U.S. patent number 3,680,142 [Application Number 04/863,914] was granted by the patent office on 1972-07-25 for circularly polarized antenna.
Invention is credited to Robert J. Mailloux, Lester C. Van Atta.
United States Patent |
3,680,142 |
Van Atta , et al. |
July 25, 1972 |
CIRCULARLY POLARIZED ANTENNA
Abstract
A circularly polarized antenna is provided using a planar array
of at least two perpendicular pairs of linearly polarized elements
(slot antennas or dipoles). The distance D between a given pair of
parallel elements is selected to provide in a plane perpendicular
to the elements of the pair, a field pattern very similar to that
in a plane parallel to the elements, where both principal planes
pass through the center of the array and are perpendicular to the
plane of the array. Elements of a given pair are excited in phase,
and the two pairs are excited in phase quadrature, whereby
circularly polarized radiation is produced over a very wide sector
of space in each principal plane, and therefore in all planes
passing through the axis of the array.
Inventors: |
Van Atta; Lester C. (Wellesley,
MA), Mailloux; Robert J. (Wayland, MA) |
Assignee: |
|
Family
ID: |
25342098 |
Appl.
No.: |
04/863,914 |
Filed: |
October 6, 1969 |
Current U.S.
Class: |
343/770; 343/786;
343/853; 343/771; 343/797 |
Current CPC
Class: |
H01Q
21/24 (20130101) |
Current International
Class: |
H01Q
21/24 (20060101); H01q 013/10 () |
Field of
Search: |
;343/797,770,771,798,814,768,854,816,853,786 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Van Atta et al., IEEE Transactions on Antennas & Propagation;
May 1969; pp. 360 & 361..
|
Primary Examiner: Lieberman; Eli
Claims
What is claimed is:
1. A circularly polarized antenna comprising
a planar array of linearly polarized antenna elements selected from
a group consisting of antenna slots and dipoles, said elements
being of the same size and arranged in two orthogonally oriented
sets of parallel elements, both sets having the same geometric
center, elements of a given set being spaced a given distance apart
such that a field produced by a given pair of adjacent elements in
a set when excited in phase will produce in a first plane
perpendicular to the plane of said array, and perpendicular to said
pair of elements, at their centers, a pattern very similar to the
field pattern of said given pair of elements in a second plane
perpendicular to said first plane and to said plane of the array
when excited in phase, where said second plane intersects said
first plane midway between said given pair of elements, and
means for exciting said elements of the other set in phase
quadrature with said one set.
2. A circularly polarized antenna as defined in claim 1 wherein
each set of elements is comprised of one pair of elements.
3. A circularly polarized antenna as defined in claim 1 wherein
said elements are selected to be antenna slots, said excitation
means comprises a square waveguide, and said elements are arranged
in a plate covering one end of said square waveguide.
4. A circularly polarized antenna as defined in claim 3 wherein
said excitation means includes four side waveguide sections, each
side waveguide section being coupled to said square waveguide
section through a separate transverse slot, and each sidewave guide
section feeding a separate element.
5. A circularly polarized antenna as defined in claim 1 wherein
each set of elements is comprised of three parallel slots, said
excitation means comprises a waveguide, and said elements are
arranged in a plate covering one end of said waveguide.
6. A circularly polarized antenna as defined in claim 5 wherein
said waveguide comprises a square waveguide section and a flared
pyramidal horn waveguide section attached to the end of said square
waveguide section, and said plate is attached to the outer end of
said flared pyramidal horn waveguide section.
7. A circularly polarized antenna as defined in claim 6 further
including a large square waveguide section located between the
outer end of said flared pyramidal horn waveguide section and said
plate.
8. A circularly polarized antenna as defined in claim 1 wherein
said first set of antenna elements is comprised of parallel slots
in a plate covering the end of a waveguide and wherein said second
set of antenna elements is comprised of N/2 parallel slots in said
plate, where N is an even integer greater than four.
9. A circularly polarized antenna as defined in claim 8 wherein
said waveguide comprises a square waveguide section and a flared
pyramidal horn waveguide section attached to the end of said square
waveguide section, and said plate is attached to the outer end of
said flared pyramidal horn waveguide section.
10. A circularly polarized antenna as defined in claim 9, wherein
said plate is attached to the outer end of said flared pyramidal
horn waveguide section by a large square waveguide section.
