US3192528A - Parabolic antenna with splash plate and v-shaped dipole feed for pattern uniformity - Google Patents

Description

3,1 92 ,528 PED June 1965 G. a. SLEEPER, JR. ETAL PARABOLIC ANTENNA WITH SPLASH PLATE AND V-SHA DIPOLE FEED FOR PATTERN UNIFORMITY 2 Sheets-Sheet 1 Filed Dec. 21. 1961 F mmsd v m5 w N w R R wi g 5 m 6 June 6 G. B. SLEEPER, JR, ETAL 3,192,528

PARABOLIC ANTENNA WITH SPLASH PLATE AND V-SHAPED DIPOLE FEED FOR PATTERN UNIFORMITY Flled Dec. 21, 1961 2 Sheets-Sheet 2 EEP H 5 5? //////////4\ 2%; iv i m gk United States Patent PARABOLIC ANTENNA WITH SPLASH PLATE AND V-SHAPED DIPOLE FEED FOR PATTERN UNIFORMITY George B. Sleeper, Jr., and John E. Drake, both of Sherbnrne, N.Y., assignors to Technical Appliance Corporation, Sherburne, N.Y., a corporation of Delaware Filed Dec. 21, 1961, Ser. No. 161,002 10 Claims. (Cl. 343-809) This invention relates to antennas, and more particularly it relates to antennas of a kind employing a main reflector which is radiated or illuminated by energy from an illuminating radiator located at or near the focus of the main reflector. Such antennas are generically re ferred to as Cutler feed antennas as illustrated, for example, in US. Patent No. 2,422,184.

A principal object of the invention is to provide such an antenna with a novel configuration and orientation of parts whereby a more symmetric illumination of the main reflector is obtained while retaining wide impedance band width characteristics for the antenna.

Another object is to provide an antenna of the above noted kind which is plane polarized using a dipole illuminating unit at or near the focus of the main reflector.

Another object is to provide a novel arrangement of a dipole illuminator which illuminates a main reflector whereby the relations between the E-plane and H-plane radiation characteristics are improved.

A feature of the invention relates to an antenna employing a main reflector dish which is illuminated by radiation from a dipole, the dipole cooperating with a subsidiary reflector in such a way that the E-plane and H-plane radiation patterns from the main reflector are more nearly equalized or more efliciently proportioned.

Another feature relates to an antenna which has a main reflector dish or disc which is illuminated by a dipole radiator, which radiator has its radiating elements diverging away from the main reflector and toward a subsidiary reflector located at or near the focus of the main reflector, whereby the illumination of the main reflector by the subsidiary reflector provides more desirable characteristics to the antenna.

A further feature relates to an improved plane polarized antenna of the Cutler feed kind.

A still further feature relates to the novel organization, arrangement and relative location and orientation of parts for producing a more efficient antenna at microwave frequencies while retaining the desired wide band impedance characteristics.

Other features and advantages not specifically enumerated will be apparent after a consideration of the following detailed descriptions, and the appended claims and drawings.

In the drawing which shows, by way of example, certain preferred embodiments,

FIG. 1 is a plan sectional view of an antenna according to the invention;

FIG. 2 is a sectional view of FIG. 1 taken along the line 2-2 thereof;

FIG. 3 is a plan sectional view of a modification of the antenna of FIG. 1;

FIG. 4 is a sectional view of FIG. 3 taken along the line 4-4 thereof;

FIG. 5 is a schematic diagrammatic view of a conventional dipole and reflector, used in explaining the invention;

FIGS. 6 and 7 are respective graphs used in explaining the invention.

In order that the functioning and improvements achieved by the invention may be more readily understood, reference may be had to FIG. 5, which shows a conventional dipole antenna having the usual colinear dipole arms 10, 11 connected to transmission line 12. The dipole is shown located at a distance d from an infinitely large or flat plane reflector 13, it being understood that the spacing d can be adjusted in the well known manner. The radiation patterns of such an antenna in the respective E and H-planes are defined by the following formulations:

E-plane F(0)=2K cos 0 sin (d cos 0) H-plane F(B)=2K sin (d cos B) wherein:

F is the radiation pattern intensity,

0 is horizontal angle in degrees,

d is radiator to reflector spacing in electrical degrees,

and

B is vertical angle in degrees.

