U.S. patent number 3,623,118 [Application Number 04/838,143] was granted by the patent office on 1971-11-23 for waveguide-fed helical antenna.
This patent grant is currently assigned to Raytheon Company. Invention is credited to John R. Ehrhardt, George J. Monser.
United States Patent |
3,623,118 |
Monser , et al. |
November 23, 1971 |
WAVEGUIDE-FED HELICAL ANTENNA
Abstract
A helical antenna excited from a waveguide having sidewalls of
reduced height to provide an improved impedance match between the
waveguide and the helix, one end of the helix being attached to the
waveguide whereby heat may be conducted therefrom during
operation.
Inventors: |
Monser; George J. (Santa
Barbara, CA), Ehrhardt; John R. (Santa Barbara, CA) |
Assignee: |
Raytheon Company (Lexington,
MA)
|
Family
ID: |
25276374 |
Appl.
No.: |
04/838,143 |
Filed: |
July 1, 1969 |
Current U.S.
Class: |
343/883; 333/34;
343/895 |
Current CPC
Class: |
H01Q
11/08 (20130101); H01Q 1/36 (20130101); H01Q
13/02 (20130101) |
Current International
Class: |
H01Q
11/08 (20060101); H01Q 1/36 (20060101); H01Q
11/00 (20060101); H01Q 13/02 (20060101); H01Q
13/00 (20060101); H01q 001/36 (); H01q 001/50 ();
H03h 007/38 () |
Field of
Search: |
;343/863,824,872,840,895,908,700,705,707,709 ;219/10.49,10.55
;333/34 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
1,046,122 |
|
Dec 1958 |
|
DT |
|
1,332,450 |
|
May 1963 |
|
FR |
|
Other References
"Microwave Transmission Circuits" (Ragan) McGraw-Hill Book Company
New York 1948, TK6553R34; pages 339-344 and Title Page..
|
Primary Examiner: Saalbach; Herman Karl
Assistant Examiner: Nussbaum; Marvin
Claims
What is claimed is:
1. In combination:
a. antenna means comprising an elongated electrically conductive
element;
b. waveguide means coupling electromagnetic radiation into the
antenna means; and
c. cooling means connecting with the antenna means and passing
through the waveguide, the cooling means comprising fluid
circulation means within the antenna means whereby heat generated
within the antenna means by interaction with electromagnetic power
is withdrawn from the antenna means, the antenna means being a
helical antenna and the waveguide means having sidewalls which have
dimensions providing an impedance to the waveguide means which
matches the intrinsic impedance of the helical antenna.
2. A coupling electromagnetic power from a waveguide-type structure
to a helical antenna, the device comprising:
a. waveguide means having a wall and an aperture spaced from the
wall, the aperture adapted to receive an end portion of the helical
antenna so that the wall makes contact with the end portion, the
waveguide means being positioned to couple electromagnetic power to
the helical antenna;
b. flared coupling means situated on the wall and contacting the
end portion; and
c. heat sink means in thermal contact with the wall for withdrawing
heat from the helical antenna through the end portion and the
flared coupling means.
3. The device of claim 2 in which the waveguide means includes a
transition means terminating in a section of waveguide having
dimensions such that the spacing between the aperture and the wall
is substantially less than one-half the width of the wall whereby
the impedance at the terminus of the transition is substantially
equal to the intrinsic impedance of the helical antenna.
4. An antenna array including:
a. a plurality of radiating elements, each radiating element being
a helical antenna element;
b. a waveguide coupling electromagnetic power to each radiating
element; and
c. cooling means connecting with each radiating element and passing
through the waveguide, the cooling means including fluid
circulation means within each radiating element whereby heat
generated within the radiating elements by interaction with the
electromagnetic power is withdrawn from the radiating elements.
5. An antenna feed system comprising:
a. a waveguide having a top wall, and a bottom wall which are
joined by sidewalls, there being an aperture in the top wall;
and
b. a radiating element connecting with the bottom wall interior to
the waveguide and extending upwards through the aperture to a
region exterior of the waveguide whereby electromagnetic radiation
is coupled from the waveguide to the radiating element, the
radiating element having enclosed passages for circulation of
cooling fluid, the passages extending through the bottom wall
whereby cooling fluid is introduced and withdrawn from the
radiating element.
6. The apparatus of claim 5 in which the radiating element is a
helical antenna, and the sidewalls are of reduced height whereby
the impedance of the waveguide is substantially matched to the
impedance of the helical antenna.
