US3181161A - Horizontally polarized log periodic antenna over ground - Google Patents

Description

A ril 27, 1965 v. P. MINERVA HORIZONTALLY POLARIZED LOG PERIODIC ANTENNA OVER GROUND 5 Sheets-Sheet 1 Filed June 9, 1961 INVENTOR.

VITO P. MINERVA ATTORNEYS April 1965 v. P. MINERVA 3,181,161

HORIZONTALLY POLARIZED LOG PERIODIC ANTENNA OVER GROUND Filed June 9, 1961 5 Sheets-Sheet? F/G' Z INVENTOR.

VITO P. MINERVA ATTORNEYS April 27, 1965 V. P- MINERVA HORIZONTALLY POLARIZED LOG PERIODIC ANTENNA OVER GROUND 5 Sheets-Sheet 5 Filed June 9, 1961 m QR INVENTOR.

VITO P. MINERVA M d V/W% April 27, 1965 v. P. MINERVA HORIZONTALLY POLARIZED LOG PERIODIC ANTENNA OVER GROUND 5 Sheets-Sheet 4 Filed June 9, 1961 02 mmm 02 www- 52,1. E H 231 J3EE;

INVENTOR VITO F. M/A/ERVA ATTORNEYS 1 1965 v. P. MINERVA 3,181,161

HORIZONTALLY POLARIZED LOG PERIODIC ANTENNA OVER GROUND Filed June 9, 1961 5 Sheets-Sheet 5 VERTICAL PLANE H PLANE ANTENNA {ILOCATION I400 MC VERTICAL PLANE 26 ELEVATION (H PLANE) I400 MC ANTENNA LOCATION P76 /2 F/G /3 INVENTOR. VITO R MINERVA 'IZ-IAYWM/ZZZZ;

A TTOR/VEYS United States Patent Iowa Filed June 9, 1961, Ser. No. 116,090 Claims. (Cl. 343-7925) This invention relates generally to logarithmic periodic antennas (herein also referred to as log periodic antennas) and, more particularly, to a log periodic antenna which may be positioned substantially vertically over ground to produce a frequency independent vertical plane radiation pattern.

A log periodic antenna element may be defined generally as an antenna element which consists of at least two radial sections; each radial section being generally triangular in shape and having a common conductive side (also referred to herein as a boom) and a common vertex. Transverse conductive elements extend outwardly from the common side and have their outer ends defined by an angle All of the transverse conductive elements of a given radial section lie in a single plane, although all the radial sections of a given antenna element do not necessarily lie in the same plane. The transverse conductive members which extend outwardly from the boom are commonly known as teeth and are spaced with respect to one another and with respect to the vertex in a log periodic arrangement. More specifically, in a given radial section a given point on a given tooth has a radial distance measured from the vertex which bears a ratio 1- to the radial distance from the vertex to the corresponding point on the next adjacent tooth farthest removed from said vertex.

Corresponding'teeth of two radial sections making up an antenna element, however, are not usually positioned directly opposite each other on the common boom member. More often the radial distance to a particular point on any given tooth in a first radial section will bear a ratio equal to the square root of 1- to the corresponding point on the tooth of a second radial section, said tooth of the Second radial section being the tooth next farthest removed from the common vertex. Worded more generally, it can be said that the teeth on opposite sides of an antenna element having two radial sections are positioned in an alternate manner; the teeth of one radial section being positioned opposite the gaps between the teeth of the other radial section.

For certain applications it is desirable to obtain a bidirectional radiation pattern which is substantially inde-.

pendent of changes of frequencies over rather broad band widths. One known way of doing this is to employ two log periodic antenna elements positioned end-to-end in a common plane, with their vertices lying close together and pointing at each other, and their common sides lying in a common straight line. This whole structure is mounted vertically with respect to the ground plane; that is to say, the booms of the antenna elements are positioned vertically with respect to ground. Up to now it has been found that satisfactory operation can be obtained with log periodic antenna structures only when non-image antenna elements are employed as the two elements of the system. To facilitate the understanding of the term nonimage elements, assume first'that the two antenna elements are positioned so that one element is an exact mirrored reflection of the other. Such a structure constitutes a pair of image antenna elements. As indicated above, such an image system has been found to produce results which are, not nearly as satisfactory as can be obtained with non-image antenna element configurations.

