US2514821A - Antenna system - Google Patents

Description

y 1950 o. M. WOODWARD, JR 2,514,821

ANTENNA SYSTEM Filed Sept. 29, 1945 INVENTOR;

' Q 4! .4 v (LEM out requiring impedance transformers.

ever, in some cases, such as whenthe radlators Patented July 11, 1950 e UNlTED STATES PATENT OFFICE Oakley M. Woodward, Jr., Princeton, N. J., asorationof America, a corsignor to' Badio Corp poration of Delaware Application September 29, 19.45 Serial N 0. 619,401 3 Claims. (01. 25.0 -33.65)

This inventionrelates to antennas, and more particularly to improvements in multi-element arrays wherein a plurality of radiators are energized from a single source or connected to a single utilization circuit.

In usual .high frequency arrays, the radiators areresonant dipoles, often havingjimpedances ofthe order of 50 to 70 ohms. These impedances are of the same order as the characteristic impedances :of standard commercially obtainable coaxial transmission lines, so that ordinarily the dipoles can be coupled directly to the lines with Howare mounted close to a conductive reflector, the individual antenna impedance is so much lower that some impedance matching device is required. Most impedance matchingzdevices comprise resonant elements whose characteristics are superimposed 'upon those of the radiators,

seriously limiting the width of the band of frequencies through which the system will operate efliciently. i

Accordingly, it is the principal object of this invention to provide. an improved method of and means for connecting a plurality of dipole antennas inseries with each other to a common, feed line. Another object is to provide an improved type of antenna structure which is simple and rugged in construction and easily designed to provide efficient operation throughout a wide frequency band.

The foregoing and other objects will become apparent to thoseskilled in the art upon consideration of the following description, with reference to the accompanying drawing, wherein:

Figures 1 and 2 are viewsin plan and elevation respectively of one antenna structure embodying the instant'invention,

Figure 3is a schematic diagram of an equivalent circuit of the system of Figure 1, and

Figure 4 is a view partly in section, of another embodiment of the present invention.

Referring to Figures. 1 and 2, a tray or panlike structure I is provided withend walls 3 and 5 and, a central partition 1. The over-all length is substantially one wavelength at the mean fre- 'quency of operation of the system. A coaxial transmission line 9 extends through the end wall 3 and the partition 1, terminating on the end wall 5. The outer conductor of the line 9 is connected tov the walls 3, 5, and I where'it passes-through them. The inner conductor of the line 9 may stopshort 'of the wall 5 as shown, or may be conwithdiagonal slots isand I5 at points midway between the wall 3 and the partition 1 and midway between the wall 5 and the partition I respectively. These slots break the outer conductorinto three sections 11, I9 and 2|. The section -2I is one-quarter wavelength long. The section l9 isone-half wavelength long, grounded at its center by its connection to the partition I. The portion of the section I! within the pan is one-quarter wavelength long.

The inner conductor of the line 9 is not broken, but extends continuously through to the shorting plug |-I. The portion of the inner conductor within the section l9 may be made of somewhat greater diameter than theremainder, for a purpose explained hereinafter, or the inner conductor may be of the. same diameter throughout. i

A-pair ofradiator elements 23 and 25 are connected to members l1 and 19 respectively on opposite sidesof the gap i3. Similar radiator elements 2'! and 29 are connected to members 2| and 19 respectively at the gap i5. In the present illustration, the radiators are spaced about 0.1 wavelength from the surface of the pan I. However, thisspacing may be made greater or less, in accordance with various design considerations.

The. operation of the described system is as follows:

The outer conductor section 2| cooperates with the surface of the pan 1 to act as a quarter wavelength line section, short circuited at one end by the wall 5 and therefore presenting a high impedance at the other end. The end of the section 2|: adjacent the gap is thus efiectively isolated from ground at the frequency of operation.

Similarly, the left-hand portion of the section l9, grounded at the partition 1, provides a high impedance adjacent the gap 15. Thus each of the dipole elements 2! and 29 is separated from ground by the high impedance of a shorted quarterxwave line. The elements 23 and 25 are similarly isolated from ground by the right-hand portion of the section 19 and the left-hand'end current to flow from left to right on the outer.

conductor section l9, and thence outward on the radiator 25. The radiators 23 and 25 are'thus excited as elements of a dipole with equal currents flowing in on one and out on the other.

When current flows into the line section 19' at the gap l3, an equal current flows into it at the gap [5, corresponding to a phase difference of 180 between the currents at the two ends of the half wavelength line section between the gaps [3 and l5. Thus the current flows outward'on the radiator 29, and inward on the radiator 21, through the conductor 2|, the plug l I, and from left to right on the inner conductor within the section 2|.

