US3212094A

US3212094A - Vertically polarized unidirectional log periodic antenna over ground

Info

Publication number: US3212094A
Application number: US113700A
Authority: US
Inventors: David G Berry
Original assignee: Collins Radio Co
Current assignee: Collins Radio Co
Priority date: 1961-05-31
Filing date: 1961-05-31
Publication date: 1965-10-12
Anticipated expiration: 1982-10-12

Description

Oct. 12, 1965 D. G. BERRY VERTICALLY POLARIZED UNIDIRECTIONAL LOG PERIODIC ANTENNA OVER GROUND 11 Sheets-Sheet 1 Filed May 31, 1961 IN V EN TOR.

DAV/D 6. BER Y A T TORNE Y6 Oct. 12, 1965 ARI ZED UNIDIREGTIONAL VERTICA LOG- PE ODIC ANTENNA OVER GROUND Filed May 31. 1961 SEE FIG I FOR DEFINITION OF ANGLES 6 AND 4 11 Sheets-Sheet 2 H-PLANE (O= 90) IN V EN TOR.

0.4 W0 6'. BE RIP I Oct. 12, 1965 D. G. BERRY VERTIGALLY POLARIZED UNIDIRECTIO NAL LOG PERIODIC ANTENNA OVER GROUND ll Sheets-Sheet 5 Filed May 51: 1961 H- PLANE (9=90) E-PLANE P=O) H-PLANE (9 =90) H-PLANE 7O 8O 9O 4O 50 O IN DEGREES PERFECT GROUND IN V EN TOR.

A 7' TORNE Y5 Oct. 12, 1965 D. G. BERRY VERTICALLY POLARIZED UNIDIRECTIONAL LOG PERIODIC ANTENNA OVER GROUND ll Sheets-Sheet 4 Filed May 31, 1961 TRAPEZOIDAL TOOTH WIRE LOG PERIODIC ELEMENT m m C mA m R 0 mp m G 0 mm IN DEGREES o 6 2 w 2 O 2 2 9% IN OHMS INVENTOR.

W0 6. BE 7 ATTORNEYS Oct. 12, 1965 D. G. BERRY VERTIGALLY POLARIZED UNIDIRECTIONAL LOG PERIODIC ANTENNA OVER GROUND ll Sheets-Sheet 5 Filed May 31, 1961 /Z =l.995 u/g =22 O80 I00 I I I I 200 220 240 260 30 IN OHMS IN OHMS IN VEN TOR.

Oct. 12, 1965 D. G. BERRY 3,212,094

VERTICALLY POLARIZED UNIDIRECTIONAL LOG PERIODIC ANTENNA OVER GROUND Filed May 31. 1961 ll Sheets-Sheet 6 IN VEN TOR.

0.4 V/D 6. BER)? Y ATTORNEYS Oct. 12, 1965 D. G. BERRY 3,212,094

VERTICALLY POLARIZED UNIDIRECTIONAL LOG PERIODIC ANTENNA OVER GROUND Filed May 31. 1961 ll Sheets-Sheet 7 [M F/G l5 IN VEN TOR.

DA W0 6. BERRY Evy ATTORNEYS Oct. 12, 1965 D. G. BERRY 3,212,094

VERTICALLY POLARIZED UNIDIRECTIONAL LOG PERIODIC ANTENNA OVER GROUND Filed May 31, 1961 ll Sheets-Sheet 8 INVENTOR.

DAV/0 6. BERRY A T TORNE Y5 11 Sheets-Sheet 9 D. G. BERRY VERTICALLY POLARIZED UNIDIRECTIONAL LOG PERIODIC ANTENNA OVER GROUND 2 EN LT OS l hmm O T o C M 0 R WM AC 0 M O X X Oct. 12, 1965 Filed May 51, 1961 INVENTOR.

DAV/D G. BERRY ATTORNEYS Oct. 12, 19.65 D. G. BERRY 3,212,094

VERTICALLY POLARIZED UNIDIRECTIONAL LOG PERIODIC ANTENNA OVER GROUND Filed May 31, 1961 11 Sheets-Sheet 10 INVENTOR.

DAV/D 6. BERRY BYWW 4;

l1 TTOR/VEYS Oct. 12, 1965 D. G. BERRY VERTICALLY POLARIZED UNIDIRECTIONAL LOG PERIODIC ANTENNA OVER GROUND l1 Sheets-Sheet 11 Filed May 51, 1961 155; A 5; my 12 G K 6 5% 251% 5 HM INVENTOR.

DAV/D 6. BERRY M I f United States Patent Iowa Filed May 31, 1961, Ser. No. 113,700 30 Claims. (Cl. 343-749) This invention relates generally to logarithmic periodic antenna arrays and, more particularly, to logarithmic periodic antenna arrays in which one or more logarithmic periodic antenna elements are placed over a reflecting surface, such as ground, and the real antenna elements are fed against the reflected image elements, thus effecting a reduction in the number of actual antenna elements required in a given array.

Logarithmic periodic antennas, hereinafter sometimes referred to as log periodic antennas, are a recent development in the antenna art. Perhaps the most important feature of the log periodic antennas lies in their ability to maintain a constant radiation pattern over large frequency changes on the order of or 20 to 1, or even greater. Such antenna systems (log periodic antenna systems) may be described generally as consisting of a plurality of individual antenna elements, each antenna element being generally triangular in shape, having a vertex, and being confined within an angle at extending from a vertex. A boom of conductive material is positioned along the bisector of the angle a and functions to supply electrical signals to the antenna elements, as well as to support said elements. Each antenna element is comprised of at least two radial sections, each section being generally triangular in shape with a common vertex and a common side, said common side being the boom referred to above. The outer side of each triangularly shaped radial section is defined by a radial line extending from the vertex at an angle a/2 formed with respect to said center line or boom of the antenna element. Further, each radial section has a plurality of teeth comprised of elements which are positioned in a generally transverse manner with respect to the center line of the antenna element. Such teeth are all similar to one another in shape, but become progressively larger and spaced progressively farther apart as the distance from the common vertex increases. The above-mentioned size and spacing relationships may be expressed by stating that in a given radial section the radial distance from the vertex to a given point on any given tooth bears a constant ratio 7 to the radial distance to a corresponding point in the adjacent tooth next farthest removed from the vertex than said given tooth. In the most general case, where each antenna element employs two radial sections lying in the same plane, the teeth of one of the radial sections are positioned opposite the gaps between the teeth of the other radial section. It is to be noted that throughout this specification a single tooth of an antenna radial section will sometimes be referred to as a monopole.

