The present invention relates to a planar antenna with diversity of radiation. It relates more particularly to an antenna that can be used in the field of wireless transmissions, particularly within the framework of transmissions in a closed or semi-enclosed environment such as domestic surroundings, gymnasiums, television studios, theatres or similar rooms.
In the known high-speed wireless transmission systems, the signals transmitted by the transmitter reach the receiver by following a plurality of paths resulting from the many reflections of the signal on the walls, furniture or similar elements. When combined at the level of the receiver, the phase differences between the different rays having taken paths of different lengths gives rise to an interference figure that can cause fading or a significant degradation in the signal.
Now, the location of the fading changes over time according to the modifications in the environment such as the presence of new objects or the movement of people. The fading due to multipaths can lead to significant degradations both at the level of the quality of the signal received and at the level of the system performances. To overcome these fading phenomena, the technique most often used is a technique that implements spatial diversity.
This technique consists, among other things, of using a pair of antennas with wide spatial coverage connected by feed-lines to a switch. However, the use of this type of diversity requires a minimum spacing between the radiating elements to ensure that there is sufficient decorrelation of the channel response viewed from each radiating element. An inherent disadvantage to its implementation is the distance between the radiating elements that present a cost, particularly in terms of size and substrate.
Other solutions have been proposed to overcome this problem. Some of these solutions use diversity of radiation as described for example in the French patent A-2 828 584 in the name of the applicant.
The present invention proposes a new planar type antenna with diversity of radiation.
Hence, the present invention relates to a planar antenna realised on a substrate comprising a slot of closed shape dimensioned to operate at a given frequency in a short-circuit plane of at least one feed-line. In this antenna, the perimeter of the slot is designed such that p=kλs where k is a integer greater than 1 and λs the guided wavelength in the slot. Moreover, it comprises at least a first feed-line placed in an open circuit zone of the slot and a second feed-line placed at a distance d=(2n+1) λs/4 from the first line, where n is an integer greater than or equal to zero.
According to a first embodiment, each feed-line terminates in an open circuit and is coupled to the slot according to a line/slot coupling such that the length of the line after the transition equals (2k′+1)λm/4 where λm is the guided wavelength under the line and k′ a positive or null integer. The line/slot coupling can also be realised in such a manner that the microstrip line terminates in a short-circuit located at 2k″λm/4 where λm is the guided wavelength under the line and k″ is a positive or null integer.
According to a second embodiment, each feed-line is coupled magnetically with the slot according to a tangential line/slot transition.
Moreover, the shape of the slot can be annular, square, rectangular, polygonal, or in the form of a clover leaf. If the slot is of a rectangular shape, the feed-lines can be equidistant from an axis of symmetry of the slot or one of the feed-lines is positioned according to an axis of symmetry of the slot.
Other characteristics and advantages of the present invention will emerge upon reading the following description of different embodiments, this description being made with reference to the drawings attached in the appendix, in which:
a and 3b respectively show the radiation patterns of the antenna of
a and 7b respectively show the radiation patterns of the antenna of
a and 8b representing the parameters S of the antenna of
a and 11b respectively show the radiation patterns of the antenna of
To simplify the description, the same elements have the same references as the figures.
FIGS. 1 to 5 relate to a first embodiment of the invention. As shown in
As shown in
In accordance with the invention, a second feed-line 4 realised in microstrip technology and crossing the slot according to the Knorr method is positioned at the level of a SC zone. The length of the feed-line 4 is determined according to the rules mentioned above. Thus, when the access is realised by line 4, a second radiation pattern is obtained that is complementary to the first one. More specifically, the second line is located at +/−45° or +/−135° with respect to the first line, namely at a distance d such that d=(2n+1) λs/4. This relative position of the two accesses enables a good level of isolation to be obtained.
The dimensions taken for an embodiment compliant with that of
As shown in
Moreover, according to the radiation patterns shown in
It should also be noted that with this antenna, the radiation is produced in the plane of the substrate, which enables a horizontal coverage to be obtained for a single stage use, for example.
In accordance with the present invention, the second access, namely the microstrip line 4, can be placed at +/−135° (+/−3λs/4) in relation to the first access, namely the feed-line 3. This enables an improvement of approximately 8 dB in the isolation level to be obtained, as shown in
A description will now be given, with reference to FIGS. 6 to 8, of another embodiment of an antenna in accordance with the present invention. In this case, as shown in
In accordance with the invention, the first feed-line 12 is positioned on an axis of symmetry of the structure, namely the axis x, x′ whereas the second feed-line, namely line 11 is positioned at a distance d=(2n+1) λs/4 where n is an integer greater than or equal to zero. In these conditions, access to the feed-line 11 is not obtained by symmetry of the axis realised by the feed-line 12. This asymmetry is located at the level of the impedance matching of the ports. Indeed, an imbalance occurs between the S11 and S22 impedance matching in terms of central frequency and impedance matching band.
In this case, the frequency can be recentered by modifying the quarter wave (Lm′Wm′) located between the access port and the line-slot transition as will be explained below.
With a rectangular shape as shown in
The following describes a practical embodiment of an antenna as shown in
L=32.92 mm
W=11.24 mm
D=18.84 mm
Ws=0.4 mm
Lm=Lm′=8.85 mm
Wm=Wm′=0.15 mm.
As shown in the curves of
A third embodiment will be described below with reference to FIGS. 9 to 11. In this case, the antenna constituted by a slot with a closed shape is realised by a rectangular slot 20 with two accesses formed by the feed-lines 21, 22 that are symmetrical in relation to the line x x′. With this symmetrical access structure, a balanced matching is obtained if the perimeter p of the rectangular slot is selected such that p=2λs=2(W+L) where W is the rectangle width and L its length, λs being the guided wavelength in the slot. As mentioned above, p can also be chosen such that p=kλs. Moreover, the distance between the access of the line 22 and the access of the line 21 is such that d=(2n+1) λs/4 where n is an integer greater than or equal to zero and the accesses formed by the lines 21 and 22 are equidistant from an axis of symmetry XX′ of the rectangular slot.
In this case, as shown in
The antenna structure of
The embodiments shown above are related to planar antennas constituted by a slot of a closed, annular or rectangular shape. However, as shown in
In this case, a higher order mode of the slot is used, which enables complementary radiation patterns to be obtained. Particularly, the structures proposed radiate in the plane of the substrate, which is not the case with a slot antenna operating in its fundamental mode.
According to a variant of the present invention as shown in
In accordance with the present invention and as shown in
The use of this type of structure thus enables a good level of isolation to be obtained and a diversity of order 2 for reception with very low overall dimensions when an integrated switching device is used.
It is evident to those in the profession that modifications can be made to the structures described above without falling outside the scope of the claims attached. In particular, the feed-lines can be realised using techniques other than the coplanar technology or coaxial cables, the outer core of which is connected to the substrate.
Number | Date | Country | Kind |
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0309366 | Jul 2003 | FR | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/FR04/50357 | 7/27/2004 | WO | 9/11/2006 |