To transform a pair of image log periodic antenna elements into a pair of non-image antenna elements, one of the image antenna elements is simply rotated about its boom Now, if the two input leads carrying the signal to be transmitted are applied across the two antenna elements a bidirectional radiation pattern can be obtained. This bidirectional radiation pattern consists of two lobes extending outwardly from opposite sides of the plane in which the two antenna elements lie.

It is apparent that the above-mentioned prior art structure can present certain difiiculties in construction, particularly if lower frequencies are employed, since the length of the longest transverse conductive element of a radial section must be about one quarter wavelength of longest wavelength employed. Thus, with lower frequencies the resultant structure is quite large and must be built stronge enough to withstand wind, sleet, snow, and erosion. The resultant cost is quite high.

Since mirror image arrangements comprising two real antenna elements have been found to produce unsatisfactory results, it would seem to follow that the positioning of a single log periodic antenna element vertically with respect to the ground plane would not co-act with its reflected image to produce a substantially frequency independent bidirectional radiation pattern. Therefore, it would mark a definite improvement in the art toprovide a log periodic antenna element having a configuration which when placed over ground would cooperate with its mirror image to produce a bidirectional radiation pattern which would be substantially independent over large ranges of frequencies.

It is an object of the present invention to provide such a log periodic antenna configuration which will produce frequency independent bidirectional radiation patterns when positioned vertically over a ground plane.

Another purpose of the invention is to provide a relatively simple and inexpensive antenna system which will produce a bidirectional radiation pattern which is substantially independent over a large range of frequencies.

A third aim of the invention is to provide a log periodic antenna configuration which is capable of being fed against its mirror image to provide a bidirectional radiation pattern substantially independent of frequencies over a large bandwidth.

A fourth object of the invention'is the improvement of antenna systems, generally.

p In accordance with the invention there is provided an antenna element comprised of two radial sections having a common side and lying in the same plane. The common side, which is conductive, also forms a supporting boom for the structure and is mounted perpendicularly with respect to the ground plane so-that the vertex is just a small distance above the surface of the ground; such small distance being of the order of one quarter wavelength of the highest frequency of the operating bandwidth of the antenna. The two radial sections of the antenna system are comprised of a plurality of rod-like teeth which are spaced along the boom in accordance with the ratio 1 discussed above. The teeth of the two radial sections are spaced alternately so that the radial distance of the teeth of one radial secion as measured from the vertex, bears V a ratio equal to the square root of 1- to the radial distance of the corresponding teeth of the other radial section. A coaxial cable, or other suitable feed-in means, has one terminal connected to the vertex of the vertically positioned antenna and the other terminal connected to ground potential. The simple structure descnibed immediately above will function to produce a bidirectional radiation pattern which is substantially independent of changes in' frequency over large frequency ranges.

the general contour of a gable roof with the center line along the top of the gable passing directly under the vertex of the antenna and lying in the plane of the antenna ele ment. The purpose of such gable-like rise is to facilitate the reflection of radiation from the vertex of the antenna generally transverse to the plane of the antenna rather than directly back up and out the rear end of the antenna element, in which direction the energy would be largely unusuable.

The above-mentioned and other objects and features of the invention will be more fully understood from the following detailed description thereof when read in conjunction with the drawings in which:

FIG. 1 is a view of the invention as it might be actually employed;

FIG. 2 is a semi-schematic representation of the antenna showing its mirrored image;

FIG. 3, in the vertical plane, is a chart showing the radiation pattern of the structure of FIG. 2;

FIGS. 4 through 11 are charts showing the radiation pattern in the vertical and horizontal planes over a 'frequency range of about 263 megacycles of the structure of FIG. 1; and

FIGS. 12 and 13 show modifications of the invention. Referring now to FIG. 1, the antenna element is designated generally by the reference character 20 and is comprised of two radial sections designated by the reference characters 21 and 22. Each of the radial sections 21 and r 22 has a plurality of rod-like teeth, such as teeth 23, 24,

. Thus,

'Rn+1 R Similarly, the radial distance R' of the tooth 25 bears a ratio r to the radial R of the tooth 24. Thus,

In the embodiment of the invention shown in FIG. 1, the radial distance R to the radial distance R is equal to the square root of '1'. Similarly, the ratio of the radial distance R to the radial distance R' is equal to the square root of 1-. Thus,

The outer ends of the monopoles (teeth), such as monopoles 23, 24, 25, and 26, are defined by the angle a.