The log periodic antenna elements described in the preceding paragraphs may be arranged in many different combinations to perform desired functions. Usually, the antenna elements are employed in multiples of two, i.e., in pairs. For example, a pair of log periodic antenna elements may be arranged in such a manner that the vertices are near each other (but not quite touching), and which lie in the same plane. Such an arrangement is known in the art as a planar array "of log periodic antenna elements. For a more detailed description of such structure, the readers attention is directed to the following Patent Applications which are hereby incorporated by reference into the present specification: United States patent application, Serial No. 721,408, filed March 14, 1958, by Raymond H. DuHamel and Fred R. Ore and entitled Logarithmically Periodic Antenna, now Patent No. 3,079,602; United States patent application, Serial No. 804,357, filed April 6, 1959, by Raymond H. DuHamel and David G. Berry, entitled Unidirectional Frequency Independent Coplanar Antenna, now Patent No. 2,989,- 749; United States patent application, Serial No. 841,391, filed September 21, 1959, by Raymond H. DuHamel et a1., entitled Antenna Arrays, now Patent No. 3,059,234; United States patent application, Serial No. 841,400, filed September 21, 1959, by Raymond H. DuHamel et al., entitled Broadside Antenna Arrays, now Patent No. 2,984,835; United States patent application, Serial No. 31,068, filed May 23, 1960, by David G. Berry, entitled Unidirectional Circularly Polarized Antenna, now Patent No. 3,113,316.

It has been found that the cost of construction of the antenna arrays described in the preceding paragraphs, and in the applications incorporated herein by reference,- has been quite high, especially in the lower frequency bandwidths. Such high cost is due primarily to the fact that the log periodic antenna arrays require a number of large antenna elements which are mounted in the air, usually many feet above the ground, on large masts. Structural difliculties are encountered in that the antenna elements usually consist of rather long dipole elements mounted on suitable booms. In the presence of wind or sleet the dipole elements function as cantilever levers and provide rather serious stresses and strains at the point of connection to the boom elements. Because of these problems the cost of the arrays is quite high.

One method that has been employed to simplify a log periodic antenna array has been to mount an antenna element over a reflecting surface, such as ground, with the vertex located near the reflecting surface and the remainder of the antenna element being slanted upwards. The radial antenna element is then fed against the image element produced in the reflecting surface. Such an arrangement obviously eliminates one-half of the antenna elements required and can be used to form either coplanar arrays, nonplanar arrays, or combination coplanar and nonplanar arrays with each antenna element of the array being fed against its image produced in the reflecting surface. A serious problem from the viewpoint of cost still remains, however. More specifically, this problem lies in the fact that the rear of the individual antenna elements, which is the heavy portion of the antenna elements (since the radiation occurs off the vertex which is regarded as the front of the elements), must be supported well above the ground surface. Such support again involves large supporting masts to support the booms of the individual antenna elements and also involves the cantilever action of the dipole elements on their supporting booms, as discussed hereinbefore, in the presence of wind or ice.

It is an object of the invention to provide a log periodic antenna array in which no supporting mast is required and in which the cantilever action of the individual monopole or dipole elements is minimized.

A further object of the invention is to provide a log periodic antenna array which is relatively inexpensive.

Another aim of the invention is the improvement of log periodic arrays, generally.

In accordance with a preferred form of the invention a single antenna element having two radial sections mounted at right angles to each other on the boom thereof is positioned so that the boom is parallel with, and just a small distance above, a reflective surface, such as the surface of the earth. The monopoles making up one of the radial sections are positioned vertically with respect to the reflective surface and function as the radiating section to produce a vertically polarized electric field. The monopoles forming the second radial section are positioned parallel with respect to the ground surface and, because of their cooperation with their images produced in the reflecting surfaces, will function as sections of transmission lines instead of radiating elements. More specifically, the monopoles forming the second radial section will function as loading elements along the boom; said loading being a necessary requisite to radiation from the vertically positioned monopoles. It should perhaps be noted at this point that the current flow in the individual monopole elements positioned parallel to the reflecting surface is of opposite plurality to the current flow in its image monopole element produced in the reflecting surface. Since these two currents are in opposite directions, the radiating effect of each is concelled out by the radiating effect on the other.

In another form of the invention the stubs may be replaced by other structures which will perform the same loading function. More specifically, such other structure may take the form of a resonator which consists of a helical winding enclosed within a cylinder; one end of the helical winding being connected to the boom at the geometric mean between the two adjacent vertical monopoles with the outer end of said winding floating and with the cylinder being connected to the ground surface. Such a resonator is constructed to resonate at the same resonant frequency as the stub it replaced.

In another form of the invention the stubs are replaced with a loading means comprised of an inductor and a capacitor connected in a series between ground potential and the geometric mean point of the boom between the two adjacent vertical monopole elements.

In accordance with another embodiment of the invention the boom of the antenna element can be a coaxial type structure with the vertical positioned monopoles being connected to the inner conductor of the coaxial structure through holes drilled in the outer conductor of the coaxial type structure. Appropriate means are provided to insulate the vertically positioned monopoles from said outer conductor. In this form of the invention the stubs arereplaced by another coaxial type structure which has its inner conductor connected to the inner conductor of the boom and its outer conductor connected to the outer conductor of the boom.

In accordance with other features of the invention the various types of antenna radial sections maybe employed. More specifically, there may be employed radial sections having vertical teeth formed of single rods, solid rectangularly shaped teeth comprised of sheets of metal, rectangularly shaped teeth formed of rods bent to form said rectangularly shaped teeth, and triangularly shaped teeth formed of a rod bent to fashion the triangularly shaped teeth.

