TAPERED SLOT ANTENNA

TECHNICAL FIELD
The present invention relates to the field of antenna technology and
especially a tapered slot antenna element, a feeding probe for a tapered slot
antenna element and a tapered slot antenna arrangement.
BACKGROUND ART
Tapered slot antennas are commonly known within the art. A tapered slot
antenna is structured, such that a slot ine radiates an electromagnetic wave
directed parallel to the plane of the antenna. The slot line is commonly fed by
a feeding line, which crosses the slot line. The feeding line is integrated in the
tapered slot antenna and is connected to a circuit board. There are antennas
in which the circuit board is integrated with the antenna element, these
antennas have the antenna and the circuit board in the same plane, and
thereby, connector means between the feeding line and the circuit board is
not needed, since the feeding line can be etched directly on the circuit board.
However, in some applications it is whished that the antenna element is not
in the same plane as the circuit board, whereby the antenna and the circuit
board must be separated. There is further a demand to replace defect
antenna elements or the circuit board without having to replace both of them.
Thereby the antenna element and the circuit board must be connected with
each other with connectors, such that the feeding line is properly contacted to
the circuit board. Further, an attachment interface where the antenna
element can be mounted must also be provided. The connector and the
attachment interface obviously mean additional cost in both materia! and
mounting time, especially in an antenna system comprising thousands of
antenna elements. Thereby is there a need for an inexpensive and
exchangeable antenna element.
SUMMARY OF THE INVENTION
The present invention is defined by the appended independent claim. Various
examples of the invention are set forth by the appended dependent claims as
well as by the following description and the accompanying drawing.
Considering afore mentioned problems, the object of the present invention is
to suggest an inexpensive and easy to mount tapered slot antenna.
The object is achieved through the inventive idea that a coaxial probe can be
used as signal transition between the tapered slot antenna element and the
circuit board. Thereby is the object of the invention achieved through a
tapered slot antenna element according to claim 1, a feeding probe according
to claim 6 and a tapered slot antenna arrangement according to claim 10.
The inventive idea is to create a coaxial field within the tapered slot antenna
element. Said coaxial field crosses the slot line of the tapered slot, and which
thereby can feed the tapered slot. Hence the feeding signal is fed into the slot
line by the coaxial field. Due to this inventive design a connector between the
tapered slot antenna element and the circuit board is not needed any more.
The tapered slot antenna element according to the invention comprises a
tapered slot with a narrow inner part. The tapered slot can be any kind known
in the art, i.e. a tapered notch, a stepped notch, vivaldi or a bunny ear. The
type of tapered slot antenna does not influence the inventive idea, which just
comprises the feeding of the tapered slot antenna and can be used with any
antenna type.
The tapered slot antenna element further comprises a cavity for receiving a
feeding probe. An inner wall of said cavity is provided with a layer comprising
an electric conductive material, and said cavity is provided with an open end.
The cavity is adapted such that a feeding probe can be inserted into the
cavity through the open end. The layer comprising the electric conductive
material is adapted such that the coaxial field can be build up between the
feeding probe and said layer of electric conductive material. Hence, said
layer can be a homogenous layer or a wire netting or the like, as long as a
coaxial field can be build up between the electric conductive layer and the
feeding probe.
The feeding probe comprises a conductive core and is adapted such, that
when it is inserted into the cavity, the conductive core and the layer of electric
conductive material is the inner wall of the cavity is distanced from each
other. The coaxial field can thereby be build up in the space between the
conductive core and said layer of electric conductive material in the inner wall
of the cavity. The space between the conductive core and said layer of
electric conductive material can be filled with air or a dielectric material. The
tapered slot is arranged in the antenna element, such that it cuts the coaxial
field, whereby the tapered slot can be fed by the coaxial field. Thereby a
radio frequent signal can be fed into the tapered slot through the coaxial field.
This is further explained in conjunction with fig. 1.
The slot of the tapered slot antenna element is located such that when said
conductive core is mounted in the cavity, it extends inside the cavity such
that it at least reaches beyond the point where the slot line cuts the cavity.
Thereby it is secured that the coaxial field reaches the slot line.
A preferred and effective shape for the cavity, the feeding probe and the
conductive core is circular cylindrical, and wherein the conductive core is
placed symmetrical within the cavity. With such a configuration it is possible
to build up a homogenous and coaxial field between the conductive core and
the layer comprising the conductive material, which is located on the inner
wail. However, the inventive tapered slot antenna element, feeding probe and
tapered slot antenna arrangement is not limited to a circular cylindrical
configuration. As long as a coaxial field can be build up between the
conductive core and the layer comprising electric conductive material in/on
the inner wall of the cavity, the individual elements can have arbitrary
shapes, and in any combination thereof.
The inventive tapered slot antenna element can be made of any material;
however, it is important that the layer comprising the electric conductive
material in/on the inner wall of the cavity is enabling a coaxial field to be build
up between the inner wall and the conductive core of the feeding probe. The
layer comprising the electric conductive material is preferably the outer layer
of the inner wall.
