US3389396A - Log periodic type antenna for operating at less than a half wavelength mode - Google Patents

Description

June 18, 1968 v. P. MINERVA ETAL 3,389,395

LOG PERIODIC TYPE ANTENNA FOR OPERATING AT LESS THAN A HALF WAVELENGTH MODE Filed July i4, 1965 5 Sheets-Sheet l FIG, l HSSL-lgl-dfo gllb'u l-go gum] June 18, 1968 v, P. MINERVA ETAL 3,389,396

LOG PERIODIC TYPE ANTENNA FOR OPERATING AT LESS THAN A HALF WAVELENGTH MODE 5 Sheets-She'et 2 Filed July 14, 1965 INI .v6

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INVENTORS v|To R MINERVA BY DAVID e. BERRY ATTcRNEYs June 18, 1968 v. P. MINERVA ETAL 3,389,396

LOG PERIODIC TYPE ANTENNA FOR OPERATING AT LESS THAN A HALF WAVELENGTH MODE L8 BMT i? EQ mxxmmr-85 INSULATED INVENTORS VITO P. MINERVA DAVID G. BERRY @a ww@ ATTORNEYS Patented June 13, i968 LG-G PERODIC TYPE ANTENNA FR @PERATING AT LESS THAN A HALF WAVELENGTH MODE Vito i. Minerva and David G. Berry, Canoga Park, Calif.,

assignors to Dorno and Margolin, inc., Westbury, N.Y.,

a corporation of New York Filed .luly 14, 1965, Ser. No. 471,873 22 Claimsa (Cl. 343-7925) This invention relates to antennas and more particularly to planar antennas of reduced physical size which are capable of operating at less than a half wavelength mode over a wide bandwidth.

Recent developments in the antenna art have produced several types of antennas capable of operating over relatively wide bandwidths. One such type is the so-called logarithmically periodic (log periodic) antenna. This antenna has been found to be very useful in the very high frequency (VHF) and ultra high frequency (UHF) ranges of radio frequency energy since it has a relatively large bandwidth of operation as contrasted with prior VHF and UHF antennas which had relatively narrow bandwidths.

Log periodic antennas are generally considered to be those in which the spacing between radiating elements and the lengths of these elements vary in accordance with a predetermined and constant Scale factor. They are generally classied as slow wave structures and for proper operation of a log periodic antenna it is necessary to generate a slow wave on the structure. Stated another way, the phase velocity of the wave on a log periodic antenna structure must be slightly faster than the critical phase velocity. The critical phase velocity is defined as the velocity at which the first space harmonic begins to be radiated on an infinitely long, uniformly loaded periodic structure.

Log periodic antennas produced by recent developments can be placed into two general categories. The irst category includes log periodic antennas which are operated elevated above ground and oriented for either horizontal, vertical, circular, or other type polarization. This category includes the original log periodic antennas in which one of the principles of operation is based on employing antenna radiating elements equal in length to at least onehalf wavelength of the antennas lowest operating frequency. This half wavelength radiating element principle, called the half wave operating mode, was followed in all the following log periodic antennas which were to be used as elevated antennas, either horizontal or vertical, or as horizontal antennas fed against or over ground. Since in antennas of this type the length of the longest element is onehalf wavelength at the antennas lowest operating frequency, where the antenna is to be used for relatively low frequency operation this physical limitation often necessitates the use of elements whose physical lengths renders the use of the antenna impractical or at least diiiicult.

The second category of log periodic antennas includes those which are vertically or horizontally polarized and fed against a reflecting plane, such as ground, employing the image principle. In this category one of the operating characteristics observed was that of employing antenna elements only one-quarter wavelength long at the antennas lowest operating frequency as a radiating element. This type of antenna is designated as operating in a quarter wavelength Inode. Originally, this category of antenna was only used for vertically polarized antennas since a vertically polarized antenna seemed to be the only one which would lend itself to elements only a quarter wavelength long at the lowest operating frequency.

As an outgrowth of the operation of log periodic antennas of the second category, it was discovered that horizontally polarized log periodic antennas and log periodic antennas operating above ground (elevated) could be constructed using radiating elements operating on less than a half wavelength mode, and possibly as low as a quarter wavelength mode. The theory and operation of several types of such antennas is disclosed in the copending application of David G. Berry and Vito P. Minerva, Ser. No. 378,646, entitled Series and Shunt Loaded Log Periodic Antennas, now abandoned, which is assigned to the same assignee. In that application several log periodic antennas are disclosed which operate on less than a half wavelength mode, using series and shunt inductive and capacitive loading for the antenna elements to generate the required slow wave for the antenna structure.

