U.S. patent number 3,611,396 [Application Number 05/047,504] was granted by the patent office on 1971-10-05 for dual waveguide horn antenna.
This patent grant is currently assigned to N/A. Invention is credited to Howard S. Jones, Jr..
United States Patent |
3,611,396 |
Jones, Jr. |
October 5, 1971 |
DUAL WAVEGUIDE HORN ANTENNA
Abstract
A dual waveguide horn antenna is provided with a rigid foam
having a dielectric constant approximately equal to that of air and
tapered to conform to the shape of a conventional horn antenna. Two
tapered walls are corrugated and all four walls are covered with a
thin metallic coating of sufficient thickness to carry the RF
current produced by the propogation of an electromagnetic wave
through the dielectric. A metallic septum divides the dielectric
into first and second waveguide sections and individual coaxial
inputs are provided to each of the sections. Energy coupling
between the two sections of the waveguide are significantly reduced
by means of a microwave resistive material secured to the septum at
the enlarged end of the dielectric. The resistive strip may
comprise a carbonized substrate or an insulating material coated
with the resistive film. Additionally, a thin film of paint may be
applied directly to the metallic septum by various techniques
including vacuum deposition.
Inventors: |
Jones, Jr.; Howard S.
(Washington, DC) |
Assignee: |
N/A (N/A)
|
Family
ID: |
21949351 |
Appl.
No.: |
05/047,504 |
Filed: |
June 18, 1970 |
Current U.S.
Class: |
343/776; 343/786;
343/784 |
Current CPC
Class: |
H01Q
13/0291 (20130101) |
Current International
Class: |
H01Q
13/00 (20060101); H01Q 13/02 (20060101); H01q
013/00 () |
Field of
Search: |
;343/776,783,784,785,786 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Lieberman; Eli
Claims
I claim as my invention:
1. A dual waveguide horn antenna comprising:
a. a rigid foam dielectric material having a dielectric constant
approximately equal to that of air and having tapered walls to
conform to the shape of a conventional horn antenna;
b. a thin metallic coating covering the walls of the dielectric,
said coating having sufficient thickness to carry the RF current
produced by the propagation of an electromagnetic wave through said
dielectric;
c. a metallic septum for dividing said dielectric into first and
second waveguide sections;
d. an electromagnetic window located at the enlarged end of said
tapered dielectric foam; and
e. means for applying electromagnetic energy to the tapered end of
said dielectric.
2. The antenna of claim 1 wherein two of said tapered walls are
corrugated to provide a slow wave structure.
3. The antenna of claim 1 wherein said thin metallic coating and
said metallic septum comprise copper plating.
4. The antenna of claim 1 further comprising means for reducing
energy coupling between said first and second waveguide
sections.
5. The antenna of claim 4 wherein said means for reducing energy
coupling comprises a microwave resistive material secured to said
septum and located at the enlarged end of said dielectric.
6. The antenna of claim 5 wherein said resistive strip comprises a
thin film resistive material secured to the surface of said septum
by vacuum deposition.
7. The antenna of claim 5 wherein said resistive strip comprises a
thin film paint on the surface of said septum.
8. The antenna of claim 5 wherein said resistive strip comprises a
carbonized substrate.
9. The antenna of claim 5 wherein said resistive strip comprises an
insulating strip secured to the edge of said septum and a microwave
resistive coating on said insulating strip.
10. The antenna of claim 1 wherein said metallic septum equally
divides said upper and lower waveguide sections.
Description
RIGHTS OF THE GOVERNMENT
The invention described herein may be manufactured, used, and
licensed by or for the United States Government for governmental
purposes without the payment to me of any royalty thereon.
BACKGROUND OF THE INVENTION
This invention relates generally to electromagnetic horn antennas,
and more particularly to a dual waveguide horn antenna utilizing a
lightweight foam material whose dielectric constant approximates
that of air.
Conventional electromagnetic horn designs are usually constructed
from sheet metal such s brass or aluminum and suitably shaped to
achieve a desired radiation pattern. The disadvantages inherent in
such systems are that they tend to be very heavy and quite
expensive. Furthermore, any attempt at modification of the basic
design in order to attain a change in performance results in still
more complex and bulky structures, thereby adding further to their
expense. Additionally, the E-plane radiation pattern of horns
designed and constructed in the conventional manner have inherently
high side lobes, a high degree of energy coupling between adjacent
waveguide sections as well as other undesirable radiation pattern
characteristics.
It is, therefore, a primary object of this invention to provide a
dual waveguide horn antenna which is extremely lightweight,
inexpensive, highly efficient and capable of performing a number of
functions in electronic and radar systems.
Another object of the invention is to provide a horn antenna which
is easy and inexpensive to construct as well as to modify.
Yet another object is to provide a dual waveguide horn antenna
having high gain and low side lobes.
Still another object is to provide a dual waveguide horn antenna in
which the coupling of energy between adjacent waveguide sections in
significantly reduced.