7. An antenna array including:
a. a plurality of radiating elements;
b. a waveguide coupling electromagnetic power to each radiating
element, the waveguide having apertures through which each of the
radiating elements extends and connects with an interior surface of
a wall of the waveguide; and
c. cooling means connecting with each radiating element and passing
through the waveguide whereby heat generated within the radiating
elements by interaction with the electromagnetic power is withdrawn
from the radiating elements.
8. In combination:
a. antenna means comprising a helical radiating element;
b. waveguide means coupling electromagnetic radiation into the
antenna means, the helical radiating element extending through an
aperture in the waveguide means and connecting with an interior
surface of a wall of the waveguide means; and
c. coupling means situated on the wall and being in thermal contact
with an end portion of the helical radiating element for
withdrawing heat generated within the antenna means by interaction
with electromagnetic power, the coupling means having a flared
outer surface for coupling electromagnetic radiation between the
waveguide means and the helical radiating element.
9. An antenna array including:
a. a plurality of helical radiating elements;
b. a waveguide coupling electromagnetic power to each helical
radiating element, the waveguide having apertures through which
each of the radiating elements extends and connects with an
interior surface of a wall of the waveguide; and
c. coupling means situated on the wall and being in thermal contact
with end portions of the helical radiating elements for withdrawing
heat generated within the helical radiating elements by interaction
with the electromagnetic power, the coupling means having flared
outer surfaces for coupling electromagnetic radiation between the
waveguide means and the helical radiating elements.
10. In combination:
a. waveguide means having a top wall and a bottom wall which are
joined by sidewalls, there being an aperture in the top wall;
b. a helical radiating element having an end portion thereof, the
helical radiating element being positioned external to the
waveguide means such that the end portion of the helical radiating
element passes through the aperture toward the bottom wall;
c. coupling means situated on the bottom wall and being in thermal
contact with the end portion of the helical radiating element for
withdrawing heat generated within the helical radiating element by
interaction with electromagnetic power, the coupling means having a
flared outer surface for coupling electromagnetic radiation between
the waveguide means and the helical radiating element;
d. transition means coupling electromagnetic energy from a source
of input energy to the waveguide means, said transition means
including waveguide walls which are tapered to form a waveguide of
reduced height from a waveguide of standard cross-sectional
dimensions, said tapered walls cooperating with said flared outer
surface of said coupling means to provide an impedance match
between a waveguide of standard cross-sectional dimensions and said
helical radiating element; and
e. a horn affixed to the top wall and enclosing the helical
radiating element for directing electromagnetic energy for
radiation therefrom.
11. The device of claim 10 further comprising tuning means for
tuning the waveguide means to the helical radiating element at a
predetermined carrier frequency of the electromagnetic energy.
Description
BACKGROUND OF THE INVENTION
This invention relates to helical antennas, and more particularly,
to a helical antenna coupled to a waveguide in a manner providing
for increased continuous-wave power transmission from the helix
with optimum matching between antenna components.
A helical antenna is frequently used as a source for
electromagnetic radiation having circular polarization. Helical
antennas are used both singly and in groups as in a helical antenna
array. A helical antenna can provide a more directive beam pattern
than a radiating element, such as a radiating slot aperture in a
waveguide wall, and consequently, there is typically less mutual
coupling between neighboring helical antenna elements in a helical
antenna array than is present between neighboring slot radiators in
an array of slot radiators. Accordingly, helical antenna arrays
have more uniform radiation directivity patterns with reduced side
(or grating) lobes.
In situations requiring high continuous-wave (hereinafter sometimes
referred to as CW) power transmission in a broad region of space,
antenna arrays are normally utilized with the number of radiating
elements kept small, since large arrays tend to narrow the beam of
radiation. However, in a high-powered array containing relatively
few elements, each element itself must be capable of radiating
large quantities of electromagnetic power. And furthermore, if
circular polarization is desired, then only such elements as are
capable of radiating circularly polarized radiation may be
utilized.
A typical radiator for operation at high power levels is the horn
radiator fed directly from a waveguide. Horn radiators have been
utilized both singly and in an array to radiate energy at high
power levels, but such radiation is inherently linearly polarized.
To provide circular polarization from such a horn radiator, a
dielectric or metallic vane is inserted into the horn. However,
high-powered CW radiation may overheat and damage the dielectric
vane, thereby restricting the use of such an antenna to lower power
levels; and a metallic vane greatly reduces the bandwidth of such
an antenna thereby restricting the use of such an antenna to
relatively narrow bandwidth applications. Furthermore, horns occupy
a substantially larger volume of space than do helical antennas, so
that in certain applications such as with airborne equipment where
relatively little space is available for antennas, the helical
antenna is preferred.
