US2549783A - Antenna - Google Patents

Description

April 24, 1951 l.. A.`DE RosA E-rAL 2,549,783

ANTENNA Filed June 20, 1945 2 Sheets-Sheet 1 April 24, 1951 ANTENNA Filed June 20, 1945 729 .5a/RCE HI-f T0 SOURCE ai@ l0.

L. A. DE ROSA ET AL 20 d/ Z1 2l 11 ed@ fz Patented Apr. 24, 1951 UNITED STATES PATENT OFFICE ANTENNA Application June 20, 1945, Serial No. 600,464

7 Claims. l

This invention relates to antennas and more particularly to antennas comprised of metallic surfaces provided with an -aperture or slot to edges of which is coupled a transmission line for the transfer of radiant energy with respect to such surfaces.

In certain applications in the radio communications and allied arts, such as direction finders, for example, it often becomes necessary to mount .antennas on aircraft to provide radiation transfer patterns with respect Vthereto which have directive characteristics. Besides directivity, another prime requisite for such antennas is that they provide substantially no wind resistance.

We find that negligible wind resistance as well as directive characteristics can be obtained by employing an aperture type of antenna formed in a metallic sheet or plate arranged as a part of the skin of the aircraft, cr as an independent unit in close proximity to the skin surface of the aircraft. We nd that the radiation pattern of such in antenna arrangement can be predetermined. For instance, we have discovered that when an aperture contained in a sheet of metal is fed with energy at two points on the edges thereof, the aperture having a perimeter corresponding to the mean wavelength of the applied energy, current maxima are established at spaced points or zones over the surface of the sheet. The

points or zones of current maxima are strongest adjacent the aperture and progressively weaker farther away from the aperture. These current zones act like small radiators and each contributes to the antenna radiation pattern. The

number and location of these points of current maxima can be predetermined or controlled by selecting the shape and size of the aperture and by determining the boundary of the radiating portion of the sheet containing 'the antenna aper ture.

In accordance with 'the theory of standing waves, the points of maximum current occur approximately half a wavelength apart along radii of the surface, their occurrence and location being determined at least in part by reflection from the perimeter or other impedance boundary of the sheet and by the nature and size of the surface and'of the slot or aperture.

By'way of example, assume a radiating surface of this type having a shape which substantially follows a chosen current loop of indeterminate extent, and which has a centrally situated aperture. Upon decreasing the extent of the original surface in a given radial direction, the number and occurrence lof the current loops and the lo.-

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cation of the maximum current points therein may be made subject to selection. By choosing the extent of the decrease in the diameter or radius of the original surface in a given direcltion, the total number of current maxima will be controlled such that, for instance, if the radial distance from the aperture outward in a given direction is cut down to, say about half a wavelength, a single maximum in that direction will be included at the most. Also, by varying the shape of the apertiu'e to form a narrow longitudinal slot, the characteristic of the antenna may be made to approach that of a dipole, that is, the predominance of two symmetrically occurring maxima or radiation i'leld peaks may be achieved thereby, although a similar effect may be obtained with other shaped apertures.

The operative radial extent of the energy transferring surface may be determined by various means. If a large single surface is to be used, the desired shape and extent of the surface may be determined by cutting out the desired surface and spacing or otherwise insulating it from the remainder. For other applications, where it may be impracticable or undesirable to cut out a smaller surface from a larger one, the boundary of such individual radiating surfaces may be obtained by providing suitable impedances defining the boundary or extent of the desired radiating surface.

The effect of these impedances is based on the fact that the current loops are diverted or interrupted thereby, and thus, the current maxima in a given area are selectively limited. In connection with the use of these antennas on aircraft, it may be necessary to apply several of these antennas in the form of an array or system. An array of this type may be used for instance in a direction finding system to produce a directive characteristic. rIhe array may be formed of a plurality of surface type antennas arranged in fairly close proximity to one another.

It is accordingly an object of this invention to provide an antenna comprised of a radiant energy transferring surface having a given radial extent and provided with an aperture formation disposed substantially at the center thereof whereby the number and location of current loops can be selectively controlled.

It is also an object of this invention to provide an antenna which is provided with a radiant energy transferring surface having an apertured formation, wherein both the surface and the formation have operative dimensions which are related to the mean operative wavelength.

Another object of this invention is to provide an antenna in accordance with the above-named objects which has a surface of a radial extent as to permit the establishment thereon of .a given number of points of current maxima.

It is a further object to provide an antenna which is characterized by a minimum of radiative coupling with other antennas which may be placed closely adjacent thereto.

It is a further object to provide an antenna which offers a minimum of aerodynamic resistance.

Still another object is to provide a multiple antenna array both for transmission and reception wherein a minimum of coupling occurs between individual radiators of the antenna.

