Broad band antenna

May 17, 1960 m. w. scheldorf

BROAD BAND ANTENNA

Original Filed Sept. 30, 1952

2,937,372

Sheets-Sheet 1

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May 17, 1960 m. w. scheldorf 2,937,372

BROAD BAND ANTENNA Original Filed Sept. 30, 1952 6 Sheets-Sheet 2

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May 17, 1960 m. w. scheldorf 2,937,372

BROAD BAND ANTENNA

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May 17, 1960

M. W. SCHELDORF

BROAD BAND ANTENNA

Original Filed Sept. 30, 1952

2,937,372

Sheets-Sheet 4

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May 17, 1960

2,937,372

M. W. SCHELDORF

BROAD BAND ANTENNA

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May 17, 1960 _M. w. scheldorf 2,937,372

BROAD BAND ANTENNA

Original Filed Sept. 30, 1952 6 Sheets-Sheet 8

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2,937,372

Patented May 17, 1960

United States Patent Office

2,937,372

BROAD BAND ANTENNA

Marvel W. Scheldorf, Palos Heights, HI., assignor to Andrew Corporation, a corporation of Illinois

Original application September 30, 1952, Serial No. 312,235, now Patent No. 2,754,514, dated July 10, 1956. Divided and this application May 26, 1955, Serial No. 511,374

Claims. (Cl. 343—769)

The present invention relates to a broad band antenna, _f and more particularly to an improved antenna element I suitable for use with or without a reflector.

This application is a division of Serial Number 312,235, filed September 30, 1952, (now U.S. Patent t 2,754,514) for a Broad Band Antenna.

For certain purposes it is desirable to provide an antenna having broad band radiation characteristics. Attempts have been made to use a combination of elements to provide such broad band operating characteristics, but not infrequently it has been found that there is an impedance limitation in the primary radiator or feed line. It furthermore has been common experience to find that an antenna element of large cross section, while perhaps having the desired radiation characteristics, presents a problem of connection between the end of the transmission feed line and the antenna radiating element. Not infrequently the transformation of impedances is not satisfactory and a distortion of the desirable qualities of the radiating element occurs.

In accordance with the present invention many of the difficulties encountered in previous attempts to obtain an antenna element for broad band operation have been obviated by an element which has a generally cylindrical configuration having an unusually large diameter to length ratio. This element is so constructed as to have a physically small space between the parts at which the transmission- line is to be connected. The length of the cylindrical Structure, is substantially the same as the circumference, thus providing the unusual diameter to length ratio.

: It: is, therefore, an object of the present invention to provide: an improved antenna having broad band trans&gt; mission characteristics.

:A further object of the invention is to provide an improved antenna element having. a relatively large cross section.

Still another object of the invention is to provide an improved antenna element of large cross section and a power feed therefor without burdensome transformation of impedances between the transmission line and the antenna element.

A still further object of the invention is to provide an antenna of broad band transmission characteristics which has a smooth transmission from the coaxial feed line to the radiating element.

Other and further objects of the present invention subsequently will become apparent by reference to the following description taken in conjunction With the accompanying drawings, wherein:

Figure 1 is a side view of the radiating element;

Figure 2 is an end view of the radiating element shown in Figure 1;

Figures 3, 4, 5 and 6 are graphical representations of the relative power radiated in the H plane at various frequencies;

Figures 7, 8, 9 and 10 are graphical representations of the relative power radiated in the E plane at various frequencies as seen perpendicular to the plane of the short circuit connection of the radiating element;

Figures 11, 12, 13 and 14 are graphical· representations of the relative power radiated in the E plane at 6 various frequencies as seen in the plane of the short circuit connection to the radiating element;

Figures 15 to 23 diagrammatically show different variations of the structure illustrated in Figures 1 and 2; . Figures 24 and 25 are end and side views respectively 10 showing another embodiment of the invention;

Figure 26 is an end view of a variation of the structure shown in Figure 1;

Figure 27 is an end view of another variation of the structure shown in Figure 1;

Figure 28 is a side view of still another variation of the invention; and

Figures 29 and 30 are an end view and a partial side view respectively of a still further modification of the structure shown in Figures 1 and 2.

²⁰ Referring to Figures 1 and 2 of the drawing there is shown a radiating element which defines generally a cylindrical structure. (It will be understood that the term “cylindrical” as herein employed refers to the surface traced by one side of a rectangle rotated around the parallel side as axis.) This cylindrical structure may have a length equal to one-half wave length at a selected frequency. In that case the diameter is approximately .16 wave length or the circumference is substantially onehalf wave length.

To define the cylindrical configuration it has been found sufficient to employ a plurality of rods 15 with the rods’ ends aligned with the ring 12. In a specific arrangement the ring 11 is located at three-fourths of the dis_g5 tance from the ring 12 along the length of the rods 15.

