US2726389A - Antenna unit - Google Patents

Description

Dec. 6, 1955 l l. R. TAYLOR 2,726,389

ANTENN UNIT Filed OCT.. 29, 1951 INVENTOR /RV/NG R. TAYLOR ,Cif/@.5 BY Q7/?? ATTORNEY United States Patent C 1 2,726,3,89 ANTENNA UNlT lrving R. Taylor, Belleville, N., l., assigner to International Telephone and Telegraph Corporaiion, a corporation of Maryland Application ctober 219,V l1,951, Serial No. 253,581

' 1,0 claims.V (ciau-16.1)

This invention relates to antenna vunits and more particularly to broad band antennas for operating at ultra high frequencies.

In many antenna systems, particularly those. used in direction finding systems, it isldesirable that they antenna. have a rotating directional pattern and be sensitive only to vertically polarized waves. It is Well-known that in order to design a Wide band dipole antenna, it is necessary to make the diameter of the dipole a substantial fraction of the wavelength of the frequency for which the antenna is designed. However, as` the diameter of the dipole is increased, the antennas sensitivity to horizontal polarizations will increase. In some instances it is desirable to rotate the directional pattern of the vertical antenna, and this may be done by means of a rotating reiiector. Horizontally polarized waves, however, tend to induce voltages in antennas havingreflectors whose width is a substantial fraction of the wavelength of the received radiation. Thus, antenna units having reflectors of this type will introduce polarization errors in the direction finding systems.

One or' the objects of this invention, therefore, is to provide a directional antenna utilizing a rotating reflector which is substantially insensitive to horizontally polarized waves.

Another object of this invention isto provide a Wide band antenna having a rotating directional pattern capable of receiving substantially only vertically polarized radia.

tions.

A further object of this invention is to provide a wide band vertical antenna arrangement having a rotating reflector and being of sturdy construction.

According to a feature of my invention, a wide band coaxial dipole antenna is mounted on a mast. A parasitic reflector is rotated around the dipole thus establishing a rotating directional antenna pattern. The reflector comprises a cylinder made of an insulating material having on an arc of its circumference a plurality of conductive strips, each strip having a length substantially equal tov a half wavelength and of a width'necessaryI for adequate conduction. Due to the relatively narrow width of' the strips, the rellector has a minimum response to hori* zontally polarized radiations and because of itslength has a maximum response to vertically polarized waves.

'in accordance with a further lfeature of this invention for use at low frequencies, the reiieetor strips may be composed of zigzag or Grecian fret strips of conductive material in order t6 reduce the overallphy-sicai length of the half wavelength reflector.,v

The above-mentioned and other features and objects of this invention and the manner of attaining them will become more apparent by reference to the following description taken,V in4 conjunction with the accompanying drawings, wherein:

Fig. 1 is a vertical cross-segnala@ viewv of a preferred .embodiment of this invention;

Fig. 2 is` a perspective View with parts broken away showing the antenna and reflector arrangements of the invention coupled in circuit for direetion finding purposes;

Figs. 3f and 4 are illustrations of alternate forms of the reflector strips for use at lower frequencies; and

Eig. 5 is a cross-sectional viewgf `a eonstruetional de- Referring to Figs. 1 and 2 of the drawing, wherein a preferred embodiment of this invention is illustrated, it is shown that the antenna unit comprises a coaxial dipole antenna 1. A coaxial transmission line 2, terminating at Vone end in a coaxial connector 3, has its inner conductor 4 coupled to the upper element 5 of said dipole 1 and its outer conductor 6 coupled to the lower element 7 of said dipole 1. The dipole 1 is electrically insulated from and supported by a supporting structure 8 by means of a dielectric material V9. Concentric to said dipole 1 is a cylinder 10 composed of an insulating material such as fiberglass which does Vnot affect the radiationupattern of the antenna. A plurality of conductive strips 11-15 is disposed either within the wall of the cylinder 10, Figs, l and 5, or on the surface thereof, Figs. l, 3, and 4, which function as a parasitic reilector. The cylinder 10 supporting the reiiector is supported by means of bearings 16 and 17 which permit the reflectorto be rotated around the dipole 1, thus rotating the directive pattern of the antenna unit. The reector cylinder 10 is mechanically rotated by means of a motor 18 and gearing mechanism 19. A mechanical link 26 between the motor 13 and alternator 21 permits the alternator 21 to be'driveri in synchronism with the reflector cylinder 10. Surrounding the antenna unit is a protective drum 22 composed ofv a material such as fiberglassI which does not affect the radiation pattern of the antenna. Bearing 16 is supported by the top of the protective drum 22 which also supports the top of the dipole antenna 1.