T he 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 perspective view showing one form of the invention;

- FIGS. 1a and lb show blown-up views of the small segments of the main boom and a horizontally positioned monopole;

FIGS. 2 through 6a show radiation patterns in the H and E plane of the structure of FIG. 1 for various parameters thereof;

FIG. 7 is a curve showing variation in the E and H plane as functions of c and r;

, FIG. 8 is a graph showing the variations of the phase center of the structure of FIG. 1 as a function of 0c and the variations of the phase center of log periodic antenna element having wire-formed trapezoidal teeth;

FIGS. 9, 10, and 11 are charts showing the variations of the over-all antenna impedance as functions of various parameters of the structure;

FIGS. 12, 13, 14, 15, and 16 show various forms of the invention;

FIGS. 17, 18, 19, and 20 show modifications of the invention wherein other impedances are substituted for the transmission stubs shown in prior figures;

FIG. 21 shows an impedance chart;

FIG. 22 shows a pictorial representation of an embodiment of the invention; and

FIG. 23 is a chart showing the variation in standing wave ratio with frequency of the structure of FIG. 22.-

Referring now to FIG. 1, there is shown an antenna element which consists of a boom 30, a radial element 29 including radiating monopoles 31, and a set of stubs 32 which with their images 33 form sections of transmission lines. The entire structure shown in FIG. 1 is positioned a short distance above a reflecting surface 106, which can be a copper screen laid on the surface of the ground 107. The exact distance that the boom 30 is placed above ground is determined by several factors which will be discussed in more detail hereinafter. At this time it is perhaps suflicient to say that the characteristic impedance z of the stub is the important factor and is in part controlled by the spacing of the boom from ground. As shown in dotted lines in FIG. 1, there is a mirrored image of the antenna element 29 reflected in the ground reflecting surface 36. From an examination of the figure it will be seen that the real vertical monopoles 31 and the reflected vertical monopoles 35 function to produce a radiated electromagnetic field, whereas the real stubs 32 and the reflected stubs 33 function to cancel out any radiating effects on each other they might have had. Consider the function of the vertical monopoles 31 and their images 35 in detail. The current flow at any given time in a given vertical monopole 31 and its reflected monopole will be in the same directions. Such similarly phased currents will function to produce a single beam radiation pattern on the E plane, that is the vertical plane, off the apex 36 of the antenna structure. For the purposes of illustration, the instantaneous current flow in monopole 113 and the reflected monopole 37 is represented by arrows drawn on the monopoles.

The reflected instantaneous currents in the real stubs 32 and the reflected stubs '33 flow in opposite directions. However, since any real stub and its reflected image are positioned close together, side by side, and parallel with respect to each other, the radiation effects from each of the two elements function to cancel the radiation effects of the other.

The stubs 32 and the reflected image 33 thus become short sections of transmission line, each of which present an impedance to the transmission line formed by the boom 30 and its image, as follows:

jz Cot Bl 1 where 2 is the characteristic impedance of the stubs and where l is the length in wavelengths of a particular stub. The stubs are located at the geometric mean between the vertical monopoles, and the lengths of the stubs are such that their first resonance occurs at a frequency which has a ratio r to the resonant frequency of the adjacent nearest vertical monopole next farthest removed from the vertex. As will be discussed later herein, the stubs may be replaced by lumped constant loading means. The entire array is fed by means of an underground coaxial cable 108 (see FIG. 1a) comprised of an outer conductor 109 connected to the copper screening 106 and an inner conductor 110 connected to the boom 30'. A generator (not shown) supplies its output to the coaxial cable 108.

In FIG. la there is shown also a view of the relationship of the boom to ground. The boom 30 is supported on a suitable support means 37 which is of an insulative material and which provides the desired physical spacing of the boom 30 from the reflecting surface 106. The characteristic impedance Z of the boom 30 is determined in conventional manner by the diameter of the boom 30' and its physical distance from ground (surface 106'). It is to be noted that the blown-up view of FIG. la is taken at the front end of the antenna structure, that is, at the vertex 36.

In FIG. 1b there is shown a blown-up view of an end of one of the stubs and its relationship to the copper sheet 106". A spacing and supporting means 40 is employed to space the stub 41 a desired distance from surface 106". The diameter of the stub 41 and its physical spacing from the ground 38 determines its characteristic impedance 2 Such characteristic imped-ances Z and 2 are impedances which are independent of frequency. In the case of a stub the particular impedance presented to the boom at a given frequency is given by Expression 1 as set forth hereinbefore.

At this point it is, perhaps, appropriate to note the impedance for the entire antenna structure, such impedance being defined by the Expression 2 below:

Z (monopole array) Where Z is the input characteristic impedance of the entire array Z, is the characteristic impedance of the stubs Z is the characteristic impedance of the transmission line (the boom) Z is the average characteristic impedance of a monopole and is approximately equal to apng yl h is the monopole height a is the monopole radius In Expression 2 the second term of the denominator is the contribution of the vertical monopoles 31 to the overall input characteristic impedance.

The third term of the denominator of Expression 2 1/ 1' tan g Z0 represents the contribution of the stubs to the over-all input characteristic impedance of the array. By examination of Expression 2 it can be seen how the characteristic impedance of the entire antenna array Z differs from the charatceristic impedance of the boom 30. More specifically, if the impedance of the monopoles ZOGW) and the impedance of the stubs were to go to infinity, then the second and third term of the denominator would go to zero and drop out, leaving the following expression:

mo o which, of course, states that if the impedance of stubs and monopoles are removed from the structure, the remaining impedance is equal to Z the characteristic impedance of the boom.

The operation or performance of the antenna array shown in FIG. 1 can best be described in qualitative manner inasmuch as the precise theory of the operation of such antenna is, at present, not thoroughly understood. Assume that a signal having a frequency near the midband of operation is supplied to the vertex of the antenna between ground potential and the boom 30 by coaxial cable (FIG. la) and launches a balanced TEM mode on the line which is loaded alternately with the shunt admittances of the stubs and the monopoles. Near the vertex of the structure the resonant frequency of the stubs Will be considerably greater than the frequency of the generator so that the shunt admittances presented by the monopoles and stubs will be quite small and quite re active. Consequently, the shunt admittances in this region will have comparatively little effect upon the transmission mode which will then travel along the boom with a velocity just a little less than that of light. As the transmission mode progresses further down the antenna boom the increasing admittances will affect it in an increasingly greater degree. Such phenomena will continue until a point on the antenna structure is reached at which one of the stubs is close to resonance and has a very large admittance with respect to the transmission line (boom) impedance characteristcs. Such large admittance will occur when the term Bl approaches in the Expression 1. At this point almost all of the supplied energy will be either radiated or reflected back towards the generator and only a small amount of the energy (down roughly 30 or 40 db) will progress past this point. Consequently, the portion of the antenna beyond such point of resonance is of small consequence; i.e., at this particular frequency of operation.

