US3143737A

US3143737A - Folded sigma-shaped dipole antenna

Info

Publication number: US3143737A
Application number: US214777A
Authority: US
Inventors: Virginia T Norwood
Original assignee: Individual
Current assignee: Individual
Priority date: 1962-08-03
Filing date: 1962-08-03
Publication date: 1964-08-04
Anticipated expiration: 1981-08-04

Description

Aug. 4, 1964 v. T. NORWOOD 3,143,737 FOLDED S-SHAPED DIPOLE ANTENNA Filed Aug. 3, 1962 FIG.2.

j] FICA.

SOURCE INVENTOR VIRGINIA r. uoawooo g BY SOURCE ATTORNEY United States Patent Office 3,143,737 i 'atented Aug. 4, 1964 3,143,737 FOLDED S-SHAPED DIPOLE ANTENNA Virginia T. Norwood, Los Angelles, Calif., assignor, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Filed Aug. 3, 1962, Ser. No. 214,777 7 Qlairns. (431. 343797) This invention relates to a radio frequency antenna, and more particularly to a radiating antenna of the folded dipole type of an S-construction which is capable of being fed by a balanced open-wire line lying in the plane of polarization of the radiated power.

One of the most common and simple methods of feeding a multiple array of antennas is the use of a balanced open-wire line to carry the radio frequency energy from the source to each of the spaced antennas. The balanced open-wire line consists of a pair of straight conductors forming a transmission line. These conductors would lie in a horizontal line below the antennas. Vertical conductors from each of these horizontal conductors then carry the energy from the transmission line to the appropriate feed points on each of the radiating antenna structures, which are so spaced and oriented with respect to one another as to give the desired radiation pattern.

If each of the radiating antennas of an array is of the dipole or folded dipole configuration, the arms thereof extend horizontally, but in a horizontal direction perpendicular to the direction of the balanced open-wire line. In such an array, the balanced open-wire line will also be perpendicular to the polarization of the energy radiated from each of the antenna elements.

In some situations it becomes desirable to employ a pair of such multiple antenna arrays with one array having a polarization perpendicular to that of the other array; this is known as cross polarization. Thus the energy from one array will be radiated in a direction perpendicular to the direction of radiation from that of the other array. The signals from one array will not be received by the antennas of the other array since the arms do not lie in the direction of polarization of those signals. However, the open-wire line feeding each array will be extended in the direction of polarization of the other array of antennas and can be expected, unless shielded, to receive substantial quantities of the radiation transmitted from that other array resulting in interference between the two with the signal to be transmitted therefrom. Should a circumstance occur in which this mutual interference were undesirable or intolerable, it would be necessary to provide shielding of each of the open-wire lines from the radiated energy of the opposite array.

It is an object of the present invention to provide an antenna configuration having essential characteristics of a folded dipole antenna which may be fed from an openwire line which lies in the plane of polarization of the radiated energy.

Another object of this invention is to provide a new and improved antenna for radiating radio frequency energy in the manner of a folded dipole.

A further object of this invention is to provide a novel antenna array, which may be constructed from a plurality of antennas having a novel configuration.

Various other objects and advantages will appear from the following description of the several embodiments of the invention, and the most novel features will be particularly pointed out hereinafter in connection with the appended claims.

In the drawing:

FIG. 1 is a pictorial representation of the basic antenna configuration according to the invention;

FIG. 2 a pictorial representation of a modification of the basic configuration of the antenna of the present invention;

FIG. 3 is a representation of a multiple antenna array employing the basic antenna configuration with a balanced open-wire feed line; and

FIG. 4 is an illustration of the top view of a composite antenna array composed of a pair of arrays of the type shown in FIG. 3, which are orthogonally arranged and polarized with respect to one another.

In FIG. 1, is shown the basic antenna structure 10 in which a conductive metallic strip 11 is bent in the manner of a flattened S to form the radiating element of the antenna. The flat S-shape has an elongated center portion, which is approximately one wavelength long for most efficient operation; this center portion may vary, however, as in construction of the normal folded dipole antenna, from about three-quarters to one and a quarter wavelengths to give efiicient operation in radiating the radio frequency energy of a particular frequency. The end portions of the radiating strip 11 are bent back upon the center portions on opposite sides thereof to form the fiat S-shape. These end portions extend to approximately the mid point of the elongated center strip where they are attached dividually to a pair of

perpendicular coupling strips

12 and 13 to form the feed points of the antenna. The coupling strips 12 and 13 feed the radio frequency energy to the radiating strip 11 from which it is radiated into the surrounding space. It is to be noted that the mode of operation of the present antenna in many ways parallels that of the simple folded dipole. The energy fed to each of the folded end portions excites the center portion to produce fields thereon in exactly the same manner that the short portions of the folded dipole connected to the feed points induce a current in the continuous element connected thereto. However, it is to be noted that the feed points on the instant S-shaped antenna are located on a line perpendicular to the elongated direction of the antenna whereas in the folded dipole the two feed points lie opposite one another in a line parallel to the elongation of the antenna element. Since the direction of polarization of the radiated energy is in the direction of elon ation, the feed points in the instant antenna lie athwart the direction of polarization Whereas in the normal folded dipole they lie in the same direction as polarization.

