US2557951A - Antenna system - Google Patents

Description

June 26, 1951 A. DE RosA ETAL} 2,557,951

ANTENNA SYSTEM 2 Sheets-Sheet 1 Filed June 19. 1945 X 1 VA .VWMMXX 5 WW y m m M AM. m. s ,a T w m. A 7 m r g June 26, 1951 L. A. DE ROSA ETAL ANTENNA SYSTEM Filed June 19. 1945 2 Sheets-Sheet 2 5M am Y 0 T MM M m m 4 m 7 w A :2 0 M w h Patented June 26, 1951 ANTENNA SYSTEM Louis A. De Rosa, Staten .Island, and Frank J.

Lundburg, New York, N. Y., :and Harold Norman Capen, Passaic, N. J., assignors to Federal Telephone and Radio Corporation, New York, -N. -Y., a corporation of Delaware Application June-19, 1945, Serial No. 600,254

12 Claims. Y (01. 25 33. 53)

This invention relates to antennas and more particularly to surface type antennas and the means for defining the extent thereof and to separate them when arranged in multiple.

In our copending application, Serial No. 600,464 filed: June 20, 1945, Patent No. 2,549,783, granted April 24, 1951, we have disclosed an antenna comprising a substantially flat energy transferring surface provided with an aperture or slot, the extent both of the surface and the aperture bearing a relationship to the mean operating wavelength. This type of antenna is particularly useful where aerodynamic considerations are important and in an arrangement Where several antennas are mounted side by side in a common base surface such as the skin of an airplane fuselage for radio direction finding applications.

We find that when a large uninterrupted conductive sheet is provided with an antenna aperture or slot, a plurality of distinct points or zones of current maxima or radiation centers are established at spaced points about the aperture. The radiations due to these points of current maxima located one-half wavelength from the center are the strongest, those farther away being progressively weaker. These radiation centers or points of current maximum occur about every half Wave along various current loops extending between the terminals which feed the antenna at opposite points on the edge portions of the aperture.

In order to obtain a definite desired radiation pattern, it is necessary in accordance with the above mentioned copending application to pick out or select a number of current loops and to thereby selectively limit the number of radiation centers or current maxima. The selective retention of a desired number of loops or current maxima may be achieved by various means. Such means form the subject matter of this specification. Moreover, when a plurality of antennas of this type are used side by side in a common sheet of radiating material undesirable interaction occurs. We have discovered various antenna isolating means to effectively minimize such interaction even though they are formed in the same metallic base surface. The same antenna isolating means, however, may be used with single apertured surface to substantially eliminate undesired current maxima and thereby provide the desired radiation pattern.

Accordingly, it is one of the objects of this invention to provide a sheet of conductive material containing a slot or aperture type of antenna with means to determine the operative extent thereof and thereby, the radiation characteristics of the sheet.

It is another object of this invention to provide means to separate effectively two apertured surface type antennas which are formed in the same common conductive surface.

Another object of this invention is to minimize or control the interaction between the antenna units of an antenna array which is formed of a number of aperture type radiators in a common substantially flat metallic member.

It is another object of the invention to provide in an array of apertured or slot antennas contained in a common conductive member, means for effectively separating the operative radiant energy transferring areas of the antennas.

In accordance with one feature of our invention, We provide the surface of a conductive member with means which constitutes an effective impedance to at least the stronger of the undesired loops of current extending between the feed terminals. This might be accomplished by any one of a plurality of different means, one of which may for example comprise quarter wavelength strips or skirts of conducting material connected to and spaced in parallel relation to the conductive antenna member. Other means may comprise a series of fins disposed normal to the surface of the antenna member, or small slots cutting the current loops the maxima current points of which are undesired.

These and other objects and features of our invention may best be understood from certain embodiments set forth in the following description and accompanying drawings in which:

Fig. 1 represents an antenna arrangement in accordance withcertain features of our invention;

'Fig. '2 is a plan view of an array of antennas the extent of which is defined in accordance with Fig. 1;

.Figs. 3, 5 and '7 are representations of radiators showing various embodiments of antennas in accordance with the invention;

'Figs. 4, 6 and 8 are sectional views of the antennas of Figs. 3, 5 and '7, respectively;

Fig. '9 is the representation of a variation of the antenna of Figs. 3 and 4;

'Fig. 10 is a schematic representation of a radiatorshowing another embodiment of an antenna inaccordance with'the invention; and

Fig. 11 is a view in perspective showing an array of antennas formed in the side of a cylinder.

