US2599705A - Short wave antenna - Google Patents

Description

June 10, 1952 w, s, wm 2,599,705

SHORT WAVE ANTENNA Filed June 16, 1948 r\ m m k/ k/ \J U limwnfor (Ittorncu TUNAB'fE 5' ELECT MAL "5m Patented June 10, 1952 SHORT WAVE ANTENNA Wesley S. Erwin, Detroit, Mich., assignor to General Motors Corporation, Detroit, Mich., a corporation of Delaware Application June 16, 1948, Serial N 0. 33,332

3 Claims.

The present invention relates to the design of antennas for the propagation or reception of ultra high frequency electric waves. More particularly it relates to antennas having an omnidirectional pattern in a horizontal plane, for the propagation and reception of microwaves. Electric waves in the microwave or ultra high frequency spectrum generally follow only straight or line-of-sight paths. Propagation or reception of such waves is enhanced by use of elevated points for the antennas and also by the use of antennas with high horizontal directivity.

For instance, previous to the present invention, it was common practice to use a series of vertically stacked dipoles or other unit radiators all similarly phased. This whole array was then located on top of a tall building, tower, or hill. The propagation or reception of electric waves in the spectrum where a quarter wave length is greater than a practical antenna dimension is simple where omnidirectional characteristics are desired and difficult where directional characteristics are desired. In the range of frequencies where the antenna may be one-quarter wave length and still be of such size as to emit appreciable power, the problem of both omnidirectional and directional propagation and reception is greatly simplified. It is quite diflicult in the propagation of microwaves with present antennas, to obtain satisfactory antenna gain with omnidirectional field patterns.

Previous to the present invention it was common practice to use a single dipole or a series of stacked dipoles or dipoles arrayed in a particular pattern so as to obtain suflicient antenna gain.

The present invention utilizes the axial propagation characteristic of an antenna which is several wave lengths long. Previous to the present invention it was thought undesirable to use continuous antennas of greater length than onehalf wave length since the propagation in a plane normal to the antenna is not increased by increasing the length of the antenna, their propagation being essentially only in an axial direction. The present invention utilizes a reflector which may be of inverted conical shape to convert the directional propagation parallel to the antenna to an omnidirectional propagation in a plane normal to the antenna. Any downward radiation along the vertical wire could be refiected by a flat wire mesh reflector located in a plane normal thereto and near the lower extremity thereof.

It is, therefore, an object of the present invention to produce an antenna of several wave lengths having an omnidirectional characteristic in a plane normal to the antenna.

It is a further object of the present invention to produce an antenna of several wave lengths with maximum propagation in a normal plane intersecting a point near the top of the antenna.

It is a still further object of the present invention to produce a highly eflicient antenna for microwaves.

Other objects of this invention will become ap parent upon reading the specification and inspection of the drawings and will be particularly pointed out in the claims.

Referring to the figures in the drawing:

Figure 1 illustrates standing waves;

Figure 2 illustrates parallel directional propa gation of an antenna in free space;

Figure 3 illustrates propagation from a vertical antenna;

Figure 4 illustrates an embodiment of the present invention for stationary transmitters and receivers;

Figure 5 illustrates a second modification of the present invention utilized on mobile transmitters and receivers.

Referring more particularly to the figures of the drawing, Figure 1 shows a conductor 2, several wave lengths long with a point source of energy 3. If such a conductor is terminated with any load impedance other than the characteristic impedance of the line system, of which the conductor is a part, a so-called standing wave results from the series of reflected waves caused by the discontinuity in impedance at the termination. This standing wave approaches a sine wave shape as a maximum. In Figure 1 this Wave is shown as 4. Due to the arrangement of potentials caused by this standing wave, such a conductor as 2, if placed in free space, would propagate waves in a direction which coincides with the direction of the conductor.

Referring to Figure 2 such a conductor in free space is shown as 8 with a point source of energy 8 located at some place in its length. Such a conductor may be considered as terminated in an impedance very different from the characteristic impedance of the transmission line system which includes the conductor. Under these circumstances the directional propagation of the antenna is illustrated by the arrows l0 and I2. If such an antenna is placed over a plane conduct ing surface normal to the antenna such as shown in Figure 3, the wave propagated by I 2 is reiiected by this surface I4 as illustrated by the arrows l6 and [8. In this illustration the antenna and point source of energy 22 may be considered the equivalent of the conductor 6 and the point source of energy 8 in Figure 2. This antenna, similar to the antenna shown in Figure 2, in addition to reflecting wave l8, has the direct waves 24 propagated therefrom. Such an antenna is illustrated in Figure 3. It has directional characteristics and propagates a. wave front in a direction axial to the antenna, here shown as vertical. rectional pattern, into an omnidirectional. pattern normal to the antenna, a convex hyperbolic In order to change this dior inverted cone reflector of conductingmaterialf is attached to the top of the antenna.

