This application claims the benefit under 35 U.S.C. §365 of French patent application No. 0113955 filed Oct. 29, 2001 and French patent application No. 0205419 filed Apr. 30, 2002.
The present invention relates to an antenna system for the transmission of electromagnetic signals which can be used in the field of wireless transmissions, especially in the case of transmissions in a closed or semi-closed environment such as domestic environments, gymnasia, television studios, cinemas and theatres, or the like.
In known high bit rate wireless transmission systems, the signals transmitted by the transmitter reach the receiver along a plurality of different paths. When they are combined at the receiver, the phase differences between the various rays having travelled paths of different lengths give rise to an interference pattern likely to cause fading or significant degradation of the signal.
Furthermore, the location of the fading changes over time depending on changes in the environment such as the presence of new objects or the passage of people. This fading due to the multiple paths may lead to significant degradation, in terms of both the quality of the signal received and system performance.
To combat fading, the technique most often used is a technique with spatial diversity. This technique consists inter alia in using a pair of antennas with large spatial coverage such as two antennas of the patch type combined with a switch. The two antennas are separated by a length 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 is possible to demonstrate that the probability of having both antennas simultaneously in a region of fading is very low. Furthermore, by virtue of the switch, it is possible to select the branch connected to the antenna having the highest signal level by examining the signal received via a control circuit.
The above solution has the main drawback of being relatively bulky. Consequently, the applicant has proposed various alternative solutions to the solution described above. These solutions are applicable to antennas of the slot type supplied by a line/slot transition and which make it possible to obtain radiation diversity.
Research has therefore been carried out on an antenna of the slot type, such as an annular slot supplied by a tangential line/slot transition. An antenna of this type is shown in FIG. 1. This antenna is produced on a substrate 1 such as the Chukoh Flo CGP500 substrate where Er=2.6, TanD=0.0018 and the height h=0.76 mm. It comprises an annular slot 2, the perimeter of which is of the order of k′λs where k′ is an integer and λs the wavelength guided in the slot.
As shown in
However, contrary to this assertion, the applicant has noticed that, in a structure of the above type with positioning of the microstrip line with respect to the slots so that one is in a short-circuit plane of the microstrip line, the two annular slots radiate in phase, which gives constructive radiation along the axis having linear polarization of very high purity.
The present invention therefore relates to an antenna system for the transmission of electromagnetic signals using slot-type antennas supplied by a line/slot transition as described above, making it possible to obtain compact antennas with a broad frequency band, and with linear polarization of very high purity.
The present invention also relates to a novel topology of antennas as described above, making it possible to obtain a compact device with radiation diversity on reception.
The subject of the present invention is an antenna system for the transmission of electromagnetic signals comprising a first means for the transmission of signals of the slot antenna type and a first supply line for connecting the said first means to means of exploiting signals, the first supply line being electromagnetically coupled by a line/slot transition to the first means for the transmission of signals of the slot antenna type, characterized in that it comprises a second means for the transmission of signals of the slot antenna type which is symmetric with the first means with respect to a first point P, the second means being electromagnetically coupled by a line/slot transition with the said first supply line which is in a plane passing through the first point of symmetry, the said transition being close to the short-circuit plane of the supply line.
With this structure, it is possible to obtain an antenna with a linear polarization of high purity.
According to another feature of the present invention, the first and second means for the transmission of signals of the slot antenna type are provided with perturbations positioned at around 45 or 135 degrees from the plane passing through the centre of said means of transmission and the first point of symmetry. The addition of perturbations transforms the linear polarization into a right or left circular polarization according to the chosen angle.
According to another feature of the present invention, making it possible to obtain radiation diversity in transmission, the system comprises a third means for the transmission of electromagnetic waves of the slot antenna type supplied by a line/slot transition which is symmetric with one of the two electromagnetic wave transmission means with respect to a second point and a second supply line connected in common with the first supply line to means of exploiting signals, the second supply line being electromagnetically coupled to the electromagnetic wave transmission means of the slot antenna type supplied by a line/slot transition and being in a plane passing through the second point of symmetry, the free end of the first and of the second supply lines being connected to a component making it possible to simulate a short circuit or an open circuit at the end of one of the lines and an open circuit or a short circuit at the end of the other line.
According to an additional feature of the invention, the length of each supply line between the component and the point of symmetry is about kλm/4 where k is an integer and λm the wavelength guided in the line, so as to restore an electrical short-circuit or open-circuit plane depending on the state of the component in the plane containing the points of symmetry. In this case, if the line measures kλm/4 where k=2, it is enough to reverse the diode state in order to find the same behaviour. Thus, for k=1, an on diode (CC) plus a quarter-wavelength line gives an open circuit CO at the transition and, for k=2, an off diode (CO) plus a half-wavelength line gives an open circuit.