The rings 13 and 14 support a similar number of rods 16 in an arrangement corresponding to the arrangement of the rings 11 and 1'2 and the rods 15. In the particular construction illustrated the cylindrical surface is ade₄₀ quately defined by the use of sixteen rods on each half of the cylinder. A short circuit connection 17 is provided between the rings 12 and 13. A coaxial transmission line conductor 18 extends adjacent the ring 12 and forms a feed point on the opposite side of the short circuit connection 17 at the position 19. The feed is produced by fastening the outer conductor to one ring 12 with the inner conductor extended out to connect with the other ring 13. In the particular arrangement shown the feed point is displaced 15° away from the _βθ point diametrically opposite the short circuit element 17. ' The particular construction is mounted on a central insulated support element or rod 20 having suitable radial insulated support members 21, 22, 23 and 24. To further illustrate the construction reference is herewith 55 ^made to the dimensions of a particular embodiment. The various rings 11, 12, 13 and 14 where constructed of tubing of seven-eighths inch dimeter and having a circle diameter of thirty-three inches. Sixteen rods such as 15 and 16 for each half of the cylindrical configuration 60 ^emPl°y^e|i, the rods each being five-eighths of an inch in diameter and forty inches long. The rods 11 and 14, therefore, were located ten inches from the outer extremities of the rods 15 and 16 respectively. The two rings 12 and 13 were spaced four inches apart. A3 65 mmf. capacitor was connected across the input terminal 19. A satisfactory impedance relationship was obtained between the transmission line and the radiating element without the use of any matching transformer.

The graphical representations in Figures 3, 4, 5 and 70 6 show the relative power of the radiation patterns as given by curves A, B, C, D, E, F and G for frequencies of 49, 57, 65, 73, 81, 89 and 97 megacycles respectively.

3,937,372 ³

These are the H plane patterns obtained with the unsymmetrical feed for the cylindrical radiating element.

The curves Η, I, J, K, L, M and N of Figures 7, 8, 9 and 10 are the patterns obtained in the E plane as seen perpendicular to the plane of the short circuit connection 17 of Figure 1, at the same frequencies 49, 57, 65, 73, 81, 89 and 97 megacycles respectively. The curves Ο, P, Q, R, S, T and U are for the same frequencies respectively as seen in the plane of the short circuit connection.

It will be noted that in the H plane patterns there is a transition toward a traveling wave antenna pattern in a direction directly away from the feed terminals 19. While the theory for obtaining the desirable characteristics in a structure of this kind has not been developed, it would appear that if the distance from the short circuit member 17 to the feed terminals 19 becomes appreciable in terms of the wave length of the energy being radiated, the antenna element operates both as a standing wave radiator and a traveling wave radiator. Because of the displacement between the short circuit element 17 and the feed terminals 19 from the diametrically opposite points, there is a difference in loading around the peripheries of the rings 12 and 13 in opposite directions from the feed terminals 19. Hence the longer periphery has a greater loading, and hence a great deal more of the relative traveling wave components. This is believed to produce the bending of the radiation pattern to a greater extent than the measured angle between the terminals 19 and the point diametrically opposite the short circuit element 17. It, of course, is to be appreciated that while the foregoing explanation has been given in an attempt to describe the invention and to facilitate the understanding thereof by those skilled in the art, the explanation is to be without prejudice to the invention or to the inventor since subsequent research and explorations may provide a basis for a modification or different analysis.

In order to teach the present invention, thus far a particular embodiment has been illustrated and described. It will be understood that numerous variations are contemplated. While for a particular band of frequencies to be radiated it was found advantageous to connect the feed line a short distance from the point opposite the short circuit, other operating conditions might be made to better advantage by connecting the feed line at the point opposite the short circuit or at a plurality of points along the slot.

Some of the variations contemplated are shown in Figures 15 to 30 of the drawings. Figure 15 is a diagrammatic representation of one-half of the structure shown at Figure 1. The variation contemplated is a change in the lengths of the rods 16 of Figure 1 which may increase in length from a point at the connector bar 17 or termination in a somewhat linear manner. Accordingly this variation has been given reference characters such as 13«, 14«, etc. to indicate a comparable structure having somewhat different dimensions than those suggested by the construction illustrated in Figure 1.

Still another variation is illustrated in Figure 16 wherein the rods 16b vary in a logarithmic manner so that the shortest rod 16b is in alignment with the feed point or with the termination 17b. For certain operating conditions the length of the rods 16c may Vary as indiacted in Figure 17 where the longest rods are in the vicinity of the termination 17c and the feed points 19c.