The present invention also relates to antenna structures usable with the general log periodic antenna principles which are capable of operating in situations where the radiating elements are less than one-half wavelength long at the lowest antenna operating frequency. In particular, the invention is directed to planar antennas, that is antennas whose elements all lie in a single plane, of reduced size (radiating elements less than one-half wavelength long at the lowest operating freguency) having wide bandwidth operating characteristics and gain approaching those of conventional log periodic antennas operating in the half wavelength mode.

According to the present invention these advantages are obtained by constructing the antenna so that certain of the antenna elements are fed from a transmission line coupled to a source while other elements are fed by coupling energy thereto from elements whose energy is originally supplied from the transmission line. While the foregoing described arrangement is particularly adaptable to antennas of the log periodic type and excellent results have been achieved therewith, it may also be utilized in antennas where a departure is made from the tixed scale factor for element spacing and/ or length of conventional log periodic antennas. By using the principles of the in vention planar antennas have been constructed and successfully operated elevated above ground in the quarter wavelength mode and successfully operated with elements only one-eighth wavelength long using the image principle.

It is therefore an object of the present invention to provide planar antennas capable of operating at less than a half wave operating mode and in a mode as low as the quarter wave operating mode.

Still a further object is to provide .a planar antenna whose radiating elements subtend a projection of an vangle corresponding to the antennas radiating aperture which is smaller in length than onehalf wavelength at the antennas lowest operating frequency.

Another object is to provide a planar antenna whose radiating elements subtend a projection of an angle corresponding to the antennas radiating aperture which is substantially equal in length to one-quarter wavelength at the antennas lowest operating frequency.

Another object is to provide planar antenna structures in which energy is supplied to certain antenna elements from a transmission line feed and coupled to other elements from the elements fed from the line.

A further object is to provide planar antennas following log periodic principles and capable of operating at less than a half wavelength operating mode.

An additional object is to provide planar antenna structures following the general principles of log periodic antennas in which energy is coupled to certain of the antenna elements from other elements on the structure.

Yet another object is to provide planar antennas operating with image principles wherein the radiating elements subtend the projection of an angle corresponding to the antennas radiating aperture which is smaller in length than Ei one-quarter wavelength at the antennas lowest operating frequency.

Still a further object is to provide planar antennas operating with image principles wherein the radiating elements subtend the projection of an angle corresponding to the antennas radiating aperture which is substantially equal in length to one-eighth wavelength at the antennas lowest operating frequency.

Other objects and advantages of the present invention will become more apparent upon reference to the following specification and annexed drawings in which;

FIGURE l is a top plan schematic view of one form of an antenna operating above ground made in accordance with the present invention;

FIGURE 1A is a top plan schematic View of a portion of the antenna of FIG. l showing a modification thereof;

FIGURE 2 is a side elevational schematic view of another form of antenna made in accordance with the present invention using image principles;

FIGURE 3 is a top plan schematic view of an array of planar antennas made in accordance Iwith the present inyention; and

FIGURE 4 is a top plan schematic view of another embodiment of the invention.

Since the details of construction and assembly of 'antennas is a highly developed and conventional art, all of the antennas of the present invention are shown in schematic form. It should be understood that any suitable fabrication techniques may be used, such as for forming the various antenna elements and connecting them to the transmission line. Therefore, no description is given for such constructional details since their application would be obvious to a person skilled in the art.

As will be described, this preferred embodiment of antenna follows the general principles of log periodic antennas. Antenna It) includes a number of dipole elements itl-ll, 11-2, lll-3, lll-n, which are numbered progressively from the rear end of the antenna to the front (apex). The notation l-n is used to indicate that as many elements as desired may be employed. The antenna is fed from a suitable source of alternating current energy 12 by a two wire transmission line I4 which forms the antenna central axis. The transmission line can, of course, be either of stiff or flexible material. In the latter case a boom is provided for supporting elements Il.

Each of the dipole elements 11 has its two portions connected to the two wires of transmission line 14. The transmission line 14 is formed to produce Ia transposition from one wire of the line to the other for adjacent elements of the antenna. This gives the 180 phase shift needed between elements to produce a radiation pattern in the backfire direction toward the apex (front) of the antenna. This is in accordance with the theory for log periodic antennas.

