US 2767395 A
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16, 1956 D. 1.. MARGERVUM ET AL 2,767,395
BEACON ANTENNA 3 Sheets-Sheet 1 Filed Jan. 2, 1952 I 1 I I I l l ll INVENTORS DONALD L. MARGERUM STANLEY A. PRYG A ATTORNEY 06L 1956 D. MARGERUM ETAL 2,767,395
' v BEACON ANTENNA Filed Jan. 2, 1952 a Sheets-Sheef 2 INVENTORS DONALD 1.. MARGERUM BY STANLEY A. PRYGA ATTORNEY Oct. 16, 19 56 D, MARGERUM ET AL 2,767,395
BEACON ANTENNA 3 Sheets-Sheet 3 Filed Jan. 2, 1952 FIG. 5
IN V EN TORS 'DONALD L. MARGERUM BY STANLEY A. PRYGA ATTORNH United States Patent BEACON ANTENNA Donald L. Margerum, Long Beach, and Stanley A. Pryga, .Bellflower, Calif., assignors to North American Aviation, Inc.
Application January 2, 1952, Serial No. 264,482 Claims. (Cl. 343-729) This invention relates to beacon antennae, and particularly to a beacon antenna adapted to radiate substantially 'omnidirectional elliptically polarized electromagnetic waves having a ratio ellipticity of less than two to one, and a radiation intensity which is substantially constant in a plane normal to the axis of the antenna.
A beacon antenna must respond to plane polarized electromagnetic waves whose polarization may vary in direction, and to circularly polarized electromagnetic waves. In addition, the antenna must be capable of interrogation from almost any direction relative to the axis of the antenna.
,This invention contemplates a beacon antenna having almost omnidirectional radiation characteristics and adapted to respond to nearly circularly polarized electromagnetic waves. The substantially omnidirectional radiation characteristic in combination with substantially circularly polarized radiation is achieved by the combination of a dipole and :a complex slot-and-skirt arrangement for propagating electromagnetic waves with plane polarization normal to the axis of the antenna in a very broad toroidal pattern. In Patent No. 2,735,093, issued February 14, 1956, to Robert Krausz and Donald L. Margerurn, for Airborne Beacon Antenna, there is shown and described a beacon antenna which provides a dipole with a pair. of diametrally opposed axial slots in the coaxial wave guide which feeds the dipole. However, since the polarized electromagnetic waves radiatedfrom the slots are mutually out of phase, the resultant radiation pattern in a plane normal to the axis of the antenna resembles a large figure 8 with nulls at 90 from the slots.
This invention contemplates means for eliminating these nulls in the electromagnetic energy polarized normal to the axis of the antenna, with the result that an even larger radiation pattern is achieved.
It is therefore an object of this invention to provide a beacon antenna having omnidirectional radiation characteristics.
It is another object of this invention to provide a beacon antenna adapted to radiate substantially circularly polarized electromagnetic waves.
It is another object of this invention to provide a beacon antenna adapted to radiate elliptically polarized electromagnetic waves in substantially all directions.
Other objects of invention will become apparent from the following description taken in connection with the accompanying drawings, in which Fig. 1 is an elevational view of the invention;
Fig. 2 is a side view of the invention partly in section;
Fig. 3 is a sectional view of the invention taken at 3-3 in Fig. 2; and
Figs. 4 and 5 are plots of the radiation pattern achieved by the invention.
Referring to the drawings, there is shown a modified section of coaxial wave guide comprising a central cylindrical conductor 1 surrounded by an outer hollow cylindrical conductor 2, said conductors being separated by a partial hollow cylinder 3 of dielectric material. A single 2,767,395 Patented Oct. 16, 1956 axial slot 4 is cut in conductor 2 and is positioned as near as possible to the terminus of conductor 2. Surrounding conductor 2 is an upper skirt 5 connected to conductor 2 at its upper end and extending downward. Conductor 1 extends beyond conductor 2 to form a dipole with skirt 5 as shown. Lower skirt 6 also surrounds conductor 2 and is connectedthereto at its lower end. Skirts 5 and 6 have cut in them diametrally opposed slots 7 and 8 of length equal to half the wave length of the electromagnetic energy transmitted. Slots 7 and 8 are displaced by from slot 4. Skirts 5 and 6 are separated by circumferential slot 9. From Fig. 3 it will be noted that partial cylinder 3 does not entirely fill the space between conductors 1 and 2 so that the dielectric medium separating conductors 1 and 2 is nonhomogeneous. Surrounding the entire structure is closed cylindrical envelope 10 of dielectric material having a dielectric constant of 6 or less for protection of the device from the elements.
In operation, electromagnetic energy in the TEM mode is furnished to the lower end of the device and is transmitted by conductors 1 and 2 as in an ordinary coaxial wave guide. However, because of the nonhomogeneity of the dielectric medium separating the two conductors which form the wave guide, unsymmetrical modes are generated, resulting in the coupling of a portion of the electromagnetic energy transmitted in the guide through slot 4 into the chamber separating conductor 2 from skirts 5 and 6. This energy is transmitted in this space in the rectangular TEOI mode, since this structure may be considered to be equivalent to a rectangular wave guide which is curved in the plane of the short dimension thereof. This wave guide is formed by the skirts as an upper boundary, conductor 2 as a lower boundary, and the end connections between the skirts and conductor 2 as the sides. This energy is transmitted then to slots 7 and 3 where it is radiated in phase, i. e., as shown by the electric field lines indicated in Fig. 3. The electromagnetic energy propagated from slots 7 and 8 is in phase, thus eliminating the nulls associated with the device shown and described in Patent No. 2,735,093, to which reference has been made. The electromagnetic energy propagated by slots 7 and 8 is, of course, plane polarized normal to the axis of conductors 1 and 2.
