U.S. patent application number 09/375319 was filed with the patent office on 2002-06-06 for aperture coupled slot array antenna.
Invention is credited to KUNYSZ, WALDEMAR.
Application Number | 20020067315 09/375319 |
Document ID | / |
Family ID | 23480406 |
Filed Date | 2002-06-06 |
United States Patent
Application |
20020067315 |
Kind Code |
A1 |
KUNYSZ, WALDEMAR |
June 6, 2002 |
APERTURE COUPLED SLOT ARRAY ANTENNA
Abstract
A planar, phased-array antenna including a nonconductive
substantially planar substrate and a transmission line disposed on
one surface is disclosed, a segment of the transmission line
forming an arc of radius R centered on the antenna axis. A
conductive layer on the other antenna surface includes two or more
slotted openings, each slotted opening having one end located
within a distance R of the antenna axis, such that, when an
electromagnetic signal is fed into one end of the transmission
line, electromagnetic energy is sequentially coupled into the
slotted openings, and a circularly-polarized signal is radiated
from the antenna substantially in the direction of the antenna
axis. An amplifier or a connector may be electrically connected to
one or both ends of the transmission line, or one end of the
transmission line may be terminated in an impedance load to form a
leaky-wave antenna. The slotted openings may comprise either or
both straight and curved segments, and may be of the same or
unequal lengths. Curved slotted openings may be oriented clockwise
or counter-clockwise to transmit or receive either left-handed or
right-handed polarized signals.
Inventors: |
KUNYSZ, WALDEMAR; (CALGARY,
CA) |
Correspondence
Address: |
PATRICIA A. SHEEHAN
CESARI AND MCKENNA, LLP
88 BLACK FALCON AVENUE
BOSTON
MA
02110
US
|
Family ID: |
23480406 |
Appl. No.: |
09/375319 |
Filed: |
August 16, 1999 |
Current U.S.
Class: |
343/770 ;
343/769; 343/895 |
Current CPC
Class: |
H01Q 9/27 20130101; H01Q
13/106 20130101; H01Q 13/20 20130101; G03F 7/091 20130101; H01P
1/2005 20130101; H01Q 1/36 20130101 |
Class at
Publication: |
343/770 ;
343/895; 343/769 |
International
Class: |
H01Q 013/12; H01Q
013/10; H01Q 001/36 |
Claims
What is claimed is:
1. An antenna, suitable for transmitting and receiving
electromagnetic signals of wavelength .lambda., said antenna
comprising: a nonconductive substantially planar substrate having
first and second surfaces bounded by a common peripheral edge, said
peripheral edge enclosing an antenna axis orthogonal to said first
and second surfaces; a transmission line disposed on said first
surface, said transmission line comprising a first end, a second
end, and an inner edge extending between said first and second
ends, at least a portion of said inner edge forming an arc of
radius R centered on said antenna axis; and a conductive layer
disposed on said second surface, said conductive layer comprising a
plurality of m slotted openings, each said slotted opening having
one end located within a distance R of said antenna axis, whereby,
when an electromagnetic signal is fed into said first end,
electromagnetic energy is coupled sequentially into respective said
slotted openings such that a radiated signal is transmitted from
said slotted openings substantially in the direction of said
antenna axis.
2. The antenna of claim 1 wherein said transmission line inner edge
has a guided wave length of at least .lambda..
3. The antenna of claim 1 wherein said transmission line comprises
at least one member of the group consisting of a microstrip and a
coplanar waveguide.
4. The antenna of claim 1 further comprising a connector
electrically attached to one said transmission line end.
5. The antenna of claim 1 further comprising at least one amplifier
electrically connected to at least one said transmission line
end.
6. The antenna of claim 1 further comprising an impedance load
electrically connected to one said transmission line end.
7. The antenna of claim 1 wherein at least a first said slotted
opening has a guided wave length of 15 a b .
8. The antenna of claim 7 wherein a second said slotted opening has
a guided wave length greater than the guided wave length of said
first slotted opening.
