US2771605A - Omnidirectional antenna - Google Patents

Description

Nov. 20, 1956 R. A. KIRKMAN OMNIDIRECTIONAL ANTENNA Filed Oct. 1l, 1954 United States Patent G OMNIDIRECTIONAL ANTENNA Robert A. Kirkman, San Diego, Calif., assignor to Cook ieltric Company, Chicago, Ill., a corporation of ois Application October 11, 1954, Serial No. 461,355 7 claims. (ci. 343-771) This invention relates to microwave apparatus, more particularly to apparatus and methods for radiating omnidirectionally microwaves which are polarized in particular planes, and it is an object or" the invention to provide improved apparatus of this character.

It is a further object of the invention to provide improved microwave apparatus and methods for radiating omnidirectionally microwaves which are polarized in a horizontal plane.

It is a further object of the invention to provide apparatus and methods for radiating omnidirectionally microwaves which are polarized vertically.

In carrying out the invention in one form, improved microwave apparatus is provided comprising a wave guide including means for circularly polarizing a wave traveling therein, and relatively stationary means at the exit of said guide equally etective in all directions at right angles to the wave guide for radiating the circularly polarized wave.

In carrying out the invention in another form, an improved method of radiating omnidirectionally in a plane an electromagnetic Wave is provided comprising generating a non-uniform eld pattern of the wave in space in a plane and rotating the eld pattern at a very rapid rate.

This application is a continuation-in-part of my copend- Iing application Serial No. 106,931, tiled on July 26, 1949, now abandoned.

For a more complete understanding of the invention, reference should be had to the accompanying drawing, in which:

Figure 1 is a vertical view in perspective and partially broken away of one form of apparatus embodying the invention;

Fig. 2 is a view similar to Fig. 1 of another form of the invention;

Fig. 3 is a diagrammatic view of a vertical cylindrical wave guide showing a transverse electric field of the dominant mode being propagated therein; and

Fig. 4 is a diagrammatic view of the transverse electric eld pattern set up at the end of the cylindrical wave guide of Fig. 3.

Referring to the drawing, there is shown microwave apparatus comprising awave guide 11, acoaxial conductor 12 for supplying thewave to the guide, and abiconical antenna 13 at the end of the guide for radiating the wave. By way of example, it is supposed that the wave being propagated is a transverse electric wave of dominant mode, although other modes may be used.

Between thecoaxial conductor 12 and thebi-conical antenna 13 is a section of the guide designated by thenumeral 14 which circularly polarizes the wave propagated in the guide.

If it is supposed that thevertical cylinder 15 of Fig. 3 has a transverse electric wave of dominant mode being propagated therein, the electric field pattern may be represented by a series ofcurved lines 16 extending across the guide or pipe. This Wave is linearly polarized in a horizontal plane. lf the pipe is open at the top and the 2,771,605 Patented Nov. 20, 1.956

wave is allowed to emanate therefrom, i. e., energy is` exists in both directions at right angles to the electricy ield lines of`force and zero intensity exists in the direction at right angles to the direction of maximum intensity. With such a eld pattern or radiation pattern energy is radiated predominantly in the direction of maximum intensity and no energy is radiated in the direction of zero intensity, there beng varying amounts of energy radiated in between.

When the radiation eld of Fig. 4 is made to rotate at a high rate of angular velocity, an equal amount of energy will be radiated into each sector around the axis of theguide 15 during any relatively long period of time. If the field pattern is rotated degrees, the direction of maximum intensity exists where the intensity previously was zero; if it is rotated degrees, the direction of maximum intensity is the same as originally; and if it is rotated 270 degrees,.the direction of maximum intensity again exists where itwas originally zero.

Rotating the tield pattern rapidly enough causes the direction of maximum intensity to exist for the same length of time in all sectors during any relatively long interval of time, so that during that interval the same amount. of radiation takes place into all sectors.

The rapid rotation of the horizontally polarized iield of Fig. 3, and consequently of the radiation field of Fig. 4, may be obtained by circularly polarizing the ield inside of the guide.

When the field is circularly polarized, the eld rotates at a rate equal to the frequency of the wave given by the relationship high, being in the order of billions of cycles per second, Y

and, consequently, the rate of field rotation is very high. To all intents and purposes, in such a case the azimuthal field pattern is omnidirectional. That is, all sectors re-:v ceive the same amount of energy during any relatively long interval of time; for example, an interval of the order of one millionth of a second.

