US2568710A - Wide-band antenna - Google Patents

Description

Sept. 25, 1951 J. T. BOLLJAHN WIDE-BAND ANTENNA Filed Nov. 13, 1945 TRANSMITTER JOHN T. BOLLJAHN Patented Sept. 25, 1951 WmE B N man John T. Bolljahn, Washington, 1)."0." Application masher. 13, 1945, Serial No. 628,339 10 Claims. (or'zali-gae) l (Granted under the act of March-3,,1883, as amended 30, 1928; 370 G. 757),

.-..Thi invention relates. to antennas and, more particularly,:to-wide-band antennas.

An object of theinvention is to provide an antenna capable of eincient operation over a wide band of frequencies.

,Another object of the invention isto provide arwide-band antenna suitable for mounting on the exterior surface of a high-speed aircraft.-

A further object of the invention is to provide alwide-i-band antenna which has a low resistance to the flow-of air at high velocity. ,7 The,iradiating element of an antenna in. accordance with the invention comprises a. thin sheet of conductive material, which projects through .an opening in an extended conductive surface. Means, which ma comprise a pair of, tapered conductors, are provided for coupling the radiating element to a transmission. line. The other end of the line maybe connected to a Wave signal translator, suchas a radio receiver or transmitter. Inductive stubs conductively'attached tothe radiating element are provided for neutralizing the normal reactance of the radiating element, thereby providing a substantially non-reactive-termination at the antenna end of the-transmission line. 3

Other objects, features and advantagesof the invention will be apparent from consideration of thefollowing description and the accompanying drawing, inwhich Fig. 1 is an elevation view of an exemplary embodiment of the invention, and y Fig. 2 is a sectional view of the, embodiment shown in.,Fig. 1, taken in the plane. 2-2.

Referring now to the drawing, the, radiatingelement of an antenna according to the invention may comprise a thin conductive sheetll. Means comprising tapered conductors I3, l5- are provided for, efiecting a gradual dimensional transition between the radiating element H and a coaxial transmission line H. A pair of inductive stubs comprising conductive sheets l9, 2| are positioned on each side of the radiating element H and are conductively connected thereto between the ends thereof by the shorting bars 23, 25.

The outer tapered conductor I 5 is connected at the wide end thereof to an extended conductive surface 21. The inner tapered conductor [3 may .bea continuation of the radiating sheet element H projecting below the conductive surface 21, .the width of the sheet being tapered down to the diameterof the inner conductor of theline H at the junction therebetween. If, as is shown, the thickness of the radiating element II is substantially the same as the diameter of theinner conductor of the line H, the thickness of conductor I3 need not be tapered.

The conductive surface 21 may comprise, for example, the metallic outer surface of an airrection of air flow. It has been found that minimum wind drag of the antenna is obtained on highspeed aircraft when the ratio of width to thicknessof. the antenna is aslarge as is practicable. Consequently, the invention provides an antenna which is well adapted for use on high speed aircraft.

I The antenna structure projecting above, the conductive surfaceZ'l: may, be enclosedin a dielectric housing 29 of appropriate dimensions to protect and strengthen the structure.

The height of the radiating element H above the conductive surface, 21 is preferably of the orderof one-quarterwavelength near the center of the frequency band over which wide-band operation is desired, The width of element ll may be of ,the order of one-eighth wavelength.

The tapered conductors efiect a smooth dimensional transition betweenthe line I! andthe ane tenna. When the antenna has the dimensions mentioned above, the impedance .of the antenna provides a satisfactory termination for a -ohm transmission line; Consequently, if line, H has a characteristic impedance of 50 ohms, the tapered conductor sections l3, I5 are designed to maintain a 50 ohm characteristic impedance throughout their length between the line H and the radiating element H. However, the tapered conductors may constitute an impedance transformer if the desired line impedance is not matched .satisfactorilyby. the, antenna impedance. I

.While a radiating element II has been shown comprising a rectangular sheet, it will be apparent that sheet elements having other than rectangular shapes may be used without departing fromthe scope ofthe invention. For example, diamond-shaped,- triangular, elliptical or other plane figures maydefine the edges of radiating element l I. I

The inductive stubs l9, 2| are provided to neutralize thereactive componentof the antenna impedance. The stubs I 9,,2l together withelement ll effectively constitute sections of transmission line having plane conductors, which are short-circuited atone end by shorting bars 23, 25. In accordance with known transmission line theory, the length of the stubs and their separation from element Il may be computed so as to 1 cause the studs to present an inductive reactance ofv substantiallyequal magnitude to the capacitive reactance of the radiating element ll, over a wide band of frequencies. Thus, means are provided for maintaining a substantially nonreactive termination of the line 11 by the an- The invention described herein may be manuefactured and used by or for the Government of the United States of America for governmentar purposes without the payment ofany royalties,

thereon or therefor.