9. The antenna of claim 7 wherein said first slotted opening has a
width substantially smaller than the guided wave length of said
first slotted opening.
10. The antenna of claim 1 wherein said m slotted openings are
arrayed about said antenna axis such that at least two adjacent
said slotted openings are spatially separated by an angle of 16 2 m
.
11. The antenna of claim 1 wherein at least one said slotted
opening comprises a straight slotted portion.
12. The antenna of claim 1 wherein at least one said slotted
opening comprises a curved slotted portion.
13. The antenna of claim 12 wherein said curved slotted portion
comprises a shape selected from the group consisting of a
conical-section arc, a spiral arc, a logarithmic arc, and an
exponential arc.
14. The antenna of claim 1 further comprising a reflector disposed
in spaced parallel relationship to said first surface.
15. The antenna of claim 1 further comprising an enclosed cavity
disposed adjacent said first surface.
16. An antenna, suitable for transmitting and receiving
electromagnetic signals of wavelengths .lambda..sub.1 and
.lambda..sub.2, said antenna comprising: a nonconductive
substantially planar substrate having first and second surfaces
bounded by a common peripheral edge, said peripheral edge enclosing
an antenna axis orthogonal to said surfaces; a transmission line
disposed on said first surface, said transmission line comprising a
first end, a second end, and an inner edge extending between said
first and second ends, at least a portion of said inner edge
forming an arc of radius R centered on said antenna axis; and a
conductive layer disposed on said second surface, said conductive
layer comprising a first array of m slotted openings, each said
first array slotted opening having a peripheral end located
proximate said peripheral edge and an axial end located within a
distance R of said antenna axis, each said first array slotted
opening having a guided wave length of integer multiples of 17 1
4between said peripheral end and said axial end, at least one said
first array slotted opening spatially separated from an adjacent
said first array slotted opening by an angle of 18 2 m ;said
conductive layer further comprising a second array of m slotted
openings, each said second array slotted opening having a
peripheral end located proximate said peripheral edge and an axial
end located within a distance R of said antenna axis, each said
second array slotted opening having a guided wave length of integer
multiples of 19 2 4between said peripheral end and said axial end,
at least one said second array slotted opening spatially separated
from an adjacent said second array slotted opening by an angle of
20 2 mwhereby, when an electromagnetic signal is fed into said
transmission line via said first end, electromagnetic energy is
sequentially coupled into respective said slotted openings such
that a radiated signal having a wavelength of either or both
.lambda..sub.1 and .lambda..sub.2 is transmitted from said slotted
openings substantially in the direction of said antenna axis.
17. The antenna of claim 16 wherein at least one said slotted
opening comprises a shape selected from the group consisting of a
conical-section arc, a spiral arc, a logarithmic arc, and an
exponential arc
18. The antenna of claim 16 further comprising a connector
electrically attached to said transmission line first end.
19. The antenna of claim 16 further comprising at least one
amplifier electrically connected to at least one said transmission
line end.
20. The antenna of claim 16 further comprising an impedance load
electrically connected to said transmission line second end.
21. The antenna of claim 16 further comprising a reflector disposed
in spaced parallel relationship to said antenna first surface.
22. The antenna of claim 16 further comprising an enclosed cavity
disposed adjacent said antenna first surface.
23. A planar antenna suitable for transmitting or receiving an
electromagnetic signal, said antenna comprising: an array of m
slotted openings disposed in a first surface of the planar antenna,
said slotted openings for receiving or transmitting the
electromagnetic signal, said array of slotted openings defining an
antenna axis; and means for coupling the received or transmitted
electromagnetic signal with said slotted openings, said means for
coupling disposed on a second surface of the antenna so as to
substantially enclose said antenna axis.
24. The antenna of claim 23 wherein said means for sequentially
coupling comprises a transmission line comprising a plurality of m
coupling regions, each said coupling region comprising a segment of
said transmission line disposed proximate a corresponding said
slotted opening such that an electromagnetic signal transmitted
through said transmission line is coupled sequentially into
respective said slotted openings.
