The present invention relates to a device for receiving and/or emitting electromagnetic signals with radiation diversity, it being possible for the said device to be used in the field of wireless transmissions, especially within the context of transmissions in a closed or semiclosed environment such as domestic environments, gymnasia, television studios, theatres or the like.
In the known high-speed wireless transmission systems, the signals transmitted by the emitter reach the receiver along a plurality of paths. When they are combined at the receiver, the phase differences between the different rays that have travelled paths of different lengths give rise to an interference pattern capable of causing significant signal fading or detorioration.
Furthermore, the location of the fading changes over time, depending on modifications to the environment such as the presence of new objects or the movement of people. The fading due to the multiple paths may lead to significant detorioration both in the quality of the signal received and in system performance. To combat these fading phenomena, the technique most often used is a technique implementing spatial diversity.
As shown in
Slot-type antennas may also be replaced by patch-type antennas. With this type of device, it is possible to demonstrate that the probability of the two antennas simultaneously fading is very small. The demonstration results in particular from the description given in “Wireless digital communications” by Dr Kamilo Feher, chapter 7: “Diversity techniques for mobile wireless radio systems”. It is also possible to demonstrate it by means of a pure probability calculation on the assumption that the levels received by each antenna are completely independent. By virtue of the switch 3, it is possible to select the branch connected to the antenna having the highest level by examining the signal received by means of a control circuit (not shown). In fact, since the two antennas 1, 2 are sufficiently separated, two uncorrelated channel responses are obtained. It is thus possible to switch to the better of the two antennas and thus reduce considerably the probability of fading.
The aim of the present invention is to provide an alternative solution to the conventional solutions using spatial diversity such as the solution described above.
The subject of the present invention is therefore a device for receiving and/or emitting signals comprising at least two means for receiving and/or emitting electromagnetic waves of the slot antenna type and means for connecting the said receiving and/or emitting means to means for exploiting the signals, characterized in that:
The solution described above provides a new antenna topology operating according to the principle of radiation diversity. It is based on switching omnidirectional radiating elements placed close to each other.
According to one embodiment, the means for receiving and/or emitting electromagnetic waves of the slot antenna type consist of resonant slots produced by printed or coplanar technology. The slots have an annular, square or rectangular shape or are formed by dipoles. According to a variant, the slots are fitted with means enabling a circularly polarized wave to be radiated.
Furthermore, according to the present invention, if the electronic component providing the switching is perfect, that is if it has a perfect short circuit and open circuit, the length of the supply line between the electronic component and the slot coupled electromagnetically to the said line is equal to the central operating frequency, at kλm/4 where λm=λ0/√εreff and where λ0 is the wavelength in a vacuum, εreff is the effective permittivity of the line and k is an odd integer. If the electronic component is not perfect, the line length must be matched to take account of the parasitic elements.
According to a preferred embodiment, the electronic component consists of a diode, an electronic switch, a transistor or any switching circuit such as a micro-electromechanical system known as a “Micro-ElectroMechanical System” or MEM.
Other characteristics and advantages of the present invention will become apparent on reading the description of various embodiments, this description being made with reference to the appended drawings in which:
a,
3
b and 3c show the radiation of the device of
A first embodiment for receiving and/or emitting electromagnetic signals with radiation diversity according to the present invention will first of all be described.
As shown in
According to the present invention, in order to achieve radiation diversity, the two annular slots are arranged either so as to overlap, as in the embodiment shown, or so as to be separate but placed very close to each other. Preferably, the extreme length between the two antennas of the slot antenna type is equal to 2 ×λs/π where λs is the wavelength guided in the slot at the operating frequency.
As shown in
According to the present invention, and as shown in
State 1: if the bias voltage v is chosen such that v>V1, in this case, the diode 15 is on while the diode 16 is off. As a result, the annular slot 11 is excited in a favoured manner while the annular slot 10 acts more as a reflector.