In a commonly used design for such a conventional antenna, the objective is to arrange the dimensions so that the field patterns in both the E and H-planes are 10 db down at the reflector edge. In such a customary design, that is 68 degrees olf center and corresponds to a reflector f/d ratio of 0.375 where ,f" is the focal length of the reflector and d is the diameter of the reflector.

If the spacing d is chosen, for example as O.18)\, the E-plane and H-plane patterns are as shown in FIG. 6, and these patterns can be only slightly altered, as for practical purposes the reflector is of finite area. If such a feed is placed at the focus of a parabolic reflector 14, the radiation pattern from the reflector will be represented by the E-plane and H-plane graphs of FIG. 7. An examination of FIG. 7 will show that with such a conventional arrangement the E and H patterns are not equal in width, which is, of course, directly traceable to the corresponding unequal widths of the E and H patterns of FIG. 6. These unequal Width patterns result in a reduced efficiency and comparatively poor performance. To a degree, that kind of compromise has heretofore been accepted as a necessary evil, although attempts have been made to reduce the inequality as much as possible. The present invention has for one of its main objects, therefore, an arrangement of parts whereby such inequality is greatly if not entirely reduced.

Heretofore the problem has been attacked by some kind of loading down the dipole, either by arranging it in very close proximity to the reflector 13 or by changing the lengths of the dipole arms and the length of the reflector to distort the E and H patterns, or by shaping the reflector 13 to effect such pattern distortion. While a reduction in the spacing d produces a somewhat satisfactory pattern compromise, such close proximity of the dipole to the reflector 13 makes impedance matching very difficult and greatly narrows the useful impedance band width. On the other hand, while making the spacing d where:

G is actual antenna gain,

7 qrD) A is gain for uniform illumination, 11' is a constant,

D is reflector diameter, is wavelength.

We have discovered that by bending or inclining the arms of the dipole toward the reflector 13 so as to act as an illuminating source for a main reflector, a wider E-plane primary pattern can be achieved. By controlling the degree of bend or divergence of the dipole arms and the spacing between the dipole arms and the illuminating reflector, practically equal width patterns can be achieved. As a result, not only are the major secondary lobe beam widths equal, but also the efliciency of the antenna and the level of the secondary and minor lobes are greatly improved. Furthermore, good performance characteristics are obtained over very wide band widths.

Referring to FIGS. 1 and 2, there is shown an antenna comprising a parabolic reflector 14 through the center of which passes a transmission line 12. Line 12 may comprise an outer tubular conductor or pipe 15 and a coaxial center conductor 16. Interposed in the center conductor is any well known form of impedance matching transformer 17. The forward end of conductor 15 is provided with two diametrically opposite resonant feed slots 18, 19 and a short circuiting bar 20 interconnects the center conductor 16 with the conductor 15, thus providing a balanced slot feed between the transmission line and the dipole arms 10, 11.

Fastened, for example by screws 21, 22, to the outer conductor 15 is a metal strip or plate 23 having its forward end inclined away from the reflector 14. Likewise fastened by screws 24, 25 to the conductor diametrically opposite to strip 23 is a similar metal strip 16 having its forward end 11 also inclined away from the reflector 14. Preferably, the angle of inclination of arm 11 is the same as that of arm 10. Thus, the arms 10 and 11 constitute a dipole which is fed with microwave signals from the transmission line 12. If desired, the members 23 and 24 may be replaced by a tubular metal sleeve which is fastened to the conductor 15 and this sleeve may have the two cars or bars 10 and 11 projecting therefrom. Such a dipole has a forward directivity pattern in the direction of the full line arrow.