25. The antenna of claim 23 wherein at least one said slotted
opening comprises a curved slotted portion.
26. A method for emitting a circularly-polarized signal from a
planar antenna, said method comprising the steps of: transmitting a
first electromagnetic signal of wavelength .lambda..sub.1 along a
transmission line disposed on the rear antenna surface, said
transmission line comprising an arc-shaped segment having a radius
R centered on the antenna axis; and sequentially coupling said
transmitted signal into two or more slotted openings formed within
a conductive layer disposed on the front antenna surface, each said
slotted opening having an end located within a distance R of the
antenna axis, said slotted openings arrayed about the antenna axis
such that a signal is emitted having wavelength .lambda..sub.1 with
one of a right-hand or a left-hand circular polarization.
27. The method of claim 26 wherein said step of sequentially
coupling comprises the step of producing a radiation field
extending from said transmission line to said slotted openings.
28. The method of claim 26 further comprising the steps of:
transmitting a second electromagnetic signal of wavelength
.lambda..sub.2 along said transmission line; and sequentially
coupling the transmitted signal into said slotted openings such
that a signal of wavelength .lambda..sub.2 is emitted.
29. The method of claim 26 further comprising the steps of:
transmitting a second electromagnetic signal of wavelength
.lambda..sub.2 along said transmission line in a direction opposite
to that of the direction of transmission of said first
electromagnetic signal; and reverse sequentially coupling the
transmitted signal into said slotted openings such that a signal is
emitted having the other of a right-hand or a left-hand circular
polarization.
30. A method for receiving a circularly-polarized radiated signal
by means of a planar antenna, said method comprising the steps of:
receiving the radiated signal at two or more slotted openings
formed within a conductive layer disposed on the front surface of
the antenna, each said slotted opening having a first end located
proximate the antenna periphery and a second end located within a
distance R of the antenna axis; and sequentially coupling the
received signal from each said slotted opening into a transmission
line disposed on the rear surface of the antenna, said transmission
line comprising an arc-shaped segment having an edge radius of R
centered on the antenna axis.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention is related to planar broadband
antennas and, more particularly, to an antenna for transmitting or
receiving circularly-polarized signals.
[0003] 2. Description of the Prior Art
[0004] Antennas producing circularly-polarized signals are known in
the art. U.S. Pat. No. 5,861,848, issued to Iwasaki, for example,
discloses a circularly polarized wave patch antenna with short
circuit portion. The directivity of a patch antenna can be
increased by incorporation of a choke ring ground plane, but this
increases the weight of the antenna.
[0005] U.S. Pat. No. 5,815,122, issued to Nurnberger et al., for
example, discloses a slot spiral antenna with a single spiral slot
on one side of the antenna, and a spiral microstrip feed line on
the reverse side. The reference teaches primarily a single-slot
configuration which results in an antenna having a low directivity.
Moreover, the placement of an additional component, such as a
low-noise amplifier, on the antenna itself is impractical.
[0006] While the art describes planar antennas producing
circularly-polarized radiation, there remains a need for
improvements that offer advantages and capabilities not found in
presently available devices, and it is a primary object of this
invention to provide such improvements. It is another object of the
invention to provide such a planar antenna with an improved
directivity.
[0007] It is yet another object of the present invention to provide
a slot array antenna having a distribution feed line which matches
the input/output signals with the spatial angular configuration of
the antenna slots.
[0008] It is further another object of the present invention to
provide such a planar antenna which allows for the mounting of
active circuitry on the antenna substrate.
[0009] Other objects of the invention will be obvious, in part,
and, in part, will become apparent when reading the detailed
description to follow.