As stated hereinbefore, the currents produced in the vertical monopoles cause radiation. The function of the open-circuitedstubs is to adjust the phase and the amplitude of the currents of the vertical monopoles to produce a unidirectional radiation pattern. The log periodic arrangement of stubs and monopoles allows the radiation pattern (as well as the other characteristics of the antenna) to be substantially frequency independent. It is to be noted, again, at this point that it is not completely understood how the monopoles and the stubs co-act to produce the necessary phase relationships in the currents in the vertical monopoles to produce a unidirectional radiating field.

In FIGS. 2 through 6a there are shown the radiation patterns of the antenna element of FIG. 1 as a function of the angle a with a fixed 7'. The angle 0 represents the angle of elevation, measured from a vertical line, at which the pattern was sampled and the angle represents the azimuth, measured from the line along which the boom lies, at which the pattern was sampled. It can be seen that the radiation in the E plane is substantially constant over a rather wide range of at angle values, but that the radiation pattern in the H plane increases substantially as the at angle increases.

In the chart of FIG. 7 there is shown graphically the half-power beam width formation as a function of both or and 1-. Although only one pattern is shown for each set of parameters, patterns at all frequencies in the bandwidth of the antenna will be substantially identical.

As indicated hereinbefore and as discussed in some detail, in United States patent applicaton, Serial No. 841,391, mentioned above, a number of antenna elements, such as the one shown in FIG. 1, may be arrayed together with a common vertex to form a more complex and versatile antenna system. Since such antenna elements would extend out radially from a common vertex, it is apparent that the phase centers of each of the antenna elements will not fall along a straight line if each of the antenna elements is identical in structure. The phase center is defined as that point in the antenna from which the radiated signal appears to radiate. Such phase center will vary with frequency. As described in the copending application, Serial No. 841,391, the various antenna elements may be stretched or shrunk to produce phase shifts in the radiated signal so that for any given frequency the phases of the signals radiated from each of the antenna elements are coincident along a straight line, thus providing for a plane wave front of maximum intensity, since the vectorial sum of all of the radiated signals will be maximum under these conditions.

It should perhaps be noted, in passing, that the phase center at a given frequency does not usually coincide with the frequency represented by the length of the monopole at the phase center. In FIG. 8 there is shown in chart form the distance from the vertex 36 to the phase center in wavelengths as a function of the angle a/Z. As might be expected, the distance in wavelengths will decrease markedly as oz/ 2 increases. The impedance of the antenna structure of FIG. 1 will now be discussed in some detail. The over-all antenna impedance can, perhaps, be best described by first determining the characteristic impedance of an antenna structure having specific parameters of Z0, z /Z, 1- and Then the standing-wave ratio with respect to such characteristic impedance can be determined.

Over a period of frequency the impedance, as plotted on the Smith chart of FIG. 21, progresses in a circular or elliptical path along the point around the real axis of abscissa. The characteristic impedance of the antenna is defined as the geometric mean of the highest (the point 45) and the lowest (the point 46) values of resistance intersected on this path during the period (and, of course, every other period). The standing-wave ratio is defined as a ratio of the maximum value of resistance at point 45 to the characteristic impedance. In FIGS. 9 through 11, (the lower group of curves in each figure), there is shown graphically the values of the characteristic impedance and the standing-wave ratio as a function of the parameters z z /Z a and 7. From the curves of FIGS. 9, 10, and 11, it can be seen that a fairly large variation of characteristic impedance can be achieved with a quite good standing-wave ratio for a given value of u and 'r. The use of a and 'r as criteria of good performance is important because oz and 1- are the two principal factors determinative of the shape of the antenna element and the number of monopoles required per unit length of the antenna. For example, in FIG. 9 assume that it is desired to have an antenna characteristic impedance of 50 ohms. Now, if the antenna is constructed so that the ratio of z /Z is 1.26, it can be seen as such and that the curve representing such ratio will cross the 50-ohm antenna characteristic impedance level at point 47. Worded in another way, the foregoing sentence means that as the diameter of the stubs and their spacing from ground is varied so as to vary Z and as the diameter of the boom and its spacing from ground is varied so as to vary Z but in a manner such that z /Z is always equal to 1.26, then the over-all characteristic impedance of the antenna will be 50 ohms when 2 is 140 ohms. It should, perhaps, be noted that the data for the charts of FIG. 9, and also of FIGS. and 11, was obtained by conducting field tests on antennas having various sized stub diameters and boom diameters and processing such data to create the curve shown in FIGS. 9 to 11.

Referring now to the group of curves at the top of FIG. 9, and selecting the curve where the z /Z ratio is 1.26, it can be seen that the standing-wave ratio is about 1.8, as shown at point 48. The standing-wave ratio can be improved, however, by selecting a z /Z ratio of 1.995 which crosses the 50-ohm level at point 49 in the lower group of curves of FIG. 9. In the upper group of curves the standing-wave ratio can be seen to be about 1.45 at point 50, which is a considerable improvement compared to the standing-wave ratio obtained with a z /Z ratio In FIG. 10 there is shown the variation obtained in antenna characteristic impedance when the ratio z /Z and ot are held constant and 1- is varied. It can be seen that as a general rule the larger 1- is, the lower the standing-wave ratio will be.

In FIG. 11 there is shown the variation of standing- .wave ratio and antenna characteristic impedance when .the ratio z /Z and T are held constant and when the '8 angle a. is varied. It can be seen that as a grows smaller the standing-wave ratio decreases somewhat.

It might facilitate an understanding of the charts of FIGS. 9, l0 and 11 to describe briefly some of the dimculties and techniques involved in securing a low standing-wave ratio at the input terminals of the antenna. As indicated hereinbefore, the actual length of both the stubs and the monopoles will vary somewhat from their electrical lengths. If the exact relationship between the electric lengths and the physical length of both the vertical monopoles and the stubs were known it would be possible to have angle a/ 2 for both the monopoles and the stubs of such a value that the comparative electrical lengths of the two would always be in accordance with the geometric constant 'T'. It is also to be noted that while the angle 06/2 is used both with respect to the monopoles and the stubs, that in actual practice these two angles might be somewhat different due to the fact that the ratio of the electrical length to physical length will not be quite the same for both the stubs and the monopoles. As a practical matter, the relationship between the electrical length and the actual length of the stubs can be quite accurately determined by analysis. However, electrical length of the monopoles cannot be so easily determined. To overcome this problem the following scheme was devised to determine experimentally the proper value of oz associated with the stubs for a given on associated with the monopoles. This was done by constructing the antenna so that the or associated with the stubs was equal to the a associated with the monopoles. Then the on of the stubs was reduced until a standing-wave ratio at the input terminals of the antenna was reduced to the minimum value. By this method the antenna array was made as nearly frequency independent as possible and test data obtained for the curves of FIGS. 9, 10, and 11 was felt to be quite accurate.

