U.S. patent number 3,798,652 [Application Number 05/287,789] was granted by the patent office on 1974-03-19 for pitot tube dielectric antenna system.
This patent grant is currently assigned to General Electric Company. Invention is credited to Earl E. Williams.
United States Patent |
3,798,652 |
Williams |
March 19, 1974 |
PITOT TUBE DIELECTRIC ANTENNA SYSTEM
Abstract
A metallic conductor protruding from a surface, for example, a
pitot tube protruding from an aircraft surface is coated on its
periphery with a low loss dielectric in order to form an antenna.
Functions of the pitot tube and antenna are combined in one
structure, and the need for a radome is eliminated. Monopulse feed
may be provided to the dielectric rod comprising the antenna.
Inventors: |
Williams; Earl E. (Poland,
NY) |
Assignee: |
General Electric Company
(Utica, NY)
|
Family
ID: |
23104359 |
Appl.
No.: |
05/287,789 |
Filed: |
September 11, 1972 |
Current U.S.
Class: |
343/708; 343/853;
343/785 |
Current CPC
Class: |
H01Q
1/44 (20130101) |
Current International
Class: |
H01Q
1/44 (20060101); H01q 001/28 () |
Field of
Search: |
;343/705,708,785,853 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Lieberman; Eli
Claims
What is claimed as new and desired to be secured by Letters Patent
of the United States is:
1. A radio frequency antenna for use on an aircraft comprising, in
combination:
a metallic cylindrical tube forming a part of a pitot tube mounted
at the nose of said aircraft;
Rf feed means for coupling RF energy to said tube, said feed means
including an E plane hybrid with first and second waveguides
branching from said hybrid and connected to opposed sides of said
tube at the end thereof adjacent the nose of said aircraft; and
a layer of low loss dielectric material covering the outer surface
of said tube, said layer tapering from a maximum thickness near the
nose of said aircraft to a minimum thickness at the end of said
tube farthest from said nose, said layer acting to minimize side
lobes in the energy pattern radiated by said tube.
2. The antenna set forth in claim 1 wherein said RF feed means
further comprises:
a second E plane hybrid with third and fourth waveguides branching
therefrom and connecting to opposed sides of said tube between said
first and second waveguides; and
means for feeding said first and second E plane hybrids with RF
signals having the same frequency and a 90 degree relative phase
difference whereby said antenna radiates a circularly polarized
wave pattern.
Description
BACKGROUND OF THE INVENTION
This invention relates to radio wave antennas, and more
particularly to an active antenna which is preferably part of an
aircraft.
The present invention is directed toward an antenna for inclusion
on a pitot tube projecting from the nose of an aircraft. The pitot
tube takes in air, and the air flow therethrough is used for
sensing airspeed. It should also be realized that other protrusions
from a surface may be equivalent. Antennas may be placed at the
front of an aircraft for many applications: for example, range only
radar, angle tracking radar, navigation, or for countermeasures
purposes. In the past, dielectric rod antennas have been provided.
However, this type of antenna is not suited for inclusion at the
nose of an aircraft on a pitot tube. Also, structures have been
provided which include both a dipole antenna and a pitot tube in
different portions of the structure. However, the construction may
affect the aerodynamics of a pitot tube, or require the use of a
longer pitot tube to reach air undisturbed by the dipole antenna.
However, in the past an antenna has not been provided integrally
with a pitot tube. Also, prior dielectric rod antennas have been
excitable in only one mode of radiation. Consequently, they could
not be used for monopulse radar.
SUMMARY OF THE INVENTION
It is therefore a particular object of the present invention to
provide a unitary pitot tube-antenna structure for airborne
use.
It is a more general object of the present invention to provide an
antenna structure for incorporation with a projection from a
surface.
It is another object of the present invention to provide an
airborne antenna of minimum bulk.
It is a further object of the present invention to further provide
an airborne antenna, the performance of which is not degraded by
the presence of a radome and the radiation pattern of which is not
effected by blockage due to objects such as a pitot tube.
It is also an object of the present invention to provide a
dielectric antenna of the type described particularly suited for
forward looking radar applications.
It is yet another object to provide a dielectric antenna of the
type described which may be excited in more than one mode of
radiation.
It is a particular object in one form of the present invention to
provide an antenna of the type described for monopulse radar.
Briefly stated, in accordance with the present invention there is
provided an antenna for incorporation on an object such as a pitot
tube.
In the preferred embodiment, a pitot tube at the nose of an
aircraft is coated with a low loss dielectric, and radio frequency
energy is coupled to or from the tube by means of a waveguide
transducer or a coaxial transducer. Alternatively, means are
provided for exciting the antenna in more than one mode of
radiation.
BRIEF DESCRIPTION OF THE DRAWINGS
The means by which the foregoing objects and features of novelty
are achieved are pointed out with particularity in the claims
forming the concluding portion of the specification. The invention,
both as to its operation and manner of organization, may be further
understood by reference to the following description taken in
connection with the following drawings.