SUMMARY OF THE INVENTION
[0010] A planar antenna includes a nonconductive substantially
planar substrate and a transmission line disposed on one surface, a
segment of the transmission line forming an arc of radius R
centered on the antenna axis. A conductive layer on the other
antenna surface includes two or more slotted openings, each slotted
opening having one end located within a distance R of the antenna
axis, such that, when an electromagnetic signal is fed into one end
of the transmission line, electromagnetic energy is sequentially
coupled into the slotted openings, and a circularly-polarized
signal is radiated from the antenna substantially in the direction
of the antenna axis. The electrical phase length of the
transmission line is matched to the spatial angular difference
between two consecutive slotted openings, so as to provide for a
phased-array operation.
[0011] An amplifier or a connector may be electrically connected to
one or both ends of the transmission line, or one end of the
transmission line may be terminated in an impedance load to form a
leaky-wave antenna. The slotted openings may comprise either or
both straight and curved segments, and may be of the same or
unequal lengths. Curved slotted openings may be oriented clockwise
or counter-clockwise to transmit or receive either left-handed or
right-handed polarized signals.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] The invention description below refers to the accompanying
drawings, of which:
[0013] FIG. 1 is a diagrammatical view of the back side of an
antenna in accordance with the present invention showing an
arc-shaped transmission line disposed about an antenna axis;
[0014] FIG. 2 is a cross-sectional view of the antenna of FIG. 1
showing a conductive plane disposed on the antenna front side;
[0015] FIG. 3 is a diagrammatical view of the front side of the
antenna of FIG. 1 showing an array of slotted openings disposed in
the conductive plane;
[0016] FIG. 4 is an end view of the antenna of FIG. 3 showing the
placement of an optional reflector to increase the proportion of
electromagnetic energy transmitted in the antenna forward
direction;
[0017] FIG. 5 is a first embodiment of an antenna including four
equal-length slotted openings arrayed at 90.degree. intervals about
the antenna axis;
[0018] FIG. 6 is a view of the back side of the antenna of FIG. 5
showing an signal amplifier and an impedance load attached to the
ends of a transmission line;
[0019] FIG. 7 is a second embodiment of an antenna including curved
slotted openings with straight radial slotted segments to increase
coupling between the slotted openings and a transmission line;
[0020] FIG. 8 is a third embodiment of an antenna including
clockwise spiral slotted openings of two different lengths for
transmitting or receiving left-hand polarized signals of two
different wavelengths;
[0021] FIG. 9 is a view of the back side of the antenna of FIG. 8
showing a wide transmission line for optimally coupling signals of
two different wavelengths;
[0022] FIG. 10 is a front view of a fourth embodiment of an antenna
with high directivity including twelve spiral-shaped slotted
openings equally arrayed about the antenna axis;
[0023] FIG. 11 is a front view of a fifth embodiment of an antenna
including an array of straight slotted openings; and
[0024] FIG. 12 is a rear view of the antenna of FIG. 11 showing
low-noise signal amplifiers attached to the ends of a transmission
line.
DETAILED DESCRIPTION OF AN ILLUSTRATIVE EMBODIMENT
[0025] FIG. 1 is a diagrammatical view showing the back side of a
substantially planar antenna 10 for receiving or transmitting
electromagnetic signals of wavelength .lambda., in accordance with
the present invention. A back surface 13 of the antenna 10 is
bounded by a peripheral edge 17. The peripheral edge 17 encloses an
antenna axis 11 oriented orthogonal to the back surface 13. A
transmission line 21, which may be a microstrip, a coplanar
waveguide, or other such conductive component as known in the
relevant art, is disposed on the back surface 13. The transmission
line 21 includes an input end 23 for receiving or outputting the
electromagnetic signals. The input end is electrically connected by
a first conductive lead 12 to a connector 22, such as an RF
connector, for interfacing with external circuitry. A terminal end
25 of the transmission line 21 is electrically connected to a load
impedance 24 via a second conductive lead 14. The transmission line
21 is in the shape of a circular arc, where an inside edge 29 of
the transmission line 21 lies at a radius of R and an outside edge
27 lies at a radius of R+w from the antenna axis 11. The guided
wave length of the transmission line is equal to one or more
transmitted (or received) wavelengths .lambda..