In order to have a response over a comparatively wide frequency range, the antenna 1 is a low Q wide band coaxial dipole. The design of such a dipole antenna, in order to have a wide frequency response, requires a di'- ameter which is relatively large when compared to the wavelength of the radiations for which it is designed, and because of this large diameter, the antenna will be sensitive to horizontal polarization. The lower half '7 of the dipole is coupled to the outer conductor 6 of the coaxial transmission line 2 and shields the transmission line, thus preventing it from affecting the radiations received by the antenna unit. The length of the dipole is designed so that itis resonant at the median frequency of the fre,- quency band for which Yit is to b e used.y The reiiecting strips 11-15 each have an electrical length equal to onehalf the Wavelength at the lower end of the frequency band of the low Q dipole. The width of each conducting strip is made as narrow as possible consistent with the requirement that the strips provide adequate conduction. 4"ixus, they may consist of a plurality of wires er ribbons of conductive material, or they may be painted on the cylinder lil With a metallic or conductive paint. The reflector, because of the narrow width of the reflecting strips, is insensitive to horizontal polarization buty does reflect vertically polarized waves, Vthus, in effect, cancelling the tendency of the wide band dipole to be sensitive to horizontal polarizations. The spacing between strips is small enough to provide adequate reflection of the vertically polarized waves and wide enough to prevent excess capacitance between strips 11-15 which might change the electricall length of the strip or might present the equivalent of a solid reflector area and thus rellect horizontally polarized radiations. The distance between dipole 1 and the reflector strips is of the order of .07 to .l2 wavelengths.

The parasitic reliector may be formed by placing the that may be used in manufacturing `the refiector-.fea-

ture of the invention.

One form of antenna mit that has been tout@ satisfactory for a frequency band of 225 megacycles to 40() megacycles comprises a coaxial dipole 19 inches long and conducting reector strips 22 inches in length which are electrically resonant at 215 megacycles. The reflector strips are painted on-the insulating lmaterial of the relector cylinder with silver paint, each being an eighth` of an inch wide and spaced one half inch apart upon a radius of four inches. The spacing between dipole and reilector is 31/2 inches. n

Referring to Eig. 2, the embodiment of this invention is shown connected in a circuit for direction nding purposes. Inthis arrangement the reilector is rotated by means of the motor 18 which also drives alternator 21 in synchronism therewith. The alternator 21 feeds a reference voltage to the stator windings 23 of a phase meter 24. The antenna transmission linel 2 is coupled to the rotor winding 25 of the Vphase meter 24 through a receiver and amplifier 26 and a high impedance 27. The azimuth of the received signal may be indicated by the rotation of the rotor V25 and phase meter 24 in response to the phase relation of thereceived signal from the dipole antenna land the reference voltage from the alternator 21.

When a received signal is fed to the rotor winding 25, the phase meter 24 will act as a motor. To counteract the tendency of the phase meter to act as a motor, it is necessary to reduce the current in the rotor winding 25. This may be done by introducing a high impedance into the transmission line A2 between the amplier 26 and the rotor winding 25 of the phase meter. This high impedance may take the form of a high impedanceV transformer v27 between theamplier26 and the vrotor winding 25 of the phase meter 24. y

When used in lower frequencies, the physical length of .the retlector strips would be excessive. In order to overcome this, alternate configurations of the rellector strips may be used as shown in Figs. 3 and 4. Fig. 3 shows two reflector strips 2S and 29 in zigzag form. The zigzag angle a should not be less than 45 in order to minimize the capacitance between adjacent portions of the reflector strip. Y Parallel zigzag strips may be added, but these additional strips should be limited to two or three due to the capacity between strips which would tend to simulate a continuous surface and thus reect horizontal polarizations.

