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The loop antenna with director arrays of loops and rods

Appel-Hansen, Jørgen

Published in: I E E E Transactions on Antennas and Propagation

Publication date: 1972

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Citation (APA): Appel-Hansen, J. (1972). The loop antenna with director arrays of loops and rods. I E E E Transactions on Antennas and Propagation, 20(4), 516-517.

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andmounting the 26- and 104-element arrays. Low-loss flexible coaxial feed line used in the 104-element array was kindly provided by W. IC. Klemperer from IYOAA’s Space Environment Laborat.ory, Boulder, Colo. K. Weal, also of the Space Environment, Laboratory, provided the time-shared computerprogram used for impedance transformation.

REFERENCES 111 J. D. Kraus Antennas. New Yqfk:McGraw-Hill. 1950, cf. ch. 4. [Z] P. V. Handel and W. PEster, Ausbre~tung derMikrost.rahlen,” . . Zentralefiir technischwissenschaftliches Benchtswesen Bber Luft- fahrtforschung;, Germany, Res. Rep. ,FB338. May 6, 1935. [31 S. I. F., Fayard. 4u brevet d’inventlon No. 782.801 (Insaddition) -~- Perfectlonnements aus antennasde T.S.F.. hGnistrvof Cornrnercd andIndustry -France patent published Se6t 12 193% ~ ~- Fig. 1. Directive looparray antenna. t41 H. B. Hollmak Physk und Technik der Ulfr&u&n Wellen, Berlin, Germany:Springer, 1936. (See“Konzentrische Rohrleltuugals ObserweUenantenna.” after Pflster in Fig. 54. pp. 74 of v01. 11, “Die ultrakurzen Wellen in der Techruli.”) I51 H. 4. Wheeler, “A vertlcal ant.enna made of transposed sections of cozual cable,” in 1956 IRE Conv. Rec.. vol. 4. Dt. 1. [61 G. R. Oehs, “The large 50 Mc/s dipole array at Jicamarca Radar

~ Observatory,” Nat. Bur. Stand, Boulder, Colo.,Rep. 8772, Mar. 5, - . 1965.

.. ., ., The Loop Antenna with DirectorArrays of Loops and Rods I

J. APPEL-HANSES

Abstract-Experiments indicate thatthe gain of a Yagi-Uda antenna arrangement depends only upon the phase velocity of the surface wave traveling along the director arrayand not to any significant extent upon the particular forms of the director elements.

Inthe common Yagi-Uda antenna, rod directors are usually 1 used. According t.0 Ehrenspeck and Poehler [l], the phase ve1ocit.y of t,he surface wave traveling along the array of rod directors can €3 0 FLAT PLATE LOOPS be used as t.he design crit.erion for maximum gain. This seems to 0 WIRE LOOPS indicate that t.he magdude of t.he gain depends only on the phase x RODS velocity of t,he surface wave and not on the particular form of the directorelements. The purpose of the present invedgation is to verify whether an array of short-circuited loops in front. of the loop ” . antenna provides the same gain as an array of rod directox 7 I,h -- In Fig. 1, the geometry of the directive loop arrayantenna is 0.0 1.0 2.0 30 LO shown. It consists of a feeding loop, a reflector loop, and an array Fig. 3. Gain as function of arral- lengt,h. of equispaced loop directors of equaldiameter. The feeding loop is a shielded loop made of coaxial cable of 4-mm diameter. The .reflector and director loops are made of l.25-mm aluminum plate. a,{ of the director loops. In Fig. 2, as an example, t,he gain as a The difference between inner and outer radius of these flat-plate function of kad for an array 2h long is shoxn. It is seen that a loops is 1 cm. When a radius of a loop is indicated, it designatej nlaxinlunl gain of 13.8 dB was measured. In Fig. 3, the maximum the average radius of the loop in quest.ion. The measurements were gain obtained in t.lk manner by varying the director loop diameter carried out in a radio anechoic chamber at. 650 MHz. The gain over for the different. array lengths 1 is shown. The same measurement procedure nyscarried out for a director array consisting of 2 mm an isotropic radiator was measured. wire loops. In complet.ion it should be mentioned that t.he results ~ The measurements started with an optimization of the diameter of the shielded feeding loop. A gain of 3.4 dB was obtained at a do not change \\-hen the loop directors are open circuited inone or both of their current minima. . circumference of ka, = 1.10, where k = 2~/his t.he wavenumber, FolIoaing t.his, an array of rod directors: 1vit.h equispacing 0.2h h is the wavelengt.h, and a, the radius of t,he feeding loop. After this optimization, a reflector of t,he same diameter as the xa< placed in front of the feeding arrangement.This time, by varying the length of the rod directors, the maximum gain for feeding loop was added. By optimizing several times in t.nrns, the spacing between feeding loop and reflector loop, the diameter of several array lengths bet.n-een 0.4~and 4.Oh was measured. For the reflector, and the diameter of t.he feeding loop, an optimum gain comparison between thethree typm of directorelements, the of 7.8 dB mas obtained. This compares well with results obtained result* for the rod direct013 are also shown in Fig. 3. From Fig. 3, we may conclude that. there is no more than about by It,o et al. [2]. In front. of the feeding arrangement. so obtained, a director array 1-dB difference betneen the gain of t.he various types of direct,or of short circuited loops with an equidist.ance of 0.2h was placed. elements. For the array lengths considered the flat-plate loops seem to be more effect,ive for lengths less t.han 2X, whereas t.he wire loops The length of t,his array mas varied in skps of 0.4h from Oh to 41. For each length, t.he gain waz measured as a funct.ion of the radius are the least effective for lengths larger t.han 2X. Due to the small differenre between the rejults, the experiments seem t.o confirm that t.he maximum gain only depends upon the phase velocity of