It will be apparent that mechanically rotating antennas are not possible because sufficiently high rates of rotation are not obtainable to radiate energy uniformly into all sectors. Hence, according to the invention, the apparatus is relatively stationary and eld rotation is produced in one form of the invention as described.

Referring to Fig. l, theportion 14 constitutes means for circularly polarizing the wave. This means comprises a portion of the wave guide having the same diameter as the wave guide proper, and a pair of conductingrods 21 and 22 extending diametrically across the guide at an angle of 45 degrees to the direction of thecentral conductor 23 of thecoaxial conductor 12. Thecentral conductor 23 is a probe for exciting the guide with the wave to be propagated therein.

By choosing the diameter of therods and the spacing between them properly, circular polarization of the wave may be obtained. It is understood in this art that conducting rods placed ina wave guide cause a phase change in waves polarized in a direction parallel to the direction of the rods, but do not cause any phase change in waves polarized at right anglespto the direction of the rods,'pro`-z vided' that th'e rod diameter is small compared to the wave length and the guide diameter; Since a wave propagated through the guide may originally be oriented so that it has components parallel and perpendicular to the rods, it will be apparent that one component will' have a phase lea'd over the other, the amount depending upon the diameter and thev spacing of the rods. Moreover, the rods may be placed at 45 degrees to the direction of the electric lield'Y so that the parallel and perpendicular' components are equal. If the diameter of the rods chosen is such thatV the inductive suscept'ance thereof is twice the characteristic admittance of the wave guide, and if the longitudinal spacing between the rods is three-eighths of a wave length', then a phase change between the two components of the wave of 90' degrees isY obtained. Or the resulting wave', being' propagated along thewave guide portion 23, i. e., followingportion 14, is circularly polarized, though still in a horizontal plane.

While one form of means for producing plane circular polarization has been described, it'will be understood that others may be used, such, for example, as properly dimensioned and placed diametrically opposed metallic ns or a dielectricI plate in the guide.

A circularly polarized wave as by thesection 14 will be' radiated out of the open end of the guide and will be radiated omnidirectionally, as already has been described. However, the vertical field pattern of the wave being so radiated is such that much of the energy is directed upwardly rather than in the horizontal or outflowing direction. Accordingly, thebi-conicalv antenna 13 comprising thecones 24andV 25 is placed above the wave guide in order to concentrate the energy in the horizontal plane, and to radiate the wave which is polarized in a single plane, the dimensions and the angle of the cone being chosen as is well' understood to produce the desired vertical field pattern.Cone portion 25 may be attached directlyl to the upper end of the guide, andcone portion 24 is spaced upwardly therefrom by some form of mechanical support, such, for example, as theinsulating rods 20 and 26. The energy radiated from the bi-conical antenna will have a vertical electrostatic vector and is thus referred to as vertically polarized energy as described above.

The apex of thecone portion 25 is open to permit the wave to emanate therefrom, whereas thecone portion 24 has a sharp apex lying on the axis of the guide. The spacing of thecone portion 24 above thecone portion 25 is such as to match the impedance of the bi-conical antenna to the impedance of the wave guide so as to prevent reflection of the wave.

The connection betweenrods 20and 26 and the cone portions may be adjustable, if desired, in order to obtain the impedance match, or they may be fixed as shown after the impedance match has been made.

Inside of the lower end of thewave guide 11, aplunger 27 is threaded in acap 28. By rotating aknob 29 the position of theplunger 27 relative to the portion ofconductor 23 inside of the guide may be changed so as to produce an impedance match at this point. Preferably,plunger 27 is spaced one-quarter wave length or multiples thereof below theconductor 23, the adjustment of the plunger being such that spacing from zero to one-quarter wave length or multiples thereof may be obtained.

The embodiment of the invention shown in Fig. 2 is similar to the embodiment of Fig. l in respect to thewave guide 11 in general, thecoaxial conductor 12 for exciting the guide, and theportion 14 for circularly polarizing in a horizontal plane the linearly polarized wave supplied to the guide. The embodiment of Fig. 2 differs from the embodiment of Fig. l in its inclusion of awave guide section 31 having a series of narrow longitudinal slots` 32 equally spaced around the periphery of the guide.

Eachslot 32 serves to radiate outwardly therefrom, the radiation from all of the slots combining to produce a radiation pattern which to all intents and purposes is continuous in theho'rizontal plane, since the electric field inside the guide is circularly polarized. In order to obtain the desired vertical eld pattern a series of rows of slots is used. In the figure, three rows are shown by w'ay of example, the slots of one row being staggered relative to the slots of the row above or below, but any number of rows may be chosen, as is known in this art.