The shorter dipole elements 11-n through 11-6, Working from the front to the rear of the antenna, have only substantially straight portions while each of the elements 11-5 through elements 11-1 has a corresponding portion I1-5a through Ill-1a at the end thereof bent or folded substantially at right angles to the portion of the respective element attached to the transmission line. The folded portions are directed toward the rear end of the antenna and increase in length from elements 11-5 through 11-1. These bent ends run generally parallel to the transmission line but, if desired, they can be bent at some other angle. The purpose of this bending is to reduce the physical size of these antenna elements for lo'wer operating frequencies and also for achieving desired electrical operating characteristics. The latter is described in detail below.

The antenna has a radiating aperture angle designated by the angle a in FIG. 1. This angle subtends the straight portion of the longest element 11-1, that is, the portion generally transverse to transmission line 14, the apex of the angle is generally the apex, or front, of the antenna.

As can be seen, the folded ends ll-Sa of element 11-5 are spaced slightly from the corresponding folded ends 11-4a of the next adjacent larger element 1li-4. The folded ends IIL-4a of element 1li-4 partially overlap in spaced relationship a small portion of the corresponding folded ends I1-3a of element 1li-3 While the folded ends 1l-3a of element lll-3 overlap in spaced relationship a larger portion of the corresponding folded ends of element Il-Z. Similarly, the folded ends Irl-2a of element Il-Z overlap in spaced relationship the folded ends III-1a of element lil-I. The ends of element Ill-1 also have a second folded portion lil-1b which is generally transverse to the transmission line ltd.

Considering now the electrical operation of the antenna of FIGURE l, the elements at the front end of the structure are excited by energy from source I2 supplied over transmission line f4. This excitation mode exists until a point is reached on the structure where the folded ends of one element overlap and are in signal coupling relationship with the corresponding folded ends of the next larger dipole element. At that point, excitation current in the folded ends of one dipole element is coupled to the folded ends of the adjacent next larger element which lie generally parallel to the transmission line.

In the antenna of FIGURE l, dipole elements ll-n through I-S (from front to rear of the antenna) are excited directly at their centers from transmission line 14. Element 11-4 is considered to be a transitional element since it is excited at its center from the transmission line and it couples energy from its folded ends I1-4a to the corresponding parallel folded ends lll-3a of element 11-3 which are electrically coupled thereto. The energy feed arrangement is described in greater detail below. There may also be some energy coupled from the folded ends lI-Sa of element Til-5 to the folded ends 11-4a of element 11-4. The other elements 11-2 and 11-1 are end fed by energy coupled from the folded ends of the preceding larger elements lI-S and 11-2 respectively.

To summarize the feed relationship of the structure of FIGURE l, the elements at the front of the antenna (elements lI-n through ILS) are center fed while the elements at the rear of the antenna (elements 11-4 through 11-1) are end fed. With this type of feed mechanism, a more uniform current distribution is obtained. This maintains a reasonable level of radiation resistance and effective radiating current over a wide bandwidth of operation.

In the antenna of FIG. l, the length of the longest dipole 11-1 prependicular to transmission line 14, that is the unfolded part of dipole Ill-1 which is the portion subtending the projection of the aperture angle a, is less than one-half wavelength long at the lowest operating frequency and it may be as small as one-quarter wavelength long. In a conventional log periodic antenna this length would be one-half wavelength. Since this length determines the overall size of the antenna, and since it can be made as small as one-quarter wavelength at the lowest operating frequency of the antenna, the reduction from the usual half wavelength size used in conventional antennas is readily apparent.

The departure from the use of conventional half wavelength long elements is permitted by the end feed provided by coupling energy from the folded portions of one element to the next at the rear of the antenna. The end feed of the rear elements may be thought of as a capacitive feed which effectively increases the electrical length of the straight portions of the elements fed in this manner. The amount of coupling between the end fed elements can `be adjusted, by bringing the folded portions bearing the suixes a closer together or further apart, thereby effectively adjusting the electrical lengths of the unfolded portions of these elements.

The coupling between the folded end portions of the antenna of FIG. 1 is effectively brought about by the distributed capacity between adjacent folded portions. While sufficient variation in coupling can normally be obtained by changing the distance between these folded portions, in some cases it may ybe desirable to use a lumped capacitor. This is shown in FIG. 1A wherein only a portion of several of the monopole members of the dipoles having folded portions are shown. Here, a capacitor 19 is connected between folded end portions 11-1a and 11-2a; ll-Za and :t1-3a; and 113rz and 11-4a. If desired, a capacitor may be connected between end portions 1li-fia and 11-5a but this `is not usually necessary.