It should also be noted that the configuration allows the polarization of the radiated energy to be rotated degrees without changing the feed points by simply using a radiating element in which the conductive radiating strip 11 is bent in backward fashion. The advantage of this feature will be later explained in more detail.

The antenna It may be constructed with a dielectric material 14 to fill in the spaces between the center conductor elements and the two outside portions of the elements in order to form a more rugged antenna structure, as commonly known in the art. The reactance of the instant radiating elements may be controlled by varying one or more of several parameters, such as the length of the radiating elements along the direction of the elongation, the width of the conductive strip, and by using materials for the dielectric filling 14 having different dielectric constants, all of which are well known in the art. Also variations in the resistance of the antenna can be accomplished by changing the spacing between the inner conductor and the two outer portions of the conductor in accordance with known principles applicable to folded dipole antennas, or by metallic loading at the feed points.

In addition to the well known methods of changing the impedance of antennas of the folded dipole varieties, this antenna configuration provides an additional method which may be employed. This additional method, as

illustrated in FIG. 2, consists of removing some or all of the inner conductor in the region between the feed points of the antenna. This may be done by cutting a notch 15 in the normally uniform antenna strip, as illustrated, or even by completely removing that portion of the strip. By thus varying the width of the metallic strip in this region, the shielding between the terminals is lessened and the impedance of the antenna is greatly increased. Obviously the impedance may also be decreased by increasing the width of the strip between the feed points. In each case an appropriate line length correction or an addition of metal blocks at the terminal points should be inade to maintain the resonance of the antenna input. In this manner the impedance of the antenna can be made to range from high levels of 400 ohms to low levels of 75 ohms by simply changing the width of the strip in the region of the feed terminals. Similar changes may also be made by varying the thickness instead of the width of the conductive strip between the two feed terminals.

In FIG. 3, three S-

shaped antennas

16, 17 and 18 are fed by an open wire line 19, which extends from a source of radio frequency energy 21. The antennas are spaced along the open-wire line 19 in such a manner as to give a desired radiation pattern for the radio frequency energy. In each case the

antennas

16, 17 and 18 are fed from the open-wire line and are polarized in the direction of the open-wire line 19. This is done without the necessity of bending or twisting the vertical feed element extending from the open wire line 19 to each of the antenna feed points. In the illustration of FIG. 3, the center antenna element is mounted in a mirror image or backward 8 fashion as compared with each of the

end antenna elements

16 and 13. As aforementioned, this provides a 180 degree phase shift in the radiated signal from this antenna 17 as distinguished from that which would ordinarily be produced by the spacing of the antennas along the open wire feed line 19. This accomplishes a result which could be obtained with the normal folded dipole only by feed line cross over or by a phase adjustment along the feed line.

In FIG. 4, a pair of

multiple antenna arrays

22 and 23 are shown disposed in orthogonal relation to one another. The energy radiated by the antenna elements of the array 22 will have a polarization which is perpendicular to that of the polarization of the multiple array 23. Thus, due to the orthogonal polarization, the energy radiation from one array does not interfere with that from the other array nor do the antenna elements receive any substantial portion of the energy radiated from the other array. In addition, the S-shaped antennas permit the open-wire lines feeding each of the arrays to be in orthogonal relation to the radiated energy from the opposite array. Therefore, one array may be operated in time coincidence with the other without either array receiving or interfering with the radiation of the opposite array either in the antenna elements or the openwire line feeding these elements. No substantial portion of either array or its feed lines will be in the direction of polarization of the other.

Thus, it may be seen that the normal configuration of the S-shaped antenna of the present invention provides a radiating antenna element having radiation characteristics similar to the normal folded dipole but having certain novel advantages thereover.

It will be understood that various changes in the details, materials, and arrangements of parts, which have been herein described and illustrated in order to explain the nature of the invention, may be made by those skilled in the art, within the principle and scope of the invention as claimed in the appended claims.

What is claimed is:

l. A radio frequency radiating antenna comprising a conductive element having a straight central portion, a pair of elongated straight portions parallel to said central portion and on opposite sides thereof, one end of each of said pair being conductively joined to an opposite end of said central portion and the other end of said pair being adapted to be connected to the terminals of a source of radio frequency energy, said other ends being adjacent one another on opposite sides of said central portion.

