US 3836975 A
The invention relates to a logarithmic, periodical antenna array with dipoles of varying length attached to a boom, surrounding feeders in contact with the radiator elements of the dipoles. The antenna preferably has adjustable operating direction. In order to enable the use of the antenna for two different frequency ranges, each half-wave dipole has a central portion protruding from the boom and surrounded by two tubular collinear members separated by a gap. The inner member is only secured to the boom, and the outer member only to the end of the arm. Free outside and along it, at least one of the tubular members has a metal member, only attached to the end of the tube at the gap. In the lower frequency range the current distribution half-wave reaches between the outer tubular members in each dipole pair, and in the higher frequency range the outside metal members will give one current distribution half-wave over each radiator element in a dipole pair.
Claims available in
Description (OCR text may contain errors)
United States Patent Cassel Sept. 17, 1974 LOGARITHMIC, PERIODICAL ANTENNA Primary Examiner-James W. Lawrence ARRAY Assistant ExaminerT. N. Grigsby  Inventor: Erland Cassel, Djursholm, Sweden Attorney or F'rm Kenyon & Kenyon Remy Carr & Chapin  Assignee: Allgon Antenn AB, Akersberga,
Sweden  ABSTRACT  Filed; Man 1, 1973 The invention relates to a logarithmic, periodical antenna array with dipoles of varying length attached to PP 337,176 a boom, surrounding feeders in contact with the radiator elements of the dipoles. The antenna preferably  Foreign Application Priority Data has adjustable operating direction. in order to enable Mar 9 1972 Sweden 4082/72 the use of the antenna for two different frequency ranges, each half-wave dipole has a central portion  U S Cl 343/792 5 343/801 343/802 protruding from the boom and surrounded by two tu- 343/807 bularbcollinear1 membersi separhateg by a gap; Tkhe inner mem er 1s on y secure to t e oom, an t e outer  l Holq 9/16 Hmq 9/28 Holq 11/10 member only to the end of the arm. Free outside and  Field of Search 343/792 5 801 802 807 along it, at least one of the tubular members has a  References Cited metal member, only attached to the end of the tube at UNITED STATES PATENTS the gap. In the lower frequency range the current distribution halfwave reaches between the outer tubular 2,683,808 7/1954 Shumaker 343/807 members in each dipole pair, and in the higher fre- 3,534,369 10/1970 Rea quency range the outside metal members give one FO N PATENTS QR APPLICATIONS current distribution half-wave over each radiator ele- 710,92s 6/1965 Canada 343/7925 mem a dipole pair 2 I I I I r I I I 7 Claims, 4 Drawing Figures PATENTEDSEPI 71914 SHEET 2 BF 2 FIG.3'
LOGARITHMIC, PERIODICAL ANTENNA ARRAY The invention relates to a logarithmic, periodical antenna array with dipoles, a so-called log-periodic antenna, each pair of dipoles of which being of half-wave type, and the feeding of which is taking place through feeders, which are disposed in a boom supporting the dipole elements. The basis for the invention is an antenna array, preferably of the kind made for variable inclination and for rotation around a vertical shaft.
An antenna array of said log-periodic kind consists of dipole radiator elements which are mutually arranged in parallel perpendicularly to two conductors which may be arranged in a supporting boom. In each pair of such co-operating radiator elements one element is connected to one of the conductors and the other element to the other conductor, and the elements in the following pairs change conductors in the boom, and the pairs of dipole elements are both with respect to the length of the elements and to their mutual distances along the boom forming geometric series. Furthermore, for the feeding special rules apply, which in this connection are left to be understood.
When designing log-periodic antenna arrays for broadcasting within the short-wave range, it is often desirable to make it possible to elevate the antenna around a horizontal shaft and to rotate the antenna around a vertical shaft to provide for adjustment of the operating direction of the antenna. For high-power antennas the supporting boom often has considerable dimensions and moreover often requires some sort of cooling. It is usual that the outer contour of the antenna is sharply plough-shaped, thereby making it possible to use the antenna within a large frequency range with a limited boom length. In such an antenna array at most three pairs of dipoles will be active for each operative frequency of the antenna. The remaining radiator elements, the number of which may for instance be pairs, will thereby be inactive, In order to be able to cover a large part of the short-wave range and simultaneously be able to satisfy the above mentioned design requirements, for mechanical design and economical reasons one is compelled to limit the directivity of the antenna. This increases with increasing boom length for a given band width of the antenna. If the boom length is maintained and if the plough-shape is influenced by varying the relation between the shortest and the longest dipole pair, one finds that the directivity increases if said relation goes towards unity, but this then takes place at the cost of the band width of the antenna.
The directivity could also be increased by using socalled stacking of several antenna arrays. This, however, implies a considerable increase of dimensions and weight of the antenna, and for the above stated reasons such a solution will be less usable.