In accordance with the invention .we provide an antenna which is composed of a substantially fiat metallic surface having an operative radial extent so as to contain only those current maxima required for a desired radiation pattern. An aperture placed at the center of the surface may assume various coniigurations, the perimeter of which, however, preferably corresponds to substantially a full wavelength of the mean operating frequency. The antenna is connected for transfer of radiating energy to a balanced type transmission line having two conductors which are terminated at points on opposite edge portions of the slot or aperture, located preferably as close to one another as possible. These antennas which may be composed of conductive metallic surfaces such as sheet metal may be arranged to form an array, as by being placed, in

multiple, flush with the outer surface of an airplane fuselage and spaced in accordance with a given desired pattern and minimum mutual coupling.

These and other objects and features of our invention may be best understood from the appended claims and the following detailed description of certain embodiments thereof as applied to the drawings, in which:

Fig. 1 is a plan view of an aperture type of antenna illustrating the principles of our invention:

Fig. 2 is a plan view of another form of our antenna;

Fig. 3 is a view in elevation of the antenna of Fig. 2;

Fig. 4 is an alternative form of an antenna according to our invention;

Fig. 5 is still another form of our antenna;

Fig. 6 is a view in elevation of an antenna in accordance with our invention and of a typical radiation pattern resulting therefrom;

f Fig. '7 is a view of a still further form of our antenna; l Y

' Fig. '8 illustrates a plurality of antennas arranged in the form of an array in the same surface:

9 is a view in section on the line 9 9 in Fig. 8; and

Fig. 10 is a plan view of an antenna in association with a cylindrical reiiector.

Referring to the drawings, the antenna of Fig. i lcomprises a substantially at sheet of metallic material havingl a circular aperture 2 provided with energy transfer terminals 2a and 2b. At 3, 3a, 4, (a, 5 and 5a etc., we indicate current loops which we iind appear to exist between the terminals 2a and 2b. These loops correspond to the sinusoidal character of the current supplied, that is, they include maxima and null points spaced a quarter wave apart. Thesev standing waves- 4 thus establish various points or zones of maxlmum currents such as indicated roughly at 6, 1, 8, and 9, for example. These current maxima points of radiation modes are strongest in the loop adjacent the aperture and progressively weaker for the loops farther away like loops 4 and 5. f a limited area is taken out of the larger surface I, a given number of these maximum current zones can be selectively retained for radiation purposes, each such zone having individual energy radiating characteristics. Thus. if desired, the two loops 3 and 3a may be exclusively retained in an area providing the area has some suitable boundary located as indicated by line I Il. Since the boundary line Il cuts all the loops except 3 and 3a, the currents are more concentrated in loops 3 and 3a, thereby giving improved radiation from the zones of current maxima in these loops. We note also that the restricting boundary. such as IIJ appears to displace or squeeze the loops 3 and 3a in toward the periphery of the aperture.

In Fig. 2, an antenna is shown which comprises a flat substantially circular radiating surface I2 preferably in the form of a disc which may be. for instance, one half of a wavelength in diameter` a side view of which may be seen in 3. Centrally disposed in the surface I2 is a slot I3 in the form of a symmetrical cross the perimeter of which is made to equal, preferably, one wavelength of the mean operating freduenc'y. rllerzninals I4 and I5 have been pro'- rided at'two opposite inside corners of the slot to which two conductors I6 and Il may be connested for venergization of the antenna. v A

If aerodynamic considerations are important the slot may be filled with insulating material, also if the area where the antenna plate may be curved or dished, such curvature or dishing may he made, such for example as shown in Fig. 4. Curvature of the plate may also be desirable to obtain certain radiation patterns from the current maxima which in this form of antenna occur as generally indicated at I2a and I2b.

In Fig. 5 another surface is shown in the shape of a square I9. This form is shown provided with a longitudinally rectangular slot 20 with terminals 2! and 22 on opposite edge portions of the slot. The dimensions may be as indicated in the drawing. that is, approximately by 3A for the surface and a full wavelength for the slot perimeter. It will be understood, however,- that these dimensions are' given by way of example only and may be varied depending upon which radiative current maxima and how many such maxima are desired f or a'given pattern. As indicated at ISa and `Iilb, the current maxima zones occur at the ends ofthe slot and are distorted by the narrowness of the plate portionatthose points. 4These current zones or modes may be varied considerably by varying the length and/or shape of the aperture as well as the boundary of the antenna member with relation to the perimeter of the aperture.

vIn the schematic representation of Fig. 6, an' antenna is indicated at 23 which is fed Aat the edges of a slot 24 over two conductors 25 and26.vv A'refiector 2'! has been disposed at the rear and parallel to the antenna 28 so that substantially all of the radiation is in the forward direction;

The pattern in this instance has a substantially pear-shaped form 29, the stem portion of which is centered in the slot. The transmitting and. receiving .radiation patterns may be compressed.

laterally by a suitable variation in the location of the feeding terminals.

