US2755465A - Aerials - Google Patents

Description

J. F. RAMSAY July 17, 1956 AERIALS 4 Sheets-Sheet 1 Filed 06:. 2, 1950 5 a r ill J. F. RAMSAY July 17, 1956 AERIALS 4 Sheets-Sheet 2 Filed Oct. 2, 1950 y 7, 1956 J. F. RAMSAY 2,755,465

' AERIALS Filed Oct. 2, 1950 4 Sheets-Sheet 3 J. F. RAMSAY July 17, 1956 AERIALS Filed Oct. 2, 1950 4 Sheets-Sheet 4 Jji /a. 1 749. gym

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United States Pat f f pany Limited, London, England, a company of Great Britain Application October 2,1956, serial No. l87,i3 Claims priority, application Great Britain October 149 9 Claims.

This invention relates m a'erials and more particularly though not exclusively to aerials for use on very short waves such, for example, as are today" employed television transmission and reception. The invention seeks to provide improved aerials, of great mechanical simplicity and convenience, which shall be very and be adapted to provide a reasonably good impedance match, and at the same time, not be unduly frequency selective i. e. which shall be capable of efficiently handling reasonably wide frequency bands. t

According to this invention an aerial consists of a rectangular or approximately rectangular conductor and either (I asymmetrical means for feeding: it at or near the middle point of one of the Iong er sides or (bl synimetrical means for feeding it at points situated between one of the shorter sides and the middle points of the longer sides. v

Ari aerial in accordance with this invention may befed from or feed into a transmission line or a wave guide.

Preferably the rectangle or approximate rectangle about one half wave length long and about one eighth of a wave length or less wide though these dimension are not critical and other dimensions may be preferred. a

A plurality of aerials" in accordance with the invention may be conveniently employed in' conjunction with a common feeder or a common wave guid efor example to constitute an aerial array. I y Y I g In'the case where asymmetrical feeding means is employed the aerial may be of the slot type instead of being constituted by an actual rectangularly or approximately rectangularly bent conductor. In other words, according to a feature of the invention, a slot aerial and associated feeder arrangement comprises a rectangular or approximately rectangular slot and an unbalanced feeder the live conductor of which extends substantially parallel to and mid-way between the longer edges of the slot from one of the shorter edges of the said slot, until opposite the mid-paints of the said longer edges when it is bentover' and connected to one of said mid-points. Thoughgdinie'ii'si'on's" are not critical the slot may be about half a wave length l'o'ng' (electrically) and about A of a wave length wide. Alternatively the slot may be about a wave length long.

The invention is illustrated in and in' connection with the accompanying h Figs; r, 2; 6, 7, 9, 10, 11, 12, 13, 14, 15,1 17, 18 19, 25, 21', 22 and 23 are schematic illustration s'of etnbodn ments'a'nd Figs. 3, 4, and 8 are explanatory diagrams} In one embodiment of the invention suitablefor use" for examplefor frequency modulated broadcast reception on frequencies of the order of 90 mc./s. tran'sriiittefd with horizontally polarized waves, an aerial in th'e'fo'r'mof a wire rod or thin tube 1 bent into a rectangle is supportedina vertical plane and with the long side vertical by means of a mast 2 attached at the middle of the lower short side of the rectangle. A cable feeder is provided: This may be either a concentric, unbalanced feeder or a two wire, balanced feeder. 111' either case the feeder may further erpraieea drawings in w an illustrated in Fig. 1.

2,755,465 harmed July 17, 19%

be runalo'ngside the mast or the said mast may be tubular and the feeder may be run inside it. In the case of a concentric feeder the outer or earthy conductor may be constituted by themast itself. This arrangement is The earthy conductor, in this case the mast 2-, iscontlecfed to the mid-point of the lower short side of the rectangle while the live conductor 3 is in elfect extended upwards in the form of a thin rod or tube ,4 to which wire 3 is connected, this conductor extending parallel to the long side of the rectangle,'-ii1idway between the two long sides, and in the plane of said rectangle, until it reaches approximately the middle of the rectangular area bounded by the aerial wire. At this point it is bent through a right angle as shown" at 4d towards one of the longer sides and is connected to said side approximately at the mid-point thereof.

