RING-TYPE ANTENNA, WITH REDUCED CENTER WORKING FREQUENCY, AND VEHICLE EQUIPPED WITH AT LEAST ONE SUCH ANTENNA

ANTENNE ANNULAIRE A FREQUENCE DE TRAVAIL CENTRALE REDUITE ET VEHICULE EQUIPE D'UNE ANTENNE DE CE TYPE AU MOINS

English Abstract

ABSTRACT OF THE DISCLOSURE
The disclosure relates to ring-type antennas,
namely antennas comprising a ground plane, a conductive
flat ring parallel to the ground plane and a dielectric
layer separating the ring from the ground plane. These
antennas work in a standard way in TM02 or TM11 mode.
The antenna is designed to work with a configuration of
the electromagnetic field between the ring and the
ground plane according to the TM01 mode but with a
working frequency that is reduced as compared with a
standard working frequency. For this purpose, the
conditions of propagation of the waves between the ring
and the ground plane are modified by the introduction
of a short-circuit plane between one of the rims,
namely the internal or the external rim, of the ring
and the ground plane. The center working frequency is
thus reduced by a ratio of 3 to 4 as compared with
standard working in TM02 mode. The disclosed device can
be applied to antennas for radio- communications made,
for example, from aircraft.

Claims

WHAT IS CLAIMED IS:
1. A ring-type antenna comprising a ground plane
and a conductive flat ring that are positioned in
parallel, and a dielectric layer separating the ring
from the ground plane, the ring having an internal
circular rim and an external circular rim, and the
antenna having working frequencies and being designed
to work in TMO1 mode, with a reduced center working
frequency and comprising, for this purpose,
short-circuit means forming an electromagnetic screen
for the working frequencies of the antenna, this screen
connecting one of the circular rims of the ring to the
ground plane.
2. An antenna according to claim 1, made according
to the technology of printed circuits.
3. An antenna according to claim 2, wherein the
dielectric layer overlaps the ground plane on a surface
located within the circumference constituted by a
projection of the internal rim of the ring on the
ground plane.
4. An antenna according to claim 1, designed for a
vehicle having an external wall and wherein the ground
plane is constituted by the external wall of the
vehicle.

