This application claims the benefit, under 35 U.S.C. § 365 of International Application PCT/FR03/00065, filed Jan. 10, 2003, which was published in accordance with PCT Article 21(2) on Jul. 24, 2003 in French and which claims the benefit of French patent application No. 0200665, filed Jan. 14, 2002 and French patent Application No. 0201562, filed Feb. 8, 2002.
The present invention relates to a device for receiving and/or transmitting electromagnetic waves with radiation diversity which can be used in the field of wireless transmissions, notably in the case of transmissions in closed or semi-closed environments such as domestic wireless networks, gymnasiums, television studios, show venues or similar places, but also in wireless communication systems requiring a minimal size for the antenna system such as in mobile telephones.
In the known high-bit-rate wireless transmission systems, the signals transmitted by the transmitter reach the receiver via a plurality of different routes. When these are combined at the receiver, the phase differences between the various radio waves having followed pathways of different lengths give rise to an interference figure which can cause a tendency to fade or a significant degradation of the signal. Moreover, the position of the tendency to fade changes over time, depending on changes in the environment, such as the presence of new objects or passing people. This tendency to fade, caused by the multiplicity of pathways, can lead to a significant degradation both in the quality of the received signal and in the performance of the system.
In order to fight against this tendency to fade, the technique most often employed is a technique known as spatial diversity. This technique consists notably of using a pair of antennas having a wide spatial coverage, such as two antennas of the “patch” type, linked to a switching unit. The two antennas are spaced out by a distance which must be greater than or equal to λ0/2, where λ0 is the wavelength corresponding to the operating frequency of the antenna. With this type of antenna, it can be shown that the probability of having both antennas in a fading condition simultaneously is very low. Moreover, the switching unit allows the branch connected to the antenna presenting the highest signal level to be selected by examining the received signal using a monitoring circuit. However, the main drawback with this solution is that it is relatively voluminous since it requires a minimum spacing between the radiating antennas in order to ensure an adequate decorrelation of the channel responses seen through each radiating element.
Various solutions have been proposed for reducing the size of the antenna system while still ensuring an adequate diversity. Some solutions have been the object of several patent applications filed in the name of THOMSON Multimedia Licensing S.A. They consist, notably, of using several antennas of the slot type supplied via line-slot transitions and comprising means allowing a diversity of radiation to be obtained, notably diodes allowing switching onto one or other of the antennas depending on the level of the received signal.
Furthermore, in the IEEE article, Vol. 49, No. 5 May 2001, entitled “Diversity antenna for external mounting on wireless handsets”, it has also been proposed, in the field of mobile telephones, to link a λ/4 slot with a monopole to produce a diversity radiation system. However, the proposed system is a relatively complex, three-dimensional structure.
The aim of the present invention is therefore to propose a new solution for a device for receiving and/or transmitting electromagnetic waves with radiation diversity having an extremely compact structure while still exhibiting radiation patterns with a very good complementarity. It also provides a device for receiving and/or transmitting electromagnetic waves with radiation diversity having a relatively low cost of manufacture.
Consequently, the subject of the present invention is a device for receiving and/or transmitting electromagnetic waves with radiation diversity, characterized in that it comprises, on a common substrate, at least one antenna of the slot type formed by a closed curve, electromagnetically coupled to a first supply line, and an antenna radiating parallel to the substrate such as a monopole, a helix operating in transverse mode or similar, positioned inside the slot antenna and connected to a second supply line, said first and second supply lines being connected via a switching means to means for exploiting the electromagnetic waves.
The device for the reception and/or transmission of electromagnetic waves described above exploits the fact that antennas of the slot type formed by a closed curve, hereinafter referred to as slot antennas, as well as antennas of the monopolar or helical type operating in transverse mode exhibit virtually omnidirectional radiation patterns with minima situated, respectively, in the plane of the substrate for the slot antenna and along the axis of the monopole or helix for the other antenna. Thus, switching from one antenna to the other allows the channel response through the antenna to be modified and allows the system to thus benefit from a gain in diversity.