Fig.2 illustrates a variation of Fig; lin which a two'- wire balanced feederreplaces the unbalanced feeder of Fig. 1., As before the feeder lies in the lane of the rectangle and extends vertically upwards from the center of the lower side where the mast is attached to a point between said lower side and the line joining the ifiidpoints of the longer sides of the rectangle. At this point the wires 5, 6 of the feeder are bent outwardly through a right angle in each case, extending horizontally outwardly to their respective points of connect'ibn 7, 8 with the longer sides of the rectangle; These points are, as shown at equal distances along their respective sides" from the lower short side i. e. are in the same lior'ifzcntal plane. The points 7; 8 are preferably adjustable, e". g. connection maybe made by means of clamps which can he slid al the longer sides of the rectangle and then lccke'd' in their final adjusted positions. Such an arrangement nearticularly convenient where the two wire feeder is of the well known flexible type with wires'e'rnbe dd'ed' in a low loss plastic. In Figs. 1 and 2 the height of the rectangle is so chosen that the two wire line which is in eifect constituted by the two longer sides thereof and is terminated at its eras by the shortcrsides thereof, will sustain its lowest freqi'iejficy natural oscillation. In essence the rectangle is a two wire transmission line resonator having several natural modes of oscillation. In the theoretical limiting case which the shorter sides of the rectangle are of zeroljengthor are otherwise rn'ad'e of zero reactance, the electrical length ofeach longer side would be half a wave length to support the lowest frequency mode, radiation be'ing ig'nor'edl ing to the'finite rea'ctance of the short sides of the re tangle, and owing also to radiation, the ranger sjides must be a little less than half a wave length lon'gto support the desired mode. The theoretical limiting case above referred to is conventionally illustrated in Fig. 3, the very short sides of the rectangle being here assumed to belojf zero impedance. In Fig. 3 A is the wave length, the full line curve Y shows the current'distr ibution'and the broken line curveX the voltage distribution. Fig". 4 h ows' the practical case where the short'sides are of finite inductive impedance, the arrow heads representing the dii ti s of instantaneous simultaneous currents. The cu'rreh in the shorter sides are heavy and in' the saiiie directions and in phase and the said side's accordingly r adiates tr fig ly. A voltage maximum exists between the mid-points of the longer sides so that the rectangular naneiiaay be excited by applying a voltage between these points as con ventionally indicated by the generator G in Fig; 4. This method of'fe'eding may be termed shunt feed as will 'be apparent, the load on the voltage source will' consist'of two' transmission lines in parallel eacli'ternii by a'load' imposed by a short side. For the lowest quency mode each transmissionlinei a'nme less than a quarter of a wave length long.

The spacing between the two longer sides of the rectangle is in the neighborhood of one eighth of a weve length and radiation from these two sides is vary small. The total radiation accordingly is approximately that from two in-phase current elements (the shorter sides of the rectangle) so that the said radiation is with the polarization parallel to the shorter sides, with the electric plane pattern a broad figure-of-eight diagram and the magnetic plane pattern a narrower figure-of-eight diagram.

-Assuming the rectangle to have its longer sides vertical,

the solid radiation pattern consists of two surfaces approximating to two oblate spheroids with tangential equators. Since the spacing between the shorter sides is little under the half-wave length, the spheroids merge slightly into one another instead of having point contact as would be the case were the spacing at least one halfwave length. In Fig. 5 which is a conventional diagrammatic figure, H is the magnetic (H) plane or vertical pattern and E the electric plane or horizontal pattern. The aerial gain, the measure of which is the solid radiation pattern may readily be made better than that of a dipole over an isotropic source and is comparable to that of a dipole with a reflector but, as will be apparent, constructionally the rectangular frame of this invention is much to be preferred to a horizontal dipole and horizontal refiector.

Since a rectangular frame in accordance with this invention may be fed by either a balanced or an unbalanced feeder, balance-to-unbalance transformer couplings are unnecessary. Indeed, the unbalanced co-axial feeder arrangement inherently provides an unbalance-to-balance connection.

In one practical embodiment of the invention which has been tested experimentally for the reception of horizontally polarised waves at 500 mc./ s. the rectangular frame was arranged in a vertical plane with its longer sides vertical. The said longer sides were each a little under one half of a wavelength long and each shorter side was about one eighth of a wave length long. The arrangement was as in Fig. l and with a 70 ohm co-axial line feeding the central tube 4 (Fig. 1) a standing wave ratio of better than 2/1 was obtained over a wide band of frequencies. Figure-of-eight polar diagrams were obtained in both the horizontal and vertical planes.