2. The antenna of claim 1 further comprising a solid dielectric material filling the area between each of said pair and said central portions.

3. A radio frequency radiating antenna comprising a radiating portion composed of a conductive strip, a pair of terminals at each end of said strip adapted to receive radio frequency energy to be radiated, said strip being bent upon itself in a single plane to form an S-shape having an elongated central portion and a pair of elongated end portions parallel to said central portion and on opposite sides thereof, said central portion being approximately three-quarters to one and a quarter times the wavelength of the radio frequency energy to be radiated, said pair of terminals being adjacent the same point on said central portion on opposite sides thereof, whereby radio frequency energy received at said terminals is radiated with a polarization parallel to said elongation in folded dipole fashion.

4. An antenna array comprising a plurality of antennas, each of said antennas comprising a conductive element having a straight central portion, a pair of elongated straight portions parallel to said central portion and on opposite sides thereof, one end of each of said pair being conductively joined to an opposite end of said central portion and the other ends of said pair being adapted to be connected to the terminals of a source of radio frequency energy, said other ends being adjacent One another on opposite sides of said central portion, a balanced open-Wire feed line disposed parallel to said elongated straight portions of said antennas, and a plurality or pairs of coupling conductors disposed at right angles to said open-wire feed line connecting one of said terminals of each of said antennas to a respective one of said openwire feed lines.

5. An orthogonal radio frequency radiating arrangement comprising a pair of antenna arrays comprising a plurality of antennas, each of said antennas comprising a conductive element having a straight central portion, :a pair of elongated straight, portions parallel to said central portion and on opposite sides thereof, one end of each of said pair being conductively joined to an opposite end of said central portion and the other ends of said pair being adapted to be connected to the terminals of a source of radio frequency energy, said other ends being adjacent one another on opposite sides of said central portion, a balanced open-wire feed line disposed parallel to said elongated straight portions of said antennas, and a plurality of pairs of coupling conductors disposed at right angles to said open-wire feed line connecting one of said terminals of each of said antennas to a respective one of said open Wire feed lines,.said elongated portions of the antennas and the open wire transmission lines of each of said arrays being perpendicular the elongated portion the antennas and the open-wire transmission line of the other array, whereby the antennas and feed lines of each array are orthogonally polarized to that of the other array.

6. A radio frequency radiating antenna comprising a radiating portion composed of a conductive strip, a pair of terminals at each end of said strip adapted to receive radio frequency energy to be radiated, said strip being bent upon itselfin a single plane to form an S-shape having an elongated central portion and a pair of elongated end portions parallel to said central portion and on opposite sides thereof, said central portion being approximately to 1% times the wave length of the radio frequency energy to be radiated, said pair of terminals being adjacent the same point on said central portion on opposite sides thereof, the portion of said conductive strip in the vicinity of said same point having difierent crosssectional area from the remainder of the conductive strip, whereby radio frequency energy received at said terminals is radiated with the polarization parallel to said elongation and folded dipole fashion.

7. A radio frequency radiating antenna comprising a radiating portion composed of a conductive strip, a pair of terminals at each end of said strip adapted to receive radio frequency energy to be radiated, said strip being 10 bent upon itself in a single plane to form an S-shape having an elongated central portion and a pair of elongated end portions parallel to said central portion and on opposite sides thereof, said central portion being approximately to 1% times the Wave length of the radio frequency energy to be radiated, said pair of terminals being adjacent the same point on said central portion on opposite sides thereof, a portion of said conductive strip in the vicinity of said same point being removed, whereby radio frequency energy received at said terminals is radiated with the polarization parallel to said elongation and folded dipole fashion.

References Cited in the file of this patent UNITED STATES PATENTS 2,505,098 Cornelius Apr. 25, 1950 3,025,524 Thies Mar. 13, 1962 FOREIGN PATENTS 289,640 Italy Oct. 22, 1931 560,461 Canada July 15, 1958

Claims

1. A RADIO FREQUENCY RADIATING ANTENNA COMPRISING A CONDUCTIVE ELEMENT HAVING A STRAIGHT CENTRAL PORTION, A PAIR OF ELONGATED STRAIGHT PORTIONS PARALLEL TO SAID CENTRAL PORTION AND ON OPPOSITE SIDES THEREOF, ONE END OF EACH OF SAID PAIR BEING CONDUCTIVELY JOINED TO AN OPPOSITE END OF SAID CENTRAL PORTION AND THE OTHER END OF SAID PAIR BEING ADAPTED TO BE CONNECTED TO THE TERMINALS OF A SOURCE OF RADIO FREQUENCY ENERGY, SAID OTHER ENDS BEING ADJACENT ONE ANOTHER ON OPPOSITE SIDES OF SAID CENTRAL PORTION.