Mounted in spaced relation to the dipole arms 10, 11 is the flat metal plate 13 which constitutes an auxiliary reflector, by means of which the forward radiation from the dipole arms 10, 11 is reflected backwardly to the main reflector 14. The plate 13 is preferably located at or near the focus of the reflector 14.

Reflector 13 is insulatingly supported from the transmission line 12 by means of a radome 27 which has a cylindrical collar portion 28 cemented or otherwise fastened integrally to a metal sleeve 29 which fits closely around the line conductor 15. Sleeve 29 abuts against the ends of members 23 and 26 and is locked in place by a locking ring 30. A resilient O-shaped sealing ring 31 is provided between sleeve 29 and conductor 15.

The radome has a funnel-shaped portion 32. arranged to be fastened to the refletcor 13 by a plurality of bolts 34, 35 and respective fastening nuts 36, 37. The resilient sealing ring 38 is interposed between the flange 33 and the plate 13. By this arrangement the transmission line and also the radome can be filled with any suitable inert gas under pressure for purposes well known in the antenna art.

FIGS. 3 and 4 show a modification of FIGS. 1 and 2, but without using a pressurized radome and pressurized transmission line. However, the transmission line is weatherized against egress of water, ice and the like, which would tend to pass through the feed slot. The parts of FIGS. 3 and 4 which function the same as those of FIGS. 1 and 2 bear the same designation numerals. In the embodiments of FIGS. 3 and 4, the feed between the transmission line 12 and the dipole arms 10, 11 is effected by an aperture or slot 39 which provides a balanced feed between the transmission line and the dipole arms. The bar is a short circuit between the conductor 16 and the arm 10 only.

In this embodiment the outer conductor 12 is closed by a metallic disc or flange 41 which closes off the interior of the transmission line between the coupling device and the forward end of the transmission line to form a cavity 42 which can be filled with plastic or rubber foam to maintain the characteristics of the line against weatherizing. Mounted in a hole in 41 is a feed-through or panel connector 40. To one side of connector 40 is attached center conductor 16 and outer conductor 15 by virtue of plate 41. To the other side of the connector is attached any suitable coaxial transmission line 45. Thus, transmission line 12, which is rearward of flange 41, becomes a support member 44.

The forward end of the conductor 15 is closed by means of a metal cap 43 which is welded or brazed around the conductor 15 and that cap may carry reflector plate 13. If desired, the plate 13 may take the form of bars or strips in alignment with the respecitve dipole arms 10 and 11. The manner of operation of the antenna of FIGS. 3 and 4 is similar to that of FIGS. 1 and 2 and has the advantages hereinabove described. It will be understood, of course, that the invention is not limited to any particular manner of feeding the dipole arms 10 and 11 provided those arms are bent or inclined away from the main dish reflector 14 and providing they are in the proper relatively closely spaced relation to the auxiliary reflector 13. As one example of such an antenna that was found to be useful to produce plane polarized radiation from the reflector 14 in the range between 1990 and 2200 megacycles, the dipole arms 10 and 11 had a length each of approximately 0.69 inch and each formed an acute angle facing the auxiliary reflector 13 of approximately 45 degrees. The spacing between the end of conductor 15 and the reflector 13 was approximately 1.4 inches and the reflector 13 was a circular plate of approximately 5.0 inches diameter. The distance between that plate and the center of the dish 14 was approximately 36 inches, and the dish 14 was of parabolic shape and had a diameter of approximately 96 inches. The resonant slots 18 were 1.25 inches long by 0.125 inch wide. It will be understood, of course, that if the backward reflection characteristic of the antenna is to be employed, the dish 14, instead of being made of a non-perforated plate, may be made of mesh or other openwork metallic material. It will be understood, of course, that the transmission line 12, carrying the dipole arms, the radome and the auxiliary reflector, can be anchored at the central portion of the dish 14 in any suitable manner. It also will be understood, of course, that the transmission line 12, carrying the radome, dipole arms and auxiliary reflector, can be rotatably mounted with respect to the axis of dish 14 for any desired polarization of the radiation from the main reflector.