[0026] FIG. 2 is a cross-sectional view of the antenna 10 as
indicated by the sectional arrows in FIG. 1. The antenna 10
comprises a substrate 19 of nonconductive or dielectric material
having a thickness t, where the transmission line 21 is disposed on
the back surface 13 of the substrate 19 and a conductive layer 31
is disposed on a front surface 15 of the substrate 19. The front
surface 15 is likewise bounded by the peripheral edge 17.
[0027] FIG. 3 is a diagrammatical view of the front side of the
antenna 10 showing that the conductive layer 31 includes a
plurality of similar curved, slotted openings 33, 35, 37, and 39,
where each slotted opening 33, 35, 37, and 39 extends through the
conductive layer 31 to the front surface 15 of the substrate 19.
The antenna 10 may thus be fabricated from a two-layer printed
circuit board (PCB), where the transmission line 21 and the slotted
openings 33, 35, 37, and 39 can be formed by suitably etching
portions of the respective cladding layers to form the slotted
openings 33, 35, 37, and 39 and the transmission line 21. It should
be understood that, although four slotted openings are shown for
purpose of illustration, the present invention is not limited to
this number and may comprise m slotted openings of varying shapes
and lengths, where m.gtoreq.2, as explained in greater detail
below.
[0028] Moreover, the slotted openings can be curved in shape as
shown, or can be straight segments or a combination of both
straight and curved segments, as described in greater detail below.
The curved shapes can be a conical section (i.e., a circular,
elliptical, parabolic, or hyperbolic arc), an Archimedean spiral, a
logarithmic spiral, or an exponential spiral. Straight slotted
openings are equivalent to dipoles and, as such, a single slotted
opening produces a linearly polarized signal. However, an array of
straight slotted openings can be used to transmit, or receive, a
circularly-polarized signal, as described in greater detail below.
Circular polarization can also be produced by using an array of
curved slotted openings, where the respective slotted openings are
curved in the direction of the desired circular polarization (i.e.,
a clockwise curvature to receive or transmit left-hand circularly
polarized signals). By using curved slotted openings having the
equivalent guided wave lengths of straight slotted openings, the
physical size of the antenna can be reduced.
[0029] The slotted openings 33, 35, 37, and 39 have respective
axial ends 33a, 35a, 37a, and 39a proximate the antenna axis 11,
and respective peripheral ends 33p, 35p, 37p, and 39p proximate the
peripheral edge 17. Axial ends 33a, 35a, 37a, are, respectively,
d.sub.1, d.sub.2, d.sub.3, and d.sub.4 from the antenna axis 11
where d.sub.i<R. That is, the respective axial ends 33a, 35a,
37a, and 39a of the respective slotted opening 33, 35, 37, and 39
lie inside the circle of radius R defined by the transmission line
21 (here shown in phantom) on the opposite side of the substrate
19. Accordingly, when the antenna 10 is used to transmit signals,
electromagnetic energy is fed into the transmission line 21 and is
electromagnetically coupled to the slotted opening 33, 35, 37, and
39. This coupling occurs at the four respective regions where the
slotted openings 33, 35, 37, and 39 which lie on the front surface
15, are located most proximate to and directly opposite the
transmission line 21 which lies on the back surface 13 of the
planar antenna 10.
[0030] For example, a portion of the slotted opening 33 is located
a distance equivalent to the substrate thickness t from the
transmission line 21 at a coupling region 43. As is well known in
the relevant art, the electromagnetic energy passing through
transmission line 21 will produce a radiating field across the
slotted opening 33 in the coupling region 43. This electromagnetic
energy will be similarly coupled into slotted openings 35, 37, and
39 at coupling regions 45, 47, and 49 respectively. The degree of
coupling is a function of the thickness t of the substrate 19, the
width w of the transmission line 21, the width v of the slotted
opening 33, and the dielectric properties of the substrate 19.
Conversely, when the antenna 10 is used to receive signals,
radiation energy is received at the slotted openings 33, 35, 37,
and 39 is coupled into the transmission line 21 at the respective
coupling regions 43, 45, 47, and 49.