Fig. 6 illustrates a further practical embodiment suitable for use as an outside aerial for television broadcast reception of vertically polarized waves. As will be seen the arrangement is generally similar to that of Fig. 2 the main ditference being that (the waves being vertically polarized) the rectangle is mounted with its two longer sides horizontal and in a vertical plane instead of the shorter sides being horizontal and in a vertical plane. For a wave length of 45 mc./s. the frame was ft. 8 in. by 1 ft. 6 in. The mast 2 supports the aerial at the middle of the lower long side. A 75 ohm flexible twin wire transmission line embedded in low loss dielectric has it wires 5, 6 connected to the rectangular frame by clips at points 7, 8 the wires being flared out to the connections as shown. This aerial gave a received signal strength superior to that of a half-wave dipole, had figure-of-eight directivity and gave a picture quality superior to that of a commercial dipole and reflector.

For indoor aerials an arrangement generally similar to that of Fig. 6 may be used with advantage, though it is generally more convenient to replace tubing by wire and, of course, there is no mast. In two such cases the rectangle dimensions were 11 ft. by 2 ft. and 11 ft. by 2 ft. 9 in. Good results were obtained in both cases.

Fig. 7 shows another indoor aerial, again of the same general arrangement as Fig. 2, mounted in a loft. Tubing is again used and the mast is replaced by a standard 2a supported by a clamp 2b adapted to clamp on to a loft rafter 9. The standard 2a is rotatable to allow the directhe clamp connections 7, 8 are adjustable along the tubing.

Aerials in accordance with this invention, despite their low radiation resistances, are easily matched to conventional feeders, for high impedances exist between the midpoints of the longer sides of the rectangles and low impedances exist at the end thereof, intermediate values of impedance existing at intermediate points between these middle and end positions. This is shown in Fig. 8 in which the impedance relations for a rectangle M2 long are indicated. In Fig. 8 Zn represents high impedance and Zr. represents low, Zr being between Zn and Zn. According in the case of a balanced feeder as in Fig. 2, impedance matching is easily attained by adjusting the connection points 7, 8 along the longer sides of the rectangle. In the case of a balanced feeder as in Fig. 1 although the low impedances of the radiators (the short sides of the rectangle) at the ends of the rectangle are transformed into a high impedance between the centers of the long sides of the rectangle and this impedance is, in general too high to suit a normal coaxial cable, the conductor 4 (Fig. l) in cooperation with the adjacent parts of the long sides of the rectangle acts as an impedance transforming section reducing the impedance, at the point of connection to the cable proper (2, 3, Fig. 1) to a value reasonably well suited to a normal co-axial cable.

Obviously the rectangular frames of this invention may be of any of a wide variety of conductive materials besides the tubing and wires already mentioned, e. g. strip, rod, girder sections or even foil or metal sprayed deposit, insulating supports or framing of wood or plastic, for example being provided as necessary. Further the conductors need not be perfectly rigid or supported so as to be perfectly rigid, for wire, wire braid or stranded wire may be used.

Further, although rectangular frames have been referred to hitherto they need not be rectangular in the strict geometrical sense and shapes such as those shown in Fig. 9 may be used.

The physical length of the longer sides of a rectangular or approximately rectangular frame aerial in accordance with this invention may be reduced, if required, and the required resonance conditions still obtained by providing additional capacity-which may be adjustable for tuning purposesbetween the mid-points of the said longer sides. This expedient, which enables substantial reductions of length and has the effects of reducing the directivity in the magnetic plane and also reducing the bandwith, is illustrated in Figs. 10 and 11 for the case of a balanced feeder and unbalanced feeder respectively. In Fig. 10 the added capacity K is directly between the mid-points of the longer sides of the rectangle and is such as to allow the length to be reduced to that of a quarter wave. Even with this amount of reduction of length, the aerial gain and bandwith may be readily made of the same order as those of a single half-wave dipole. In Fig. ll, which illustrates the unbalanced feeder case, the condenser K is between the right angled bend 4a in the central conductor 4, which should be physically about one eighth of a wave length long. To secure a quarter wave transformation this central conductor must be capacity loaded both at the frame center and at the coaxial line input and, in Fig. ll, a second condenser K1 is shown at the latter position. The frame loading condenser and the center wire loading condenser at the frame centre may be, as illustrated in Fig. 11, physically one condenser.