Each of the capacitors 19 is shown as being of the variable type to provide a desired range of capacitance. The use of the capacitors 19 has several advantages in that it permits increased coupling and provides a readily adjustable coupling. The latter is considerably advantageous in manufacturing of the antenna since the variable `capacitance can readily compensate for any variance in coupling `between folded portions due to manufacturing tolerances and/ or errors. Of course, a xed value lumped capacitance may also be used or any combination of fixed and variable capacitors.

The overall length of element 11-1 from tip to tip, that is the folded and unfolded portions, can be made as long as one-half wavelength at the lowest operating frequency of the antenna and the overall lengths of the other elements working progressively toward the front of the antenna are changed in size, usually made smaller, in accordance with some predetermined factor.

The overall half wavelength of element lI-L and the overall lengths of the other folded elements Ill-2 through 11-5, is not altogether critical. In general, some predetermined sealing factor is used, such as the log periodic sealing factor, to determine the overall length of each folded element. Variation in length can be compensated for by adjusting the energy coupled from one element to the next. In practice, the exact lengths are determined empirically after some initial predetermined lengths are selected, to account for end capacity from the ends of the dipole.

It should be noted that even if the overall length of element 11-1 is one-half wavelength, the length of the unfolded portion of this element 11-1 and the other higher numbered elements having folded portions, is less than yoneehalf wavelength. In practice they have been made as small as lone-quarter wavelength which is a preferred operating mode of the invention. As can be seen in FIG- URE l, the lengths of the unfolded portions (perpendicular to the transmission line) of the dipole elements having the folded portions, that is elements 11-1 through 11-5, are shown as being substantially the same, with some difference being needed to achieve coupling. As indicated previously, the coupling can be adjusted, meaning the lengths of the unfolded portions are also adjustable to vary the coupling between the folded portions of adjacent elements.

As indicated previously, element Ill-I has two folds or bends 11-1a and ll-Ib at its end, with the second folded portion lll-1b being generally transverse to transmission line 14 and the folded portion II-Za of element IIJ/l. This second folded portion Ill-1b aids in reducing the size of the structure since the overall length of element 11-1 can be one-half wavelength but the space it occupies transverse to line 14 need be only one-quarter wavelength. The second folded portion lll-1b also reduces the side- Wards radiation from element ll-L that is, the radiation traverse to the line 14. If the second fold lll-Ib was not provided, then a large part of element 11-1, approximately one half, would be parallel to the transmission line and uncoupled from folded portion 112a of element 11-2 and therefore free to radiate sidewards. The second fold 11-1b eliminates this undesired result.

In a preferred embodiment of the structure of FIGURE l, log periodic element spacing and element lengths are d utilized. Consequently, thc spacing between elements 1I along the transmission line varies in accordance with the log periodic scale factor so that, as shown,

(l) La L- 2. L

z-l--rl/ ,and Ll-r FIGURE 2 shows another embodiment of the invention. Similar suffix notations are used for the various folded and unfolded portions of the antenna elements as in FIGURE l. Here, the antenna 5@ operates on the image principle so that the respective lengths of the elements need only be one half as long as the corresponding elements of the structure of FIGURE 1. Therefore, the unfolded portion of the longest element need be only one-eighth wavelength long at the antennas lowest operating frequency. The antenna 50 is supplied radio frequency energy `from a source 42. One side of the source is connected to a reiiecting plane 44, which may be ground on another conductive plane, while the other side is connected to the transmission line 46. Line 46 is spaced above and runs generally parallel to the reflecting plane 44.

A plurality of monopole radiating elements 51-1 through SI-n, from the rear of the antenna to the apex, are connected to line 46. Since line 46 is only a single wire, the element feed transposition used with the two wire feed line of FIGURE l cannot be used to produce the necessary 186 phase shift between elements. Instead, a respective reactive network 53 is placed between two adjacent elements to serve as a phase shifter. Networks 53 are illustratively shown as series resonant circuits formed by lumped constant inductances and capacitances. Other similar elements such as quarter wave open circuited transmission lines or resonator elements also may be used. Each of these types of circuits and elements is capable of producing the desired phase shift between adjacent radiator elements. Where the log periodic design scale factor is used for the antenna the resonant frequencies of the adjacent phase shift circuits 53 are also related by the design ratio T. Thus, the resonant fre quencies (fr) of circuits 53 have the following relationship:

Each phase shifter circuit 53 is preferably located at the geometric mean between the two adjacent radiator elements 51 with which it is associated.