11. A circularly polarized antenna as defined in claim 1 wherein
each of said antenna elements is selected to be a dipole.
12. A circularly polarized antenna as defined in claim 11 wherein
each of said two sets of antenna elements includes one pair of
dipoles.
13. A circularly polarized antenna as defined in claim 12 wherein
said excitation means comprises:
a 90.degree. hybrid adapted to receive a signal;
a first power divider having its input connected to one output of
said 90.degree. hybrid and its outputs connected to both dipoles to
one pair of said antenna elements; and
a second power divider having its input connected to a second
output of said 90.degree. hybrid and its outputs connected to both
dipoles of the other pair of said antenna elements.
Description
ORIGIN OF THE INVENTION
The invention described herein was made by employees of the United
States Government and may be manufactured and used by or for The
Government for governmental purposes without the payment of any
royalties thereon or therefor.
BACKGROUND OF THE INVENTION
This invention relates to antennas and more particularly to
circularly polarized antennas. The prior art has attempted to
provide circularly polarized antennas and a large number of quasi
omnidirectional circularly polarized antennas have been designed
and developed. These antennas vary from simple crossed-slot
antennas to equi-angular spiral antennas. Each end of this spectrum
of antennas has certain disadvantages. For example, crossed-slot
antennas cannot provide circularly polarized antenna beams over
wide angles. Equi-angular spiral antennas have the disadvantage
that their sector of good polarization (effective beamwidth) cannot
be varied over a fairly wide range by simple design changes. That
is, complex design changes must be made to an equi-angular spiral
antenna to vary its sector of good circular polarization over a
wide range.
Therefore, it is an object of this invention to provide a
circularly polarized antenna.
It is also an object of this invention to provide a circularly
polarized antenna that provides a circularly polarized beam over a
wide sector of space, which sector can be varied by simple changes
to the antenna configuration.
It will be appreciated by those skilled in the art and others that
it is particularly desirable to provide an antenna having a
circularly polarized beam that can be flush mounted on a vehicle
such as an airplane or a space vehicle.
Therefore, it is yet another object of the invention to provide an
antenna having a circularly polarized beam that is suitable for
flush mounting.
It is a still further object of this invention to provide an
antenna having a circularly polarized beam that is formed of slot
antenna elements to provide a relatively narrow beam.
SUMMARY OF THE INVENTION
In accordance with a principle of this invention, a circularly
polarized antenna is provided. The antenna comprises two sets of
linearly polarized antenna elements. The sets of antenna elements
are arrayed in similar patterns in two planes with the first set
being positioned orthogonal to the second set. The two sets are
driven in phase quadrature.
In accordance with another principle of this invention, each set of
antenna elements comprises a plurality of slots in a parallel
array. In addition, the two sets of plural slots are mounted on the
end of a waveguide structure which provides the driving phase
quadrature signals.
In accordance with a still further principle of this invention, the
waveguide structure includes a flared pyramidal horn and an end
cover in which cover is formed the two sets of plural slots. In
accordance with yet another principle of this invention, the two
sets of plural slots each include only two slots.
In accordance with an alternative embodiment of the invention, the
two sets of antenna elements are formed of dipole elements -- one
set of dipole elements being arrayed orthogonal to the other set of
dipole elements.
It will be appreciated from the foregoing brief summary of the
invention that the invention provides a circularly polarized
antenna which can be formed of either slot or dipole elements. When
the antenna is formed of slot antenna elements, it is suitable for
flush mounting on an aircraft or space vehicle. The antenna is
structurally uncomplicated in that it requires only two sets of
slots or dipoles arrayed in parallel -- one set being arrayed
orthogonal to the other set. In addition, the antenna of the
invention requires that the first set be driven in phase quadrature
with respect to the second set. By changing the length of the slots
or their separation, the antenna's beam-width, and therefore its
sector of good polarization, can be easily varied over a wide
range.
BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing objects and many of the attendant advantages of this
invention will become more readily appreciated as the same becomes
better understood by reference to the following detailed
description when taken in conjunction with the accompanying
drawings, wherein:
FIG. 1 is a pictorial diagram illustrating one antenna slot
configuration for broad beamwidth formed in accordance with the
invention;
FIG. 2 is a graph of normalized field patterns v. angle (.theta.)
from the antenna beam axis for the antenna configuration
illustrated in FIG. 1;
FIG. 3 is a pictorial diagram of an alternate antenna slot
configuration for narrow beamwidth formed in accordance with the
invention;
FIGS. 4A and 4B are diagrams of alternate waveguide configurations
having the slot configuration illustrated in FIG. 1 mounted on the
ends of the waveguides;
FIG. 5 is a pictorial diagram of an antenna dipole configuration of
the invention;
FIGS. 6A and 6B illustrate further alternative slot configurations
formed in accordance with the invention;
FIGS. 7A and 7B illustrate further waveguide systems for applying
quadrature signals to the slot configurations formed in accordance
with the invention; and
FIG. 8 illustrates a still further waveguide system formed in
accordance with the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Prior to discussing the preferred embodiments of the invention, the
theory of operation of the invention as best understood is
presented. The antenna element patterns of simple linearly
polarized antenna elements (either slots or dipoles) are different
in the two principal planes of operation of the elements. The
invention combines a set formed of two or more of such antenna
elements in a specific array so as to make the array pattern of the
combined antenna elements nearly similar in the two principal
planes of operation. In addition, this first set is combined with a
second set also formed of two or more antenna elements. The second
set is positioned orthogonal to the first set and its elements are
driven in phase quadrature with respect to the elements of the
first set. When this overall antenna structure is driven in this
manner, a nearly circularly polarized antenna beam operating over a
wide sector of space is produced. Because the antenna can be formed
of slot elements, it is suitable for flush mounting on an aircraft
or space vehicle.
FIG. 1 is a pictorial diagram illustrating one embodiment of the
invention formed of antenna slot elements. Four antenna slot
elements 11, 12, 13 and 14 are illustrated in FIG. 1, geometrically
arrayed in an X-Y plane as two parallel pairs 11 and 12, and 13 and
14, with one pair being orthogonal to the other pair. The Z axis of
the coordinate system intersects the geometric center of the
antenna slot configuration.
The distance between a parallel pair of antenna elements 11 and 12
or 13 and 14 is designated D, and the length of each antenna slot
is designated 2h. The angle .phi., illustrated in FIG. 1, is the
angle from the X-axis of a particular beam sector, and the angle
.theta. is the angle from the Z-axis of the beam sector.
In operation, the four slot elements 11, 12, 13 and 14 formed in a
plate 15 are excited in pairs for broadside radiation; that is, the
first pair at elements 11 and 12 are excited in phase with each
other, and the second pair of elements 13 and 14 are excited in
phase with each other. The first pair of elements is excited in
phase quadrature with respect to the second pair of elements so as
to produce a circularly polarized beam at broadside.
The field pattern in the plane containing the axis located between
either pair of antenna elements (for example, the X-Z plane for the
first pair 11 and 12) is determined by the element field pattern of
the pair, and, hence, by the electric field (current) on the pair
of slot elements. This field pattern is zero in the far field at
Z=0. The field pattern of the same pair in the plane normal to the
antenna axis between the pair (in this case the Y-Z plane) is
determined entirely by the array factor of the two antenna elements
forming the pair. Hence, this distribution or pattern can be
considerably modified by varying the distance D. Thus, it is
possible to make the field pattern in this plane (Y-Z plane) very
similar to the field pattern in the axis plane (X-Z) over a wide
range of angles near broadside. When this is done for both pairs of
antenna elements and when the pairs of antenna elements are excited
in phase quadrature, a circularly polarized antenna beam extending
over a wide range of angles in the X-Z and Y-Z plane is provided. A
typical far field pattern showing the horizontally polarized
(E.theta. cos .phi.) and the vertically polarized (Ey) fields at
.phi.=0 are illustrated in FIG. 2. E is the normalized
(horizontally or vertically) polarized field pattern.
The field of the embodiment of the invention illustrated in FIG. 1
is approximately circularly polarized even in the planes determined
by setting .phi. = .+-. 45.degree.. Hence, this combination of
antenna elements assures extremely good circular polarization for
all angles of .phi., even for large angles of .theta.. In one
actual embodiment of the invention, the antenna element slots
illustrated in FIG. 1 were designed so that with 2h/.lambda. = 0.50
(.lambda. being the free space wavelength at the frequency of
operation) the orthogonal polarizations were matched at the half
power point. The parameters resulted in D/.lambda. = 0.397 and a
half power beamwidth of 78.degree. .