As already explained substantially equal instantaneous currents flow in the same direction in the short sides of a frame aerial in accordance with this invention. This direction can be reversed by reversing the phase of the energizing source or in the case where a balanced feeder tional qualities of the aerial to be taken advantage of and 15 is employed, by transposing the wires of the feeder. In

ease-gee the unbalanced feeder case r'e ers'al may also be obtained by shifting the point of connectionof the central con ductor (4 in Fig. 1') from one lcn'g sideto'the correspond ing point in the other. It is oftenconvenient to provide switching or similar means to enable reversal of current direction to obtain at will if required.

In the embodiments so far described the aerials are fed by transmission lines. Wave guide feeding is, however, possible. One, such arrangement suitable for use on a frequency of the order of 3000 mc./s2 is illustratedin Fig. 12. Here the feeding wave guide WG is of rectangular crosssection excited in an H01 wave guide mode. A small circular hole WG'H is provided in the center line of the top broad face of the guide and symmetrically on either side of this hole and on the center line of the said face, are mounted two similar strips ST1 and 8T2 which lie in a plane perpendicular to the said broad face and passing through the center line thereof. H These strips are connected together atthe top by a short third length of strip ST3 which may beinteg ral with ST1 and S T2-. The strips ST1, ST3 and STZ in conjunction with the part of the wave guide top face between ST1 and ST2 constitute a' rectangular aerial in accordance with this invention and this aerial is fed by a fourth length ofstrip 8T4, attached to, or integral with, the side STZ (or ST1) at about the middle of its length, this strip having a rectangular bend and being generally arranged after the manner of the conductor 4 of Fig. The lower end of strip 8T4 passes through the hole WGH and acts as a probe inside the guide. This arrangement may be regarded as the wave guide equivalent of the arrangement of Fig. 1. The radiation is substantially horizontally polarized i e'. the predominant polarization is parallel to the broad face of the guide. The whole construction comprising parts ST1, ST2, 8T3, 8T4 may be stamped out of sheet.

Aerials in accordance with this invention may, of course, be arranged in arrays and one of the numerous possible arrays are illustrated in Fig. 13. In Fig; 13 the aerials, which may be wire (or sheet as in Fig. 12') are co-planar and spaced at intervals of ig/4 (where Ag is the guided wave length) the phases being reversed in pairs in the manner described above. In this way a substantially broadside array is obtained with a good match, since reflections spaced by )tg/4 tend to" cancel. This array compares favorably with the comparable array of dipole aerials illustrated in Fig. 14 where the finite length of the arms of the dipole prevents the dipoles from" being arranged in line, alternate dipoles having to be offset from the center line of the broad face of the wave guide. On the other hand, where desirable, this offsetting may be applied to the aerials according to the invention, since it has been established experimentally, and accounted for theoretically, that there is an offset-ting distance at which there is a minimum mutual coupling between adjacent rectangles, a feature simplifying the design. V

Where a reflector is required in association with an aerial in accordance with this invention it may be constituted by a similar rectangular frame without any feeders. Such a reflector if correctly designed and positioned, will be excited parasitically when near resonance. For this purpose the short sides of the reflector are mounted parallel to the polarization of the incident radiation. Such an arrangement is schematically illustrated in Fig. 15 in which a reflector aerial RA is shown in association with an aerial of the type of Fig. 2. I 7

Although, in the embodiments above described, the rectangular or approximately rectangular aerials are planar this is by no means essential and, where desired, the rectangle or approximate rectangle may lie on a desired curved or bent surface, Sumter example, as a cylindrical or spherical surface, so long as the curvature or bending is not excessive. Typical examples of this are indicated in Fig. 16 in which (it) shows a single rectangular frame bent to lie on a cylindrical surface (b) shows an arrangement wherein different parts of a rec- 6 tangular frame lie in diife'reri-t' planes which cut one other and (a) shows a four-aerial array which embraces a cylindrical surface.

Figures 17 to" 23 inclusive illustrate the a plication of the invention to slot aerials, Figs. 17 and 18 beingrnutually perpendicular, schematic views of one embodiment, Figs. 19' and 20' being similar views ofanother, Figs. 21 and 22 being similar views of a third slot embodiment and Fig. 23 being a schematic perspective view of a fourth slot embodiment.

Referring to Figs. 17 and 18 a slot SL about half a wave length long and one tenth of a wave length wide, is cut in a sheet S of suitable metal. The slot is fed through a co-axial feeder 2, 3 the outer 2 of which is earthed at and cut off short at the middle point of one of the shorter edges of the slot. If it be assumed that the slot is arranged in a vertical plane with its two longer sides vertical, the feeder outer 2 may terminate as shown at the middle of the lower short edge of the slot. The live central conductor 3 of the feeder is continued vertically to extend mid-way between and parallel to the two longer slot edges until it reaches the central point of the slot area, when it is bentthrough a right angle and continued and connected to the mid-point of one or other of the longer slot edges.

