US2432858A - Antenna system - Google Patents

Description

Dec. 16, 1947. G. H. BROVVUN 2,432,858

ANTENNA SYSTEM Filed March 31, 1943 L 15 610 i DEV/(5: l I Inventor fik'o yz-filimwn Gmrncu Patented Dec. 16, 1947 UNITED STATES PATENT OFFICE 2,432,858 ANTENNA SYSTEM George H. Brown, Princeton, N. J-., 'assigno'r to Radio Corporation of America, acorporation of Delaware Application March 31, 1943, Serial No. 481,218

This invention relates to directive antennas and more particularly to antennas for providing alternately or sequentially overlapping directive patterns. Such antennas are generally applicable to radio aircraft locators, radio direction finders, object detectors and the like. Directive a'ntenna systems for ultra high frequencies frequently include a parabolic reflector with one or more radiator elements disposed at or near the focal point. The directive characteristic of the reflector is superimposed upon the field pattern of the radiator, providing substantially a single narrow pattern lobe. The axis of this lobe may be altered with respect to the axis of the reflec- -tor by moving the radiator system off center, or

necessary switching may be done at any convenient point in the feed system between the antenna and associated radio apparatus.

I A further object is to provide a structure of the above described type which is mechanically strong.

These and other objects will become apparent to those skilled in the art upon consideration of the following description with reference to the accompanying drawing, of which Fig. 1 is a perspective view of a radiator structure according "to the instant invention, Fig. 2 is a schematic diagram of thestructure of Fig. 1 and the associated transmission line circuits, and Fig. 3 is a schematic diagram of a portion of the system of Fig. 1. Similar reference characters indicate similar elements in the drawing.

Referring to Figs. 1 and 2 a coaxial transmis- "sion line I has its inner conductor connected to a radiator 3 substantially A; wave length long. Four radiator elements 5, I, 9 and i I are provided at the end of the outer conductor of the line I and extend radially therefrom along two lines at right angles to each other. Each of the elements 5, "1,9 and II comprise an inner conductor I3, which is connected to the outer conductor of the line I, and an outer conductor connected to the inner conductor at the outer end thereof by a plug I5. The outer conductors are made slightly shorter than the inner conductors to avoid contact 7 Claims. (Cl. 250-11 2 with the line I. Each of the radiator elements :5, I, 9 and-I I is approximately /4 wave length long.

Four coaxial lines I'I, I9, 2| and 23 surround the line I with their outer conductors connected to the outer conductor of the line I. The inner conductors of the lines I119, 2| and 23 are connected to the outer conductors of the radiator elements 5, 1, 9 and II respectively. The above described structure is positioned in a parabolic reflector, not shown. The focal point of the refiector lies approximately in the plane of the radiator elements 5, l, 9 and I I.

The lines I! and 2| are connected together at a point 25 which is one-half wavelength further from the radiator 5 than from the radiator' 9. so

odd number of half wavelengths. A transmission line 21 is connected to the point 25 and through a line section 29 one-half wavelength long to a line 3|. A switch 33 is connected across the section 29. The radiatorelements I and II are similarly connected to a junction point 35, aline 31 one-half w'ave section 39, a line 4i and a switch 43. The lines 3| and 4| are connected to a double throw switch '45 which is connected to the line I and through a line 4'! to a radio device, not shown,

A power division network may beprovidediin the connections between the line 41, the line I and the switch 45 if necessary to provide the proper ratio between the energizati'ons of the element 3 and the radiators 5, I, 9 and II. The total length of the line from the switch 45 to each of the elements 5, I, 9 and II is an odd number of quarter wavelengths. The switches 33, '43 and 45 may comprise rotatable variable capacitor means connected with resonant line sections or any other well known type of radio frequency circuit making and breaking devices. These switches may be mechanically ganged together for sequential operation by means of an electric motor-46 or the like.

The operation is as follows:

Assuming the antenna is to be used for transmission, the radiator 3 is constantly energized through lines I and 41. The switch '45 alternately connects the lines 3| and 4|, energizing the respective dipoles 5, 9, and I, II. When the line 3| is connected to the line 41, the open circuit presented at the lower end of the line 4| is transformed to a short circuit at the upper ends of the lines I9 and 23, efiectively grounding the outer conductors of the members I and II. The radiators and 9 are similarly grounded when the radiators I and II are energized. When the switch 33 is open the total length of the line between the switch 45 and the radiators 5 and 9 is one-half wave longer than when the switch 33 is closed. Thus by opening and closing the switch 33, the polarity of the dipole 5, 9 is reversed. Similarly when the lines 4| and 41 are connected together by the switch 45, operation of the switch 43 reverses the polarity of the dipole I, II.