In this case, a radiation pattern as shown in
State 2: the bias voltage v is such that v<V1. In this case, the diode 15 is off while the diode 16 is on. A situation symmetric with state 1 is obtained. As a result, the annular slot 10 is excited while the annular slot 11 acts as a reflector. A radiation pattern as shown in
State 3: the bias voltage is equal to 0. In this case, the two diodes 15 and 16 are off, the two annular slots 10, 11 are simultaneously excited, with parallel electric fields in opposite senses. The resulting radiation pattern is that shown in
The radiation patterns of
Thus, with a device as shown in
This solution provides an antenna of low overall size requiring only the use of two diodes or similar switching elements such as MEMs for controlling the pattern.
Various embodiments of a device according to the present invention, made using printed technology, will now be described with reference to
According to the present invention, the two antennas 20, 21 are supplied by two supply lines 22, 23 starting at the point P0 and going towards the inside of the antenna consisting of a square-shaped slot and having, in a known manner, a length equal to kλm/4 where λm=λ0/√εreff with ε0 the wavelength in a vacuum at the central operating frequency, εreff the effective permittivity of the line and k an odd integer.
A diode 25, 26, mounted in an identical manner to the embodiment of
Two other embodiments of the emitting/receiving devices according to the present invention will now be described with reference to
In this case, the antennas of the slot antenna type allow a circularly polarized wave to be radiated. In the embodiment of
According to the present invention, the antennas 30, 31 are supplied by supply line 32, 33, 34 having the same characteristics as the supply lines 12, 13, 14 of FIG. 2. Furthermore, the supply lines 32, 33 are connected to diodes 36, 35 mounted between the end of the supply line and earth, in the same way as the diodes 15, 16 in the embodiment of FIG. 2. Consequently, operation of the device of
According to the present invention, the ends of the two line elements 52, 53 are connected to the earth formed by the metal layer A via specially connected diodes 56, 55. The two coplanar line elements 52, 53 are connected to a perpendicular supply line 54 along a plane passing through the point B, this line itself also being produced by coplanar technology.
Yet another embodiment of the present invention will now be described with reference to FIG. 8. In this case, the two antennas consist of dipoles which are symmetrical with respect to a plane P1. In this case, the two antennas consist of T-shaped dipoles 60, 61, the branches of the T of which have a length close to λ0/2 where λ0 is the wavelength in a vacuum. Each branch of the T is provided in its middle with a slot 60′, 61′. Each dipole is supplied by means of electromagnetic coupling by a supply line 62, 63 produced by printed technology. The supply lines 62 and 63 are both connected to a common supply line 64 which is in the plane of symmetry P1. The supply lines 62, 63 have a length to the slot 60′, 61′ equal to λm/2, and then extend beyond the slot by a length of the supply line equal to λm/4 where λm is the wavelength guided in the microstrip line, this in the case where the switching component is perfect.
According to the present invention, diodes 65, 66, connected in a manner which is identical to the other embodiments, are provided at the ends of the two supply lines 62, 63. Thus the diode 65 is connected in reverse bias between the end of the supply line 62 and earth while the diode 66 is connected in forward bias between the end of the supply line 63 and earth.
As shown in the figure, the supply lines 62 and 63 are electromagnetically coupled with the slots 60′, 61′ at a distance λs/4 from the bottom of the inner end of the said slots. Furthermore, in the embodiment shown, the supply lines 62, 63 are at a distance λs/10 from the end of the dipole.
Number | Date | Country | Kind |
---|---|---|---|
01 10696 | Aug 2001 | FR | national |
Number | Name | Date | Kind |
---|---|---|---|
4587525 | Parsons et al. | May 1986 | A |
4719470 | Munson | Jan 1988 | A |
5193218 | Shimo | Mar 1993 | A |
6246377 | Aiello et al. | Jun 2001 | B1 |
20030011520 | Lee | Jan 2003 | A1 |
Number | Date | Country |
---|---|---|
0707 357 | Apr 1996 | EP |
2 785 476 | May 2000 | FR |
Number | Date | Country | |
---|---|---|---|
20030034929 A1 | Feb 2003 | US |