Itwill be seen that, with this arrangement, the length of live conductor 3 running up the slot, in co-op'era tion with the longer edges thereof constitutes,- in effect, a so-called quasi split-co axial transmission line, while the short continuation, which is parallel to the shorter slot edges, corresponds to the short-circuit connection to one side normally provided in the well-known splitco-axial balance-to-unbalance transformer arrangement. The part of the slot in which there is not live feeder conductor, provides in effect a short-circuited quarter} wave length of two wire transmission line connected to the equivalent of the short ci'rcuited quarter wave length of two-wire transmisison line which is seen on mor ing back from the balanced load in the ordinary well known split-co-axial balanced-to-unbalanced arrangement. These two shorted quarter wave lines, connected together end-on as they are, together form a resonant slot. Accordingly the arrangement, mechanically simple though it is, operates electrically as a radiating splitco-axial balanced-to-unbalanced arrangement, with a balanced slot fed from an unbalanced feeder.

The impedance at the balanced output may be satisfactorily matched to the feeder impedance by suitably (limensioning the quarter-Wave transformer which is, in effect, constituted by the central length of live feeder and the slot edges parallel thereto.

Adjustment of the inductance of the short length or live feeder which runs parallel to the shorter edges of the slot has a first order effect on the transformed slot impedance as seen at the feeder input.

As would be expected from first principles improvement of the bandwidth can be obtained by making the distance from the feeder input point (the middle of one shorter edge of the slot) to the centre of the slot one half instead of one quarter of a wave-length long (electri-' cally): in other words by making the overall electrical length of the slot one wave length instead of half a wavelength. This is especially useful in cases Where the slot is to be backed by a closed cavity as is illustrated in Figs. 19 and 20. Here the slot SL is constituted by the mouth of an otherwise closed box-like cavity BC and the co-axial feeder l2, 3 led centrally along and earthed to one of the narrow sides of the box, the live conductor 3 (which may be fiat strip, if desired) being extended mid-way between two of the longer edges of the mouthuntil the middle of the mouth is reached, after which it is bent up (or down) and connected to the middle of one (or other) of the longer edges of the mouth. The mouth '15 is arranged to lie in the plane of, and to constitute a slot 7 in, a sheet S of conductive material. The cavity aperture or mouth need not necessarily be resonant.

Slot aerial arrangements in accordance with this invention are most convenient for employment in combination to constitute slot aerial arrays. Thus, as shown in Figs. 21 and 22 two slots, SL1, SL2 each one wave length long, arranged end to endfor example with their longer sides vertical-may be cut in a plate S, the adjacent short edges of the slots being connected by a centrally situated, fairly narrow communicating neck. A co-axial feeder 2, 3 with its outer 2 earthed to the plate is led to a point P between the two slots and the inner or live conductor of the feeder extends into the neck where it connects with a wire W which runs vertically up and down mid-way between the longer edges of the two slots. This wire extends to the two middle points of the said two slots and is then bent over rectangularly, its two extreme ends being connected to the two middle points, respectively, of two longer slot edges, one in each slot as shown.

The principles of the invention as above set forth with reference to slot aerials, are applicable to the supply of energy to, or the taking of energy from, a wave guide. A wave guide is, of course, physically quite distinct from a slot aerial but, from the theoretical view point now considered, a cross section of a wave guide may be regarded as a special case of a slot aerial. In accordance with a feature of this invention, therefore, as applied to wave guides, a rectangularly sectioned wave guide and associated feeder arrangement includes, in addition to the wave guide, an unbalanced feeder the live conductor of which is extended substantially parallel to and mid-way between the longer sides of the wave guide cross section from one of the shorter sides of said cross section until the mid-point of said cross section is reached, when it is bent over and connected to the mid-point of one or other of said longer sides. This is illustrated in Figure 23 in which G represents the wave guide section and 2, 3 is the feeder. One end of the wave guide, e. g. the shaded end E6 of Fig. 3 may be constructed as a slidable piston which is, in practice, adjusted until the distance from said slidable end to the input plane of the feeder is substantially one quarter of the guided wave length. A similar arrangement can, of course, be used for taking energy from a wave guide.