In FIGS. 12 through 17 there are shown various modifications of the structure shown in FIG. 1. In FIG. 12 the ends of adjacent pairs of the monopoles and the stubs are joined together by conductive elements. For example, the monopoles and 51 are joined together by transverse element 52. The principal advantage of this modification is one of mechanics. For example, if the monopoles and stubs are formed of rods, the rods can be bent to form the trapezoidal-shaped teeth, as shown in FIG. 2, which will have a degree of mechanical strength substantially greater than the individual monopoles.

The structure of FIG. 13 shows an antenna array employing solid teeth. Such solid teeth might be employed advantageously in circumstances where the antenna would be supported upon a wall, for example.

In FIG. 14 there is shown an antenna array employing triangularly shaped teeth. The principal advantage of this type of an array is greater structural strength, particularly where stiff rods are used to form the individual teeth. The stubs, such as and 61, are also shown as being triangular in shape. Such triangular shape, however, for the stubs is primarily a matter of design and they could be straight rods, such as shown in the structure of FIG. 15, positioned at the geometric mean between adjacent ones of said triangular teeth, with an electrical length equal to the geometric mean of the electrical length of the adjacent teeth.

In FIG. 15 there is shown a structure which is very similar to the structure shown in FIG. 1. However, in FIG. 16 some of the monopoles are of a zigzag configuration which produces an effective lengthening of the electrical length of the vertical monopoles. More specifically, the zigzagging functions to introduce shunt capacitance along the monopole, which is represented generally by the

broken line capacitors

62 and 63, which are in reality stray capacitances and not component capacitors. Normally, a dipole element will present a capacitive reaction to a signal having a frequency less than the resonant frequency of the dipole element. Thus, if

the capacitive reactance of the transverse dipole element can be reduced, the resonant frequency of the transverse dipole element will also be decreased. Since capacitive reactance is inversely proportioned to capacitance and since capacitances are added in parallel, it follows that the capacitive reactance of a transverse dipole element and thus the frequency of resonance will be decreased if shunt capacitance is created across the transverse dipole element. As indicated above, such shunt capacitance is created by the zigzag configuration of FIG. 15. In summary, such shunt capacitance will increase the apparent electrical length of monopole elements of FIG. 15, thus extending the lower frequency element of the lower antenna element without increasing the over-all size of the antenna element. For a more detailed discussion of the operational and constructural characteristics of the zigzag type monopole reference is made to United States patent application, Serial No. 63,372, filed October 18, 1960, entitled Antenna by Vito P. Minerva, now Patent No. 3,106,714.

Referring now to FIG. 16, there is shown another form of antenna element in which shunt capacitance is added to increase the electrical length of the individual monopoles. Specifically, the shunt capacitance is added by means of members, such as members 111 and 112, which are positioned generally transverse to the main portion of the monopole. The length of each of these transverse elements, such as 111 and 112, bear a ratio 7 to the length of the element on the tooth-like element next farthest removed from the vertex. Thus, the length of element 112 bears the ratio -r to the length of element 111. For a more detailed discussion of the theory of operation of such transverse elements reference is herein made to United States patent application, Serial No. 63,299, filed October 18, 1960, by Raymond H. DuHamel et al. and entitled Side Loaded Logarithmically Periodic Antenna, now Patent No. 3,127,611. The specific advantage of the structure of FIG. 16 is one of construction. With the structure of FIG. 16 it is possible to construct an antenna array somewhat in the manner shown in FIG. 22. It is apparent that the structure of FIG. offers considerably more practical difliculty than that of FIG. 16, particularly when the type of supporting structure employed is that shown in FIG. 22.

As mentioned hereinbefore, the stubs may be replaced by lumped constant means of loading. There are several types of substitute loading means which may be employed in lieu of the stubs. For example, in FIG. 17 there is employed a series of

resonators

68, 69, and 70, each of which may be placed at the geometric mean be tween the adjacent monopoles and each of which has a rsonant frequency having an electrical length equal to the electrical length, multiplied by 1 and at the same frequency, of the adjacent monopole next farthest removed from the apex. The foregoing sentences will, perhaps, be more clearly understood from the following example. As discussed hereinbefore, the electrical lengths of the

dipoles

70 and 71 are somewhat different from their physical lengths. The radial distance R of the monopole 71 bears a ratio 1- to the radial distance R, of the monopole 70. Thus, the geometric mean between the

monopoles

70 and 71 is equal to T times the radial distance R The electrical length of a monopole existing at this geometric mean (no such monopole is actually shown in FIG. 17), would be 7 times the electrical length of the monopole 70. The electrical length of such a hypothetical monopole represents a quarter wavelength of a particular frequency. The resonator 68, which is shown in more detail in FIG. 18, has a resonant frequency equal to the aforementioned particular frequency. Similarly, the resonant frequency of the resonator 69 corresponds to the resonant frequency of a monopole located 'at the geometric mean between

monopoles

71 and 72. The structure of the resonator is Well-known in the art and will not be described herein. It should be suflicient to point out that the resonator 68' of FIG. 18 is comprised of a helix 75 of a conductive material having its upper end connected to the boom 73, also of conductive material, and having its lower end floating free. Positioned around the helix 75 is a cylinder 74, also of a conductive material, and being connected to ground potential. The particular resonant frequency of a given resonator is determined by the physical parameters of the helix and the cylinder in a manner well-known in the art.

In FIG. 19 there is shown an alternative means for providing loading along the boom 73", such alternative means consists of an inductor 76 and a capacitor 77, which form a series circuit having a resonance equal to the resonant frequency of a hypothetical monopole located at the geometric means between the adjacent monopoles. The principal advantage of the structure of FIG. 19 over that of FIG. 18 is lower cost. However, this advantage only exists at relatively small power levels. If higher power outputs are desired the cost of the capacitor becomes very large inasmuch as it must be an air capacitor in order to withstand the high power levels. The structure of FIG. 18, on the other hand, is readily adapted to handle large power requirements.