What is claimed is: f 1. An antenna comprising a conductive sheet having a length of substantially one-quarter of the operating wave -length and; g. width'whieh is a fraction less than unity of the operating wavelength, a transmission line, and means for coupling the line to the conductive sheet comprising a tapered flat divergent conductor section interposed between the line and the conductive sheet.

2. An antenna comprising a conductive sheet having a length of substantially one-quarter of the operating wave-length, and a width which is a fraction less than unity of the operating wavelength, a transmission line, and means for coupling the line to the conductive sheet comprising a tapered flat divergent conductor" section interposed between the line and the conductive sheet, and -a dielectric housing enclosing the conductive sheet.

3.1m combination, an antenna comprising a conductive sheet having a'length of substantially one-quarter of the operating wavelength, and .a width which is a fraction les than unity of the operating wavelength, meansdefining an extended ground plane conductive supporting surface for the antenna, a transmission line, and tapered fiat divergent conductor means for coupling the line to the antenna; r i l 4; In combination an antenna comprising a conductive sheet having a lengthof substantially one-quarter of the operating wavelength, a finite thickness, and a width which is substantially one-eighth of :the operating wavelength, a coaxial transmission line, having an inner conductor With-a diameter equal to the thickness of the conductive sheet, means defining an extended ground plane conductive supporting sure face for the antenna, and a taperedflat divergent section of the transmission Je-ine foraeffectingsa gradual transition between the widths of the icon ductive sheet and thecross-sectionaldimensions of the line. 1 e

5. In combination an antenna -.comprising =a conductive sheet .having a length of substantially one-quarter of the operating wavelength and a width which is substantially one-eighth .of the operating .;,wav:elength, .means defining an ex tended ground plane conductive supporting ,=su r.-

{ace for :the antenna,'=a pair of conductive elements positioned parallel to the conductive sheet on opposite sides thereof and connected -:to the sheet intermediate the ends thereof, a coaxial transmission line, and :taperedmonductor :means coupling the line to the conductive sheet.

6. An antenna comprising a conductivesheet having a length of substantiallyone-quarterof the operating wavelength and a width which is substantially one-eighth of said "Wavelength, and a pair of inductive transmission line elements shorter than :the conductive sheet positionedparallel to the sheet and conductively connected to l the sheet atone end of eachrelement.

wavelength, a pair of conductive elements shorter than the conductive sheet positioned parallel to the sheet and conductively connected to the .sheetat one end of each element, a transmission line, and tapered conductor means for coupling the line to the antenna.

,8. An antenna comprising a conductive sheet having a length of substantially one-quarter of I the operating wavelength and a width which is substantially one-eighth of said wavelength, a

pair of conductive elements shorter than the conductive sheet positioned parallel to the sheet and conductively connected to the sheet at one end of each element, a transmission line, and tapered conductor means for coupling the line to the antenna, and means defining anextended ground plane conductive supporting surface for the antenna, the antenna and the line extending in opposite directions from the conductive surface.

9. An antenna comprising, a conductive sheet having a length of substantially one-quarter of the operating wavelength, and a width which is substantially one-eighth of the operating wavelength, means defining an extended ground plane conductive supporting surface for the antenna, a transmission line, a tapered planar conductive member coupling one conductor of the transmission line with the conductive sheet, and a pair of divergent tapered flat planar conductive'members disposed on opposing sides of the planar conductive member connecting'a second conductor of the transmission line with the aforementioned means. 10. Anantenna comprising, a conductive sheet having a length of substantially one-quarter of the operating wavelength, a finite thickness, and a width which is substantially one-eighth of the operating wavelength, means defining an extended ground plane conductive supporting surface for the antenna, a transmission line having at least a first conductor equal in thickness to the thickness of the conductive sheet and a second c0n-- ductor, a tapered planar conductive member coupling the first conductor of the transmission line to the conductive sheet, and a pair of divergent tapered flat planar conductive members disposed on opposing sides of the planar conductive member connecting a second conductor of the transmission line with the aforementioned means.

JOHN T. BOLLJAHN.

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

V v UNITED STATES PATENTS Number

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