U.S. patent number 3,778,838 [Application Number 05/311,210] was granted by the patent office on 1973-12-11 for circular symmetric beam forming apparatus.
This patent grant is currently assigned to Hughes Aircraft Company. Invention is credited to Alvin Clavin.
United States Patent |
3,778,838 |
Clavin |
December 11, 1973 |
CIRCULAR SYMMETRIC BEAM FORMING APPARATUS
Abstract
An antenna is disclosed having an X-section pattern that is
circular symmetric, i.e., the antenna produces a beam having equal
E and H plane patterns of the type required to achieve circular
polarization over a large angular portion of the beam. In general,
the antenna is implemented by no less than one slot in a ground
plane across the bottom of a conductive cylindrical cup and
mutually coupled to and straddled by two dipoles that are normal to
the ground plane. In a circularly polarized version of the
invention, crossed slots are excited by a rotating electric
field.
Inventors: |
Clavin; Alvin (Calabasa,
CA) |
Assignee: |
Hughes Aircraft Company (Culver
City, CA)
|
Family
ID: |
23205892 |
Appl.
No.: |
05/311,210 |
Filed: |
December 1, 1972 |
Current U.S.
Class: |
343/727; 343/767;
343/853; 343/771 |
Current CPC
Class: |
H01Q
13/18 (20130101); H01Q 25/04 (20130101); H01Q
21/29 (20130101) |
Current International
Class: |
H01Q
13/18 (20060101); H01Q 25/04 (20060101); H01Q
25/00 (20060101); H01Q 13/10 (20060101); H01Q
21/29 (20060101); H01Q 21/00 (20060101); H01q
021/00 (); H01q 013/10 () |
Field of
Search: |
;343/727,767,770,771,789,853 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Lieberman; Eli
Claims
What is claimed is:
1. A circular symmetric beam forming antenna comprising a ground
plane; no less than one slot in said ground plane; first and second
conductive posts disposed on one side of said ground plane on
opposite sides of and mutually coupled to each of said no less than
one slot; means disposed on the side opposite from said one side of
said ground plane for providing a cavity including said no less
than one slot in a side wall thereof; a conductive cylinder of a
height less than that of said first and second conductive posts
disposed symmetrically about said no less than one slot in contact
with and on said side of said ground plane thereby to provide an
antenna element; and means coupled to said antenna element for
exciting said element with electromagnetic energy to be
transmitted.
2. The circular symmetric beam forming antenna as defined in claim
1 wherein said means coupled to said antenna element for exciting
said element with energy to be transmitted constitutes a
180.degree. hybrid element having an input and first and second
outputs, said first and second outputs being connected to said
first and second conductive posts, respectively, whereby a signal
applied to said input excites said antenna element.
3. The circular symmetric beam forming antenna as defined in claim
1 wherein said means coupled to said antenna element for exciting
said element with energy to be transmitted constitutes means for
exciting said cavity thereby to excite said no less than one slot
in a side wall thereof.
4. The circular symmetric beam forming antenna as defined in claim
1 wherein said no less than one slot in said ground plane
constitutes first and second crossed orthogonal slots and said
means coupled to said antenna element for exciting said element
with energy to be transmitted includes cylindrical waveguide means
for exciting said first and second crossed orthogonal slots with
two TE.sub.11 orthogonal modes of a phase difference equal to
90.degree. thereby to provide a circularly polarized output from
said antenna element.
5. The circular symmetric beam forming antenna as defined in claim
1 wherein the diameter of said conductive cylinder is less than one
free space wavelength of said electromagnetic energy to be
transmitted.
6. A circular symmetric beam forming antenna comprising a section
of rectangular waveguide; a ground plane having first and second
sides, said ground plane being disposed transversely across one
extremity of said section of rectangular waveguide, in contact with
said first side, the portion of said ground plane enclosed by said
waveguide having a centrally disposed slot parallel to the broad
side walls of said waveguide; first and second conductive posts of
substantial dipole length disposed on said second side of said
ground plane on opposite sides of and mutually coupled to said
slot; a conductive cylinder of a length less than the height of
said first and second conductive posts disposed symmetrically about
said slot in contact with said second side of said ground plane
thereby to provide an antenna structure; and means for launching a
fundamental mode electromagnetic wave in said section of
rectangular waveguide whereby a circular symmetric beam is radiated
by said antenna structure.
7. The circular symemtric beam forming antenna as defined in claim
6 wherein said first and second conductive posts are of a length
that differs from said dipole length to produce a 180.degree. phase
difference in a signal radiated therefrom as compared to a driving
signal radiated from said slot.