The invention relates to a solution of the problem, for a given boom length and by maintaining the other dimensions of the antenna, to increase the obtainable directivity. The new features of the invention is that in a first, lower frequency range each co-operating collinear pair of radiator elements on the boom is fed to give a current distribution characteristic for a half-wave dipole with a maximum current point at the boom, whilst in a second higher frequency range the same pair of radiator elements is fed in order to give two collinear half-wave dipoles with a current distribution for each one of the said half-wave dipoles, having a maximum current point substantially at the middle of each dipole element.
According to the invention the operative frequency range of the antenna is thus divided into two portions, and the entire antenna array is used for both portions. Within a first, lower frequency range the antenna array is then used as a conventional log-periodic antenna with a half-wave dipole using two collinear radiator elements. By using the special solution according to the invention the same antenna array can be used for the second higher frequency range and then one half-wave dipole appears across each radiator element and two half-wave dipoles will thus be collinear within every dipole pair.
Further details and features of the invention will be described below in connection with the enclosed drawings with FIGS. 1-4. FIG. 1 schematically shows a longitudinal section through a dipole pair of an antenna according to the invention, the supporting boom and the feeders being shown in cross section. FIG. 2 is a cross section according to line AA through one radiator element in FIG. 1. FIGS. 3 and 4 show projections, similar to those in FIG. 1, of two modifications according to the invention.
From FIG. 1 it is apparent that each radiator dipole element consists of a central arm 1, which is surrounded by two tubular parts 2 and 3 arranged collinearly, and preferably having the same diameter and being separated from each other by a gap 4. The inner tube part 2, i.e., the one which is nearest to the boom 5, which is made as a parallelepipedic box with rectangular cross section, is at its circumference secured to the boom, for instance by welding, and extends, without contact with the arm 1, along said arm. At the gap 4 between the two tube parts 2 and 3 the outer tube part 3 is supported by the arm 1 by a distance member 10 of insulating material, secured to the periphery of said tube part. The second tube part 3 is thus without galvanic connection with the arm 1. According to this embodiment of the invention both the tube part 2 and the tube part 3 have at least one, in the shown case two, metal members arranged outside the tube part, which metal member extends along the tube part and which for each tube part is only secured at the gap 4. For the tube part 2 two metal members 6 and 7 are thus arranged in parallel to the tube part and are only secured at the gap 4, so that galvanic connection with the tube part is lacking at the ends of the metal members nearest to the boom 5. For the tube part 3 two metal members 8, 9 are also arranged in parallel to the tube part and these too are only secured at the gap 4 and are free from the tube part at the outer end of the radiator element.
From FIG. 2, which shows a radial cross section through a whip in FIG. 1 in direction towards the boom 5, according to the line A A is evident that the two metal members 8 and 9 (and in this case also the parts 6 and 7) are not surrounding the tube part 3, but are leaving approximately equal parts of its circumference free. FIG. 2 also shows the arm 1 and the distance element 10, whereby the tube part 3 is supported by said arm.
The right-hand radiator element in FIG. 1 is built in the same manner as is described for the left-hand element in the dipole pair.
The antenna operates in the following mamner: The feeding of a radiator element, the left-hand one, for instance, takes place from one 11 of the feeders in the parallel feeder 11,12, in the boom 5. The voltage between the feeder ll and the boom is coaxially transferred to the gap 4 of the radiator element in accordance with the arrow 13. For low frequencies the voltage at the gap together with the corresponding voltage of the opposite element, which is fed from the second feeder 12 (with opposite polarity), will give a current distribution I normal for dipole antennas, with a current maximum at the boom 5. For high frequencies the voltage supply to the two gaps 4 of the collinear radiator elements will take place in the same manner as for the lower frequency range, but now the currents will utilize the additional metal members 6 9 of the tube parts 2 and 3, so that these metal parts of the elements will form a dipole of half-wave type with a current maximum according to the curves I at the gap 4. Thereby the arrow 14 will be applicable.
The new antenna array can be built with a smaller plough shape, i.e., with a minor length difference betweenthe longest and the shortest pair of dipoles, than for an antenna with a strong plough shape, and in spite thereof the antenna will be able to cover a large frequency range, as the antenna array is used twice within the whole frequency range. This also means that more than three pairs of collinear radiator elements will now be active for each frequency within each portion of the frequency range, which will increase the directivity for the lower portion of the frequency range. Within the higher portion of the frequency range both the same advantage will be obtained and also the effect that within one and the same antenna array two automatically stacked log-periodic antennas will be obtained. By means of suitable dimensioning of the antenna array one can avoid discontinuity at the transfer between the portions of the frequency range. With respect to the embodiment according to FIG. 1, it may be added that the arm 1 is secured in a cavity in the wall of the boom 5 by means of a dielectric disc 15.
In the embodiment according to FIG. 3 a similar projection as in FIG. I is shown. The boom 5 with the parallel feeder ll, 12 is supporting two radiator elements in the form of arms 1, which in this case are tubular and by means of dielectric discs are secured in cavities in the wall of the boom. In the same way as in FIG. 1 two tube parts 2 and 3 are arranged around and on the arm 1. In this case, however, only the tube part 2 is provided with metal members according to FIG. 2, for instance. On each radiator element there will be obtained for the higher frequency range a dipole pair across the metal members 6, 7 and the tube part 3. In this case current curves corresponding to those in FIG. 1 are obtained.