The entire antenna structure 20 is mounted over ground with the: boom 27 positioned vertically with respect to the ground plane 52. In the embodiment shown in FIG. 1 the ground is represented by the dotted section 30. It will be observed that ground immediately below the antenna is formed to create a small rise 54 which has its peak just below the vertex 28 of the antenna structure.

A conductive sheet 53, which may be copper screening, is placed over the ground below the antenna to provide a good electrical mirror. his to be understood, of course, that an image of the real antenna 21 is created by reflection below the surface of the ground. Such image is shown more clearly in FIG. 2 and the specific effects of such image will be discussed more fully. when the structure of FIG. 2 is discussed. A portion of such image ele ment is, however, shown in FIG. 1 and represented, generally, by the reference. character 32.

Energy issupplied to the antenna structure by suitable means, such as coaxial cable 33, which has its outer conductor 34 connected to the copper screen 53 and its inner conductor 35 connected to the conductive boom 27 of the real antenna element 20. 7

The antenna structure shown in FIG. 1 is physically supported by posts 37 and 38 which are mounted rigidly in the ground. Supporting tie lines or guy wires, such as wires 99, 39,, 40, and 41, are connected between the posts and insulators, such as insulators 42, 43, 44, and 45, which function to insulate the guy wires from the antenna element 20. Additional guy wires, such as guy wires 47 and 48, function to provide vertical support for the antenna element 20. Further, guy wires 47 and.48 have their upper ends secured to posts 37 and 38, respectively, at points 50 and 51 and are rigidly secured to all of the insulators, such as insulators 42 through 45, which exist at the end of each of the teeth. Other suitable guy wires, such as guy wires 97 and 98, may be employed to radiation pattern of the real and the image element. The

real element is represented, generally, by the reference character and'the reflected antenna element is represented, generally, by the reference character 61. It is to be understood that the radiation pattern 71 is not actually in the plane of the antenna (i.e., drawing) but is actually normal to the plane of the antenna. Energy is supplied to the systemby means of a coaxial cable 62, the outer conductor 63 thereof being connected to a grounded conductive sheeting 79, which may be copper screening. Such connecting of the outer conductor 63 is the electrical equivalent of being connected to the image antenna 61. The inner conductor 64 is connected to the real antenna 60. For purposes of simplicity, the sloping ground configuration 54, shown in the structure of FIG. 1 just below the apex of the real antenna 20, is omitted in the structure of FIG. ,2.

In FIG. 2 assume, for example, that a signal of the given frequency f is'being suppliedto the antenna 60. The apparent phase center of radiation of such signal will be from a point, such as point 67 on the boom 70, at

, which point the electrical length of 'a tooth is approxi- The function of this rise will be described in more detail later. For the present it would be noted that generally such use functions to provide sloping sides whereby the energy which is radiated off the'apex of the antenna element 20 is radiated generally outwardly, and transversely, I

to the plane of the antenna rather than being deflected directly back along the boom of the antenna and radiated out the rear end thereof.

mately one quarter wavelength of the signal being transmitted. It is to be understood that the phase center will move upward on the boom or downwards on the boom as the frequency of the signal decreases or increases sothat the electrical distance of the phase center from the vertex 66 of the antenna element will always beconstant. Since the vertex 66 is very close to the ground level (usually less than half a wavelength of, the highest operating frequency), assume that the distance h, which distance is measured from the phase center 67 to the surface of the ground, represents this constant electrical length from the phase center to the vertex 66 of the antenna element.