The radiation pattern of the radiator 3, neglecting the effect of the reflector is approximately the shape of a torus with an inner radius of zero, maximum energy being radiated in all directions at right angles to the axis of the radiator 3,

The reflector 24 modifies the pattern by concentrating it in a forward direction to'form a relatively narrow hollow conical beam, with maximum radiation in all directions at apredetermined small angle to the axis. This pattern is substantially the same Whether one pair or the other of the elements 5, 1, 9 and II is grounded. When the switch 45 connects the line 3| and the switch 33 is closed, current flows in the radiator elements 5, 9, and 3 as indicated by the solid arrow in Fig. 2. The current through the elements 5 and 9 provides a toroidal radiation pattern with the axis of minimum radiation along the axis 5, 9. The reflector 24 modifies this pattern to form a single narrow lobe with its maximum intensity along the axis of the element l3.

At a point R in space ahead of and to theright of the array, the electric field vectorproduced by the element 3 is at right angles to the line between the antenna system and the point R, and is directed toward the center. The electric field vector produced by the dipole 5, 9 at point R is.

also'at right angles to the radial line CR, but extends in the opposite direction. Thus the fields tend to cancel.

At a point L to the left of the; axis of the radiator 3 the field vector produced by the radiator 3- is again at right angles to the line from the antenna to the point L and directed inwardly. The field vector at L produced by the dipole 5, 9 is also at right angles to the line CL but extends in the same direction as that produced by the element 3 at point L. Thus the total radiation pattern is asymmetrical, having a point of maximum intensity to the left of the axis of the radiator 3.

If the switch 33 (Fig, 2) is now opened, the

polarity of the dipole 5, 9 is reversed, producing field vectors at points L and R as indicated by the dash arrows. The fields are now added at the points to the right of the axis of the radiator 3 and subtracted at points to the left of radiator 3.

Thus by operating the switch 33 two overlapping radiation lobes are produced alternately by the elements 35 and 9. The axis of maximum radiation of two lobes lie in the plane defined by the elements 3, 5, and '9. The operation of the radiators 1 and II, when the switch 45 is thrown to connect lines 4! and 47 is identical with the above described operation. However, the axis of maximum radiation will now lie in the plane determined by the elements 3, l and l I. By operating the switches 33, 43 and 45 in the proper sequence, four overlapping directive patterns are provided pairs of said coplanar radiators.

2. An antenna system including two pairs of collinear radiators lying in a common plane, said pairs being disposed at an angle to each other, two concentric transmission lines each connected between the adjacent ends of the radiators of one of said pairs, two branch concentric lines each connected to one of said first mentioned lines at a point one-quarter wave length distant from the midpoint thereof, each of said branch lines including a one-half wave line section and means for selectively including and removing said section from the circuit thereof, a main transmission line, means for connecting said main transmission line selectively to one of said branch lines, and a radiator element disposed at right angles to the plane of said coplanar elements and connected to saidmain transmission line.

3; The invention as set forth in claim 2 wherein each of said two coplanar radiator elements comprises a concentric line section substantially onequarter wave length long and short-circuited at its outer end and with its inner conductor to the end of the outer conductor of said main transmission line.

4. The invention as set forth in claim 2 including a substantially parabolic reflector arranged with its focal plane lying substantiall in the plane of said coplanar radiators.

5. An antenna system comprising pairs of collinear radiator elements lying in a common plane, each of said elements comprising a coaxial line section substantially one-quarter wave length long with its inner conductor connected to a grounded supporting member at one end and to its outer conductor at the other end, two concentric lines each connected between the outer conductors of a respective pair of radiators, each of said concentric lines being substantially an odd number of half wave lengths long, two branch lines, one connected to each of said first mentioned lines at a point one-half wave length further from one radiator element than from the other radiator element of the respective pair, a fifth radiator element extending at right angles to two of said coplanar elements and connected to a main transmission line, and means for selectively connecting said branch lines to said main transmission line.

6. The invention as set forth in claim 5 wherein each of said branch lines includes means for changingthe length of the transmission path through said branch lines by one-half wave length.

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