8. A circular symmetric beam forming antenna comprising a ground
plane having a slot therein; a cavity in contact with one side of
said ground plane whereby a portion of said ground plane provides a
side wall for said cavity, said portion including said slot; first
and second conductive posts of dipole length disposed through said
ground plane from said one side thereof on opposite sides of said
slot thereby to effect mutual coupling therewith; a conductive
cylinder of a length less than said dipole length disposed
symmetrically about said first and second conductive posts in
contact with the side opposite said one side of said ground plane;
and a 180.degree. hybrid having an input and first and second
outputs, said first and second outputs being connected to said
first and second conductive posts, respectively, on said one side
of said ground plane thereby to drive said first and second
conductive posts in response to a signal applied to the input of
said hybrid with signals differing in phase by 180.degree..
9. A circularly polarized circular symmetric beam forming antenna
comprising a section of cylindrical waveguide; a ground plane
having first and second sides, said ground plane being disposed
transversely across one extremity of said cylindrical waveguide
with said first side thereof in contact therewith, said ground
plane additionally having first and second crossed orthogonal slots
centrally disposed within the area thereof enclosed by said
cylindrical waveguide; first, second, third and fourth conductive
posts of substantially dipole length disposed on said second side
of said ground plane in respective quadrants thereof formed by said
crossed slots; a conductive cylinder of a length less than said
dipole length disposed symmetrically about said first, second,
third and fourth conductive posts in contact with said second side
of said ground plane; and means for launching a signal in the form
of first and second orthogonal TE.sub.11 modes 90.degree. out of
phase along said cylindrical waveguide towards said first and
second crossed orthogonal slots in said ground plane thereby to
radiate a circularly polarized circular symmetric beam.
Description
BACKGROUND OF THE INVENTION
A circular symmetric beam having substantially equal E and H plane
patterns is required in many applications such as feeds for
circular apertures, or as data links. In U.S. Pat. No. 3,594,806,
entitled "Dipole Augmented Slot Raidating Elements", broadband
posts were placed intermediate the slots of an array to produce
equal E and H plane patterns of the elements and to reduce mutual
coupling between array elements. Multiple slots in an array
configuration without a cylindrical cup reflector were disclosed in
this case. In U.S. Pat. No. 2,846,679, entitled "Beam Forming
Antenna", on the other hand, a dipole radiating element was
disposed parallel to the bottom surface of a cylindrical cup
reflector. In this device there is no slot radiating element
mutually coupled to the dipole to equalize the E and H plane field
intensity patterns.
SUMMARY OF THE INVENTION
In accordance with the present invention, a slot in a ground plane
is excited by a waveguide, for example. Energy radiated from the
slots parasitically excites dipoles straddling the slot out of
phase with each other. When closely spaced the dipoles radiate very
little; as spacing is increased the dipoles radiate more strongly
until a drop off occurs when coupling to the slot falls off. The
relative phase between dipole radiation and slot radiation is
controlled by the length of the dipoles. When short, the dipoles
are capacitive and lead the driving voltage. When longer than at
resonance, radiation from the dipoles lags the driving excitation.
This effect, together with a cylindrical cup reflector, is used to
control the antenna pattern. The antenna can be excited by either
coaxial or waveguide lines. Also, the dipoles can be driven and the
slot parasitically excited.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a perspective view of a slot excited embodiment of the
present invention;
FIG. 2 illustrates a cross-sectional view through the slot of the
antenna of FIG. 1;
FIG. 3 illustrates a plan view of the reflector cup of the antenna
of FIG. 1;
FIG. 4 shows a partially sectional schematic view of an antenna in
accordance with the invention having driven dipoles and a
parasitically excited slot;
FIGS. 5 and 6 show a perspective and end view, respectively, of a
circularly polarized version of the antenna of the invention;
FIG. 7 illustrates E and H characteristics of the antenna of FIG.
1; and
FIG. 8 illustrates the manner in which the E field patterns of the
antenna of FIG. 1 combine to give the resultant E field.
DESCRIPTION
Referring now to FIGS. 1-3 of the drawings, there is shown a
preferred embodiment of the circular symmetric beam forming antenna
of the present invention. More particularly, the antenna includes a
segment of rectangular waveguide 10 terminated at one extremity
with a circular ground plane 11 having a slot 12 symmetrically
disposed therein within the cross-section of waveguide segment 10
parallel to the broad side walls thereof. The remaining extremity
of waveguide segment 10 is blanked off by means of a conductive end
plate 13 disposed transversely thereacross. Coupling to the
waveguide segment 10 is provided by a conductive probe 14 inserted
through an aperture 15 centrally disposed in a broad sidewall
thereof one-quarter wavelength from the inner surface of end plate
13. A coaxial connector 16 attached to the broad sidewall of
waveguide segment 10 about the aperture 15 has a center conductor
17 which connects to the probe 14.
Exterior to the waveguide segment 10, dipoles 18, 19 are straddled
across the slot 12 midway therealong and normal to ground plane 11.
Lastly, a conductive cylinder 20 is disposed about the periphery of
ground plane 11 to provide a reflector for the radiating slot 12
and coupled dipoles 18, 19.