The antenna 5t) of FIGURE 2 operates in the same manner as the antenna 10 of FIGURE 1, with the eX- ception that antenna Sti employs the well-known image principle. This principle dictates that where an antenna is fed against a conductive plane, a mirror image of the current pattern in the physical antenna is produced in the conductive plane. This halves the physical size of the structure.

In antenna Sti, elements Slt-n through 51-5, going from the front to the rear of the antenna, are fed from transmission line d6; element Sli-4 is a transition element; and elements 51-3 through SLI are end fed. Each of elements 51-5 through 51-2 has a corresponding single folded portion 5ft-5a through l-Zrz while element 51-1 has two folded portions 51-`1cz and Ell-lb.

Antenna Sil operates in the same manner as antenna it?, with the exception of the use of the image principle rather than another physical half antenna structure symmetrical with the structure shown. Also, the aperture angle for antenna 5t) is 1t/2 rather than a since only one half the structure of FIGURE 1 is used. Where the log periodic design formula is used the spacing between eletments is equal to: 3 eze:

As explained with respect to the antenna of FIG. l,

the overall unfolded lengths of the elements S1 also may be of a length in accordance with the log periodic design factor. These overall lengths are shown as progressively decreasing from the rear to the front of the an tenna. The factors determining these lengths have been de* scribed previously with respect to the antenna elements li of FIGURE l, but the elements 53 need be only half as long las elements 1l. due to the use of the image principle. Therefore, the unfolded portion of the longest eiement i'l-l is less than one-quarter wavelength long and, in the preferred operating mode, they are made one-eighth wavelength along. The unfolded portions of the other elcments having folded portions, that is elements 11-2 through 1li-5, subtend the projection of the aperture angle tnt/2 having a length equal to or less than one quarter wavelength at the antennas lowest operating frequency, this length determining the antennas overall di lnension in a direction transverse to the feed litre. The preferred length is one-eighth wavelength.

The coupling between the folded ends of elements 53 may be varied in the manner previously described with re speet to FIGURE l, either by adjusting the spacing and/ or using a lumped capacitance.

FIGURE 3 shows an antenna array 55 made in accordance with the present invention. Here, two antennas 60 tand 70 of the type described with respect to FIG. 1 are used. Each Aantenna 60 and 70 are designed to have a certain bandwidth of operation and when they are connected in series to the common transmission line 74, the array 'has the bandwidth of :both antennas 60 and 70. As illustrated, antenna 50 operates over a lower frequency range than `antenna 70 since elements 63 have greater physical length `than elements '73. The operating ranges of the antennas `can he separate fro-rn each other or oven lapping to provide a continuous band `of operation. As many antennas as desired may be stacked together `to form an array having a required overall bandwidth. While only one completely unfolded and center fed element 63-6 and 73-6 is shown for each antenna, it should be understood the additional elements may be placed toward the front end of each such antenna. rIhese tare not shown since they would unduly complicate the drawing.

The selection of the lengths of the elements for antennas 60 and 70, the spacing therebetween and the manner by which the inter-element coupling can be varied, is as described with 4respect lto the antenna of FIG. l. The principles of the antenna array of FIG. 3 may also be used with an array of :antennas of the type shown in FlG. 2 using the image principle. This reduces the size of the array to one-half that shown in FIG. 3.

FIG. 4 shows another embodiment of antenna constructed in accordance with the present invention. Here, the antenna S is of the same general .construction Vas the :antenna of FIG. 1 but elements 81-1, Sli-2, Sil-3 and 81-4 are left uncoupled from :the transmission line 14. This is indicated by the insulated portions S5 holding togather the monopoles of each dipole element. With elements 81-1 through 81-4 removed from the transmission line the antenna will still function properly although its overall performance may be somewhat poorer than if the elements 814i through 81-4 were left connected to the line 14. rlhe latter affords a second antenna tuning variable useful in obtaining good performance. However, the overall size reduction and planar characteristics are still obtained. Antenna 80 also can be used in the array form shown in FIG. 3 and the capacitors 19 of FIG. 1A can be used to `adjust Ithe coupling between the folded portions of the elements.