Referring to the drawings, the antenna of Fig. 1 comprises a substantially fiat sheet of metallic material having a circular aperture 2 provided with energy transfer terminals 20. and-2b. At-3, 3a, "4a, 5 and 5a, .etc., we indicate the current loops which we "find appear to exist between the terminals 2a and 217. These loops correspond to the sinusoidal character of the current supplied,

that is, they include maxima and null points spaced a quarter wave apart. These standing waves thus establish various points or zones of maximum currents such as indicated roughly at 6, '7, 8, and 9, for example. These current maxima points of radiation nodes are strongest in the loop adjacent the aperture and progressively weaker for the loops farther away like loops 4 and 5. If a limited radiation area is desired we find that current loops are not desired can be substantially eliminated or their radiation efiects at least greatly minimized by providing narrow high impedance slots or slits crosswise of the current lines at the points or zones of current maxima. The lines of current will tend to deviate around the slits but if the slit is properly located, it will intercept the current lines and substantially eliminate the radiation node that would otherwise occur. Slit-s of this character are shown at In, ll, l2 and E3 on loops t, do, 5 and 5a. Thus two loops 3 and are unobstructed and they carry substantially the entire current flow between the terminals 2a and Any current maxirna occuring beyond loops ii, So for example will be negligible because of their distance from the aperture and also because of the impedance effects of the slits, or if desired, other impedance boundary defining means may be provided as hereinafter described in detail.

In Fig. 2, a relatively large conductive surface or member l5 has been provided with three separate antenna slots or apertures l5, l6, and ll. Crossed slits i8 have been arranged in the surface it to interrupt and thereby eliminate undesired current loops connecting the energy transfer terminals of slots i5, i6 and if outside of a roughly elliptical area about the apertures. This ellipsoid area, of course, is only illustrative and may be of any desired extent and form. This effectively limits and defines the operative radiation transfer surface around each of the slots and at the same time sets up effective impedances between the various radiative areas. While a crossed slit has been illustrated other forms of slits, of course, may be employed so long as they provide a high impedance to the lines of current which produce the points or zones of current maxima.

In Figs. 3 and a, there is illustrated another antenna ned a longitudinal slot 19 in a conductive surface 22. The slot 59, similarly to the above described forms has energy transferring terminals 25 and 22. In order to define the limits of the operative radiating surface of the antenna and to minimize the intercoupling between antennas that may be placed adjacent thereto, means for limiting and thereby isolating the radiating unit has been provided. In this embodiment the means defining the boundary limits of the unit comprise an annular quarter Wavelength conductive skirt 23. This skirt may be as shown,

impedance or characteristics of the skirt varies accordingly. Where the perimeter of slot H) is substantially equal to a Wavelength and the inner perimeter is about a half wavelength in diameter, the current maxima are squeezed down and assume some such shape as indicated at 20a and 205. Should the impedance boundary be enlarged and/or the aperture changed in shape, the resulting current maxima would also change as will be apparent from the forms shown in Figs. 5 and 7.

In accordance with the embodiment shown in Figs. 5 and 6 the impedance skirt may assume the form indicated at 25 and 26. These skirts are rectangular and are spaced from and comprise two sections of a narrow square parallel to the slot 27 so as to limit radiation transfer to current maxima occurring beyond the ends of slot 21 as indicated roughly at 27a and 211).

Another means for isolating the radiator aperture may be seen in the case of the antenna of Figs. 7 and 8, wherein a plurality of circular, circumferential fins 2?, 29 and 36 have been provided as a boundary impedance. The aperture of this antenna is in the form of a cross 32. Obviously, longitudinal slots such as slot [9 or 21 may be used in this case with a correspondingly arranged in parallel array of the fins analogous to parallel skirts 25 and 26, if desired. The radiation maxima occur substantially as indicated at 32a and 3217.

In Fig. 9 an alternative construction for the form of the antennas in Figs. 3 and 5 is shown. This form is preferred when aerodynamic considerations are important, the radiation transfer surface 33 now underlying the main metallic base 34. The skirts are here formed in the main surface as as indicated at Zia and 34b. The opening 35 may contain a non-conductive and protective material such as Plexiglas, for streamlining and to shield the surface 33 from foreign matter such as rain, snow and solid particles.

' quarter wavelength slots 52 and 43 forming the an annularly formed metallic structure which two halves of the half wave slot 36. The two halves 42 and d3 of the slot 345 will be effectively decoupled from one another so that they will perform the radiation transfer functions of two separate aperture type antennas.

