Patent Grant
6987486
The invention relates to the ground arrangement of a device using wireless data transfer, such as a mobile phone. By means of ground arrangement one tries to improve the electric properties of the device antenna as well as the performance of the device.
Wireless terminal devices such as mobile phones must meet various requirements. As the physical size of the devices gets smaller, their size imposes their own requirements e.g. on the device structure, and particularly on the ground structure of the device. The antenna is a very important part of a terminal device operating at high frequencies, since it converts the signal received from the transmitter into electromagnetic waves and the electromagnetic waves into the signal to be received.
The antenna has to be capable of receiving and sending signal as well as possible under all circumstances. The frequency and output of a signal passing through the antenna may vary even to a great extent depending on the device, system and conditions, so as concerns the functioning of the device, it is substantial that the antenna operates under all circumstances as well as possible. In practice all antennas need a properly operating ground arrangement in order to efficiently function as emitters. The ground arrangement is herein also referred to as the “antenna ground”, which is generally used to refer to the earth current arrangement that is used to achieve a low-impedance coupling to the ground potential or to the common reference point.
In practice, interfering signals are received into the antenna, which render difficult the normal functioning of the device, at least to some extent. The devices in use themselves cause interfering signals that may e.g. harm the operation of the components in the device.
Devices operating at a radio frequency cause electric and magnetic fields while in use. Such a place or point at which there is, or at which there each time is created, a concentration of electric or magnetic field is called a so-called hot spot. From the distribution of currents induced by the fields it is possible to approximately calculate the specific absorption rate (SAR), which indicates the output absorbed (e.g. by the bodily tissue) per mass unit. By means of the ground arrangement of the antenna it is possible to affect the magnitude of the SAR value.
In addition to the output, the SAR value depends e.g. on the frequency, the distance of the antenna in relation to the user, the service position of the phone and the antenna type. While the SAR values of the devices on the market are very small, there is an attempt to design the new devices in such a manner that one could get the SAR values smaller than before.
It is known to attach to the terminal devices various additional components that help extend the antenna ground of the terminal device when necessary, which means that the antenna amplification is bigger. The user has had e.g. to detach an additional component from the terminal device in order to introduce the ground extension. The aforementioned solution is therefore cumbersome in use.
The objective of the invention is to improve the features of the device as concerns the above-mentioned facts and to achieve a method more workable than before for controlling and changing the ground configuration of the device. In addition, the objective is to achieve a solution by means of which it is possible to direct the earth currents to a place as optimal as possible in such a manner that the created field concentrations are as far as possible from the user, in which case it is possible to obtain a small SAR value.
The objective of the invention is to achieve a solution for a wireless terminal device by means of which it is possible to simply and flexibly optimize the electric properties of the device antenna, the performance of the device as well as to minimize the SAR value to be measured from the device.
This goal is achieved by a solution that has been described in the independent claims.
The idea of the invention is to form in the device, in addition to its actual ground lead i.e. ground route, one or more additional ground leads, and to change by means of it/them the ground configuration of the antenna, such as the effective length and/or area of the ground leads by automatically forming a galvanic coupling between the ground lead and one or more additional ground leads based on predetermined coupling criteria and by automatically releasing the coupling in question based on predetermined release criteria. In this manner it is possible to affect not only the SAR value but also the electric performance of the antenna. The ground lead and additional ground leads as well as the coupling criteria are designed for the device beforehand in such a manner that the desired features are achieved under varying transmission or reception circumstances.
The solution in accordance with the invention is used to achieve not only a small SAR value but also a low-loss antenna structure that has a VSWR value (VSWR=Voltage Standing Wave Ratio) as small as possible. By means of the invention it is also possible to achieve an antenna structure that operates in each situation with an optimal amplification.
In one advantageous implementation mode of the invention, the additional ground lead/leads are at least partly disposed in the cover part of the device, which enables one to implement various additional ground leads, and the place of the hot spots can be changed when necessary. The additional ground leads may be disposed on the surface of the cover material or inside it.
In another advantageous implementation mode of the invention, the additional ground leads are disposed in different layers of a multi-layer PC board. In this manner it is possible easily to implement additional ground leads that possess even very different sizes and shapes. The additional ground leads are easy to implement in respect of manufacturing technique on a multi-layer PC board, which makes the solution also cost-effective.
Since the effective length of the ground leads can be increased when necessary, it enables one to easily implement various ground configurations, from which the one each time most suitable is chosen. In practice, especially the frequency band to be used has an effect on the selection of the ground configuration (i.e. the additional ground lead each time most suitable).
The ground configuration in accordance with the invention can be easily implemented, and the user does not have to do anything in order to introduce a new ground configuration, but the introduction is performed automatically based on predetermined criteria.
For a better understanding of the present invention and in order to show how the same may be carried into effect reference will now be made to the accompanying drawings, in which:
The terminal device of
The ground arrangement according to the invention comprises an actual ground lead, one or more separate additional ground leads and coupling means, which enable one to automatically achieve a galvanic coupling between the ground lead and one or more additional ground leads in order to change the ground lead configuration to correspond to the changed transmission and reception circumstances, if desired. The number of cover parts of the terminal device is thus not so important as concerns the operability of the invention, instead substantial is that the device cover offers a space in which it is possible, e.g. in the manufacture phase of the device cover, to form one or more additional ground leads for the ground solution in accordance with the invention. The possible locations of the actual ground leads and additional ground leads are handled in more detail hereinafter.