Referring now to the structure of FIG. 20, there is shown a third means which can be employed as a substitute for the stubs of FIG. 1, for example. The structure of FIG. 20 comprises a boom 78 which corresponds to the boom 73 of FIG. 17. The boom 78 of FIG. 20, however, is different from the boom of FIG. 17 in that boom 78 is really a large coaxial type structure comprising an inner conductor 79 and an outer conductor 80. The individual vertical monopoles, such as 70' and 71 are electrically connected to the inner conductor 79 through apertures provided therefor in the outer conductor 80. Insulating spacing means, such as

spacers

81 and 82, are provided to electrically insulate the monopoles, such as 70' and 71' from the outer conductor of the boom 78'. The loading means consists of another coaxial type arrangement 83 which comprises an outer conductor 84 and an inner conductor 85. The inner conductor 85 is connected to the inner conductor 79 of the boom 78 and the outer conductor 84 is connected to the outer conductor 80 of the boom 78. The

outer conductors

80 and 84 of the boom and of the loading stub 83 are grounded. More specifically, the boom 78 is layed upon a conductive ground reflecting surface in such a manner that the stubs, such as stub 83, extend outwardly and parallel to said ground surface. An image of the structure will then exist in reflective ground surface and the input signal is applied across the input conductor 79 of the boom 78 and ground potential in a suitable manner, similar to that shown in FIG. la.

Referring now to FIG. 22, there is shown a view of an actual construction of an antenna, as shown in FIGS. 18-20. A supporting cable 86 is supported between pole 87 and tower 88.

Guy wires

89, 90, 91, 92, 93, 94, 95, and 96 support the pole 87 and the tower 88. The individual monopole elements are supported from the tie wires, such as

tie wires

98, 99, and 100, which in turn are supported from the main cable 86. Insulating means, such as insulating means 101, function to provide a means of physically connecting the upper end of the monopoles to the short supporting tie wires, such as tie wire 100, without making electrical contact therewith. The bottom ends and the vertical monopoles are secured to a boom 102 which is supported on the ground by support spacers, such as spacer 103.

The loading between the vertical monopoles is accomplished by lumped constants which cannot be seen in detail in the figure, but which are positioned along the boom 102. Such lumped constants can be of the type shown in FIGS. 18, 19, or 20. In the particular structure of FIG. 21 resonators of the type shown in FIG. 18 are employed. The structure shown in FIG. 21 has an operating characteristic over the bandwidth of from 4 to 24 mc.

as shown in the curve of FIG. 23, in which the standing wave ratio is plotted against the frequency. The constants of u and T of FIG. 21 are, respectively, 60 and .915.

It is to be noted that the forms of the invention shown and described herein are but preferred embodiments thereof and that other configurations of log periodic antenna elements may be employed in a similar manner over ground surface to produce a radiation pattern WlllCl]. is substantially frequency independent over large bandwidths, without departing from the spirit or scope of the invention.

I claim:

1. An antenna system comprising a log periodic radial section having a conductive boom and a plurality of toothlike elements extending outwardly from said boom in a common plane, said radial section having an apex and being generally tri-angular in shape with the tooth-like elements having their outer ends defined by an angle 00/ 2 measured from said boom, the radial distance from said apex to a given point on any of said tooth-like elements bearing a constant ratio 'r to the radial distance of the corresponding point on the tooth-like element next farthest removed from said vertex, a substantially flat grounded surface, said radial section being positioned normal to and over said substantially flat grounded surface which is constructed to produce a reflection of said radial section therein, said radial section being farther positioned with the boom just above and substantially parallel with said fiat grounded surface, and impedance loading means positioned along said boom between said tooth-like elements.

2. An antenna system in accordance with claim 1 in which said impedance loading means is comprised of a plurality of rod-like elements extending outwardly from said boom at the geometric midpoint between adjacent ones of said tooth-like elements, all of said impedance loading means lying in a common plane substantially parallel with said flat grounded surface, each of said impedance loading means coacting with its image in said flat grounded surface to form a transmission line stub having a resonant frequency whose wavelength is equal to four times the electrical length, multiplied by 7 and at the same frequency, of the tooth-like element next farthest from the vertex of said radial section.

3. An antenna system in accordance with claim 1 in which each of said impedance loading means consists of a resonator, said resonator comprising a conductive helix having one terminal thereof connected to said boom and a cylinder of conductive material surrounding said helix and connected to said flat grounded surface, each of said helices being connected to the geometric midpoint between adjacent tooth-like elements and each of said resonators constructed to have a resonant frequency whose wavelength is equal to four times the electrical wavelength, multiplied by -r and at the same frequency, of the tooth-like element next farthest removed from the vertex of the radial section.

4. An antenna system in accordance with claim 1 in which said impedance loading means comprises a series arrangement of an inductor and a capacitor connected between said flat grounded surface and the geometric midpoint between adjacent tooth-like elements, each series circuit being tuned to a resonant frequency whose wavelength is four times the electrical length, multiplied by 7 and at the same frequency, of the tooth-like element next farthest removed from said vertex of said radial section.

5. An antenna system in accordance with claim 1 in which said boom comprises a coaxial type structure including a first inner conductor and a first outer conductor enclosing said inner conductor, said tooth-like elements being connected to said inner conductor through said outer conductor, said load impedance means each comprising a second coaxial type structure including a second outer conductor and second inner conductor, said second inner conductor being connected to said first inner conductor and said second outer conductors being connected to said first outer conductor, each of said second coaxial cables extending outwardly from said boom, said first and second outer conductors being electrically connected to said flat grounded surface, each of said coaxial stubs being constructed to have a resonant frequency whose wavelength is equal to four times the electrical length multiplied by H and at the same frequency, of the tooth-like element next farthest removed from said vertex.

6. An antenna system in accordance with claim 1 in which each of said tooth-like elements consist of a single rod-like element extending outwardly from said boom.