SUMMARY OF THE INVENTION
Briefly, in accordance with this invention, a dual waveguide
antenna is provided with a rigid foam material whose dielectric
constant approximates that of air. The dielectric is tapered to
conform to the shape of a conventional horn antenna and its walls
are provided with a thin metallic coating of sufficient thickness
to carry the RF current produced by the propagation of
electromagnetic waves through the dielectric. First and second
waveguide sections are provided by means of a metallic septum for
dividing the dielectric material. Energy coupling between the
adjacent waveguide sections is significantly reduced by means of a
microwave resistive material secured to the edge of the dividing
septum. Side lobe patterns are significantly reduced by applying
corrugations to the two tapered walls to achieve a slow wave
structure.
BRIEF DESCRIPTION OF THE DRAWINGS
The specific nature of the invention as well as other objects,
aspects, uses, and advantages thereof will clearly appear from the
following description and from the accompanying drawings, in
which:
FIG. 1 is a perspective view, partially cut away, of a dual horn
antenna in accordance with this invention.
FIG. 2 illustrates the sum and difference patterns of a dual
waveguide horn antenna in accordance with one embodiment of the
invention.
FIG. 3 illustrates the E-plane pattern in a single section of a
dual waveguide horn antenna in accordance with this invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to FIG. 1, the dual waveguide horn antenna comprises
a rigid foam dielectric material 10 whose dielectric constant
approximates that of air. The foam 10 is shaped as a conventional
horn antenna having two tapered walls 11 and 12, and two parallel
walls 13 and 14. Each of these walls is coated with a thin metallic
copper plating of sufficient thickness to carry the RF current
produced by the propagation of the electromagnetic waves through
the dielectric. Electromagnetic energy is applied to the antenna at
its tapered end by means of a pair of coaxial inputs 20 and 21, and
an electromagnetic window 22 is located at the enlarged end of the
horn antenna. The window may comprise material which is transparent
to the electromagnetic energy, or it may simply be a portion of
unplated dielectric.
Corrugations 15 and 16 are applied to tapered walls 11 and 12 in
order to achieve a slow wave structure. These corrugations have the
effect of substantially reducing diffraction and scattering at the
edges of the horn as well as significantly reducing the side lobes
and back radiation in the E-plane pattern.
The horn antenna is divided into first and second waveguide
sections, thereby providing a dual horn antenna, by means of a
metallic septum 17 which is located halfway between the two
corrugated walls 15 and 16 in the H-plane. The septum extends over
the entire longitudinal area of the dielectric between the coaxial
inputs 20 and 21 and the output window 22. The incorporation of
such a septum into a horn antenna of the type shown has the effect
of reducing the standard X-band waveguide to two half-height
waveguides. Each of these waveguides is separately fed from one of
the two miniature coaxial inputs 20 and 21. Electromagnetic energy
flowing in each section of the dual waveguide horn antenna will
cause electrical currents to be conducted at the two opposing
surfaces of the septum 17. These currents, upon reaching the edge
23 of septum 17 will tend to cross over to the other side, thereby
coupling energy from one section to the other. In order to prevent
this cross-coupling, a microwave resistive material 18 is secured
to septum 17 near its edge 23. Any electrical currents flowing
along the surface of the septum will be dissipated into heat upon
traversing the resistive material 18. Accordingly little or no
energy will be coupled between the two sections of the antenna.
Decoupling figures in excess of 30 db can be expected from the use
of this resistive element. This represents a 10 to 15 db
improvement over the use of a metallic septum without a resistive
strip as herein described.
The microwave resistive strip may be applied in a number of
different ways. One way would be to paint the edge surface of the
septum with the resistive film or to apply the resistive film to
the surface by means of vacuum deposition. Additionally, one may
employ a carbonized substrate securely attached to the terminal
portion of the septum. Finally, the resistive strip may comprise a
thin insulating material which is secured to the terminal portion
of the septum and a resistive coating applied to one or both sides
of the insulating material. Suitable resistive materials may
comprise nichrome or Synthane. The thickness of the coating as well
as the area covered would depend upon a variety of factors such as
the intensity of the radiation beam, the type of dielectric
employed as well as other factors which would be well known to
those persons skilled in the art.
The radiation patterns of the dual waveguide horn antenna used as a
monopulse antenna is shown in FIG. 2. The sum and difference
patterns are shown. It will be noted that the sum pattern has a
high gain and essentially no side lobes. FIG. 3 illustrates the
E-plane pattern of one section of the dual horn antenna.
The foam dielectric material for use in this invention may
typically comprise expanded polystyrene and polyurethane. These
materials typically have a dielectric constant of 1.05 and a loss
tangent of 0.0004, thereby approximating the characteristics of
air. Additionally, they are extremely lightweight, having a density
of about 4 pounds per cubic foot. The walls of the dielectric
waveguide as well as the septum are copper plated to a thickness of
about 0.005 inches. The technique of copper plating is disclosed in
copending application Ser. No. 739,578 filed Apr. 16, 1968.
I wish it to be understood that I do not desire to be limited to
the exact details of construction shown and described, for obvious
modifications will occur to a person skilled in the art.
* * * * *