In Fig. 7, another form of antenna is shown which is designed to approximately conform to the symmetrically disposed loops such as 'indicated at 3 and 3a in Fig. 1. It will be apparent by inspection that the conductive material beyond those loops will not be necessary so that an approximate figure-eight would be sucient to accommodate such loops. In a form of antenna of this type two current maxima points and 3l may be selectively retained so that a quasi-dipole effect can be had.

In Fig, 8, two antennas 32 and 33 are shown disposed flush within a surface or wall 34 which may be the fuselage or skin of an airplane. The antennas 32 and 33 are provided with suitable reflecting members 35 and 36 and are supplied at their respective apertures by way of conductors 31, 38 and 39, 40 respectively. The surface of the fuselage or skin of the airplane in which the antennas are located may be of metal or metallized material, and be in conductive relation with the reflectors of the antennas. The antennas themselves are shown dielectrically spaced from the conductive surface 34 by annular or similarly shaped spaces 4| and 42, it being desirable that the annular space form as small a capacity as possible at the high frequencies ordinarily used with these antennas. The spaces 4l or 42 may also be filled in or form part of an insulation annularly surrounding the antennas. In Fig. 9, the relation of the outer surface, which may be of metal to the antennas and reflectors is shown in a sectional view. The distance between antennas 32 and 33 may vary in accordance with the desired pattern.

In Fig. 10, we indicate a particular application of a curved apertured antenna. The antenna 43 may be of any desired form, the antenna plate being curved to conform with the curved surface of a cylinder 44, such as a water tank or smokestack. If desired, a plurality of such antennas may be arranged in an array (see Fig.V

8) the antennas being spaced from the cylinder 44 which acts as a reflector. The leads 45 may be brought up through the cylinders and if necessary may be protected as indicated at 46.

In operation, it has been observed that the radiation pattern resulting from the apertured antenna of the type described has a polarization in a plane including the line joining the two feed points and it is vertical in respect to the radiating surface, the polarization being substantially pure. As already indicated the generally pear-shaped pattern of Fig. 6 may be varied by a suitable curvature of the surface. It has also been found that the interaction of several antennas of this type is a minimum compared to many other types of antennas and therefore permits the arrangement thereof in a multiple antenna array as shown in Fig. 5 without troublesome interaction.

Although surfaces possessing certain definite dimensions and shapes have been shown in the drawings, it is to be understood that no definite size or shape is to be preferred as long as any one surface has been chosen to have a radial size which in any maximum dimension in relation to the operative wavelength does not permit the establishment of more than a selected number of points of current maxima, and the contour of which is such that substantially no impedances are introduced in the current loops of the desired points of current maxima. It will also be clear that antennas of this character may be used for either transmission or reception purposes.

Thus, while we have described above the principles of our invention in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation on the scope of our invention as defined in the objects and the accompanying claims.

We claim:

l. An antenna comprising a member having a conductive surface containing -an opening havingperipheral dimensions to render said opening resonant at a given operating frequency, energy transfer means coupled to points on opposed edge portions of said opening for establishing a plurality of areas of spaced current maxima on said surface at said operating frequency, said surface having a maximum dimension limited to include only a single area of said current maxima.

2. An antenna according to claim l, further comprising a conductive reector spaced behind said surface at substantially a quarter wavelength at said operating frequency.

3.Y An antenna according to `,claim 2, further comprising a continuous conductive surface spaced from the edge of the conductive surface of -said member, and substantially flush therewith, and a conductive connection between the edge of said continuous conductive surface adjacent said member and said conductive reflector.

4. An antenna according to claim 1 wherein said opening is an aperture within said surface having a periphery of substantially one Wavelength at said operating frequency.

5. An antenna according to claim 1, wherein said aperture is in the form of a circle.

6. An antenna according to claim 1, wherein said aperture is in the form of a cross.

7. An antenna according to claim 1, wherein said aperture is in the form of a longitudinal slot.

LOUIS A. DE ROSA. FRANK J. LUNDBURG. HAROLD NORMAN CAPEN.

REFERENCES -CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,234,298 Usselman Mar. 11, 1941 2,297,202 Dallenbach Sept. 29, 1942 2,369,808 Southworth Feb. 20, 1945 2,405,242 Southworth Aug. 6, 1946 2,407,068 Fiske et al Sept. 3, 1946 2,414,266 Lindenblad Jan. 14, 1947 2,455,224 Buchwalter et al. Nov. 30, 1948

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