Helical antennas provide circular polarization, are of relatively
wide bandwidth, and have been excited directly from a waveguide as
has been shown in the patent to Gammon, U.S. Pat. No. 2,863,148
which issued Dec. 2, 1958. Helical antenna elements are
advantageously used in antenna arrays since the interelement
spacing is not restricted by spacing restrictions such as are
found, for example, with an array of slot radiators in a waveguide
where a spacing of an integral number of one-half wavelengths is
utilized. However, helical antennas of the prior art have been
coupled to a source of electromagnetic wave therein, in a manner
which provides only limited means for withdrawal of heat from the
helix. As a result, CW radiation having a high power density may
overheat such antenna causing it to malfunction.
Accordingly, it is a primary object of this invention to provide a
means for coupling a helical radiating element to a waveguide-type
structure in a fashion which provides for withdrawal of the heat
produced within the helix due to the interaction of electromagnetic
radiation with the helix.
Furthermore, it is an object of the invention to provide a means
for coupling a helical radiating element to a waveguide-type
structure such that the impedance of the waveguide-type structure
matches the intrinsic impedance of the helix over a broad bandwidth
so that a maximum portion of the power in the waveguide type
structure can be coupled to the helical radiating element.
SUMMARY OF THE INVENTION
A waveguide-type structure coupling electromagnetic power to a
helical antenna, the helical antenna having a helix with an end
portion for insertion into the waveguide-type structure, the
waveguide-type structure having a top wall and a bottom wall joined
by sidewalls and having cross-sectional dimensions wherein the
height of the sidewalls is substantially less than one-half the
width of the top wall whereby the impedance of the waveguide-type
structure is matched to the intrinsic impedance of the helix to
couple into the helix a maximum portion of the electromagnetic
power supplied by the waveguide-type structure at a predetermined
carrier frequency, and a coupling means providing optimum
conduction of heat from the helix, the coupling means comprising an
aperture in the top wall, the end portion of the helix passing
through the aperture, and a flared termination on the end portion
in thermal and electrical contact with the bottom wall whereby a
broadband impedance match is provided between the helix and the
waveguide-type structure.
BRIEF DESCRIPTION OF THE DRAWINGS
The aforementioned objects and other features of the invention are
explained in the following description taken in connection with the
accompanying drawings wherein:
FIG. 1 is a side elevation view of the waveguide and helical
antenna of the invention cut away to show the connection of the
helical antenna to the waveguide;
FIG. 2 is a side elevation view of two fluid-cooled helical
antennas forming an array, the waveguide supporting the helical
antennas being cut away to show the connection of the helical
antenna with the waveguide for admission of cooling fluid;
FIG. 3 is an enlarged view of the bottom section of a helical
antenna of FIG. 2 partially cut away to show a construction of
helix by means of tubes through which fluid can pass along the
helical structure for withdrawal of heat; and
FIG. 4 is a sectional view of a fluid-cooled helical antenna taken
along the lines 4--4 of FIG. 3.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to FIG. 1, there is shown an embodiment of the
invention in which a waveguide 20 feeds electromagnetic radiation
to a helical antenna 22 positioned within a horn 24 which is
rigidly affixed, as by brazing, to a top wall 26 of the waveguide
20. An end portion 27 of the helical antenna 22 enters the
waveguide 20 through an aperture 28, preferably of circular shape,
in the top wall 26 and is rigidly supported by a bottom wall 30 of
the waveguide 20. In order to couple, regardless of frequency
within a broadband, substantially all of the electromagnetic power
within the waveguide 20 to the helical antenna 22, the impedance of
the waveguide 20 is matched to the intrinsic impedance of the
helical antenna 22 by constructing the waveguide 20 with sidewalls
having reduced height, one such sidewall 32 being shown in FIG. 1,
and supplying electromagnetic power to the waveguide 20 through a
transition 34 connecting with a waveguide 36 of standard
cross-sectional dimensions. A tuning plunger 38, preferably of
copper, may be slidably supported within an end of waveguide 20
thereby partially forming a tuned cavity, the tuning plunger 38
being positioned with the aid of handle 40 to tune the waveguide 20
to the helical antenna 22 at a predetermined carrier frequency of
the electromagnetic energy. To further improve the coupling of
electromagnetic power, the end portion 27 of the helical antenna 22
is terminated with a flare 42 of an electrically and thermally
conductive material, such as an alloy of silver, the flare 42
having an exponential shape, as shown in FIG. 1, and being affixed
to the bottom wall 30, preferably by brazing. Electromagnetic power
coupled to the helical antenna 22 interacts therewith resulting in
a conversion of a portion of this power into heat which raises the
temperature of the helical antenna 22, the temperature increasing
with increasing electromagnetic power until a state of equilibrium
is reached between the rate at which heat is produced within the
helical antenna 22 and the rate at which heat is withdrawn
therefrom. While some measure of heat withdrawal is effected by
means of radiation and of cooling by air circulating about the horn
24, these means are inadequate to maintain a sufficiently low
temperature to insure proper operation of the helical antenna 22
and reduce the chance of arcing in the presence of high
electromagnetic power. In accordance with the invention, the
temperature is maintained sufficiently low by means of the end
portion 27 and flare 42, at the base of the helical antenna 22,
through which heat is conducted to a heat sink 44 mounted
externally to the bottom wall 30 and in thermal contact therewith,
the heat sink 44 having fins 46 for cooling by air or other fluid.
