US3325815A - Ramp feed antenna - Google Patents

Description

J1me 1967 E. M. T. JONES ETAL 3,325,815

RAMP FEED ANTENNA Filed Feb. 18, 1964 1 VENTO pm a 5' 455%;- 55.52

United States Patent 3,325,815 RAMP FEED ANTENNA Edward M. T. Jones, Portola Valley, Robert L. Tanner,

Menlo Park, and Eugene D. Sharp, Palo Alto, Calif.,

assignors to the United States of America as represented by the Secretary of the Air Force Filed Feb. 18, 1964, Ser. No. 345,813 1 Claim. (Cl. 343-731) This invention relates to an antenna for transmitting or receiving radiant energy and, more particularly, to a very broad bandwidth antenna having an inherent direction selective characteristic.

One of the disadvantages in the prior art resides in the narrow bandwidth over which an antenna may be operated thereby requiring differing physical variations depending upon the operating frequency or frequencies.

The antenna of the present invention is used to couple electromagnetic waves into a region enclosed by two spaced conducting sheets. The conducting sheets are connected by a ramp-like structure. One end of the ramp terminates in the center conductor of a coaxial output cable which is connected to one of the spaced sheets. The other end of the ramp is connected to a termination resistor which is connected to the remaining spaced sheet. Depending upon the direction of the arrival of the received signal, the signal is fed either to the coaxial cable or to the terminating resistor where the signal is dissipated. Thus the antenna has an inherent direction selective characteristic. It is to be noted that hereinafter the aforementioned structure is referred to as a ramp feed antenna.

One of the advantages of the ramp antenna of the present invention is that it can be used over a very large frequency bandof the order of ten and twenty to one with input impedance being constant over this band. The radiation pattern of the ramp antenna is that of an endfire antenna of the same electrical length for a long electrical length the main lobe is narrow and for shorter electrical lengths the main lobe is wider.

An object of the present invention is to provide a broad band antenna for radiant energy having a pair of spaced conducting sheets with a ramp-like structure connecting the sheets.

Another object of the present invention is to provide a broad band antenna for radiant energy wherein electromagnetic waves are coupled into a region enclosed by two conducting sheets.

Yet another object of the present invention is to provide a broad 'band, constant impedance antenna wherein electromagnetic waves are coupled into a region enclosed by two conducting sheets and operating to provide an endfire antenna radiation pattern.

The various features of novelty which characterize this invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, however, its advantages and s ecific objects obtained with its use, reference should be had to the singly accompanying drawing and descriptive matter in which is illustrated and described a preferred embodiment of the invention.

A schematic of the ramp feed antenna is shown in the single drawing. It is named the ramp feed antenna because it resembles a ramp in the form of conductor 1 which extends from lower conducting sheet 2 to upper conducting Patented June 13, 1967 "ice sheet 3. Conductor 1 is referred to as the ramp feed and one end thereof is connected through terminating resistor 4 to conducting sheet 3; the other end is connected to center conductor 5 of coaxial transmission line 6 with outer conductor 7 of coaxial line 6 connected to conducting sheet 2. The ramp feed antenna can be used as a transmitting or receiving antenna.

Conducting sheets 2 and 3 are spaced and parallel. They may be in the form of solid conductors or of a wire mesh; their shape may be planar or curved. It is also to be noted that they may be parallel to each other or flared.

The ramp feed antenna may be comprised of one of a number of configurations. For example, the ramp feed may be a single large or small conducting wire, it may be made up of several closely or Widely spaced conducting wires; or it may 'be one or more conducting strips. In any configuration, the ramp conductor or conductors are chosen so that the characteristic impedance of the ramp is constant along its length and the resistance of the terminating resistor is chosen to be equal to the characteristic impedance.

When the ramp feed antenna illustrated in the single drawing is operating in the receiving mode, electromagnetic waves incident upon ramp feed antenna 1 induce currents in the antenna conductors 2 and 3. Depending upon the direction of arrival, the induced currents travel to the output end, coaxial line 6 or to terminating resistor 4. When the waves are coming from the right of the illustrated single drawing, the induced currents travel to the output coaxial line 6, and can be detected by a receiving system. When the waves are incident from the left in the single illustrated drawing, the induced currents travel to terminating resistor 4, are dissipated there, and are not detected in the receiving system. Thus the ramp fed antenna has an inherent direction selectively of waves depending upon their direction of arrival.

The principal advantage of the ramp feed antenna is that it can be used over a very large frequency band with the input impedance 'being constant over this band. The radiation pattern of the ramp antenna is that of an endfire antenna of the same electrical length; for a long electrical length the main lobe is narrow and for shorter electrical lengths the main lobe is wider.

The ramp feed antenna of the present invention was utilized in one instance in the 120 to 1200 me. band. The ramp feed antenna was arranged to provide a characteristic impedance of ohms. The measured input VSWR of this antenna was less than 1.5 over a ten to one frequency band when a 75 ohm resistor was used as the terminating resistor.

Although the invention has been described with reference to the reception of radiant energy, it will be apparent to those skilled in the art that the antenna described herein may also be used for transmission if desired.

Having now particularly described and ascertained the nature of our said invention and in what manner the same is to be per-formed, we declare what we claim is:

In an electromagnetic antenna system with a ramp feed to provide broad band operations comprising a first and second conducting sheet in a spaced and parallel arrangement to each other, each of said first and second conducting sheets having comparable first and second ends, a coaxial line having inner and outer conductors, said outer conductor of said coaxial line 'being connected to 3 4 said first conducting sheet in the region of said first end References Cited thereof, a resistor having a preselected impedance con- UNITED STATES PATENTS nected to said second conducting in the region of said second end thereof, a third conductor interconnecting 210951078 10/1937 PePeISOH 343-731 X said inner conductor of said coaxial line and said resistor, 5 3268896 8/1966 Spltz 343 785 X said third conductor operating as a ramp feed and having FOREIGN PATENTS a constant characteristic impedance along the length there- 1,160,096 7/1958 France of identical to said preselected impedance of said third conductor with said ramp feed receiving electromagnetic HERMAN KARL SAALBACH, P i E i energy from one direction *for dissipation in said resistor 10 ELI LIBERMAN Examiner and receiving energy from another direction for utiliza- {ion in aid oaxial line, R. COHN, S. CHATMON, JR., Assistant Examiners.

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