Fig. 4 shows a reflector strip 30 of Greek fret design. When of this design, only one reflector strip is needed for adequate reilection of the vertically polarized waves. The distance between parallel portions of the strip should be great enough to prevent excess capacitance from being in troduced and changing the electrical length of the reector strip.

Referring to Fig. 5 of the drawing, a cross-sectional view of the reector cylinder is shown with a reflector strip 11a embedded therein. The reiector may be formed by placing or painting the reector strips such as strip 11a on a surface of insulating material such as fiberglass and then applying another sheet of insulating material thereover to form a lamination incorporating the conductive strips. Alternate methods of construction of the reectors may be used such as painting the reector strips 11a on the inner surface of a cylinder or by inlaying conductive wires or ribbons in the wall of its cylinder.

While l have described above the principles of my in vention in connection with specific apparatus, it is to be clearly understood that this description is made by way of example only and not as a limitation to the scope of my invention as set forth in the objects thereof and in the accompanying claims.

' I claim:

l. An antenna system comprising antenna means having a vertically polarized characteristic vertically disposed, means to support said antenna means, a cylinder of insulating material mounted concentrically about said antenna means, conducting strips carried by said cylinder, and means to rotate saidA cylinder.

2. An antenna system comprising antenna means having a vertically polarized characteristic,v means to support said antenna means, a protective cover of insulating material surrounding said antenna means, a cylinder of nonradiating material disposed concentrically about said antenna means, means carried by said cover to support said cylinder for rotation, a plurality of strips of conducting material carried by said cylinder, and means to rotate said cylinder.

3. An antenna system according to claim 2, wherein said strips comprise a plurality of conductive wires each having an electrical length substantially equal to a half wavelength long.

4. A system according to claim 2, wherein said strips comprise a plurality of parallel painted stripes each substantiallyone-half wavelength long spaced from said dipole .07 to .12 wavelength and of a width to provide adequate reection.

5. A system according to claim 2, wherein said strips comprise a plurality of ribbonscomposed of conductive material, each a half wavelengthV long and of a width necessary to providel adequate reflection.

6. A system according to claim 2, wherein said conductive .strips are in the form of a plurality of spaced zigzag strips having a zigzag angle not less than 45 having a physical height substantially less than one-half wavelength longvand an electrical length substantially equal toene-half wavelength.

7. AY system according to claim 2, wherein said strips comprise a conductor a half wavelength long in the form of a Greek fret having al physicalheight substantially less than one-half wavelength long and an electrical length substantially equal to onefhalf wavelength.

8. An antenna systemV comprising a supporting base, a vertically disposed vertically polarized antenna carried by said base, a cylinder of non-radiating material disposedconcentrically about said antenna, a plurality of reflecting strips carried by saidk cylinder and means to rotate said cylinder.

9. An antenna system comprising a supporting base, a vertically disposed vertically polarized antenna carried by said base, a cylinder of non-radiating material disposed concentrically about said antenna, a plurality of conducting strips carried by said cylinder, a protective drum of .non-radiating material to enclose said antenna and said cylinder, said base having abearing connected to the lower end of said cylinder to support the base of said cylinder for rotation, said drum having a bearing connected to the upper end of said cylinder to support said cylinder for rotation, and means to rotate said cylinder.

l0. An antenna system comprising a 'supporting base, a vertically disposed vertically polarized antenna carried by said base, a cylinder of non-radiating material disposed concentrically about said antenna, a plurality of conducting strips carried by said cylinder, a drum of nonradiating material to enclose said antenna and said cylinder, said base having a bearing connected to the lower end of said cylinder to support the base of said cylinder for rotation, said drum having a bearing connected to the upper end of said cylinder to support said cylinder for rotation, means to rotate said cylinder about said antenna,

and means to couple a source of energy to said antenna through the bearing in said base.

References Cited in the le of this patent UNITED STATES PATENTS

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