[0031] As can be appreciated by one skilled in the relevant art,
electromagnetic energy radiated by the antenna 10 is emitted in
both directions along the antenna axis 11. To increase the
proportion of energy emitted in the forward direction and reduce
the backlobe radiation, a reflector 40 may be emplaced in opposed
parallel relationship to the back surface 13 of the antenna 10, as
shown in FIG. 4. In an alternative embodiment, an enclosed cavity
(not shown) could be used in place of the reflector 40 as is
well-known in the relevant art. The radiation pattern emitted from
the antenna 10, as well as the radiation pattern roll-off
characteristics, can also be varied as desired by increasing or
decreasing the separation between the reflector 40 and the antenna
10.
[0032] FIG. 5 is the front view of a first embodiment of a planar
antenna 50 in accordance with the present invention. The planar
antenna 50 includes four similar spiral-shaped slotted openings 53,
55, 57, and 59 each of width v and guided wave length L.sub.GW
symmetrically arrayed about an antenna axis 51 at angular intervals
of 1 2
[0033] radians. This configuration provides for a phased-array slot
antenna. Since the slotted openings 53, 55, 57, and 59 curve in the
counter-clockwise direction, the transmitted or received signals
will be right-hand polarized. Conversely, signals having a
left-hand polarization are produced (or received) when the slotted
openings 53, 55, 57, and 59 are curved in the clockwise direction.
Unwanted cross-polarization is minimized by keeping the opening
width v narrow in comparison to the guided wave length L.sub.GW.
The shape of each of the slotted openings 53, 55, 57, and 59 can be
described best in polar coordinates using the antenna axis 51 as
origin. The radial distances r(.theta.) of the interior edges of
the slotted openings 53, 55, 57, and 59 increase from r.sub.a at
the respective axial ends 53a, 55a, 57a, and 59a, to a maximum
radius of r.sub.p at the respective peripheral ends 53p, 55p, 57p,
and 59p. The radial distance from the antenna axis 51 to the inside
edge of any of the slotted opening 53, 55, 57, and 59 increases
with the polar angle .theta. and is also a function of the interval
spacing .DELTA.r for each spiral-shaped slotted opening where
.DELTA.r.ident.r(.theta.+2.pi.)-- r(.theta.). For the slotted
opening 53, the radial distance from the antenna axis 51 can be
described by means of the equation, 2 r 53 ( , r ) = r a + r 2 . (
1
[0034] The slotted opening 55 is spatially offset from the slotted
opening 53 by 3 2
[0035] radians (90.degree.). Similarly, the slotted opening 57 is
spatially offset by .pi. radians (180.degree.), and the slotted
opening 59 is spatially offset by 4 3 2 ( 270 .degree. ) .
[0036] The radial distances r(.theta.,.DELTA.r) of the interior
edges of the three slotted openings 55, 57, and 59 can thus be
determined by the respective equations, 5 r 55 ( , r ) = r a + r -
/ 2 2 , 2 ( 2 r 57 ( , r ) = r a + r - 2 , ( 3 r 59 ( , r ) = r a +
r - 3 / 2 2 , 3 2 ( 4
[0037] The guided wave length L.sub.GW of each of the slotted
openings 53, 55, 57, and 59 is specified to be a multiple of
quarter-wavelengths of the receiving or transmitting signal in
order to maximize the antenna efficiency 6 ( i . e . , L GW = n 4 )
.
