US2207781A - Ultra high frequency antenna - Google Patents

Description

G. H. BROWN ULTRA HIGH FREQUENCY ANTENNA July 16, 1940.

Filed May 1958 Ytlorneg Patented July 16, 1940 UNITE-D sT TEs ULTRA HIGH FREQUENCY ANTENNA George H. Brown, Haddonfield, N. J.," assignor to Radio Corporation of America,,a corporation of Delaware v Application May 28, 1938, Serial No. 210,605

4 Claims. 01. zso ssi My invention relates to antennas and more particularly to an ultra high frequency antenna suitable for the radiation of horizontally polariz ed waves.

It has recently become apparent that horizontally polarized waves at ultra high frequencies are more desirable for certain purposes than vertically polarized waves. One method of 'radiating a horizontally polarized field of circular pattern is shown in my U. S. Patent No. 2,636,- 976, entitled" Antenna Systems, and issued July 13, 1937. While the method there disclosed is highly efficient for producing a horizontally polarized circular rotating field, in some instances this rotation is undesirable. Horizontally polarized waves which are non-rotating may be obtained by an antenna constructed according to this invention.

It is highly desirable that the elements of an antenna be rigidly mounted. High frequency antennas are readily adaptable to the use of rigid rods as conductors because resonant lengths are not unduly long. The question of rigidly supporting such an antenna usually involves a consideration of the problem of supplying suitable insulation from the supporting medium.

It is, therefore, an object of this invention to provide an antenna which may be rigidly supported, and which does not require insulation from its supporting medium.

It is a further object of this invention to provide a high frequency antenna which produces horizontally polarized waves having a substantially circular horizontal radiation pattern.

It is a still further object of this invention to provide means for suitably phasing the elements of a horizontal loop antenna whereby a uniform horizontal radiation pattern is obtained. 7

This, invention will be better understood fro the following description when considered in connection with the accompanying drawing. Its scope is indicated by the appended claims. Similar reference numerals refer to similar elements throughout the drawing.

Referring to the drawing:

Figure 1 represents the current distribution in a dipole antenna which is folded in the form of a square, a half wave length on a side,

Figure 2 represents the current distribution in an antenna when modified in accordance with my invention by the inclusion of two quarter wave resonant lines,

Figure 3 illustrates the application of four quarter wave sections to a square antenna,

Figure 4 is a plan View of an antenna mounted on a supporting mast in the manner of my invention,-

Figure 5 is an elevation of Fig. i, and

Figure '6 is a plan'view illustrating an alternative antenna construction.

In Fig. 1' I have shown an antenna consisting of two full wave sections l and 3, each forming two sides ll, l5 and I3,-ll, of a square one half wave length on'a side. The'antenna is fed by a transmission line 5, which is connected between the adjacent ends of the two sections. At a particular instant thecurrent flowing through the antenna is as indicated by the arrows. The current distribution along each wire is as shown by the dotted lines. It will be noted thatthe current in two sections is out of phase with that in the other two. Consequently, a uniform horizontal radiation pattern will not be obtained.

Accordingly, I propose to open each section I and 3 at its mid-point and insert in each a quarter wave resonant line I and 9, as shown in Fig. 2. The total length of conductor in each line is a half wave length and is folded back upon itself; Therefore, undesired out of phase currents flow through the section without radiation, and bring the adjoining sections I l and I3 into phase with the original sections I5 and H. The new current distribution is therefore as shown in Fig. 2 by the dotted lines.

It is well known that a pair of parallel wires a quarter wave length long shorted at one end present a very high impedance at the open end. Since the voltage distribution between the sections H, I3 and I5, I1 is the same as that of the sections on either side of the quarter wave sections 1 and 9, it follows that two more similar quarter wave sections l9 and 2| can be connected between the sections H, 53 and I5, Il as shown in Fig. 3. The high impedances at the input of these sections do not affect the operation of the antenna, and the desired voltage distribution is attained.

In a practical application the value of this method becomes evident. The short circuited end of each of the quarter wave sections is a voltage node, and therefore may be grounded without affecting the operation of the antenna. Four points of support are therefore provided, and an antenna of great rigidity can be constructed- Figure 4 illustrates a practical method of utilizing this invention. The figure represents a top View of a horizontal antenna consisting of four half Wave sections H, I3, l5 and H. By extending the parallel portion of the quarter rounded corners and slightly concave sides.

Wave sections I, 9, l9 and 2|, the may be securely connected to an antenna mast 23, or the like.

Shorting bars 25, 21, 29 and 3| are provided for tuning the respective sections to resonance. The shorting bars may conveniently be variable.

Fig. 5 is a side view of such an antenna which illustrates how conveniently an antenna of this description can be mounted on a mast. Insulators are not necessary and therefore the maximum strength and rigidity can be attained. The transmission line is also conveniently supported by quarter wave sections spaced as necessary down the mast. One of these is shown at 33, and is similarly equipped with an adjustable shorting bar 35.

My-invention is not limited to an antenna having four sections but may consist of any number of sections. The antenna may have a hexagonal or even a circular shape, for example, as shown in Fig. 6. In this case, each half wave length section subtends an arc of approximately It can be shown that an antenna constructed according to this invention produces a horizontal radiation pattern which is generally square with Due to the elimination of insulators the antenna may be economically built and rigidly constructed.

I claim as my invention:

1. An antenna system which comprises a plurality of half-wave resonant radiating elements lying in a plane and positioned so as to enclose an area, phase inverting means connecting adjacent ends of said radiating elements to each other, and means including said phase inverting means for mounting said antenna.

2. An antenna system which comprises a plurality of half-wave resonant radiating elements a mast, and means including said non-radiating elements for mounting said antenna on said mast.

3. An ultra high frequency antenna system which includes a plurality of resonant half wave radiating elements defining the sides of an area in the horizontal plane, a quarter wave resonant line connecting adjacent ends of said elements, a mast for supporting said antenna, and means rigidly connecting said mast to said quarter wave lines at a point which is substantially a voltage node, whereby said antenna is supported by and efiectively insulated from said mast.

4. An ultra high frequency antenna system which includes a plurality of radiating elements positioned end to end so as to define an area, a quarter wave resonant line connectingadjacent ends of said elements, a mast for supporting said antenna, and means connecting said mast to said.

whereby said

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