Referring to Figure 4, an inverted conical reflector is used with a stationary transmitter or.

receiver 26. A lead-in wire 28 is attached to the proper point on the antenna 30ito obtain maximum transfer of energy between the antenna and thelead-in. wire. This point,- ofa tachment, of course, will vary in accordance with the particular wave length being transmitted or received. If 26 isa transmitter or receiver which is'voltage fed, thepoint. of attachment 32' will be anuneven number of quarter wave lengths from the. reflecting surface '34.. If, on the other hand, the transmitter or receiver 26 is current fed, the point of attachment :32 will be an even number of quarter wave lengths from the reflecting-surface 34. The antenna 30 shown in this modification of the invention is ofthe flexible small-diameter conductor type and is supported'in a vertical position by means of a gas-filled balloon or other buoyant element 36. Located between-the balloon 36 and. the conductorisll-is. a conioal or a hyperbolic surface of rotationwreflector: 38. Such a reflector gives good horizontal omnidirectional propagation or reception characteristics. I prefer to use an inverted conical reflector element having a vertex angleof 90 and-locatedsymmetrical-with-the line of center of the antenna. Such a reflector is also shown in the modification of my invention illustrated in Figure 5. In-Figure 5, 40 lean-automobile orothermobile unit transporting the antenna with its as.- sociated. transmitter and/or receiver- In this case the antenna 42 isofthe self-supporting type and is attached to the automobile by means of insulator M. In this modificationa conducting plane. 46 locatednormalto the antenna near. its base, replaces the reflecting. surface 34. shown in igure rib The cone has a vertex angle of 90 and is supported symmetrically-at. its. apex by the antenna 42 so that allpointsonthe reflectingv surface present an angle of. 135 with the antenna. In this modification, the vertically propagated waves are reflected at an angle of. 90? so as to be propagated in an omnidirectional pattern normal to the antenna. If this antenna is used for a receiver the received waves are reflected in a vertical direction along the antenna so as to induce a current therein.

It is to be understood also that although the invention has been described with specific reference to :a particular embodiment thereof, it is not tobe. solimited, since change -and alterations therein may be made which are within the full intended scope of this invention as defined by theappended claims.

I claim:

1; A-radioantenna for electric signals having an -omnidirectilonal horizontal wave pattern including; a-verticaljconductor for said electrical signalof a length equal to several wave lengths of said electrical signal at its operating frequency, an, inverted conical reflector with a downwardly directed vertex angle of substantially located symmetrical. with saidv conductor at the upper extremity thereof, and a horizontal conducting plane. atthe lower extremityof saidconducton:

2.. A radioantenna system for electrical Sig? nals. having an omnidirectional horizontal wave patternincluding; a vertical. conductor for said electrical signal of a length equal to several wave lengths of saidelectr-ical signal at itsopcrating frequency, an. inverted conical reflector with a downwardly directeclvertex angle of sub.- stantially- 90f located symmetrical with.said:conductor at the. upper extremity thereof, and-electrical means. connected to said antenna adjustable. to resonate. at said operating frequency.

3. In anantenna system as. claimedinclaim 2 having a horizontal conducting plane at the lower extremity of saidconductor.

WESLEY S. ERWIN.

REFERENCESv CITED The following references are of record inzithe; file. of this patent:

UNITED STATES PATENTS Number Name Date.

651,361 Kitsee- June. 12, 190.0, 744,936 Plecher Nov..24, 1903. 831,678 Osborne Sept. 25,..1906, 930,746 Eisensteinv Aug. 10,..1909 974,191 Sargent Nov. 1,.1910

1,296,687 Nichols Mar- 11-, 191.9 1,650,461 Nilson Nov. 22,,1927 1,783,025 M'eissner Nov. 25., 193.0. 2,081,274 Hahnemann May 25,1937. 2,096,501. Schuler Oct. 19,1937. 2,153,768 Morrison 1- Apr. 11', 1939. 2,166,589 Harrington July 18, 1939

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