In the embodiment according to FIG. 4 the previously mentioned metal members in the form of bodies parallelly arranged with the tube parts have been entirely excluded. Instead, wires l6, 17 have been arranged which correspond to the metal members 6 and 7 in the embodiment according to FIG. 3. Said wires are via insulators l8 and I9 drawn to the top end of supports 20, 21 which are arranged at the uppermost and the lowermost side of the boom 5. The other ends of the wires are secured to the tube part 2 at the gap 4. Here the advantage of a lighter structure is gained, since the metal members 6 -9 can be omitted, and also that the radiator elements will be stayed by the wires 16, 17. The mode of operation is unchanged.
What I claim is:
l. Logarithmic periodical directional antenna array having a number of dipoles of half-wave type, each one with a co-operating pair of radiator elements and each one being actively fed from common balanced feeder conductors disposed in a supporting and shielded boom, preferably of the kind made for variable inclination and for rotation around a vertical shaft, characterized in that each radiator element in a dipole comprises a non-radiating central arm, each arm in every dipole being'connected to one of the feeder conductors, adjacent dipoles being fed in opposite phase by shifting the connections from the feeder conductors to said central conductors; each conductor in a dipole forming part of the screened feeding system an ending at about half the length of the radiator element where an active feeding gap is constituted, and that in a first lower frequency range each co-operating collinear pair of radiator elements on the boom,'when in resonance for a given lower frequency is fed at its two gaps to give a current distribution, characteristic for a half-wave dipole with maximum current point at the boom, while in a second, high frequency range the same pair of radiator elements, owing to the presence of high frequency resonance-forming metal members extending from each active feeding gap by being directly connected there to said parts of the radiator elements and giving an extra current node adjacent to each side of the boom, when in resonance for a given higher frequency, and fed from the same active feeding gaps in order to give two collinear half-wave dipoles, have a maximum current point at said same active feeding gap substantially at the mid dle of each dipole element.
2. An antenna array according to claim 1 in which each dipole element consists of a central arm connected to one of the feeder conductors and extending from the boom and insulated therefrom, each arm being surrounded by two collinearly arranged tubes, separated from each other by a gap, the inner tube nearest to the boom being circumferentially galvanically secured to the boom and being insulated from the arm, the outer tube being secured to the arm by means of an annular spacer element, and at least along the inner tube having at least one metal member arranged outside the tube and secured to the tube at the gap between the two tubes of one radiator element but otherwise galvanically separated therefrom.
3. An antenna array according to claim 2 in which each of said metal members is substantially parallel to the corresponding tube.
4. An antenna array according to claim 2 in which at least one of the metal members comprises at least one stretched wire having one end secured to the inner tube at the gap end and its other end via insulators connected to a support extending from the boom in a direction transverse to the arms.
5. A dipole element for a log-periodic antenna array and comprising four substantially collinear substantially linear radiators which are endwise interspaced from each other to form two inner radiators and two outer radiators, said inner and outer radiators having opposed feeding ends defining gaps therebetween in each instance, radiator feeding conductors having end portions exposed at said gaps and spaced from said radiators, said conductors being otherwise shielded, said inner radiators each having a portion connected with its said feeding end and which extends therefrom backwardly to form a free end spaced from a corresponding free end of the other of said inner radiators, said radiators collectively functioning as a single dipole when fed with longer wave lengths and said inner and outer radiators in each instance functioning together as a dipole when fed with shorter wave lengths to thereby form two dipoles.
6. The element of claim 5 including an electrically conductive tubular boom, said radiators being tubular and said inner radiators being electrically and mechanically connected to opposite sides of said boom; said feeding conductors including conductive arms spaced inside of and extending through said inner radiators and shielded thereby and having outer end portions extending beyond said inner radiators said end portions at said gaps, said arms having inner end portions mounted by electric insulation in openings formed in said booms said opposite sides, and feeding conductors extending within said boom and shielded thereby and connected with said arms said inner end portions inside of said boom, said outer radiators being mounted by electric insulation on the outer ends of said arms.
7. The element of claim 6 in which said portions extending backwardly from said inner radiators said feeding ends, are tubular segments substantially parallel to said tubular inner radiators.
UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent I 3.836.975 Dated se imhpr 17 1974 Inventofl Erland Cassel It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:
Change the Foreign Application Priority date from "March 9, 1972" to -March 29, l972-.
Signed and sealed this 4th day of March 1975.
' C. MARSHALL DANN RUTH C. MASON Commissioner of Patents and Trademarks Attesting Officer USCOMM-DC 60376-P69 FORM PO-105O (10-69) v u.s. GOVERNMENT PRINTING OFFICE: I969 0-366-334,