Since the electrical distances between ground and the phase centers on the real antenna and the reflected antenna is always equal to h, the phase relationship between the radiation from the real antenna to a point P and the radiation from the reflected antenna to the same point P willalways be constant regardless of a change in fre quency. The foregoing constant phase relationship will be more fully understood, perhaps, from a specific example Assume that the phase center of the signal being transmitted is at point 67 on the real antenna 60 and that at any given distant point P from the antenna, there will exist a radiated beam designated as ray 1 from the phase center 67 to the point P. This ray 1 will have an angle 0 with the horizon. Since P is a long ways from the antenna the ray 2, radiation from the phase center 68 of the image antenna, can be regarded as being parallel to ray 1. Thus, a line 69 can be drawn between rays 1 and 2 which is perpendicular to both. Such line 69 will make an angle 0 with the boom 70 of the real antenna 60. The distance I, which is equal to 2h sin 0 then represents the phase difference between ray 1 and ray 2 with respect to the point P. It is imporant to note that as the frequency changes, the phase centers 67 and 63 will both move towards vertices of the antenna elements. But the distance l and the distance of it, although changing in absolute dimensions, will not change in electrical distance. In other words, as far as point P is concerned the phase difference between ray 1 and ray 2 will remain constant over wide frequency changes. The foregoing statements may be modified to a rather small degree in that the movement of the phase centers 67 and 68 will change the angle 0 slightly. However, since P is considered to be a point at a considerable distance from the antenna, it is apparent that the movement of the phase centers 67 and 63 up and down will change the angle 0 only very minutely, and for practical considerations the angle 9 remains substantially constant. However, if the point P is changed, say to point P, then of course, the angle 6 will undergo an appreciable change and the phase relationship between ray 1 and ray 2 will change so that a different vectorial result will be obtained.

It is to be noted that for purposes of showing the foregoing example in the same drawing as the antenna, it has been necessary to rotate both ray 1 and ray 2, and also the radiation pattern 71, 90 with respect to the antenna 69. In actuality if the antennaoti is located as shown in the plane of the drawing, then the radiation pattern 71 A and the vertical plane would be into and out of the drawing. That is, normal to the plane of the drawing. Similarly, rays 1 and 2 would enter in or out of the drawing, rather than lying in the plane of the drawing.

In FIG. 4 there is shown a radiation pattern in the vertical plane which is obtained from the structure of FIG. 1. It will be noted that there is considerably less variation directly above the antenna element in FIG. 4, as compared to the radiation pattern of FIG. 3 which was obtained from a structure similar to that shown in FIG. 2. Such dilference in patterns is due to the fact that in the antenna shown in FIG. 1 there is the gable-like structure 54 immediately beneath the apex of the real antenna 20. The energy radiated off the end of the antenna 20 strikes the sloping sides of the gable structure and is reflected off at an angle generally transversely to the antenna rather than having a substantial portion reflected straight back up, and off the rear of the antenna as occurs in the case of the structure of FIG. 2; the radiation pattern of which is shown in FIG. 3.

In FIG. 5 there is shown the radiation pattern in the horizontal plane. It will be noticed that there are two lobes of radiation: on emanating from either side of the antenna element.

FIGS. 4 through 11 show vertical and horizontal radiation patterns of the antenna system of FIG. 1 as the frequency is changed over a bandwidth or" 263 megacycles. The constancy of the radiation pattern is evident from an inspection of the drawings.

Referring to FIGS. 12 and 13, there are shown two modifications of the invention. In FIGS. 1 and 2 the monopoles are shown as being normal to the boom. In FIGS. 12 and 13 the monopoles are shown as coming oil? at angles other than 90 from the boom. More specifi- 6 'cally,'in FIG. 12 the tooth 75 is connected-to the boom 76 at an angle K which is greater than 90. In FIG. 13 the tooth 77 is shown as being fastened to the boom 78 at an angle ,a which is less than 90. The antennas of FIGS. 12 and 13 each lie in a single plane and have their teeth spaced apart in accordance with ratio 1- in connec tion with the structure'of FIG. 1.