The section 2!, the conductor inside it, and the plug ll, cooperate to function as a shortcircuited stub line in series with the radiators 21 and 29. This stub is not required unless the system is to be tuned to a frequency other than that at which the radiators are naturally resonant. If it is used, the plug II is placed at such a position that the reactance of the stub is equal to and of opposite sign to the sum of the reactances of the two dipoles.

without altering the series-connected operation. Moreover, the spacing between adjacent dipoles need not be one-half wavelength, but may be made different for certain applications by filling the short-circuited quarter wave sections, or the feed line, or both, with dielectric material.

I claim as my invention: 7

1. A radio antenna system including a coaxial feed line comprising a continuous inner conductor and an outer conductor surrounding said inner conductor, said outer conductor comprising a series of collinear sleeves, with the adjacent ends of each pair of sleeves spaced apart longitudinal1y;"a plurality of radiator elements, one connected at each end of each of said sleeves, and conductive means at least partially surrounding said sleeves and in contact therewith only at the midpoints of said sleeves, whereby each pair of adjacent radiator elements functions as a doublet, and all of said doublets are electrically in series with each other across said feed line.

2. A radio antenna including a coaxial line comprising an inner conductor and an outer conductor,'said outer conductor having a series of gaps at intervals along its length, a plurality of dipoles, one at each of said gaps, and each including two radiator'elements connected to said outer conductor respectively at opposite sides of the respective gap, and a further conductor ex- By virtue of the above described arrangement,

the current applied to the line 9 flows serially through the two dipoles, so that the impedance presented to the feed line is twice that of each dipole. The inner conductor within the half 'wave section it may be made of larger diameterto lower the characteristic impedance of this portion to match the dipoles 21 and 29, although this is not necessary to the satisfactory operation of the system.

, Referring to Figure 3, the impedances of the dipoles 23, 25 and 2i, 29 are represented by the blocks '33 and 35 respectively. The parallelresonant impedances of the quarter wave lines formed by the pan 1 and the sections of the outer conductor of the line 9 are represented by'the circuits 31, 39, 4| and 43. The impedance of the stub formed by the plug 1 l is represented by the block 45. Since the impedances 33 and 35 are equal to each other, and the impedances 31, 39,4! and 13 are all alike, the voltagesapplied to all of the radiators are equal.

Although the invention has been described with reference to a, system comprising two seriesconnected dipoles, it will be apparent that it may be extended to any number of series radiators. Referring to Figure 4, a coaxial line 9 has its outer conductorcut at a plurality of points I3, I5 at half wave intervals. Dipoles are connected across the gaps, as in the system of Figure 1. The half wavelength sections are surrounded by conductive sleeves 41, connected at their midpoints to the midpoints of the corresponding half Wavelength outer conductor sections. The operation of the system of Figure 4 is substantially identical withthat of Figure 1. It will be apparent without further illustration that the connections of every other dipole could be reversed, if desired,

by cutting all the slots in the same direction,

tending generally parallel and in spaced relationship to said outer conductor, and connected thereto at points midway between said gaps.

3. A radio antenna including a' coaxial line comprising an inner conductor and an outer conductor, said outer conductor having a series of gaps at half wavelength intervals along its length, a plurality of dipoles, one at each of said gaps, and each including two radiator elements con nected to said outer conductor respectively at op posite sides of therespective gap, a further con ductor extending generally parallel and in spaced relationship to said outer conductor, and con nected thereto at points midway between said gaps, and a reactance element connected to one end of said inner conductor and the corresponding end of said outer conductor.

' 4. The invention as set forth in claim 3, wherein said further conductor comprises a reflector for said antenna. v

5. A radio antenna system including a transmission line comprising one continuous conductor and a second conductor parallel thereto and provided with a series of gaps spaced longitudinally thereof; a plurality of dipoles each disposed adjacent one of said gaps and each comprising two radiator elements connected to said second conductor respectively on opposite sides of the respective gap, and a third conductor parallel to said line and connected to said second conductor at points midway between said gaps.

6.'A radio'antenna system including a transmission line comprising one continuous conductor and a second conductorparallel'thereto and provided with "a series of gaps at half wavelength intervals; a plurality of dipoles each disposed adjacent one'of said gaps and each comprising two radiator elements connected. to said second 0on ductor respectively on opposite sides of the re spective gap,"a third conductor parallel to said line and connected to said second conductor at points midway between said gaps, and a reactf ance element'connectedbetween one end of said first conductor "and the corresponding end of said second conductor. J I V I 7; An antenna system including a substantially rectangular pan-shaped body of conductive ma- 8. The invention as set forth in claim 5, in-

eluding a reactance element connected between one end of said inner conductor and said outer conductor.

OAKLEY M. WOODWARD, JR.

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

UNITED STATES PATENTS 10 Number Name Date 2,275,646 Peterson Mar. 10, 1942 2,287,533 Peterson June 23, 1942 2,321,454 Brown June 8, 1943 2,327,418 Goldmann Aug. 24, 1943

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