According to preferred embodiments, the first supply line is implemented in microstrip technology or in coplanar technology. Furthermore, the first supply line has a length between its end and the electromagnetic coupling point equal to kλm/4, where k is an odd integer and λm the guided wavelength on the supply line at the central operating frequency with λm=λ0/√{square root over (εreff)}, where λ0 is the free-space wavelength and εreff the effective permittivity of the line. The second supply line is implemented in microstrip technology or by a coaxial line. When the line is implemented in microstrip technology, a connection is made at the slot antenna between the part that is external and the part that is internal to the slot, this connection being formed, for example, by a conducting insert having a width equal to around two to three times the width of the line implemented in microstrip technology, so as not to interfere with the operation of the microstrip line providing the excitation. In addition, in order to minimize the interference within the slot of the slot antenna, owing to the presence of the conducting connection, this connection is situated in an electrical short-circuit plane for the slot which is therefore the plane where the microstrip line providing the excitation of the monopole or helical antenna crosses the slot antenna.
According to preferred embodiments, the slot antenna is formed by an annular slot of circular shape or formed by a closed curve of perimeter equal to k′λs where k′ is an integer and λs is the wavelength in the slot at the operating frequency and/or by a slot of polygonal shape such as a square or rectangle. According to another feature of the present invention, the device for receiving and/or transmitting electromagnetic waves with radiation diversity may comprise several slot antennas interlocking with one another so as to widen the operating band or to allow multiband applications.
Other features and advantages of the present invention will become apparent upon reading the description of various embodiments presented with reference to the appended drawings, in which:
In order to simplify the description, in the drawings the same elements carry the same reference numbers.
As shown in
Furthermore, a circular opening 5 of diameter D is provided at the center of the annular slot. This opening receives the monopole 2 in its central part which also passes through the substrate 3. An annular metallic mounting disk 5 is provided on the lower face of the substrate 3 under the monopole 2. As shown more particularly in
Similarly, in the embodiment shown, the monopole 2 is excited by a microstrip line 7.
As shown in
As presented in
In this case, the coupling between the annular slot 1 and the monopole 2 remains weak given:
Minimal mutual interference can thus be expected between the two radiating elements even though they occupy almost the same physical space.
In order to ensure correct operation of a transmission/reception device such as described above, the dimensions of the latter have been completely chosen for operation at the central frequency of around 5.8 GHz then simulated using the HFSS simulation package from Ansoft. With reference to the schematic drawings in
The substrate used is made of Rogers 4003 with relative permittivity r=3.38 and thickness h=0.81 mm.
In this case, the radiation patterns obtained at the monopole and annular slot access, respectively, are those shown in
According to a variant, shown in
The substrate used is made of Rogers 4003 with relative permittivity r=3.38 and thickness h=0.81 mm.
The matching at the two accesses as well as the isolation between the two ports are shown in
Further modifications may be included such as the use of a helix operating in the transverse mode in place of the monopole, the use of a double or multiple slot in order to widen the band or for multiband applications, tangential supply of the slot in place of a Knorr-type supply, and the deformation of the annular slot to further reduce its size, where it could also take the form of a square, a rectangle or other polygon while still remaining within the scope of the definition given above. Similarly, the monopole or helix may be replaced by antennas of the same type which can be placed at the center of the slot antenna and which radiate in a direction parallel to the substrate. The supply line of the slot antenna can be implemented as a line in microstrip technology or in coplanar technology. In addition, the slot antenna may have means, such as notches in the case of an annular slot, that allow it to operate in cross-polarization mode.
Number | Date | Country | Kind |
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02 00665 | Jan 2002 | FR | national |
02 01562 | Feb 2002 | FR | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/FR03/00065 | 1/10/2003 | WO | 00 | 7/12/2004 |
Publishing Document | Publishing Date | Country | Kind |
---|---|---|---|
WO03/061062 | 7/24/2003 | WO | A |
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4587524 | Hall | May 1986 | A |
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5714961 | Kot et al. | Feb 1998 | A |
5914693 | Takei et al. | Jun 1999 | A |
6160512 | Desclos et al. | Dec 2000 | A |
Number | Date | Country | |
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20050083236 A1 | Apr 2005 | US |