A quarter wave mode log periodic antenna according to the present invention has been constructed and successfully operated over a frequency range of 150 mc. to 1000 mc., that is a bandwidth ratio of about 7:1.

It should be understood that antennas are reciprocal devices so that the description of the antennas as transmitting devices applies equally as lwell to the same antennas used as receiving devices.

While the preferred embodiment of the invention has been described as using log periodic spacing between elements and for t-he lengths of the elements, there may be a departure fro-m the fixed scale factor design. For example, the spacing between :adjacent elements may be made the same and/or the lengths of the elements may be varied from the lo-g periodic scale factor design. This can be compensated for by varying the coupling between the end fed elements.

While preferred embodiments of the invention have been described above, it will be understood that these are illustrative only, and the invention is limited solely by the appended claims.

What is claimed is:

1. A log periodic type antenna for operating at less than a half wavelength mode comprising:

an elongated energy transmission means extending from the front to the rear of the antenna,

a plurality of elements of progressively increasing overall physical -length located along said transmission means in order of increasing overall length from the front to the rear of the antenna, means for electrically coupling certain of said elements to said energy transmission means, all of said elements having a rst portion extending generally sidewards with respect to said transmission means and selected ones of said elements toward the rear of the antenna having a second portion folded only in a direction generally towards the rear of the antenna, the rst portions of those elements having the second folded portions extending for substantially the same distance from the `transmission means, and means for coupling energy from the folded portion of an element substantially only to the folded portion of the next adjacent element toward the rear of the antenna.

2. The antenna of claim 1 wherein the energy coupl-ing means comprises the second portion of yan element overlying the second portion of the next `adjacent element toward the rear of the antenna in energy coupling relationship thereto.

3. The antenna of claim 1 wherein the energy coupling means includes lumped capacitance means connected between the folded second portions of selected ones of adjacent elements having the folded second port-ions.

4. The antenna of claim 2 wherein the energy coupling means includes lumped capacitance means connected between the folded second portions of selected ones of adjacent elements having the folded second portions.

5. The antenna of claim 1 wherein the lengths of the rst portions of those elements having second folded portions is less than one-half wavelength at the lowest effective operating frequency -of the antenna.

6. The yantenna of cla-im 1 further comprising means for electrically coupling all of said elements to said energy transmission means to receive energy therefrom.

7. The antenna of claim 1 further comprising means for electrically coupling only certain ones of said elements to said transmission means to receive energy therefrom, lat least one of said elements having a folded second portion being uncoupled from said energy transmission means.

8. The antenna of claim 1 further comprising :a third portion of one of said elements having a folded second portion, said third portion being folded with respect to said second portion in a direction different therefrom to reduce sideward radiation of energy from the antenna.

9. The antenna of claim S wherein the rearmost element of the antenna yhas said folded third portion.

10. The antenna of claim 2 further comprising a third portion on one of said elements having a folded second portion, said third portion being folded wit-h respect to said second portion in a direction different therefrom to reduce sideward radiation of energy from the antenna.

1.1. The antenna of claim 1 wherein each of said elements comprises a dipole and the total lengths of the two first portions of each dipole having the folded second portions is less than one-half wavelength at the lowest effective operating frequency of the antenna.

12. The antenna of claim 11 wherein the lengths of the total lengths of the two `first portions of each dipole having the folded second portions is substantially equal to onequarter wavelength at the lowest effective operating frequency of the antenna.

13. The antenna of claim 1 wherein each of said elements comprises a monopole for operation above a conductive plane, the length of the first portion of each monopole having a `folded second portion being less than one-quarter wavelength at the lowest effective operating frequency of the antenna.

14. The antenna of claim 13 wherein the length of the first portion of each monopole having a folded second portion is `substantially equal to oneeighth wavelength at the lowest effective operating frequency of the antenna.

15. An antenna as set forth in claim 13 wherein means are connected to said transmission means for producing a predetermined electrical phase shift between adjacent elements.

16. An antenna as set forth in claim 15 wherein said means for producing said phase shift includes a separate resonant circuit connected to the transmission means between each two adjacent elements.