7. An antenna system in accordance with claim 6 in which said impedance loading means is comprised of a plurality of rod-like elements extending outwardly from said boom at the geometric midpoint between adjacent ones of said tooth-like elements, all of said impedance loading means lying in a common plane substantially parallel with said fiat grounded surface, each of said impedance loading means coacting with its image in said fiat grounded surface to form a transmission line stub having a resonant frequency whose wavelength is equal to four times the electrical length, multiplied by T and at the same frequency, of the tooth-like element next farthest from the vertex of said radial section.

8. An antenna system in accordance with claim 6 in which each of said impedance loading means consists of a resonator, said resonator comprising a conductive helix having one of the terminals thereof connected to said boom and a cylinder of conductive material surrounding said helix and connected to said fiat grounded surface, each of said helices being connected to the geometric midpoint between adjacent tooth-like elements and each of said resonators being constructed to have a resonant frequency whose wavelength is equal to four times the electrical wavelength, multiplied by 1 and at the same frequency, of the tooth-like element next farthest removed from the vertex of the radial section.

9. An antenna system in accordance with claim 6 in .which said impedance loading means comprises a series arrangement of an inductor and a capacitor connected between said flat grounded surface and the geometric midpoint between adjacent tooth-like elements, each series circuit being tuned to a resonant frequency whose wavelength is four times the electrical length, multiplied by T16 and at the same frequency, of the tooth-like element next farthest removed from said vertex of said radial section.

10. An antenna system in accordance with claim 6 in which said boom comprises a coaxial type structure including a first inner conductor and a first outer conductor enclosing said first inner conductor, said tooth-like elements being connected to said first inner conductor through said first outer conductor, said load impedance means each comprising a second coaxial type structure including a second outer conductor and second inner conductor, said second inner conductor being connected to said first inner conductor and said second outer conductor being connected to said first outer conductor, each of said second coaxial cables extending outwardly from said boom, said first and second outer conductors being electrically connected to said fiat grounded surface, each of said second coaxial stubs being constructed to have a resonant frequency whose wavelength is four times the electrical length, multiplied by T and at the same frequency, of the tooth-like element next farthest removed from said vertex.

11. An antenna system in accordance with claim 1 in which each of said tooth-like elements consist of a trapezoidal-shaped element extending outwardly from said boom.

12. An antenna system in accordance with claim 11 in which said impedance loading means is comprised of a plurality of rod-like elements extending outwardly from said boom at the geometric midpoint between adjacent ones of said tooth-like elements, all of said impedance loading means lying in a common plane substantially parallel with said flat grounded surface, each of said impedance loading means coacting with its image in said flat grounded surface to form a transmission line stub having a resonant frequency whose wavelength is equal to four times the electrical length, multiplied by T and at the same frequency, of the tooth-like element next farthest removed from the vertex of said radial section.

13. An antenna system in accordance with claim 11 in which each of said impedance loading means consists of a resonator, said resonator comprising a conductive helix having one of its terminals connected to said boom and a cylinder of conductive material surrounding said helix and connected to said fiat grounded surface, each of said helices being connected to the geometric midpoint between adjacent tooth-like elements and each of said resonators being constructed to have a resonant frequency whose wavelength is equal to four times the electrical wavelength, multiplied by 7 and at the same frequency, of the tooth-like element next farthest removed from the vertex of the radial section.

14. An antenna system in accordance with claim 11 in which said impedance loading means comprises a series arrangement of an inductor and a capacitor connected between the flat grounded surface and the geometric midpoint between adjacent tooth-like elements, each series circuit being tuned to a resonant frequency whose wavelength is four times the electrical length, multiplied by 7 and at the same frequency, of the tooth-like element next farthest removed from said vertex of said radial section.

15. An antenna system in accordance with claim 11 in which said boom comprises a coaxial type structure including a first inner conductor and a first outer conductor enclosing said inner conductor, said tooth-like elements being connected to said inner conductor through said outer conductor, said load impedance means each comprising a second coaxial type structure including a second outer conductor and second inner conductor, said second inner conductor being connected to said first inner conductor and said second outer conductor being connected to said first outer conductor, each of said second coaxial cables extending outwardly from said boom, said first and second outer conductors being electrically connected to said flat grounded surface, each of said coaxial stubs being constructed to have a resonant frequency whose wavelength is four times the electrical length, multiplied by 1 and at the same frequency, of the tooth-like element next farthest removed from said apex.

16. An antenna system in accordance with claim 1 in which each of said tooth-like elements consist of a triangularly shaped tooth extending outwardly from said boom.

17. An antenna system in accordance with claim 16 in which said impedance loading means is comprised of a plurality of rod-like elements extending outwardly from said boom at the geometric midpoint between adjacent ones of said tooth-like elements, all of said impedance loading means lying in a common plane substantially parallel with said flat grounded surface, each of said impedance loading means coacting with its image in said flat grounded surface to form a transmission line stub having a resonant frequency whose wavelength is equal to four times the electrical length multiplied by 1 and at the same frequency, of the tooth-like element next farthest from the vertex of said radial section.

18. An antenna system in accordance with claim 16 in which each of said impedance loading means consists of a resonator, said resonator comprising a conductive helix having one of its terminals connected to said boom and a cylinder of conductive material surrounding said helix and connected to said flat grounded surface, each of said helices being connected to the geometric midpoint between adjacent tooth-like elements and each of said resonators being constructed to have a resonant frequency whose wavelength is equal to four times the electrical wavelength, multiplied by r and at the same frequency, of the tooth-like element next farthest removed from the apex of the radial section.

19. An antenna system in accordance with claim 16 in which said impedance loading means comprises a series arrangement of an inductor and a capacitor connected between said flat grounded surface and the geometric midpoint between adjacent tooth-like elements, each series circuit being tuned to a resonant frequency whose wavelength is four times the electrical length, multiplied T and at the same frequency, of the tooth-like element next farthest removed from said apex of said radial section.

20. An antenna system in accordance with claim 16 in which said boom comprises a coaxial type structure including a first inner conductor and a first outer conductor enclosing said first inner conductor, said tooth-like element being connected to said first inner conductor through said first outer conductor, said load impedance means each comprising a second coaxial type structure including a second outer conductor and second inner conductor, said second inner conductor being connected to said first inner conductor and said second outer conductor being connected to said first outer conductor, each of said second coaxial cables extending outwardly from said boom, said first and second outer conductors being electrically connected to said flat grounded surface, each of said second coaxial stubs being constructed to have a resonant frequency whose wavelength is four times the electrical length, multiplied by -r and at the same frequency, of the tooth-like element next farthest removed from said apex.