Of the drawings:
FIG. 1 is an illustration of an embodiment of the present invention
having a balanced feed.
FIGS. 2a and 2b are respectively isometric illustrations of a
further embodiment of the present invention.
FIG. 3 is a cross-section view taken along line 3--3 of FIG.
2b.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to FIG. 1, there is illustrated the nose 1 of an
aircraft having a pitot tube 2 projecting therefrom. The pitot tube
2 in the present embodiment includes a rear portion 3, which is
preferably a right circular cylinder communicating with the nose of
the aircraft at a base 4. The other end of the rear portion 3 has a
forward portion 5 projecting therefrom which terminates in an air
inlet port 6. Conventional air tubes and heater wires 15 (FIG. 2a)
run through the pitot tube 2 for connection to sensing means (not
shown) in the aircraft.
In accordance with the present invention, the pitot tube 2 is made
into an antenna by forming a dielectric layer 10 on the base
portion 3. The dielectric thickness in terms of wavelength L is
dictated by the gain to beamwidth desired. In a preferred
embodiment, the thickness of dielectric coating at the base 4 of
the pitot tube 2 is 0.15 inch and is tapered to approximately 0.01
inch at the forward end of the rear portion 3. The thickness is
also a function of the overall wavelength of the rear portion 3.
The above described dimensions are particularly useful for forming
an antenna providing an end fired slow wave. In this manner, a
narrow, forward looking lobe is provided. By well-known theory,
antenna geometry, i.e., the shape and thickness of the dielectric
coating, may be changed to modify the radiated beam. For example,
see Henry Jasik, Antenna Engineering Handbook, First Edition
(McGraw Hill Book Company, Inc., New York, 1961) Chapter 16. In the
present embodiment, by tapering the thickness of the dielectric
layer 10 from the maximum thickness at the base 4 to the minimum
thickness at the forward end of the rear portion 3, antenna gain is
maximized and pattern side lobes are minimized.
The pitot tube 2 is metallic. Coaxial cavities 12 are provided near
the base for coupling of a balanced coaxial feed 14 to the antenna
11. The cavities 12 in the preferred embodiment are in
diametrically opposed portions of the pitot tube 2, and a balanced
feed is provided. The antenna system is operative if fed at only
one side, but an optimal radiation pattern is not provided. Due to
the use of a balanced feed, the metallic portion 3 in the center of
the antenna 11 does not adversely affect radiation by the
dielectric portion 10.
The dielectric layer 10 is a low loss dielectric. The prime
criteria for the choice of material of which the layer 10 is formed
are radio frequency performance requirements and aircraft
environment. Choice of the material will dictate a well-known
method of application. The prime environmental considerations are
thermal capabilities and erosion. It is noted that at the nose of
an aircraft travelling at mach II, the temperature of a pitot tube
may reach 1,075.degree.F. A low loss radio frequency material such
as polytetrafaluoroethylene, a quartz fibre reinforced resin, or a
boron nitride reinforced material are suitable for supersonic
applications. For low speed and low temperature applications, many
well-known plastics are known to be suitable.
FIGS. 2a and b respectively represent a further embodiment of the
present invention of isometric and cross section form. The same
reference numerals are used to denote elements corresponding to
those of FIG. 1. In the embodiment of FIG. 2, the coaxial feed 14
of FIG. 1 is replaced by a multimode waveguide feed 20. The feed 20
consists of first and second E plane hybrids 21 and 22. The E plane
hybrid 21 has a sum input port 23 and a difference input port 24,
while the E plane hybrid 22 has a sum input port 25 and a
difference input port 26. First and second waveguides 29 and 30 are
coupled from the E plane hybrid 21 to diametrically opposite
portions of the base 4. First and second waveguides 31 and 32 are
coupled from the E plane hybrid 22 to diametrically opposed
portions of the base 4 and are spaced 90.degree. from the
waveguides 29 and 30.
FIG. 3 shows the arrangement of the four waveguides in the required
90.degree. spacing about the perifery of the tube 3. The end of the
tube may be slotted to receive the ends of the waveguides and the
latter may be secured in the slots by conventional techniques such
as brazing. The E plane hybrids 21 and 22 can be fed with radiation
having a phased difference of 90.degree. to radiate a circularly
polarized wave. When only one E plane hybrid is fed, either
horizontal or vertical polarization is radiated and a sum and a
difference pattern is generated in both planes. Consequently, more
than one mode of radiation may be radiated by the antenna 11. The
antenna 11 is thus useful for monopulse radar. Other well-known
waveguide arrangements can be provided.
What is thus provided is a pitot tube antenna and a dielectric
antenna excited in more than one mode of radiation. Due to the
construction of the present invention, aerodynamics of the pitot
tube are not adversely affected. Further, the construction of the
antenna does not interfer with apparatus such as air tubes and
heater wires which must extend through the center of a pitot tube.
The above teachings will enable those skilled in the art to
construct many forms of antenna in accordance with the present
invention, including embodiments having different hybrid and
waveguide feed arrangements.
* * * * *