It should be noted that for the foregoing example, 2h is greater
than D; hence, the actual slot configuration for that example was
not exactly as illustrated in FIG. 1; rather, it was as illustrated
in FIG. 3 -- that is, the slots actually intersect. The slot
configuration illustrated in FIG. 3 produces a fairly narrow beam
with good circular polarizatization; whereas, the slot
configuration illustrated in FIG. 1 produces a broader beam.
However, in both cases, the distance 2h (the antenna element
length) determines the basic pattern width. The distance D is
thereafter chosen to provide a nearly equal pattern in the two
orthogonal planes as previously described.
FIGS. 4A and 4B illustrated two types of apparatus for exciting the
slot elements in phase quadrature. FIG. 4A illustrates an inner
square waveguide 21. Located on each of the four sides of the inner
square waveguide 21 are four side waveguides 23, each one-half
wavelength long. Four transverse slots 25 (two of which are shown
dotted in FIG. 4A) are located in the sides of the square waveguide
one-quarter wavelength from the end to allow signals moving down
the inner square waveguide 21 to pass into the four side waveguides
23. The outer end of the inner square waveguide is enclosed to
short circuit signals moving down the inner square waveguide 21.
Slots are formed in the ends of the side waveguides 23. As
illustrated in FIG. 4A, the slots are in the configuration
illustrated in FIG. 1; however, any slot configuration suitable for
carrying out the broad concept of the invention as previously
described can be formed in the ends of the side waveguides.
One method of establishing equal phase quadrature signals in the
square waveguides is also shown in FIG. 4A. This figure shows the
square waveguide excited by a crossed slot pair 29 located
one-quarter wavelength from the shorted end of a feed (lower)
waveguide 31. The slots are inclined at 45.degree. from the lower
guide axis. This geometry couples equal, in-phase, orthogonally
polarized waves into the square waveguide 21. A dielectric slab 33
delays the relative phase of one of the polarizations and
establishes a circularly polarized wave. Many other methods of
accomplishing this same result are known in the art and several are
described in the "Antenna Engineering Handbook," Henry Jasik,
Editor, McGraw-Hill Book Co., 1961, Ch. 17. In general, any
suitable prior art method can be used to supply incident orthogonal
modes in phase quadrature to the slots 25. A circuit for performing
this function for the coaxial line geometry is illustrated in FIG.
5.
If the distance D is less than one-half wavelength, the waveguide
of FIG. 4A may be dielectrically loaded in order to propagate the
frequency chosen. The structure illustrated in FIG. 4A operates as
follows: two orthogonal mode signals travel down the waveguide 21
in phase quadrature. As previously described, the waveguide is
short circuited at its outer end and the transverse slots are cut
one-quarter wavelength from the end on all four sides. These slots
are excited by means of the interrupted longitudinal current and
couple into the four side waveguides in the same manner. Each of
the side waveguides supports a single mode which then excites the
slots at the ground plane resulting in a circularly polarized
antenna beam being formed in the manner previously described. As
with the inner square waveguide, the side waveguides may be
dielectrically loaded.
FIG. 4B illustrates an alternative waveguide apparatus for exciting
slots in phase quadrature. FIG. 4B comprises a square waveguide 35
with the end of the waveguide enclosed by a suitable plate in which
the antenna slot configuration is formed. In accordance with well
known waveguide principles, two orthogonal modes travel down the
waveguide and excite the slots in phase quadrature. While the
waveguide structure illustrated in FIG. 4B is less complex than the
waveguide structure illustrated in FIG. 4A, care must be taken to
assure that cross polarized components are not excited at each of
the individual slots. The FIG. 4B waveguide configuration may or
may not be dielectrically loaded to improve performance, as
desired.
It will be appreciated by those skilled in the art that the broad
beam configuration of FIG. 1 can be implemented using the waveguide
arrangements of either FIGS. 4A or 4B. The waveguide arrangement of
4B can also be used to implement the narrower beam four slot
configuration of FIG. 3.
It will also be appreciated by those skilled in the art that the
basic concept of the invention can be carried out by other
apparatus. For example, circularly cylindrical waveguides can be
used to excite the slot configuration. The techniques necessary for
the excitation of the slots using circularly cylindrical waveguide
are the same as previously described for square waveguides.