Description

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RING-TYPE ANTENNA, WITH REDUCED CENTER WORKING
FREQUENCY, AND VEHIC~E EQUIPPED WITH
AT LEAST ONE SUCH ANTENNA
BACKGROUND OF THE INVENTION
The present invention relates to ring-type
antennas, namely antennas comprising a conductive, flat
ring and a ground plane that are positioned in parallel
and separated by a layer of dielectric. The invention
also relates to vehicles fitted out with such antennas.
Ring-type antennas are known. These antennas are
generally excited to work in the TM11 or TM02 modes,
but are not excited to work in TM01 mode for their
center working frequency, which is already relatively
high in TMll and TM02 mode, would be even higher in
TM01 mode.
SUMMARY O~ THE INVENTION
The aim of the present invention is to make it
possible to reduce their center working frequency.
This is obtained by modifying the conditions of
propagation of the waves in the space between the ring
and the ground plane, and by seeking to excite the TM01
mode. With adequate modifications, it then proves to be
the case that the excitation frequency of the TM01 mode
becomes lower than that of the oher modes and,
especially, lower than that of the TM02 and TM11 modes.
According to the present invention, there is
provided a ring-type antenna comprising a ground plane
and a conductive flat ring that are posi~ioned in
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parallel, and a dielectric layer separating the ring
from the ground plane, the ring having an internal
circular rim and an external circular rim, and the
antenna having working frequencies and being designed
to work in TMO1 mode, with a reduced cen~er working
frequency and comprising, for this purpose,
short-circuit means forming an electromagnetic screen
for the working requencies of the antenna, this screen
connecting one of the circular rims of the ring to the
ground plane.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention shall be understood more
clearly and other characteristics shall appear from the
following description, and from the figures relating
thereto, of which:
- figures 1 and 2 show an antenna according to the
invention;
- figure 3 is a graph relating to the an~enna
according to the invention and to antennas according to
the prior art.
MORE DETAILED DESCRIPTION
Figures 1 and 2 respectively show a sectional view
and a top view of an antenna according to the
invention. The plane of the section along figure 1 has
been identified in figure 2 by a axial line touched by
the ends of two arrows AA that indicate which one of
the two planes resulting from the section is seen in
figure 1.
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In figure 1, the respective dimensions of the
different elements have not been maintained so as to
make the drawing clearer and the inventlon easier to
understand.
The antenna according to figures 1 and 2 is a
ring-typP antenna, with a ground plane 1, a conductive
flat ring 3, parallel to the ground plane, and a
dielectric layer 2, interposed ~etween the ring and the
ground plane. The internal radius Ri and external radii
Re of the circles that respectively demarcate the
internal and external rims of the ring 3 have been
indi.cated in figure 1.
In the example described, the ground plane 1 is
constituted by the external wall of a vehicle and, more
precisely, that of an aircraft.
A feeder line, constituted by a coaxial cable 5,
comes from the interior of the vehicle and crosses the
ground plane 1, with which it is in contact by its
external conductor. The internal conductor 50 of the
coaxial cable 5 goes through the dielectric layer 2 and
goes towards the ring 3 to which it i5 soldered.
The antenna of figures 1 and 2 further includes a
short-circuit plane 4 which connects the external rim,
with a radius Ri, of the ring to the ground plane. This
short-circuit plane, which is therefore annular, is
constituted by ten conductive links 40 to 49 which go
through the dielectric layer 3 by means of evenly
distributed holes. These holes are at a distance from
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one another that is smaller t~lan one-twen~ieth o~ the
wavelength o~ the center working frequency of the
antenna. The addition of the short-circuit plane 4, by
modifying the conditions in which the electromagnetic
~ield is set up in the space between the ring 3 and the
ground plane 1, ma~es it possible to obtain the
excitation o the TM01 mode. Without the short-circuit
plane 4, only the TM02 mode could be excited and this
would happen at a substantially higher frequency as is
shown in figure 3.
The e~arnple described corresponds to a ring-type
antenna, made according to printed circuit technology,
wherei.n:
- the radii Ri and Re are respectively equal to
15 and 50 mm;
- the resonance frequency of the oscillation mode
giving a hemispherical radiation is
substantially equal -to 0.5 GHz and the mode in
question is the TM01 mode.
With a ring--type antenna made with the same
constituent elements and the same dimensions, but
having no short-circuit plane 4, the resonance
frequency of the oscillation mode giving a
hemispherical radiation is substantially 1.85 GHz and
the mode in question is the TM02 mode. It must be noted
that, with a standard disk antenna obtained through the
simple replacement of the ring, in the antenna having
~o short-circuit plane, by a disk without any hole,

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i.e. a disk with an internal radius Ri equal to zero,
the hemispherical radiation is obtained with the TM02
mode at a resonance frequency of 1.70 GHz.
Figure 3 is a graph which shows, as a function of
the external radius Ra of the ring or of the disk
without a hole, the resonance frequency F of the mode
giving a hemispherical radiation for three types of
antenna:
- curve ~: for a ring-type antenna in TM01 mode,
by means of a short-circuit plane
~ curve B: for a ring-type antenna in TM02 mode,
without short-circuit plane;
- curve C: for a disk antenna in TM02 mode.
The comparison of the curves shows that, fox one
and the same external radius Re of the ring or disk,
the short-circuit plane makes it possible to obtain a
hemispherical radiation for a frequency that is
approximately three to four times lower with a
ring-type antenna having short-circuit plane than with
a disk antenna or a ring-type antenna having no
short-circuit plane.
The invention is not limited to the example
described. Thus the short-circuit plane, instead of
being set up at the internal rim of the ring, may ~e
set up at the external rim. To obtain the same working
frequency as with an antenna having a short-circuit
plane at the internal rim of the ring, the external
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radius o the ring should be substantially gr~ater. But
such an antenna may he useful in certain cases.
It is also possible to make the antenna otherwise
than by the technology of printed circuits, for example
by the bonding or soldering of the differen-t elements
constituting the antenna. In this case, the
short-circuit plane could be an annular element,
soldered by one side to the ground plane and, by the
other side, to the internal or external edge of the
ring; and it must be no-ted that, unlike in the case of
structures made by printed circuit technology, where
the dielectric layer may extend on either side of the
short-circuit plane 4, preferably, in order to
facilitate the manufacture oE the antenna, the
dielectric layer should not extend beyond the under
part of the ring, a~ least on the short-circuit plane
side.
The antenna accord.ing to the invention can be
applied in particular to all vehicles equipped with
radio-communications devices necessitating one or more
antennas, the radiation pattern of which is that of a
vertical dipole placed before a horizontal plane
reflector.
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Representative Drawing