Due to the inventive coaxial contact between the circuit board and the
antenna element, it is possible to produce the whole tapered slot antenna
element in one piece of material, as long as the material is electrically
conductive. A tapered slot antenna element could for example be made in
casted aluminium, iron or other suitable metal. However, a tapered slot
antenna element according to the invention comprising a plurality of materials
is just as possible, as long as a layer of electric conductive material is
provided such that the coaxial field can be build up between said layer and a
feeding probe located in the cavity of the antenna element. For example, a
light weight antenna could be produced in a composite or a plastic material.
A tapered slot antenna is commonly used as a part of an array antenna, in
which a plurality of tapered slot antennas is used. In such radars the direction
of the individual antenna elements relative each other is important to secure
a high performance of the array. To assure a correct positioning of the
individual tapered slot antenna elements, it is suggested that each antenna
element comprises one or a plurality of guides. The guides are adapted to
direct the tapered slot antenna element into its correct and desired position.
The guide is preferably located on the circuit board on which also the feeding
probe is located. However, also the feeding probe can be used as a guide.
The feeding probe is located on the circuit board, from which it is fed. The
feeding probe preferably comprises a dielectric coverage surrounding the
conductive core. Said dielectric coverage is adapted to fit into said cavity,
and at least partially fills the distance between the conductive core and the
inner wall. However it is preferred that dielectric coverage is adapted to fit
into the cavity of the tapered slot antenna element, such that it can support
the tapered slot antenna element. The dielectric coverage of the feeding
probe can be designed such that it tightly fits into the cavity, whereby the
tight fit also functions as a fixation means of the tapered slot antenna element
on the circuit board and there won't be any piay between the tapered slot
antenna element and the feeding probe.
The feeding probe is preferably but not necessary directed perpendicular
from the plane of the circuit board, thereby providing an easy mounting of the
tapered slot antenna element. However, alternative directions are also
possible, i.e. up to 90.
In a system using an array of tapered slot antenna arrangements, the
tapered slot antenna elements can be mounted in arrays or in rows, the
inventive tapered slot antenna is suitable to use in any such configuration.
To protect the tapered slot antenna elements from any radiation from the
electronic components on the circuit board, the antenna elements can be
provided with one common ground plane, wherein said ground plane is
mounted on the back of said tapered slot antenna elements.
In an alternative embodiment of the tapered slot antenna element, the before
mentioned ground plane is made of the same piece of material as a plurality
tapered slot antenna elements.
When the tapered slot antenna arrangement is used in a moving
environment, such as an airplane or a ship, the tapered slot antenna
elements has to be attached in their desired position. This can be made with
any available means, such as with a snap fitting, by screwing or gluing.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention is hereinafter explained and described in conjunction with the
enclosed drawings, on the basis of an embodiment of the invention from
which further features and advantages of the invention can be out read.
Fig. 1 discloses a principle drawing of the inventive tapered notch antenna
arrangement.
Fig. 2 discloses a schematic drawing of an inventive tapered notch antenna
element.
Fig. 3 discloses a schematic drawing of a plurality of tapered notch antenna
arrangements in a first embodiment.
Fig. 4 discloses a schematic drawing of a plurality of tapered notch antenna
arrangements in a second embodiment.
DETAILED DESCRIPTION
In figure 1 is a principle drawing of the principle of the invention disclosed in
the drawing the tapered slot antenna element 1, the slot line 2 and the layer 3
comprising conductive material surrounding the conductive core 4 are shown.
Due to difference in potential between the conductive core 4 and the layer 3
a coaxial field is built up between these two elements 3, 4 . A local maximum
of the coaxial field is built up where the slot line 4 cuts the layer 3 , whereby
the coaxial field can feed the slot line 4. The signal fed into the slot line 4 is
then transmitted through the slot line 4 and into the tapered notch 5 .
In figure 2 an embodiment of an inventive tapered slot antenna element 1 is
shown. The tapered slot antenna element 1 is provided with an aperture with
a slot line 2 . The aperture 5 is shown as a stepped slot, however other forms
of slots is just as possible, e.g. tapered slot, Vivaldi, or bunny ear. The type of
aperture 5 is not essential for the invention, which is compatible with all types
of slot antennas.
In the embodiment shown in figure 2 the tapered slot antenna element 1 is
made in one piece of material and is preferably an aluminium or aluminium
alloy cast. The antenna element 1 can however be made using any suitable
production method and/or one or several other materials, as long as it fulfils
the features of claim 1. Hence, the tapered notch antenna element 1 in the
embodiment is a mechanical antenna element without any electronic
components. Due to the inventive idea is it possible to produce the whole
antenna element 1 in one piece of material. Such a tapered notch antenna
element is simple in its design, is relative light weight, robust and is easy and
inexpensive to produce. Obviously the same inventive principle can be used
with antenna elements comprising a plurality of materials.
