inductance coil 104, which serves as a tuning device. Adjacent and parallel.

- to radiator 1-02 is parasitic radiator 103, which also works against ground and'is top loaded by network 107. In" series with radiator 103 near its grounded end is variable inductance coil 105,.which serves as a tuning means for theparasitic element. The separation between the drivenand parasiticelements is, as in the other embodiments, a

In that construction rod was very small fraction of a wavelength, so that the presence of the parasitic element doesv not disturb the directive pattern of the driven element. In this embodiment, adjustment for proper. operation should be accomplished in themanner. prescribed for. the high frequency embodiments, except that the radiating

elements

102 and 103. should be tuned, by varying. the inductance of

coils

104 and 105, insteadof by varying the lengths of the elements.

It will be understood. that the embodiments of the invention herein shown and described are exemplary only,

and that the scope of the invention is to be determined from 'the'appended claims.

The inventionv described hereinv may be manufacturedandiusedby or for the-Governmentof' the. United/States of America for governmental. purposes without the. payment of any royalties thereon or therefor.

What is claimed is:

1. An antenna having a. primary element, aground plane positioned atone end of-"the. primary: element, a transmission line havinga uniform. impedance throughout connectedbetween the groundplane. andthe primary element,. a plurality. of rods connectedto said ground plane to provide a reflector screenfor said primary. element and a. parasitic element of a length less than said primary element and positioned alongside-the primary element and'connected tothe ground planecperativeto effect a terminatingirnpedance for the transmission line equal to its surge impedance, the spacing between saidprimary element and. said. parasitic element: being: sulficiently: small to preserve thedirectivity pattern' possessed by the primary; element alone.

2. An antenna assembly including a supporting/cap cap alongside the primary element a distance less than a twentieth wavelength therefrom and conductive rod means extended at right angles from the side of the cap connected to the outer conductor of the coaxial line and to the parasitic element, the conductive rod means providing a ground plane for the primary element and the parasitic element, the parasitic element being operative to effect a terminating impedance for the coaxial line equal to its surge impedance, said spacing between said primary element and said parasitic element being sufiiciently small to preserve the directivity pattern possessed by the primary element alone.

3. In combination an antenna having a primary element, a power interchange circuit, a transmission line connecting the primary element to the power interchange circuit, and a parasitic element shorter than said primary element positioned closely adjacent to said primary element, the length of said parasitic element beingchosen to cause a match between the input impedance of said primary element and the surge impedance of said line, and the spacing between said primary element and said parasitic element being sufiiciently small to preserve the directivity pattern possessed by the primary element alone.

4. In combination an antenna having a primary element approximately a quarter wavelength long at its operating frequency, a power interchange circuit, a transmission line connecting the primary element to the power interchange circuit, and a parasitic element positioned adjacent to said primary element and of a length less than a quarter wavelength for matching the input impedance ofsaid primary element to the surge impedance of said line, the spacing between said primary element and said parasitic element being sufliciently small to preserve the directivity pattern possessed by the primary element alone.

5. A directive antenna comprising a supporting mast having a mounting part positioned at its upper end, a coaxial transmission line havinga uniform characteristic impedance throughout disposed within said mast, said mounting part providing means for connecting the outer conductor of said line to said mast, a, radiating element having one end connected to said mounting part for support thereof, said mounting part also providing means for connecting the inner conductor of said line to said radiating element, a parasitic element paralleling said primary element operative to effect a terminating impedance for the coaxial line equal to its surge impedance, said parasitic element being electrically connected to said mounting part and mechanically supported thereon, the spacing between said primary element and said parasitic element being sufficiently small to preserve the directivity pattern possessed by the primary element alone, a plurality of conductive rods extending radially from said mounting part perpendicular to the longitudinal axis of said elements to provide therefor a ground plane, and a plurality of vertical wires disposed above said rods and back of said elements to provide a reflector screen therefor.

6. An antenna comprising a radiating element and a parasitic element, coaxial transmission line means for feeding said elements, a supporting mast for supporting said elements having a sleeve surrounding the uppermost portion of said mast, said sleeve having an integrally formed shoulder extending inwardly over the upper end of said mast, an insulating cap extending over the upper end of said sleeve, a plurality of means for rigidly fixing said cap to said sleeve one of said last named means extending above said cap for engaging said parasitic element, an aperture extending through the central portion of said cap, a conductive member extending through said aperture operative to securely engage said radiating member to said cap, means for connecting the inner conductor of said transmission line to said conductive member, and means for connecting the outer conductor of said coaxial transmission line to said sleeve.

7. An antenna comprising a radiating element and a parasitic element, coaxial transmission line means for feeding said elements, a supporting mast for supporting said elements having a sleeve surrounding the uppermost portion of said mast, said sleeve having an integrally formed shoulder extending inwardly over the upper end of said mast, an insulating cap extending over the upper end of said sleeve, means for rigidly fixing said cap to said last named means extending above said cap for engaging said parasitic element, an aperture extending through the central portion of saidcap, a conductive member extending through said aperture operative to securely engage said radiating member to said cap, means for connecting the inner conductor of said transmission line to said conductive member; said shoulder of said sleeve having a recess at its upper end, a stuffing box having an outwardly flange seated in said recess, a cylindrical aperture formed in the longitudinal axis of said stuffing box extending through said flange, said outer conductor of said transmission line extending through said aperture and engaging the inner wall of said stufling box, and means for securely fastening said outer conductor to said flange.

References Cited in the file of this patent UNITED STATES PATENTS 1,745,342 Yagi Jan. 28, 1930 1,860,123 Yagi May 24, 1932 1,934,412 Englund NOV. 7, 1933 2,026,652 Ponte Jan. 7, 1936 2,274,149 Lubcke -2 Feb. 24, 1942 2,275,342 Brown Mar. 3, 1942 2,476,949 Adams et al. July 26, 1949