FIG. 5 illustrates an embodiment of the invention wherein dipole
antenna elements, as opposed to slots, are used to form the
circularly polarized antenna beam. The embodiment of the invention
illustrated in FIG. 5 comprises: a 90.degree. hybrid 41; first and
second power dividers 43 and 45; four baluns 47, 49, 51 and 53; and
four pairs of antenna dipole elements 55, 57, 59 and 61. One pair
of dipole elements are attached to and project outwardly from
opposite sides of one balun in any well known manner. More
specifically, the first pair of dipole elements 55 project out of
opposite sides of the first balun 47. In a similar manner, the
second pair of dipole elements 57 project from the second balun 49;
the third pair of dipole elements 59 from the third balun 51; and
the fourth pair of dipole elements 61 from the fourth balun 53.
In operation, the incoming signal is applied via an incoming
terminal 63 to the input of the 90.degree. hybrid 41. The
90.degree. hybrid splits the incoming signal into phase quadrature
signals that are applied to the first and second power dividers 43
and 45. The power dividers divide the signals equally. The first
power divider 43 is connected to the first and third baluns 47 and
51. The second power divider 45 is connected to the second and
fourth baluns 49 and 53. In this manner, phase quadrature signals
are applied via the baluns to the antenna dipole elements. That is,
one signal mode is applied to the first and third baluns and a
phase quadrature signal mode is applied to the second and fourth
baluns. The first and third baluns are mounted (by means not shown)
so that their respective dipole elements are arrayed in parallel in
a manner similar to the slot array of one pair of slots in the FIG.
1 embodiment. The second and fourth baluns are mounted (by means
also not shown) so that their respective dipole elements are also
arrayed in parallel, but orthogonal to the direction of the dipole
elements connected to the first and third baluns. Hence, a dipole
array similar to the slot array of the previously described
embodiments is formed. FIG. 5 illustrates that the dipoles are
mounted at a distance D.sub.z above a ground plane 65. While this
mounting is not essential to the operation of the invention, it is
illustrated because it is appropriate for many applications, such
as aerospace applications, for example.
The embodiment of the invention illustrated in FIG. 5 operates in
the manner identical to the embodiments of the invention previously
described. That is, phase quadrature signals are applied through
the baluns to the dipole elements. Due to the configuration of the
dipole element array, a circularly polarized beam is formed. As
with the previously described slot embodiments, the length of the
dipole elements (2h) , from end to end, and the distance between
the pairs (D) determines the exact configuration of the circularly
polarized antenna beam that is formed.
The foregoing description has described the basic structural
embodiments of the invention and their operation. However, the
previously described embodiments are useful only when relatively
wide beamwidths are desired. More specifically, because the minor
lobe level of the array factor increases when D exceeds .lambda./2
until D reaches a value equal to the major lobe at D=.lambda., the
number of these undesirable "grating lobes" increases with a
further increase in D. As opposed to this, when the slot length is
increased, only a single beam is formed in the element pattern,
because there is no periodicity to give rise to grating lobes.
Therefore, even though it is possible to match the main lobe
structure of a long slot with the main lobe of the two elements
array factor, the array factor side lobes are large and the side
lobe structure is, in general, very poorly matched. Hence, the
previously described four slot or dipole configurations are not
satisfactory when a very narrow beam is desired.
The slot configurations illustrated in FIGS. 6A and 6B and
hereinafter described avoid the difficulty just described. FIG. 6A
illustrates a slot configuration wherein three parallel slots 67 or
69 make up each antenna set. Each set of slots is formed orthogonal
to the other set, as previously described. The slots are formed in
a plate 70 such that each slot of one set intersects all three
slots of the other set; hence, 2h>2D. FIG. 6B illustrates an
alternative three parallel slot arrangement wherein only the center
slots of the pairs intersect; that is, 2h<2D. It will be
appreciated by those skilled in the art that while the FIGS. 6A and
6B embodiments illustrate three parallel slots making up each of
the orthogonal sets, this is merely by way of example, and that
more parallel slots could be included in each set, if desired. In
general, the slot arrays shown illustrated in FIG. 6A and 6B
illustrate that the antenna elements must be invarient under a
rotation of any multiple times 90.degree. .
Whether the geometry of FIG. 6A or FIG. 6B is used in a particular
antenna structure depends upon how the slots are excited. If the
amplitude of the orthogonally polarized fields is constant, the
orientation of FIG. 6A is required, because the field distribution
across each slot will be tapered (in fact, the field distribution
will be zero at the ends of the slots), but each of the slots must
be excited with the same amplitude as every other slot. The array
factor beamwidth is narrower than the element factor beamwidth if
the total slot array length (L) is set equal to 2h. L is defined as
(N-1)D, where N is the number of slots. For this reason, the slots
are preferably somewhat longer than the total slot array length L.