Further the tapered slot antenna element 1 comprises a cavity 6 , which has
an opening 7, into which a conductive core 4 is to be inserted. The slot line 2
of the tapered notch 5 cuts the cavity 3 , such that a RF-signal fed into the
coaxial field between the conductive core 4 and the inner wall 8 of the cavity
is fed into the slot line 2 . Since the tapered slot antenna element 1 is made
out of one piece of material, the layer comprising a conductive material is
constituted by the inner wall 8 of the cavity 6 .
In figure 3 shows an illustration of how the tapered slot antenna element 1 is
mounted on a feeding probe 9. Said feeding probe 9 is arranged on a circuit
board 1 , The tapered slot antenna element 1 is of the same type as shown
in figure 1. The feeding probe 9 comprises the conductive core 4 and a
dielectric coverage 10, which fits into the cavity 6 in the tapered notch
antenna element 1. The dielectric coverage 10 around the conductive core 4
is adapted to fit tightly into the cavity 6 , such that there is no play when the
tapered slot antenna element 1 is arranged thereon.
In figure 4 is an embodiment of a tapered slot antenna arrangement with a
plurality of tapered slot antenna elements 1 sharing the same ground plane
11. The tapered slot antenna arrangements in figure 4 are mounted on a
circuit board 12. The ground plane 11 is to protect the tapered slot antenna
elements 1 from radiation from the electronic components on the circuit
board. A common ground plane 11 made out of the same piece material as
the tapered slot antenna elements 1 is advantageous, since the tapered slot
antenna elements 1 and the ground plane 1 can be produced in the same
process, for example through casting.
The invention is capable of modification in various obvious respects, ail
without departing from the scope of the appended claims. Accordingiy, the
drawing and the description thereto are to be regarded as illustrative in
nature, and not restrictive.
CLAIMS
. Tapered slot antenna element (1) comprising a tapered slot (5) with a slot
line (2) adapted to receive a feeding signal, characterised in, that
said tapered slot antenna element ( 1 ) further comprises a cavity (6) for
receiving a feeding probe (9), wherein an inner wall (8) of said cavity (6) is
provided with a conductive layer (3), and said cavity 6) is provided with an
open end (7) into which the feeding probe (9) can be inserted, such that a
coaxial field can be build up between the feeding probe (9) and said layer (3),
wherein said slot line (2) of said tapered slot (5) cuts into said cavity (6), such
that a signal fed into said coaxial field is fed into said tapered slot (5).
2. Tapered slot antenna element according to claim 1, wherein said tapered
slot antenna element (1) is made out of one piece of materiai.
3 . Tapered slot antenna element (1) according to claim 1 or 2, wherein said
cavity is cylindrical.
4 . Tapered slot antenna element (1) according to claim 4, wherein said cavity
(6) is circular, or rectangular, or octagonal cylindrical.
5. Tapered slot antenna element (1) according to any of the preceding
claims, wherein said tapered slot antenna element ( 1) is provided with a
guide at its lower edge, wherein said guide is adapted to guide the tapered
slot antenna element (1) into a desired position.
6. Feeding probe (9) adapted for a tapered slot antenna element (1)
according to any of the claims 1-5, characterised in, that the feeding probe
(9) comprises a conductive core (4), and the feeding probe (9) is adapted to
fit into the cavity (6) of said tapered slot antenna element (1), such that the
conductive core (4) and the inner wall (8) of said cavity (6) are distanced to
each other.
7 . Feeding probe (9) according to claim 6 , wherein said conductive core (4) is
provided with a dielectric coverage (10).
8. Feeding probe according to claim 7, wherein said dielectric coverage (10)
is adapted to fit into said cavity (6), such that the dielectric coverage (10) at
least partially fills the distance between the conductive core (4) and the inner
wall (8).
9 . Feeding probe according to any of the claims 6 - 8 , wherein the feeding
probe (9) is directed 90 degrees from the surface of a circuit board (12).
10. Tapered slot antenna arrangement, comprising a tapered slot antenna
element (1) according to any of the claims 1 - 5 and a feeding probe (9)
according to any of the claims 6 - 9 , characterised in, that
the feeding probe (9) is arranged inside the cavity (6) of the tapered slot
antenna element (1), such that said conductive core (4) extends inside the
cavity (6) such that it at least reaches beyond the point where the slot line (2)
cuts the cavity (6).
11. Tapered slot antenna arrangement according to claim 9, wherein a
plurality of tapered slot antenna arrangements are mounted in a row.
12. Tapered slot antenna arrangement according to claim 9, wherein a
plurality of tapered slot antenna arrangements are mounted in arrays.
13. Tapered slot antenna arrangement according to any of the claims 11 - 12,
wherein said plurality of tapered slot antenna arrangements is provided with
one common ground plane ( 1 1), wherein said ground plane ( 1) is mounted
on the back of said tapered slot antenna elements (1).
14. Tapered siot antenna arrangement according to claim 12, wherein said
tapered siot antenna elements (1) in said tapered slot antenna arrangements
are made of one piece of material.
15. Tapered slot antenna arrangement according to any of the claims 10-14,
wherein said feeding probe (9) is arranged on a circuit board (12) and said
tapered slot antenna element (1) is adapted to be snap fitted into a desired
position on said circuit board (12).