Various changes and modifications may be made in the disclosed embodiments without departing from the purpose and scope of the invention. For example, the auxiliary reflector 13, instead of being in the form of a flat metal plate, may be concave, convex with respect to the radiation from the dipole arms.

What is claimed is:

1. An antenna comprising a dipole, a main reflector to be illuminated by said dipole, an auxiliary reflector, and means supporting said dipole with the arms thereof inclined towards said auxiliary reflector and away from said main reflector.

2. An antenna comprising a dish-shaped main reflector, and means to illuminate said main reflector with radiant energy and comprising a dipole and auxiliary reflector located at approximately the focus of said main reflector, the arms of said dipole being inclined towards said auxiliary reflector and away from said main reflector.

3. An antenna comprising a main dish-shaped reflector, a rigid transmission line passing through said main reflector and extending forwardly of said reflector, a dipole supported at the forward end of said line, and an auxiliary reflector also supported at the forward end of said line,

the arms of the dipole being inclined towards said auxiliary reflector and away from said main reflector.

4. An antenna comprising a main reflector, means to illuminate said main reflector and including a dipole with the dipole arms supported at approximately the focus of said main reflector, a divergent angle between said arms, and means to make the H-plane and the E-plane illumination substantially symmetrical, the last mentioned means including an auxiliary reflector supported adjacent the dipole arms and facing the divergent angle between said arms.

5. An antenna according to claim 4 in which said auxiliary reflector is a substantially flat plate and the arms of the dipole are substantially arcuate plates.

6. An antenna according to claim 4 in which said reflector is in the form of a pair of co-linear bars, and said dipole arms are in the form of divergent bars.

7. An antenna comprising a transmission line having a filling of inert gas under pressure, a dipole having the arms fed by said transmission line, and a sealed chamber in pressurized gas communication with the interior of said line and enclosing said dipole, said chamber comprising a radome housing transparent to radiation from the dipole, said housing having a metallic end wall which forms a reflector for said dipole, the arms of the dipole diverging towards said reflector.

8. An antenna according to claim 7 in which said transmission line is in the form of a hollow outer conductor having a coaxial center conductor, said outer conductor having the dipole supported on the forward end thereof,

and said outer conductor having a resonant feed slot for coupling the arms of the dipole respectively to the center and outer conductors of said line.

9. An antenna according to claim 7 in which said transmission line passes through a dish-shaped reflector and said dipole is supported at approximately the focus of said dish-shaped reflector.

10. An antenna comprising a transmission line having a hollow outer conductor and a coaxial center conductor, a dipole supported by the forward end of said outer conductor, a resonant feed slot in the outer conductor for feeding the dipole in opposite phase, a reflector also supported by the forward end of said outer conductor, the arms of the dipole diverging towards said reflector, means to seal the forward end of said line, and a filling of inert material within said hollow conductor and closing off said slot against ingress of foreign material into the line.

References Cited by the Examiner UNITED STATES PATENTS 2,486,620 11/49 Van Atta 343807 2,505,424 4/50 Moseley 343-781 X 2,954,557 9/60 Yang 343-786 X OTHER REFERENCES Buhler: German application Ser. No. PI0482, printed May 30, 1956.

ELI LIEBERMAN, Acting Primary Examiner.

HERMAN KARL SAALBACH, Examiner.

Claims (1)

1. 2. AN ANTENNA COMPRISING A DISH-SHAPED MAIN REFLECTOR, AND MEANS TO ILLUMINATE SAID MAIN REFLECTOR WITH RADIANT ENERGY AND COMPRISING A DIPOLE AND AUXILIARY REFLECTOR LOCATED AT APPROXIMATELY THE FOCUS OF SAID MAIN REFLECTOR, THE ARMS OF SAID DIPOLE BEING INCLINED TOWARDS SAID AUXILIARY REFLECTOR AND AWAY FROM SAID MAIN REFLECTOR.

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