It will be appreciated that the far end of the live conductor of the feeder in any of the slot aerial or guide arrangements described herein may be connected to the mid-point of either of the two longer edges of the slot or longer sides of the wave guide section (as the case may be). It will also be appreciated that the radiation phase depends upon which of the two mid-points is selected for connection of the live conductor. Where, therefore, it is desired to secure phase reversal at will, switching means may be provided to permit of connection being made to one or other of the two mid-points, as may be desired.

What we claim is:

1. An aerial consisting of a closed conductive path of substantially rectangular shape mechanically self-sustaining and having two opposite parallel longer sides and two opposite parallel shorter sides terminating said longer sides at the ends thereof, said longer sides constituting a two wire transmission line and being each of length a little less than a half wave length at the working frequency, means supporting said closed path from one of said shorter sides and feeding means extending symmetrically between said longer sides and coupled to said path centrally of one of the longer sides thereof to feed the same as a two wire transmission line resonator with the longer sides constituting the wire thereof.

2. An aerial consisting of a closed conductive path of substantially rectangular shape having two opposite parallel longer sides and two opposite parallel shorter sides terminating said longer sides at the ends thereof, said longer sides constituting a two wire transmission line and being each of length a little less than a half wave length at the working frequency and feeding means coupled to said path to feed the same as a two wire transmission line resonator with the longer sides constituting the wires thereof, said feeding means including a feeder wire extending intermediate said longer sides and symmetrically spaced therefrom and bent into a direction substantially parallel with said shorter sides and connected to substantially the middle of one of said longer sides.

3. An aerial as set forth in claim 2 wherein the feeding means includes a transmission line.

4. An aerial as set forth in claim 2 wherein the substantially rectangularly arranged conductor is substantially one half wave length long and substantially one eighth of a wave length wide.

5. An aerial as set forth in claim 2. wherein the substantially rectangularly arranged conductor lies in a plane.

6. An aerial as set forth in claim 2 wherein the feeding means includes a conductor which extends inwards from a point in one longer side of the substantially rectangularly arranged conductor to a point mid-way between the longer sides and then extends parallel to said longer sides, a further feeder connection being made to the middle point of a shorter side.

7. An aerial consisting of a closed conductive path of substantially rectangular shape having two opposite parallel longer sides and two opposite parallel shorter sides terminating said longer sides at the ends thereof, said longer sides constituting a two wire transmission line and being each of length a little less than a half wave length at the working frequency and feeding means coupled to said path to feed the same as a two wire transmission line resonator with the longer sides constituting the wires thereof, said feeding means including a feeder extending across one of said shorter sides and symmetrically between said longer sides and connected to a point which is in the middle of one of the longer sides, said feeder being wholly enclosed by said closed conductive path except at the position where the feeder crosses one of the shorter sides thereof.

8. An aerial consisting of a closed conductive path of substantially rectangular shape formed by a rigid metallic tube extending in a substantially vertical plane having two opposite parallel longer sides and two opposite parallel shorter sides terminating said longer sides at the ends thereof, said longer sides constituting a two wire transmission line and being each of a length a little less than a half wave length at the working frequency, means supporting said metallic tube in a vertically erect position from the lower shorter side thereof and a mechanically self-sustaining feeder member extending upwardly and crossing said lower shorter side of said closed path but spaced therefrom and projecting symmetrically between the longer sides of said closed conductive path and substantially parallel to said longer sides until it reaches approximately the middle of the rectangular area bounded by the closed conductive path where it is bent through approximately a right angle and directed toward one of the longer sides of said closed conductive path and where it is electrically connected to said last mentioned longer side at the mid-point thereof, said feeder member being arranged substantially coplanar with said closed conductive path.

9. An aerial as set forth in claim 8 in which said feeder member is a metallic tube which forms a junction with the longer side of said rigid metallic tube constituting part of said closed conductive path, the metallic tube constituting said feeder member being wholly bounded by said closed conductive path after said last mentioned metallic tube crosses the lower shorter side of said path.

(References on following page) References Cited in the file of this patent UNITED STATES PATENTS Blumlein Apr. 15, 1941 Engbert July 22, 1941 Barrow Apr. 13, 1943 Hansen June 7, 1949 10 Wehner Nov. 8, 1949 Kandoian May 16, 1950 Willoughby June 13, 1950 Darling June 27, 1950 Alford Sept. 23, 1952 Stolk Nov. 4, 1952

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