US2501778A

US2501778A - Broadcast antenna

Info

Publication number: US2501778A
Application number: US702426A
Authority: US
Inventors: Nils E Lindenblad
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1946-10-10
Filing date: 1946-10-10
Publication date: 1950-03-28
Anticipated expiration: 1967-03-28

Description

March 28, 1950 N. E. LINDENBLAD I 2,501,778

BROADCAST ANTENNA 5 Filed Oct. 10, 1946 rmkwrma INVENTOR ATTORNEY Patented Mar. 28, 1950 atoms BROABCAST ANTENNA Nils E. Lindenblad, Port Jefferson, N. Y., assignor to Radio Corporation of America, a corporation of Delaware Application October 10, 1946, Serial No. 702,426

7 Claims. 1

The present invention relates to broadcast antennas and more particularly to non-resonant broadcast antennas which may be used over a wide band of frequencies without discrimination.

An object of the present invention is to provide a broadcast antenna which is non-resonant. Another object of the present invention is the provision of an antenna which provides a large amount of low angle radiation for broadcast'purposes without the use of high antennastructures.

Another object of the present invention is the provision of an antenna which may be efiiciently operated at a poor location having a highresistance ground. v

The foregoing objects and others which may appear from the following detailed description are attained in accordance with the principles of the present invention by providing an antenna in the form of a conductor disposed about the circumference of a circle having a diameter of the order of several wavelengths and fed with travelling waves. The circularly arranged conductor is spaced a short distance above a poorly conducting ground surface. The conductor is therefore eiiectively located at one side of a boundary between two dielectrics. The underlying dielectric, the ground, has such relative characteristics that it provides a distorted image. The cancelling effect between the wire and the image is reduced to a high degree at low angles in the direction of the wire and away from the boundary and the image producing dielectric providing a resultant radiation in these directions. The major portion of the radiation from such an antenna is vertically polarized.

The present invention will be more fully understood by reference to the following detailed description which is accompanied by a drawing, not to scale, in which:

Figure 1 illustrates in perspective an embodiment of the present invention, while Figure 2 illustrates a modification thereof.

Referring now to Figure 1 there is shown a number of supporting poles Ill arranged around the circumference of a circle having a diameter of the order of several wavelengths at the frequency with which the antenna is to be operated. The poles support conductor M through the intermediary of insulators l2. The ring conductor it being supported in a generally circular configuration acts as the radiator. It is fed at one end by transmitter l6 and is terminated at the other end by terminating resistor IS. The terminating resistor I8 has such value of resistance as to match the surge impedance of the line 14.

2 Thus, a pure travelling wave is set up along the conductor M when transmitter I6 is energized.

Since the ground over which the antenna is arranged is a high resistance ground, the image of wire [4 produced in the high resistance ground is'distorted The cancelling effect takingplace over aground of high conductivity between the wire l4 and its closely adjacent image is especially' reduced at the lower angles in the direction of the wire due-to this distortion of the image. Thus, the major portion of the energy is radiated in a direction approaching the direction of the antenna wire and is therefore vertically polarized. Due to the circular arrangement of the wire it is radiated tangentially and uniformly in all directions and, of course, at a comparatively low, upward angle with respect to the ground as a result of the distorted image.

For operation. in the present broadcast band, for example, the antenna might have a diameter of the'order of a thousand feet and be'separated by poles 15 or ZO-feet high. It is only necessary that the poles be high enough to provide clearance for any trafiic which may have to'pass under the wires.

The modification shown in Figure 2 differs from that in Figure 1 only in that a pair of wires 24 and 26 are used. The wires are fed from transmitter 16 at the oposite ends of the diameter of the circle and are terminated by terminating resistors 28 and 33 respectively. Conductors 24 and 26 each occupy a semi-circumference of the entire circle and are fed in an inphase relationship at opposite ends of a diameter of the circle. The radiation from the antenna of Figure 2 takes place in the same way as described above with reference to Figure 1.

While I have illustrated a particular embodiment of the present invention, it should be clearly understood that it is not limited thereto since many modifications may be made in the several elements employed and in their arrangement without departing from the spirit and scope of the invention.

What is claimed is:

1. A broadcast antenna for vertically polarized radiation at low angles with respect to ground comprising a number of conductors arranged in an end-to-end relationship to form a substantially closed geometrical figure having a transverse dimension greater than several operating wavelengths, said conductors being spaced a short distance above a poorly conductive ground, means connected to one end of each of said conductors for energizing said conductors with a travelling wave and reflection preventing means connected between the other end of each conductor and ground.

2. A broadcast antenna for vertically polarized radiation at low angles with respect to ground comprising a number of conductors arranged in an end-to-end relationship in a complete circle having a diameter longer than several wave lengths, said conductors being spaced a short distance above a resistive dielectric, means connected to one end of each of said conductors for energizing said conductors with a travelling wave and reflection preventing means connected between the other end of each conductor and said resistive dielectric.

3. A broadcast antenna for vertically polarized radiation at low angles with respect to ground comprising a number of conductors arranged in an end-to-end relationship in a complete circle,

said conductors being spaced a short distance above a resistive dielectric, means connected to one end of each of said conductors for energizing said conductors with a travelling wave and refiection preventing means connected between the other end of each conductor and said resistive dielectric, said circle having a diameter of a number of wavelengths at the operating frequency.

4. A broadcast antenna for vertically polarized radiation at low angles with respect to ground. comprising a pair of conductors arranged in an end-to-end relationship in a complete circule having a diameter greater than several operating wave lengths, said conductors being spaced a short distance above a high resistance dielectric, means connected to one pair of diametrically opposite ends of said conductors for energizing said conductors with a travelling wave and reflection pre venting means connected between the other end of each conductor and said high resistance dielectric.

5. A broadcast antenna for radiating vertically polarized waves at low angles with respect to a poorly conducting ground and comprising a conductor arranged around the circumference of a circle having a diameter of several wavelengths at the operating frequency, means connected to one end of said conductor for energizing said conductor and reflecting preventing means connected between the other end of said conductor and ground.

6. A broadcast antenna for radiating vertically polarized waves at low angles with respect to poorly conducting ground comprising a conductor arranged around the circumference of a circle having a diameter of the order of several wavelengths at the operating frequency, means connected to one end of said conductor for energizing said conductor and reflecting preventing means connected between the other end of said conductor and said poorly conducting ground, said wire being spaced above said poorly conducting ground a distance which is small compared to a wavelength.

7. A broadcast antenna for radiating vertically polarized waves at low angles with respect to a high resistance dielectric surface comprising a conductor arranged around the circumference of a circle having a diameter equal to several wavelengths at the operating frequency, means con nected to one end of said conductor for energizing said conductor and reflecting preventing means connected between the other end of said conductor and said dielectic surface, the spacing between said wire and said surface being substantially less than a quarter wavelength at the operating frequency. 7

NILS E. LINDENBLAD.

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

UNITED STATES PATENTS Number Name Date 1,381,089 Beverage June 7, 1921 2,247,743 Beverage July 1, 1941