The operation of embodiment of Fig. 2 may be understood more clearly by considering that currents flow tangentially in the wave guide and spirally upwardly due to the circular polarization of the' wave in a' horizontal plane wave inside the guide. Since the slots provide interrup` tions to the ow of these currents,`potentialsrar'e developed thereacross and consequently radiation therefroml t'a'lies place. f v

The pattern of radiation given by each slot is essentially unidirectional; that is, the radiation takes place outwardly from the slot and is horizontally polarized, which pattern substantially resembles a cardioid. This becomes true progressively more so as the wave length is decreased relatively to the guide diameter; Since the electric field` inside of the guide is rotating (due to the circular pol'a'r# ization), it is clear that each slot successively radiates with maximum intensity (opposite to this direction the radiation is zero or minimum)` and the wave is' radiating at a very high angular rate. y The amount' ofrenerg'y being radiated into all sectors during a relatively long' interval is the same.

While two forms of means for concentrating the field in a vertical plane and for radiating uniformly' in all directions in a plane are shown, it will bev understood that others may be used.

While particular embodiments of the invention have been shown, it will be understood, of course, that the' i`n`- l vention is not limited thereto since many modifications may be made, and it is, therefore, contemplated by' the;

appended claims to cover any such modiiications as fall within the true spirit and scope of the invention.

The invention having thus been described, What" is claimed and desired to be secured by Letters Patent is: l. Microwave apparatus comprising a vertically' disposed cylindrical wave guide, energizing means for feed'A ing to said guide a transverse electrical wave of dominant mode polarized in a horizontal plane, means in said guide for circularly polarizing said wave in a horizontal plane, and bi-conical antenna means at the exit of said guide for radiating said wave.

2. Microwave apparatus comprising a vertically disposed cylindrical wave guide, means for feeding to said wave guide a transverse electrical wave of dominant mode polarized in a horizontal plane,means i'n said guide for circularly polarizing said wave in a horizontal plane normal to the axis of said wave guide a wave traveling therein, and bi-conical antenna means atv the exit of said guide for radiating said wave verticallyl polarized in a plane at right angles at the axis of said wave guide and having a rotating eld strength pattern.

4. Microwave apparatus comprising a vertically disposed cylindrical wave guide, energizing means for feeding to said guide a transverse electrical wave of dominant mode polarized in a horizontal plane, means in said guide for circularly polarizing said wave in a horizontal plane, and antenna means at the end of said wa've guide including a plurality of longitudinal slots spaced around the periphery thereof for radiating said wave into space uniformly in all substantially horizontal directions and maintaining said wave polarized in a plane at right angles to said guide. n

5. Microwave apparatus comprising a verticallyl dis-1 posed cylindrical wave guide, means for feeding to said` wave guide a transverse electrical Wave of dominant mode polarized in a horizontal plane, means in said yguide for circular-1y polarizing said wave in a horizontal plane, and antenna means at the end of said wave guide including a plurality of longitudinal slots spaced around the periphery of said wave guide, said antenna means being equally effective in all directions and having substantially the same radiating characteristics in all horizontal directions for radiating said wave into space uniformly in all substantially horizontal directions and maintaining said Wave polarized in a horizontal plane.

6. Microwave apparatus comprising a vertically disposed cylindrical Wave guide, energizing means for feeding to said guide a transverse electrical Wave of dominant mode polarized in a horizontal plane, means in said guide for circularly polarizing said wave in a horizontal plane, and antenna means at the exit of said wave guide for transmitting said wave into space uniformly in all substantially horizontal directions with a vector orientation fixed in a predetermined angular relationship to the axis of said wave guide and the horizontal plane.

7. Microwave apparatus comprising a cylindrical wave guide having therein means for circularly polarizing in a plane normal to the axis of said wave guide a wave traveling therein, and antenna means at the termination of said wave guide for radiating said wave uniformly in all substantially horizontal directions in a plane at right angles to the axis of said wave guide, and for radiating said energy with a Vector xed in a predetermined angular orientation relative to the axis of said wave guide and the plane of radiation.

References Cited in the tile of this patent UNTTED STATES PATENTS 2,412,320 Carter Dec. 10, 1946 2,438,119 Fox Mar. 23, 1948 2,611,087 Alford Sept. 16, 1952

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