It is to be noted that the forms of the invention shown and described herein are but preferred embodiments thereof and that various changes may be made in the mechanical configuration without departing from the spirit or the scope of the invention.

I claim:

1. An antenna system comprising a log periodic antenna element generally triangular in shape and including a conductive boom and a plurality of rod-liketeeth extending outwardly from two sides of said' boom, the ends of said rod-like teeth on each side of'said boom being defined by an angle measured firom said boom, the radial distance from the apex of the triangular antenna element to any given tooth on one side of said boom bearing a constant ratio 'r to the radial distance of the next adjacent tooth farther removed from said apex and on the same side of said boom, the teeth on one side of said boom being positioned between the teeth on the other side of said boom, a substantially flat grounded conductive surface, said antenna element being positioned over said flat grounded conductive surface with the boom normal thereto and with said apex positioned above said grounded surface a distance less than one hal-f wavelength of the highest frequency in the operable bandwidth of said antenna system.

2. An antenna system in accordance with claim 1 in which the teeth on one side of said conductive boom are located at the geometric midpoint of the teeth on the other side of said conductive boom.

3. An antenna system in accordance with claim 2 comprising a gable-like rise in the portion of the fiat grounded conductive surface under said antenna element, the peak line of said gable passing under the apex of said antenna element and being substantially parallel with the plane of said antenna element.

4. Art antenna system in accordance with claim 3 comprising a coaxial line for supplying energy to said antenna system, said coaxial cable being positioned underground and comprising an outer conductor terminating at, and electrically connected to, said grounded conductive'surface, and further comprising an inner conduc tor electrically connected to the apex of said antenna element. 7

5. An antenna system in accordance with claim 1 in which said rod-like teeth are each normal to said conductive boom.

6. An antenna system in accordance with claim 5 in which the teeth on one side of said conductive boom are located at the geometric midpoint of the teeth on the other side of said conductive boom.

7. An antenna system comprising a log periodic antenna element generally triangular in shape and including a conductive boom and a plurality of wire-like teeth extending outwardly from either side of said boom and lying in a common plane, the ends of said wire-like teeth on each side of said boom being defined by the angle measured from said boom, the radial distance from the apex of the triangular antenna element to any given ther removed from said apex and on the same side of said boom, the teeth on one side of said boom being positioned between the teeth on the other side of said boom, a substantiallyflat grounded conductive surface, said antenna element being positioned over said flat grounded conductive surface with the boom substantially normal thereto and with said apex positioned above said grounded surface a distance less than one-half wavelength of the highest frequency in the operable bandwidth of said antenna system, a pair of rigidly supported posts positioned on either side of said antenna element, a plurality of tie wires secured to said posts, means for coupling the ends of said wire-like teeth to said tie wires to support said antenna element.

8. An antenna system in accordance with claim 7 in which the teeth on one side of said conductive boom are located at the geometric midpoint of the teeth on the other side of said conductive boom.

9. An antenna system in accordance'with claim 8 comprising a gable-like rise in the fiat grounded conductive 8 surface under said antenna element, the peak line of said gable passing under the apex of said antenna element and being substantially parallel with the plane of said antenna element.

10. An antenna system inaccordance with c1aim 9 comprising a coaxial line for supplying energy to said antenna system, said coaxial cable being positioned underground and comprising an outer conductor terminating at and connected to saidgrounded conductive surface and further comprising an inner conductor electrically connected to the apex of said antenna element. 7

References Cited by the Examiner UNITED STATES PATENTS 3/61 Du Hamelet al 343-908 4/61 Wickersham et a1. 343908

Claims (1)

1. AN ANTENNA SYSTEM COMPRISING A LOG PERIODIC ANTENNA ELEMENT GENERALLY TRIANGULAR IN SHAPE AND INCLUDING A CONDUCTIVE BOOM AND A PLURALITY OF ROD-LIKE TEETH EXTENDING OUTWARDLY FROM TWO SIDES OF SAID BOOM, THE ENDS OF SAID ROD-LIKE TEETH ON EACH SIDE OF SAID BOOM BEING DEFINED BY AN ANGLE

Images