[0038] In the configuration shown, each spiral-shaped slotted
opening subtends an angle of .theta..sub.p, where 7 n 4 = 0 p ( r 2
1 + 2 ) ( 5
[0039] The width v of each of the slotted openings 53, 55, 57, and
59 is specified to be substantially smaller than the guided wave
length and large enough to enable good electromagnetic coupling
between the respective slotted opening 53, 55, 57, and 59 and a
transmission line 61, best seen in FIG. 6 which is a rear view of
the planar antenna 50. The transmission line 61 "crosses" each of
the slotted openings 53, 55, 57, and 59 at respective coupling
regions 63, 65, 67, and 69. The coupling regions 63, 65, 67, and 69
are offset by 8 2
[0040] radians (90.degree.) from one another. This configuration
provides for matching the electrical phase differences in the
coupling regions 63, 65, 67, and 69 (i.e., differences of
90.degree.) with the spatial differences of the slotted openings
53, 55, 57, and 59 when the guided wave length of the transmission
line 61 is tuned to be one wavelength .lambda.. A single,
omnidirectional beam is produced when the guided wave length of the
transmission line 61 is one wavelength .lambda., a squinted beam is
produced when the guided wave length is less than one wavelength,
and multiple directional beams are produced when the guided wave
length of the transmission line 61 is more than one wavelength.
[0041] A signal is transmitted (or received) by means of a signal
source (or receiver) connected to an input/output end 62 of the
transmission line 61 via a low-noise amplifier 71. A connector 75
provides for connecting the transmitted (or received) signal to
external circuitry via a coaxial cable, an optical fiber, or a
waveguide. An impedance load 73 is coupled to a terminal end 64 of
the transmission line 61 to provide a leaky-wave antenna
configuration and to thus ensure a uniform amplitude coupling to
all slotted openings 53, 55, 57, and 59. Alternatively, the
connector 75 can be directly attached to the input/output end 62 of
the transmission line 61 and the amplifier 71 can be located on a
separate circuit board.
[0042] For the configuration shown, a transmitted signal
originating in the low-noise amplifier 71 and terminating in the
impedance load 73 passes through the transmission line 61 in a
counter-clockwise direction (as viewed from the front of the planar
antenna 50). As the transmitted signal is successively coupled to
the slotted openings 53, 55, 57, and 59 at the respective coupling
regions 63, 65, 67, and 69, a right-hand polarized signal is
emitted from the planar antenna 50. Alternatively, the signal can
be transmitted through the transmission line 61 in a clockwise
direction and the slotted openings 53, 55, 57, and 59 can be curved
in a clockwise direction for a transmitted (or received) signal
which is left-hand polarized. For a configuration in which the
signal travels in the direction opposite to the direction of the
spiral slotted openings, both right-hand and left-hand polarized
radiation is transmitted (or received).
[0043] In a second embodiment, shown in FIG. 7, an antenna 80
comprises an array of four slotted openings 81, 83, 85, and 89
coupled to the transmission line 61 (on the back side of the
antenna 80). To improve electromagnetic coupling to the
transmission line 61, the slotted openings 81, 83, 85, and 87 each
include a straight, radial segment 89 oriented at a right angle to
the transmission line 61. The slotted openings 81, 83, 85, and 87
together with the respective radial segments 89 are tuned so as to
optimally transmit (or receive) a specified wavelength .lambda..
Because slotted antennas are broadband, the antenna 80 can transmit
(or receive) a spectral band of wavelengths, in addition to
radiation of wavelength .lambda.. If the spectral band of
wavelengths lies within 30% of .lambda., a slotted opening tuned to
a guided wave length .lambda. can also be used for transmitting (or
receiving) the spectral band wavelengths. For wavelengths lying
outside this spectral band, a second slotted opening of different
guided wave length is used.
[0044] For example, in the third embodiment shown in FIG. 8, an
antenna 90 is configured to transmit and receive left-hand
polarized signals at two wavelengths, .lambda..sub.1, and
.lambda..sub.2. Two slotted openings 91 and 95 are tuned for the
longer wavelength .lambda..sub.1, and two slotted openings 93 and
97 are tuned for the shorter wavelength .lambda..sub.2. The slotted
opening 91 can be tuned to the wavelength .lambda..sub.1 by having
a guided wave length L.sub.GW of: i) one wavelength
(.lambda..sub.1), ii) two wavelengths (2.lambda..sub.1), iii)
one-half wavelength 9 ( 1 2 ) ,
[0045] iii) one-quarter wavelength 10 ( 1 4 ) ,
[0046] or iv) some other multiple or fraction of a wavelength 11 (
a 1 b ) .