21. An antenna system in accordance with claim 1 in which each of said tooth-like elements of said radial =section is formed of a rod-like element, the portion of said rod-like element extending outwardly from said boom being telesoped upon itself to form a zigzag configuration substantially uniformly about a straight line.

22. An antenna system in accordance with claim 21 in which said impedance loading means is comprised of a plurality of rod-like elements extending outwardly from said boom at the geometric midpoint between adjacent ones of said tooth-like elements, all of said impedance loading means lying in a common plane substantially parallel with said flat grounded surface, each of said impedance loading means coacting with its image in said flat grounded surface to form a transmission line stub having a resonant frequency equal to four times the electrical length, multiplied by 1 and at the same frequency, of the tooth-like element next farthest from the apex of said radial section.

23. An antenna system in accordance with claim 21 in which each of said impedance loading means consists of a resonator, said resonator comprising a conductive helix having one of its terminals connected to said boom and a cylinder of conductive material surrounding said helix and connected to said flat grounded surface, each of said helices being connected to the geometric midpoint between adjacent tooth-like elements, and each of said resonators being constructed to have a resonant frequency whose wavelength is equal to four times the electrical wavelength, multiplied by 'r" and at the same frequency, of the tooth-like element next farthest removed from the apex of the radial section.

24. An antenna system in accordance with claim 21 in which said impedance loading means comprises a series arrangement of an inductor and a capacitor connected between the fiat grounded surface and the geometric mid point between adjacent tooth-like elements, each series circuit being tuned to a resonant frequency whose wavelength is four times the electrical length, multiplied by T and at the same frequency, of the tooth-like element next farthest removed from said apex of said radial section.

25. An antenna system in accordance with claim 21 in which said boom comprises a coaxial type structure including a first inner conductor and a first outer conductor enclosing 'said inner conductor, said tooth-like elements being connected to said inner conductor through said outer conductor, said load impedance means each comprising a second coaxial type structure including a second outer conductor and second inner conductor, said second inner conductor being connected to said first inner conductor and said second outer conductor being connected to said first outer conductor, each of said second coaxial cables extending outwardly from said boom, said first and second outer conductors being electrically connected to said fiat grounded surface each of said coaxial stubs being constructed to have a resonant frequency whose wavelength is four times the electrical length, multiplied by 7 and at the same frequency, of the tooth-like element next farthest removed from said apex.

26. An antenna system in accordance with claim 1 in which each of said tooth-like elements comprises a transverse member at the outer end thereof, the length of any of said transverse members bearing the ratio 1 to the length of the transverse member on the tooth-like element next farthest removed from said vertex.

27. An antenna system in accordance with claim 26 in which said impedance loading means is comprised of a plurality of rod-like elements extending outwardly from said boom at the geometric midpoint between each of said tooth-like elements, all of said impedance loading means lying in a common plane substantially parallel with said flat grounded surface, each of said impedance loading means coacting with its image in said flat grounded surface to form a transmission line stub having a resonant frequency whose wavelength is equal to four times the electrical length, multiplied by 7 and at the same frequency, of the tooth-like element next farthest from the apex of said radial section.

28. An antenna system in accordance with claim 26 in which each of said impedance loading means consists of a resonator, said resonator comprising a conductive helix having one of its terminals connected to said boom and a cylinder of conductive material surrounding said helix and connected to said flat grounded surface, each of said helices being connected to the geometric midpoint between adjacent tooth-like elements and each of said resonators being constructed to have a resonant frequency whose wavelength is equal to four times the electrical wavelength, multiplied by 7 and at the same frequency, of the tooth-like element next farthest removed from the apex of the radial section.

29. An antenna system in accordance with claim 26 in which said impedance loading means comprises a series arrangement of an inductor and a capacitor connected between said fiat grounded surface of the geometric midpoint between adjacent tooth-like elements, each series circuit being tuned to a resonant frequency whose wavelength is four times the electrical length, multiplied by "r and at the same frequency, of the tooth-like element next farthest removed from said apex of said radial section.

30. An antenna system in accordance with claim 26 in which said boom comprises a coaxial type structure including a first inner conductor and a first outer conductor enclosing said inner conductor, said tooth-like elements being connected to said first inner conductor through said first outer conductor, said load impedance means each comprising a second coaxial type structure in- References Cited by the Examiner UNITED STATES PATENTS 3/40 Katzin 343-908 X 3/41 Beck et al 343847 HERMAN KARL SAALBACH, Primary Examiner.

GEORGE N. WESTBY, Examiner.

Claims

1. AN ANTENNA SYSTEM COMPRISING A LOG PERIODIC RADIAL SECTION HAVING A CONDUCTIVE BOOM AND A PLURALITY OF TOOTHLIKE ELEMENTS EXTENDING OUTWARDLY FROM SAID BOOM IN A COMMON PLANE, SAID RADIAL SECTION HAVING AN APEX AND BEING GENERALLY TRI-ANGULAR IN SHAPE WITH THE TOOTH-LIKE ELEMENTS HAVING THEIR OUTER ENDS DEFINED BY AN ANGLE A/2 MEASURED FROM SAID BOOM, THE RADIAL DISTANCE FROM SAID APEX TO A GIVEN POINT ON ANY OF SAID TOOTH-LIKE ELEMENTS BEARING A CONSTANT RATIO R TO THE RADIAL DISTANCE OF THE CORRESPONDING POINT ON THE TOOTH-LIKE ELEMENT NEXT FARTHEST REMOVED FROM SAID VERTEX, A SUBSTANTIALLY FLAT GROUNDED SURFACE, SAID RADIAL SECTION BEING POSITIONED NORMAL TO AND OVER SAID SUBSTANTIALLY FLAT GROUNDED SURFACE WHICH IS CONSTRUCTED TO PRODUCE A REFLECTION OF SAID RADIAL SECTION THEREIN, SAID RADIAL SECTION BEING FARTHER POSITIONED WITH THE BOOM JUST ABOVE AND SUBSTANTIALLY PARALLEL WITH SAID FLAT GROUNDED SURFACE, AND IMPEDANCE LOADING MEANS POSITIONED ALONG SAID BOOM BETWEEN SAID TOOTH-LIKE ELEMENTS.