In order to provide a smooth edge to the aperture 28 and reduce the
chance of arcing between the edge of the aperture 28 and the
helical antenna 22 when an intense electric field is present, a
bushing 48 of dielectric material such as Teflon or boron nitride
is inserted into the aperture 28, the resilient lip 50 of bushing
48 permitting a press fit.
As an example in the construction of an embodiment of the invention
designed to operate with electromagnetic radiation having a carrier
frequency in the range of 2.5 GHz-3.5 GHz, the waveguide 36 has
inside dimensions of width 2.84 inches by height 1.34 inches, while
for the reduced-height waveguide 20, the top wall 26 has width 2.84
inches and the height of the sidewalls 32 is reduced to one-third
that of the standard dimension of waveguide 36 so that sidewall 32
has a height of 0.45 inches. The helical antenna 22 has a height of
approximately six inches above the bottom wall 30 and is formed of
five turns of wire having a diameter of one-eighth inch, there
being one inch between turns. The circular aperture 28 is one inch
in diameter, and the bushing 48 has a thickness of 0.040 inches.
The side of horn 24 extends outwardly making an angle of
approximately 25.degree. with the axis of the horn. The flare 42
has an outer diameter of 1.125 inches and a height of approximately
0.2 inches. The impedance of both the waveguide 20 and the helical
antenna 22 is approximately 135 ohms. The dialectric between the
horn 24 and the helical antenna 22 is simply atmospheric air which
provides a relatively small amount of cooling by convection, the
major portion of the cooling being done with the heat sink 44.
Thus, even at altitudes of 50,000 feet where cooling by atmospheric
air is substantially reduced from that at sea level, the helical
antenna 22 can transmit 2500 watts of continuous-wave, or average,
power.
Referring now to FIG. 2, there is an array of radiating elements,
each radiating element being a helical antenna 52 which is adapted
for fluid cooling, two such antennas being shown in the figure. The
helical antennas 52 are supported by and coupled to a waveguide 54
having reduced sidewall height whereby the impedance of the
waveguide 54 is matched to each helical antenna 52.
The fluid cooling is explained in detail with the aid of FIGS. 3
and 4 showing enlarged views of the base of the helical antenna 52.
The helical antenna 52 is composed of four tubes 56 which are
designated 56A-D, being preferably of copper, and having an outside
diameter of approximately 0.05 inch. The four tubes 56 are twisted
about each other to form a flexible cable which is bent into the
shape of a helix. The top of each helical antenna 52 is terminated
with a metallic cap 58, as shown in FIG. 2, which has an interior
void through which fluid flows, so that for example, fluid which
enters tube 56A at opening 60A passes upwards along tube 56A,
through cap 58 and into tube 56B, thence downwards through tube 56B
to exit at opening 60B. Accordingly, cooling of the helical antenna
52 is effected by forcing a fluid such as cold water or oil into
tubes 56A and 56C and withdrawing the heated fluid from tubes 56B
and 56D.
It is understood that the above-described embodiments of the
invention are illustrative only and that modifications thereof will
occur to those skilled in the art. Accordingly, it is desired that
this invention is not to be limited to the embodiments disclosed
herein but is to be limited only as defined by the appended
claims.
* * * * *