In the arrangement illustrated in Figure 1 the two circular members 12 and 13 were separated by equal distances so that the two circular members were in parallel planes. This provided a uniform slot. By positioning the rings 12 and 13 as indicated by the ring 13d in Figure 18, the slot might be tapered. The taper may run from the feed line 19d so as to increase to the termination 17d or vice versa. From the illustration of this variation in Figure 18, it also will be appreciated that the configuration of the slot between tlie two rings corresponding to 12 and 13 of Figure 1 might have some other shape.

Still another variation is illustrated in Figure 19 wherein the ring 13e and the complementary ring 12e may have a tapered configuration. Thus, the cross section of ring 13e need not be uniform as might be assumed from the embodiment shown in Figure 1.

A further variation is shown in Figure 20 wherein it will be noted that the ring 13/ defining one edge of the slot is of a smaller dimension than the other supporting ring 14/. It will also be noted that in this case the ring 14/ has been shown connected to the outer exterior of the rod 16/. This, Of course, teaches that the location of the ring 14/ might be varied dependent upon the characteristics or pattern to be desired. Figure 21 shows that the ring 14g is of smaller dimensions than the ring 13g which defines one edge of the slot. Here the ring 14g has been moved inwardly from the ends of the rod 16g.

In Fig. 2 it is apparent that the rods 14 are equidistantly spaced about the ring 14. A variation in the number] of rods or in their spacing is indicated by the top viewI shown in Figure 22 wherein the rods 16Λ are no longer equidistant nor of the same number as suggested by the J construction first shown in Figure 2.*

The arrangement illustrated in Figure 23 diagrammatically shows a structure similar to that shown in Figure 1 with the exception that the termination 17/ has has been indicated by a rectangular box bearing the symbol Z to indicate that the termination may comprise an impedance such as a resistor, capacitor or an inductor. For certain operating conditions the impedance Z may be infinite as in the case of an open circuit. Still another arrangement is illustrated in Figures 24 and 25 wherein a plurality of rings 31, 32, 33 and 34 support a plurality of folded elements 35 each arranged along a radius of the circular member 31. This forms what amounts to two concentric cylinders, one of which is a continuous cylinder while the other or outer cylinder has a slot therein.

Figures 20 and 21 illustrate antennas having a slot adjacent to two similar non-cylindrical defined surfaces. These surfaces could take other shapes, such as the ellipsoidal configuration of Figure 26. The constructional details set forth in connection with other embodiments herein described are applicable to an antenna such as that represented in Figure 26. In that antenna a change in dimensions in the major and minor axes affects the relative space phase of currents flowing throughout the antenna structure. The radiation pattern is modified to increase radiation in one plane and to decrease it in another plane. r

In place of a simple slot a folded slot might be em- । ployed which would have the appearance as shown in Figure 27. Here a structure similar to that shown in Figure is provided with a pair of additional rings 36 and 38 I in the planes of rings 13 and 12 respectively. These rings 36 and 38 each may be connected by a conductive member 37 to the rings 13 or 12 respectively. In certain embodiments the rings 36 and 38 also may be joined together by another conductive member 39 at a point diametrically opposite the conductive member 37.

A variation of the arrangement shown in Figure 27 is illustrated in Figure 28 where two rings 36 and 38 are replaced by two straight rods 40 and 41 attached directly to the rings 13 and 12. A conductive member 42 may join them in a manner similar to the conductive member 39. This provides an impedance of a different characteristic across the termination point of the rings 12 and 13. The open transmission line provided in this Figure 28 has no appreciable coupling to the remainder of the antenna, whereas the line produced by the two rings 36 and 38 of Figure 27 is coupled to the rings 13 and 12 to form a folded line. Thus it will be appreciated that the impedance appearing across the slot formed by the rings 12 and 13 might be varied by such auxiliary rings as the·

0,937,872 rings 36 and 38 and the open wire line 40, 41. It previously has been mentioned that the termination points could be placed at some other point than 180° from the feed point, and hence where other terminations, except the open circuit termination such as that illustrated diagrammatically in Figure 23 by 17/, are employed, they could be connected to the rings 12 and 13 at more than one point or a plurality of such elements might be employed at different points along the rings 12 and 13. Likewise the feed line 19 may be connected to several places on the rings 12 and 13 of Figure 1.

Figures 29 and 30 are top and side views of a structure similar to that shown in Figure 1 where each of the end rods 16 is provided with a capacity plate 43. This has the effect of lengthening the rods 16 electrically beyond their physical length. The ends of the rods 16 might be tied together by large capacitive members to produce an end capacity as may be desired.

In suggesting and describing certain variations contemplated by the showing of Figures 15 through 30 it will be appreciated that for different frequencies different solutions might be employed, particularly since it was contemplated that the frequency range which the antenna is to cover is more than one octave.

While for the purpose of illustrating and describing the present invention certain preferred embodiments have been shown in the drawings, it is to be understood that the invention is not to be limited thereby since such variations and other embodiments are contemplated as may be commensurate with the spirit and scope of the invention set forth in the accompanying claims.