For other choices of design geometry, the FIG. 6B embodiment is
preferable to the FIG. 6A embodiment.
Various types of apparatus can be used to excite the embodiments of
the invention illustrated in FIGS. 6A and 6B. For example, a
multi-mode field can be established within a horn feeding the
structure in order to improve the element pattern side lobes.
Alternatively, a similar improvement in the array pattern can be
effected by symmetrically varying the slot thickness or the slot
spacing. Further, the array pattern can be improved by using a
multi-mode excitation for each polarization in the plane
perpendicular to the slot axes.
In principle, the waveguide geometries of FIGS. 4A and 4B can also
be used to excite the N-slot configuration illustrated in FIGS. 6A
and 6B. The horn arrangements of FIG. 7 are an extension of the
basic feeding system of FIG. 4B, and the special embodiment
illustrated in FIG. 8 is a hybrid of the two excitation schemes
illustrated in FIGS. 4A and 4B. It can be used to excite a
relatively narrow beam set of six slots, and it avoids the problem
sometime encountered with the geometry of FIG. 4A with spacings for
which it is necessary to dielectrically load the center
waveguide.
FIGS. 7A and 7B illustrate waveguide systems for exciting the
general N-slot configurations illustrated in the FIGS. 6A and 6B.
The FIG. 7A system comprises a square waveguide 71 feeding a small
flare, pyramidal horn 73. An end plate or cover 75 including the
particular slot configuration being used fits over the end of the
horn 73. The dual mode signals move down the waveguide and the horn
and excite the slots in phase quadrature in accordance with well
known waveguide principles. A dielectric lens can be added to the
embodiment illustrated in FIG. 7A if larger flare angles are
desired.
The FIG. 7B waveguide system includes the square waveguide and the
pyramidal horn 73 illustrated in FIG. 7A. In addition, mounted
between the end cover 75 and the end of the pyramidal horn 73, is a
large square waveguide 77. This embodiment provides a higher order
mode aperture field distribution with a more suitable amplitude
distribution for pattern shaping than does the FIG. 7A embodiment.
Many other types of apparatus can be utilized by the invention to
feed the various slot configurations will be apparent to those
skilled in the art. Hence, the invention should not be construed as
limited to the signal feeding apparatus illustrated in the drawings
and described herein.
The horn arrangements of FIGS. 7A and 7B can in principle be used
to excite any of the slot combinations, although it is best to have
the cover plate approximately the same area as the extended area of
the array of slots. Otherwise, it becomes difficult to couple
energy out through the slots efficiently. For this reason the
geometries of 4A and 4B are preferable for the four slot
configurations.
As with the two slot configurations previously described, the slot
length of the FIG. 6A and 6B configurations is determined by the
desired beamwidth. The number of slots is determined by the
criteria that the slots spacing should be kept less than about
0.7.lambda.. The actual slot separation D is determined by matching
the main beam to that of the slot element pattern so that the
desired circularly polarized beam is formed.
In conclusion, it should be pointed out that the beam-width is
determined by the slot length 2h. Once this length is chosen, the
number of slots and the required slot spacing to set the array
factor equal to the element factor must be determined. The array
length L should be nearly the same as the slot length 2h, and at
the same time the slots should be no more than 0.6 or 0.7.lambda.
apart. This determines the minimum number of slots. The remaining
step is to equate beamwidths by choosing the slot separation
between about 0.4.lambda. and 0.7.lambda., and to do this in a way
consistent with the design sidelobe requirements of a particular
embodiment of the invention.
It will be appreciated by those skilled in the art and others that
the foregoing description has described a novel apparatus for
providing a circularly polarized antenna beam. Preferred
embodiments of the invention have been illustrated and described.
However, various other antenna configurations and feed apparatus
such as cylindrical waveguides can be utilized to carry out the
basic concept of the invention. For example, the embodiment shown
in FIG. 5 assumes that coaxial lines are used to carry signals to
and from the dipoles and therefore baluns are required to convert
the field geometry to the balanced configuration required for
exciting the dipoles. It is to be understood that a two wire line
arrangement could also be used; in this case without baluns.
* * * * *