According to another feature of the invention, the means for the transmission of electromagnetic waves of the slot antenna type supplied by a line/slot transition consist of a slot of annular or polygonal shape, it being possible for the polygonal shape to be a rectangle or a square or any other known polygonal shape.
Furthermore, the perimeter of the slot has a wavelength of about k′λs where k′ is an integer and λs the wavelength guided in the slot.
According to another additional feature of the present invention, the device further comprises a third supply line connected to a transmission means and electromagnetically coupled to the central electromagnetic wave transmission means by a line/slot transition.
According to preferred embodiments, the component consists of a diode, a transistor, an electronic switch and a microelectromechanical system. Furthermore, the supply lines are produced using microstrip technology or coplanar technology.
Other features and advantages of the present invention will become apparent on reading various embodiments, this reading being carried out with reference to the appended drawings, in which:
To simplify the description, the same elements bear the same references. In the present invention, the term “electromagnetic wave transmission means” refers to any means capable of transmitting and/or of receiving electromagnetic waves, these means being known by the term “antenna”.
An embodiment making it possible to obtain a broadband antenna system with very pure linear polarization will first of all be described with reference to
As in the case of
This type of device may be produced, for example, by using triplate technology on two substrates of permittivity εr1 and εr2. Thus, the two annular slots are etched on the top face of the first substrate. The supply line, made in microstrip technology, is produced between the two substrates and the earth plane is formed on the bottom face of the second substrate.
According to an additional feature of the invention, the two annular slots may be provided with perturbations transforming in a known manner a linear polarization into a circular one. More specifically, each annular slot is provided with two diagonally opposed perturbations, the perturbations being positioned at around 45 or 135 degrees from the plane passing through the centre of said means of transmission and the first point of symmetry. The perturbations may be done by cuts or by projections of various shapes, as known from the art.
An embodiment of the present invention making it possible to obtain radiation diversity will next be described with reference to
As shown in
As shown in
As shown in
Furthermore, the length of line 23 or 24 between the point P1 or P2 and the end 23′ or 24′ away from the port 1 is preferably about kλm/4 where k is an integer and λm the wavelength guided in the supply line.
As shown in
From the structure of
Furthermore,
To obtain a transmission channel with the antenna topology shown in
To ensure maximum isolation between transmission and reception, the two diodes 25, 26 must be in the on state, that is to say have a short circuit at the end of the microstrip lines 23 and 24 in transmission mode, and the diode 33 must be in the off state, that is to say have an open circuit CO at the end of the line 27 in transmission mode. In this case, the system shown in
The control device making it possible to manage these four states is provided by a device independently controlling each of the three diodes. This control device consists, for example, of block devices 28′, 28 mounted between the T-junction and the supply lines 23, 24. The block devices consist of DC-blocks of known type. A DC-block 29 is also provided between the line 27 and the port 2. Furthermore, line ends or “stubs” 30, 31, 32 are mounted between the respective lines 32, 24 and 27 and the terminal for biasing the various diodes 25, 26 and 33. The length of each radial line end is such that an open circuit is restored at the intersection point. In this way, the bias voltage is provided to each of the diodes, without disturbing the radiofrequency RF (transparency condition). Moreover, the DC-block device makes it possible to filter the DC current at the antenna access.
With the system shown in
Furthermore, in transmission, a radiation pattern is obtained for the device, as shown in FIG. 9. On looking at the various radiation patterns, it will be noted that a high quality of linear polarization is obtained in the axis of the antenna. Furthermore, a good level of isolation is obtained between transmission and reception and the same polarization for transmission and reception. Furthermore, this compact antenna stretcher provides radiation pattern diversity of order 3.
It is obvious to a person skilled in the art that the above embodiments are given by way of example and may be modified in many ways. Thus, the slot may have a shape other than an annular shape; it may have a polygonal shape, that is a square or rectangular shape or the like. The supply lines may be produced in microstrip technology or in coplanar technology. The diodes may be replaced by other components such as transistors, electronic switches and microelectromechanical systems.
Number | Date | Country | Kind |
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01 13955 | Oct 2001 | FR | national |
02 05419 | Apr 2002 | FR | national |
Number | Name | Date | Kind |
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6573872 | Oberschmidt et al. | Jun 2003 | B2 |
6593895 | Nesic et al. | Jul 2003 | B2 |
20030034929 | Bolzer et al. | Feb 2003 | A1 |
20040113841 | Louzir et al. | Jun 2004 | A1 |
Number | Date | Country |
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0685901 | Dec 1995 | EP |
3-024804 | Feb 1991 | JP |
3-024805 | Feb 1991 | JP |
Number | Date | Country | |
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20030080912 A1 | May 2003 | US |