’ Manuscriptreceiyed February 3, 1972. the surface n-ave and not. upon t.he particular form of the director The author IS rmth the Laborat,ory of Electromagnetic Theory, The Technical University, Lyngby, Denmark. elements.

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In all the experiments, the same feeding arrangement has been used and the cross sect.ion of the loops and rods has not been op- timized. Furthermore, for eachtype of directorelements only equispaced elements of the same magnitude has been considered. When these constraints are alleviated, a higher gain can be obtained. A reflection type of arrangement, where the surfacewave is reflected from the end, is known to give a gain increase [SI. How- ever, it is not expected that any particular typeof director elements will be significantly more effective than any othertypes. Fig. 1. Semf-inflnite conductor. REFERENCES

AP-19, Pp. 469-485, July 1971. 131 J. H Bojsen H Schjaer-Jadobsen E. Nflsson, and J. Bach dndersen, “Maximu ’gak of Yagi-Uda &rays,” Electron. Let!., vo1. 7, no. 18, pp. 531-532, Sept. 1971.

on “Diffraction by Arbitrary Comments Cross-Sectional Fig. 2. Complex z plane. Semi-Infinite Conductor”

NAGAYOSHI MORITA is investigated in det,aii for the case where X and Y tend to infinity. The integral with complex number z: Absfrucf--The far scattered fields by a semi-infinite conductor are composed of the geometric-optics and the diffraction field. By I1 = Ho(2)([z2+ (Y + Yo)z]llz)exp (-jz cos 8) dz (5) applying the technique of complex number integral, the separation 1 of these two fields in the neighborhood and other region of the is used for calculation of (4). geome@cal shadow and reflection boundaries is clarified. This Since was ambiguous in the abovepaper.1 Ho@)([zz + (Y + Y0)2]1/2) -+ O(e+) (6)

in the regions r/2 < arg (2) < ?r (the second quadrant)and When the incident electric field (3/2)1~< arg (z) < 2~ (the fourth quadrant), where z = cr + jr, it is convenient to set the branch cuts and the integral contourj E,i~~=Eoexp(-jXcos8-j(Y+Yo)sin8) (1) C1 and C2 as shorn in Fig. 2. Both contours CI and CZ start from is scattered by a semi-inkite conductor shown in Fig. 1, the total t.he point (-X,O) and arevertical straight lines in the neighborhood scattered field can simply be expressed as of (-X,O). The contours C1 and CZ are entirely to the left and right of (-.X,O), and above andbelow the real axis; they terminate at infinity in the second and fourth quadranh,respectively. Next, it will be shown that only the neighborhood of the point (-X,O) contribut.es tothe integration of I1 on the contours CI and Cz. Assume t,hat. .R,1 (XI’) dX1’ + Ho(’)(1 R - R’ I ) .Ke(R’) dc‘ (2) J, I X and Y 4 0) and X,Y >> j r I (7) which corresponds to (18) in the above paper.’ Where, the symbol where I r 1 means the absolute value of r. The point, z on CI and CZ A means the line region where K. is assumed not to be zero, and can be written as where z = -X + u + jr, (8) then, [z2 + (1- + Yd21’/2 = ([(X - Ul2 + IS + (Y + Yo) 121 Only the second term of (2) was discussed in t,he above paper.’ .[(X - cr)’ + fb - (Y + E;) 1Z11’14 In this communication, the first term

Using (7) and (9),

When z is on eit.her CIor CZ, Manuscript received October 5 1971. revised February 14, 1972. The author is with the Department 6f Electrical and CommWcation - P(X - u) SX En&fneering.Faculty of Engineering, Osaka University, Suita, Osaka. [(x- .)z + (y + y0)z11/z - [x2 + ( y + y0)z-yz Japan 565. 1 N Morita IEEETrans. Antennas Propagat., vol. AP-19, pp. 35a-366. M?S im. = - ~COSol

Authorized licensed use limited to: Danmarks Tekniske Informationscenter. Downloaded on October 2, 2009 at 10:05 from IEEE Xplore. Restrictions apply.