In operation, a signal to be transmitted is applied through coaxial
connector 16 to the probe 14 to excite the cavity formed by the
waveguide segment 10, which, in turn, causes energy to be radiated
from slot 12. The energy radiated from slot 12 has an E-plane
pattern 22, FIG. 8, which has a circular configuration. The E-plane
energy radiated by slot 12 parasitically excites dipoles 18, 19 out
of phase. The H-plane pattern of the dipoles 18, 19 vary
approximately as cos .theta. as shown by the patterns 23, 24, FIG.
8, for the dipoles 18, 19, respectively. The amplitude of the
dipole patterns 23, 24 is controlled by the spacing of the dipoles
18, 19 from the slot 12. When closely spaced, the dipoles 18, 19
radiate very little. As spacing is increased, radiation increases
until a drop-off occurs due to falling off of coupling with slot
12. The relative phase between radiation from dipoles 18, 19 and
radiation from slot 12 is controlled by the length of the dipoles
18, 19. When short relative to resonant length, the dipoles 18, 19
are capacitive and lead the driving voltage. When longer than at
resonance, radiation from the dipoles 18, 19 lags the driving
excitation. A length is selected for the dipoles 18, 19 to make the
phase of the radiation therefrom differ by 180.degree. from that of
the E-plane pattern from slot 12. When this is the case, the
H-plane patterns 23, 24 subtract, reducing the E-plane slot pattern
22 to a resultant pattern 25. The dipoles 18, 19 are symmetric in
the H-plane and, being out of phase, do not radiate in this plane.
Thus, by appropriate adjustment of the spacing of the dipoles 18,
19 from the slot 12, the E-plane pattern for slot 12 is made
substantially equal to the H-plane pattern therefor.
Referring to FIG. 7, there is illustrated an E-plane pattern 30 and
an H-plane pattern 32 for a circular symmetric beam forming antenna
of the type described in connection with FIGS. 1-3 wherein the
dipoles 18, 19 have a height of three-eighths wavelength and a
spacing of 0.22 wavelength, and the conductive cylinder 20 has a
length of one-quarter wavelength and a diameter of 0.9
wavelength.
Referring to FIG. 4 there is shown a partially cross-sectional
schematic drawing of a circular symmetric beam forming antenna in
accordance with the present invention wherein like reference
numerals refer to like elements. In this case, the dipoles 18, 19
are driven 180.degree. out of phase by appropriate connections
through coaxial lines 34, 36, respectively, from the outputs of a
180.degree. hybrid 38 having an input 40. The slot 12 in ground
plane 11 is enclosed by a cavity 42 on the side thereof opposite
from the dipoles 18, 19. Operation is the same as that of the
antenna described in connection with FIGS. 1-3 with the exception
that the slot 12 is now parasitically excited by the dipoles 18, 19
through mutual coupling thereto rather than the dipoles 18, 19
being parasitically driven by radiated energy from the slot 12.
Relative phase between the radiated energy from the dipoles 18, 19
and that from the slot 12 may be controlled by selecting the
perimeter of slot 12, i.e., by controlling the resonant length of
slot 12. The size of the cavity 42 should, of course, be sufficient
to support oscillations at the resonant frequency of the slot
12.
Referring to FIGS. 5 and 6 there are shown two views of a circular
symmetric beam forming antenna 50 for generating a circularly
polarized beam. More particularly, antenna 50 includes cylindrical
waveguide section 51 intermediate a rectangular-to-cylindrical
conversion section 52 and a ground plane 53. Ground plane 53
includes a centrally disposed slot 54 parallel to the broad sides
of the rectangular waveguide portion of section 52 and a centrally
disposed slot 55 that is normal to the slot 54. A conductive
cylinder 56 is disposed about the periphery of ground plane 53 in a
direction extending away from the cylindrical wave guide section 51
thereby to form a cylindrical cup reflector for energy radiated
from the slots 54, 55. Dipoles 57, 58, 59 and 60 are erected within
the cylindrical cup reflector equidistant from the center and
normal to the ground plane 53 along the bisectors of the quadrants
between the slots 54, 55. Lastly, a dielectric slab 62 constituting
a one-quarter wave plate is disposed across a diameter and along a
central portion of the cylindrical waveguide section 51 at a
45.degree. angle with the slots 54, 55.
In operation, energy propagating in the rectangular waveguide in
the TE.sub.10 mode is converted to the TE.sub.11 mode in the
cylindrical waveguide section 51 by the rectangular-to-cylindrical
conversion section 52 with the electric field normal to the slot
54. In traversing the one-quarter wave plate 62, the energy in the
incident TE.sub.11 mode is divided into two orthogonal TE.sub.11
modes which have a 90.degree. phase difference. The two orthogonal
TE.sub.11 modes excite the slots 54, 55 in a manner to generate a
circularly polarized wave. The dipoles function in the same manner
as the dipoles 18, 19 in the antenna of FIGS. 1-3.
* * * * *