[0047] The antenna 90 comprises a transmission line 101 having a
greater width in comparison to the width of transmission line 61
(in FIG. 6). As best seen in FIG. 9, the transmission line 101 has
an inside edge 103 of radius of curvature R.sub.1 and an outside
edge 105 of radius of curvature R.sub.2=R.sub.1+w. As well-known in
the relevant art, a signal propagating within the transmission line
101 will appear mostly at the edges 103 and 105. The guided wave
length along the inside edge 103 is smaller than the guided wave
length along the outside edge 105 by the fraction 12 R 1 R 2 .
[0048] By selecting suitable values for R.sub.1 and R.sub.2, the
transmission line 101 can be optimized for coupling more than one
wavelength into the array of slotted openings 91, 93, 95, and
97.
[0049] As stated above, the invention is not limited to a single
frequency or to only four slotted openings. In a fourth embodiment,
shown in FIG. 10, an antenna 110 comprises six slotted openings 111
tuned to a first wavelength .lambda..sub.1, and six slotted
openings 113 tuned to a second, shorter wavelength .lambda..sub.2.
The array of slotted openings 111 are disposed about an antenna
axis 115 within the array of slotted openings 113. The six slotted
openings 111 are spaced apart from one another at angular intervals
of 13 3
[0050] radians (60.degree.), and the six slotted openings 113 are
spaced apart from one another at angular intervals of 14 3
[0051] radians (60.degree.). All twelve slotted openings 111 and
113 are coupled to a transmission line (not shown) located on the
back side of the antenna 110. With twelve slotted openings, the
antenna 110 has a higher directivity and a greater pattern roll-off
from boresight to antenna horizon than, for example, the antenna
50, in FIG. 5, comprising four slotted openings.
[0052] In a fifth embodiment, shown in FIG. 11, an antenna 120
comprises eight straight slotted openings 121a, 121b, . . . , and
121h arrayed about an antenna axis 123. Each slotted opening
121a-121h is coupled to a transmission line 125 on the back side of
the antenna 120, as shown in FIG. 12. A first end 127 of the
transmission line 125 is connected to a first signal amplifier 131,
and a second end 129 of the transmission line 125 is connected to a
second signal amplifier 133. There is also provided a switching
circuit (not shown) which enables either the first signal amplifier
131 or the second signal amplifier 133 to transmit a corresponding
signal through the transmission line 125. A signal transmitted by
the first signal amplifier 131 travels in a counter-clockwise
direction, from the first end 127 to the second end 129. The input
impedance of the second signal amplifier 133 provides an impedance
load to the signal transmitted by the first signal amplifier 131.
The counter-clockwise signal is coupled first into the straight
slotted opening 121a and last into the straight slotted opening
121h. This coupling sequence produces an emitted signal having
left-handed circular polarization.
[0053] Similarly, a signal transmitted by the second signal
amplifier 133 travels in a clockwise direction, from the second end
129 to the first end 127. The input impedance of the first signal
amplifier 131 provides an impedance load to the signal transmitted
by the second signal amplifier 133. The clockwise signal is coupled
first into the straight slotted opening 121h and last into the
straight slotted opening 121a. This coupling sequence produces an
emitted signal having right-handed circular polarization. In this
way, a single antenna can be used to transmit signals of either
polarization. Alternatively, the second signal amplifier 133 can be
replaced by a receiver (not shown), and the antenna 120 can be used
to transmit left-handed circularly polarized signals via first
signal amplifier 121 and to receive right-handed circularly
polarized signals via the receiver. If the first signal amplifier
is also replaced by a second receiver (not shown), both left-hand
polarized and right-hand polarized signals can be received by the
antenna 120.
[0054] While the invention has been described with reference to
particular embodiments, it will be understood that the present
invention is by no means limited to the particular constructions
and methods herein disclosed and/or shown in the drawings, but also
comprises any modifications or equivalents within the scope of the
claims.
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