The remainder of the electromagnetic energy proceeds to the dipole formed by conductors 1 and 2 at their ends and radiated with polarization parallel to the axis of conductors 1 and 2. Since slot 4 is located so that its center is approximately one-quarter wave length from the dipole, the electromagnetic energy propagated by the dipole is in phase-quadrature with that propagated by slots 7 and 8. Consequently, the resultant electromagnetic energy propagated is elliptically polarized with substantially circular polarization over the majority of the radiation pattern.
Referring to Fig. 4, the radiation pattern of the device in a plane normal to the axis of the antenna is shown with slots 7 and 8 placed on the vertical axis. The radiation due to the slots is shown by a solid line, and the radiation due to the dipole is shown by a dotted line. It can be seen that the polarization is almost perfectly circular throughout the pattern.
Referring now to Fig. 5, the radiation pattern of the device in the plane of the longitudinal axis of the antenna and slots 7 and 8 is shown. Again, the solid line indicates the slot radiation, and the dotted line indicates the dipole radiation. The pattern is of roughly toroidal shape with least intensity directly over the end of the antenna. However, the polarization is again substantially circular over a great portion of the pattern as shown by the fact that the solid and dotted patterns are roughly congruent.
Although the invention has been described and illustrated in detail, it is to be clearly understood that the same is by Way' of illustration and example only and is not to be taken by way of limitation, the spirit and scope of this invention being limited only by the terms of the appended claims.
1 Antenna. means comprising a coaxial Wave guide, a dipole at the terminus of said guide,1an axial slot in the outer conductor of said wave guide having its center one-quarter wave length of the electromagnetic energy to be transmitted by said guide from said dipole, a cylindrical skirt attached at one end to the end of said guide near said dipole and at the other end to another portion of saidguide and separated throughout, its midportion from said guide, said skirt having cut in it two diarnetrally i opposed axial slots displaced by- 90 degrees from said slot in said guide, and a circumferential slot cut in said skirt near its midpoint; and means for distorting the electric fields in said guide, to cause propagation from the slot in said guide whereby a portion of the electromagnetic energy transmitted in said guide is coupled out the slot in said guide, is transmitted in the space between said guide and said skirt to the slots in said skirts, and.
thence is radiated from said slots with polarization normal to the axis of said guide, andthe remainder of said electromagnetic energy is propagated" by said dipole with polarization parallel to the axis of: said guide.
2. Means for propagating; circularly polarized electromagnetic Waves comprising a coaxial wave guide, a dipole at the end of said wave guide for propagating electromagnetic Waves plane polarized parallel to the axis of said guide, an axial slot in said guide situated near said dipole, a nonsymmetrical prism of dielectric material filling the space between conductors of said guide for causing propagation of a portion of said electromagnetic waves from said slot, and a cylindrical closed-ended skirt larger than said guide disposed coaxially with said guide over said slot and having a pair of dilametral'ly opposed axial slots displaced 90 degrees from the slot in said guide and a central circumferential slot centered with respect to said axial slots whereby electromagnetic waves propagated from said Wave guide slot are propagated irom said skirt slots mutually in phase with polarization normal to the axis of said guide and in phasequadrature with electromagnetic waves propagated by 4 said dipole.
3. Means for propagating substantially circularly polarized electromagnetic waves comprising a dipole, a
coaxial wave guide for supplying electromagnetic energy to said dipole, a single axial slot in the outer conductor of said wave guide having a length one-half the wave length of the electromagnetic energy transmitted by said wave guide and situated adjacent said dipole, a cylindrical skirt surrounding said guide extending from said dipole to the farthest end of said single slot and having end members for supportv by said guide, a pair of diametrally opposed axial slots in said skirt of substantially the. same. length as said single slot and displaced, angularly by 9t) degrees from said single slot, and a nonhomogeneous dielectric medium separating the. conductors of said wave guide whereby a portion of the electromagnetic waves transmitted by said guide are propagated from saidslot-s with plane polarization normal to the axis of said guide and the remainder of said electromagnetic energy is propagated from said dipole in phase-quadrature with said portion and with piano polarization parallel to the axis of said wave guide.
4. A device, as recited in claim 3 in which said dielectric medium is a sector of dielectric material extending parallel to said slot and arranged to cause propagation from said single slot.
5. Means for propagating substantially circularly po- L larized electromagnetic waves over a toroidal pattern comprising a dipole for propagating electromagnetic waves with polarization parallel to the axis of said dipole,
a coaxial" wave guide for furnishing electromagnetic waves to said dipole, a nonhornogeneous dielectric medium separating the conductors of said wave guide, a single axial slot in said guide for propagating electromagnetic waves firom said guide, and an axially slotted skirt surrounding said guide for propagating mutually in-phase electromagnetic waves with polarization normal to the axis of said guide in phase-quadrature with the waves propagated by said dipole.
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