17. A log periodic type antenna for operating at less than a half wavelength mode comprising:

an elongated energy transmission means extending from the front to the rear of the antenna,

a plurality of elements of progressively increasing overall physical length located along said transmission means in order of increasing overall length from the front to the rear of the antenna, means for electrically coupling certain of said elements to said energy transmission means, all of said elements having a first portion extending generally sidewards with respect to said transmission `means and selected ones of said elements toward the rear of the antenna having a second portion folded only in a direction generally towards the rear of the antenna so that the said second portions lie along substantially parallel lines which are spaced at approximately the same distance with respect to the energy transmission means, and means for coupling energy from the folded portion of an element substantially only to the folded portion of the next adjacent eler ent toward the rear of the antenna.

18. The antenna of claim 17 wherein the energy coupling means comprises the second portion of an element overlying the second portion of the next adjacent element toward the rear of the antenna in energy coupling relationship thereto.

19. The antenna of claim 17 wherein the energy coupling means includes lumped capacitance means connected between the folded second portions of selected ones of adjacent elements having the folded second portions.

20. A log periodic type -antenna for operating at less than a half wavelength mode comprising:

an elongated energy transmission means extending from the front to the rear of the antenna,

a plurality of elements of progressively increasing overall physical length located along said transmission means in order of increasing overall length from the front to the rear of the antenna, the overall length of said element and the spacing therebetween selected in accordance with a respective log periodic design factor which is held constant throughout the antenna, all said elements having a first Iportion extending generally sidewards with respect to said transmission means and selected ones of said elements toward the rear of the antenna having a second portion folded in a direction generally toward the rear of the antenna so that said second portions lie among substantially parallel lines which are spaced at approximately the same distance with respect to the energy transmission means, and means for coupling energy from the folded portion of an element to the folded portion of the next adjacent element toward the rear of the antenna.

21. The antenna of claim 20 wherein the energy coupling means comprises the second portion of an element overlying the second portion of the next adjacent element toward the rear of the antenna in energy coupling relationship thereto.

22. The antenna of claim 20 wherein the energy coupling means includes lumped capacitance means connected between the folded second portions of selected ones of adjacent elements having the folded second portions.

References Cited UNITED STATES PATENTS 2,083,260 `6/1937 Godley et al. 2,130,675 9/1938 Peterson 343-816 X 2,647,211 7/1953 Smeby 343-802 X 3,127,611 3/1964 Du Hamel et al. 343-7925 3,212,094 10/1965 Berry 343-7925 3,245,082 4/1966 Rosenberry 343-803 OTHER REFERENCES Reduced Size Log Periodic Antennas, D. F. .Di Fonzo,

National Communications Symposium, 9th, Utica, N.Y., Oct. 7, 8, 9, 1963.

HERMAN KAIRL SAALBACH, Primary Examiner.

PAUL L. GENSLER, Examiner.

R. F. HUNT, Assistant Examiner.

Claims (1)

1. A LOG PERIODIC TYPE ANTENNA FOR OPERATING AT LESS THAN A HALF WAVELENGTH MODE COMPRISING: AN ELONGATED ENERGY TRANSMISSION MEANS EXTENDING FROM THE FRONT TO THE REAR OF THE ANTENNA, A PLURALITY OF ELEMENTS OF PROGRESSIVELY INCREASING OVERALL PHYSICAL LENGTH LOCATED ALONG SAID TRANSMISSION MEANS IN ORDER OF INCREASING OVERALL LENGTH FROM THE FRONT TO THE REAR OF THE ANTENNA, MEANS FOR ELECTRICALLY COUPLING CERTAIN OF SAID ELEMENTS TO SAID ENERGY TRANSMISSION MEANS, ALL OF SAID ELEMENTS HAVING A FIRST PORTION EXTENDING GENERALLY SIDEWARDS WITH RESPECT TO SAID TRANSMISSION MEANS AND SELECTED ONES OF SAID ELEMENTS TOWARD THE REAR OF THE ANTENNA HAVING A SECOND PORTION FOLDED ONLY IN A DIRECTION GENERALLY TOWARDS THE REAR OF THE ANTENNA, THE FIRST PORTIONS OF THOSE ELEMENTS HAVING THE SECOND FOLDED PORTIONS EXTENDING FOR SUBSTANTIALLY THE SAME DISTANCE FROM THE TRANSMISSION MEANS, AND MEANS FOR COUPLING ENERGY FROM THE FOLDED PORTION OF AN ELEMENT SUBSTANTIALLY ONLY TO THE FOLDED PORTION OF THE NEXT ADJACENT ELEMENT TOWARD THE REAR OF THE ANTENNA.

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