In Fig. 11 we show a cylinder 44 provided with apertures 45, 56 and impedance slits t? similarly as indicated in Fig. 2. The cylinder M may be a part of a smoke stack, water tank or other structure. The curvature of the cylinder will affect the radiation pattern, but such may be desired depending on the pattern to be produced. However, the sizes and shapes of apertures as well as the impedance slit arrangement will also be factors with regard to the pattern to be produced. The apertures 45, 6 and slits 13! may be filled with insulating material.

In operation, energy transfer of the various antennas is efiected over the terminals located at juxtaposed points of the edges of the respective slots or apertures in accordance with the disclosure of the aforementioned copending application, the radiation transfer action of the surfaces preferably being somewhat analogous to that of a double dipole, that is, with the proper selection of dimensions. The effect of the skirts and isolating impedance means illustrated here is to establish quarter wavelength traps or very high impedances between the radiation transfer surfaces. This also holds true for the form shown in Fig. 10, where the slotted section 31 intermittent the two halves 42 and 43 of the slot 36 interposes a high impedance therebetween making impossible or greatly minimizing current loops from one set of terminals to the other.

It is thus seen from the above that effective means have been provided for operatively defining the operative extent of an energy transfer surface acting as an antenna and for effectively separating from each other a plurality of slot or aperture type antennas which may possess a common conductive base surface.

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:

1. An antenna comprising a member having a surface containing an aperture, energy transfer means coupled to points on opposed edge portions of the aperture for establishing a plurality of spaced current maxima on said surface, and slots arranged in certain areas of said member to provide impedance to the occurrence of at least certain of the current maxima, said aperture and slots having dielectric material therein to provide a substantially smooth surface for said member.

2. An antenna comprising a member having an electrically conductive surface containing an aperture and energy transfer means coupled to points on opposed edge portions of the aperture for establishing a plurality of spaced current maxima on said surface, said member being provided with a high impedance discontinuity on said surface transverse to the current that would produce undesired current maxima for offering impedance to the occurrence of current maxima in certain areas of said member.

3. An antenna according to claim 2 wherein the said high impedance discontinuity comprises a slot in said member crosswise of a path of said current that would produce an undesired current maximum.

4. An antenna according to claim 2 wherein said high impedance discontinuity comprises a conductive member one quarter wave in width disposed parallel to said surface and crosswise of a path of current that produces an undesired current maximum for providing said impedance.

5. An antenna according to claim 2 wherein said high impedance discontinuity comprises a plurality of fins spaced in parallel arrangement crosswise of a path of current that would produce an undesired current maximum for providing said impedance.

6. An antenna ac ordi g to cl m wher in said high impedance discontinuity comprises a conductive element having a central aperture of larger dimension than the aperture in said member, the portion of said element having said aperture being disposed parallel to said member for providing said impedance.

'7. Radiator means according to claim 2 wherein said high impedance discontinuity comprises a skirt of annular ring form in conductive relation with and substantially parallel to said surface for providing said impedance.

8. An antenna comprising a member having an electrically conductive surface containing an aperture, energy transfer means coupled to points on opposed edge portions of the aperture for establishing a plurality of spaced current maxima on said surface, said member being provided with a plurality of high impedance discontinuities on said surface transverse to the current that would produce undesired current maxima for establishing an impedance boundary along a line spaced from the perimeter of said aperture.

9. Multiple radiation transfer means comprising a metallic conductive member having an extended surface, means providing at least two apertures in said surface, means coupled to two points of juxtaposed edge portions of each of said apertures for effecting energy transfer with respect to surface portions adjacent said apertures,

\ said member being provided with a plurality of high impedance discontinuities on said surface transverse to the current that would produce undesired current maxima for providing impedance to the current flow across certain areas of the surface of said member, whereby radiation transfer units are formed by surface portions adjacent said apertures.

10. Multiple radiator means according to claim 9, wherein said member includes a skirt having an effective width corresponding to a quarter wavelength of a mean operating frequency for providing said impedance, said skirt being arranged in conductive contact with and substantially parallel with respect to said surface.

11. Multiple radiator means according to claim 9, wherein said member is provided with slits in said member for providing said impedance, said slits being arranged crosswise of paths of undesired current flow.

12. Multiple radiator means according to claim 9, wherein said member includes a plurality of fins disposed about said apertures and normal to said surface for providingsaid impedance.

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

REFERENCES CITED The following references are of record in the

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