The actual ground lead and additional ground leads are designed, in terms of qualities, (such as length, area and shape) beforehand in such a manner that the coupling and release of coupling of the additional ground leads enable one to achieve the desired effect on the functioning of the device. The physical measures of the additional ground leads are typically determined based on the frequency and output used. The seeking for the desired effect may happen also by way of experiment, as will be described hereinafter. It is possible to form even more additional ground leads, from which the one each time most suitable is chosen in order to provide the desired grounding network. It is also possible that from the additional ground leads, one chooses each time more than one to be connected to the actual ground lead.
In the selection of the additional ground lead to be used each time it is possible to take into account e.g. the transmission frequency and bandwidth of the antenna. This enables one to get the SAR and VSWR values of the device as small as possible. Furthermore, this enables one to optimize the antenna loss, and the antenna can be made to operate each time with optimal amplification.
The antenna may also be e.g. a so-called helix antenna, in which case the cylindrical coil acts as an antenna. The electrical properties of the helix antennas to be used in mobile phones are typically λ/4, 3λ/4 or 5λ/4. In mobile phones, e.g. so-called micro strip antennas and so-called PIFA antennas (PIFA=Planar Inverted F Antenna) are used in addition. The PIFA antennas enable one to achieve a particularly good radiation pattern and low VSWR value. In addition, the PIFA antennas are suitable for use at a wide frequency band.
The terminal device may comprise even several separate antennas, e.g. if the antenna utilizes several different frequency bands. The same mobile station may be used to establish connections e.g. in the frequency ranges of 900 MHz, 1800 MHz and 1900 MHz.
For the sake of simplicity, let it be stated that the device comprises, as shown in
The length, area and shape of the ground lead have an effect on the functioning and properties of the antenna and device, which is why the physical measures and shape of the ground lead may vary even to a great extent for each case specifically.
The physical properties of the ground lead have thus an effect e.g. on the SAR and VSWR values of the device as well as on the antenna amplification and antenna losses. The solution in accordance with the invention renders possible the functioning of the antenna at frequencies more several than before and in a frequency band wider than before. In practice it has been found that the solution in accordance with the invention enables one to increase the antenna amplification by over 0.5 dB and the band by over 3% as compared to the corresponding known methods.
The device further comprises a switch 90 disposed on the circuit board, which switch 90 is connected to the lead 72. More specifically, the switch 90 is connected to point A of the lead, which is the remotest point in the lead with respect to the antenna feed point 81. As discussed above, the length, shape and area of the ground lead affect the functioning of the antenna. There has been marked in the figure point B from which there is the shortest distance to the antenna feed point 81. As concerns the functioning of the antenna important is the shortest total length of the lead 72 from the antenna to the remotest point. In other words, as concerns the antenna, the effective length of the ground lead corresponds to the aforementioned shortest route along the lead 72 from point B to point A. Therefore, the length of the lead 72 “visible” to the antenna may be changed by means of an additional ground lead, if necessary.
In the example of
The galvanic coupling between a ground lead and one or more additional ground leads may be implemented e.g. using components based on the so-called MEMS technology (MEMS=Micro-Electro Mechanical Systems), which components are very small as concerns their physical size in comparison to the corresponding macroscopic counterparts, such as the semiconductor switches. The switches can be e.g. micro relays that have been manufactured using the MEMS technology. Thanks to its process engineering and structure, a micro relay is easy to encapsulate in ordinary SMD enclosures (SMD=Surface Mount Devices). Furthermore, the switches may be implemented e.g. using a PIN diode that is suitable for use in switching applications of various high-frequency signals.
The device comprises a control means 95, which is practically a microprocessor that controls the closing and opening of the switches. The microprocessor controls the switches based on predetermined switching and release criteria. Typically these criteria include at least the piece of information on the frequency band and/or transmission output used by the device. In a simple embodiment, for each frequency range, there may be an additional ground lead of its own, which is connected to the ground lead 72, when the device uses the frequency range in question. It is also possible to determine for the device with what length of ground lead and ground configuration one may obtain the most preferred SAR and VSWR values in relation to the frequency and frequency band used. When the most preferred ground lead configurations have once been determined, the lead configurations corresponding to them as well as the switching means with their corresponding switching and release criteria may be introduced in the manufacture phase of the devices.
When the device is in use, it is possible, e.g. in conjunction with the change of the frequency band, to change the ground routes (based on a definition made beforehand) in such a manner that the desired features are achieved, such as the maximal antenna amplification or the moving of the hot spot to a preferable location as concerns the SAR value.
When an additional ground lead is connected to serve as an extension of the actual ground lead, not only the length of the ground lead will change but also the additional ground lead is disposed in such place or position in relation to the actual ground lead that also the shape of the ground lead has changed to correspond to the changed transmission or reception circumstances. By changing the shape of the ground lead it is possible to further improve the features of the antenna, and it enables one to avoid the problems caused by various interference fields.
When the shape of the ground is changed, at the same change also the routes via which the high-frequency ground currents pass that have an effect e.g. on the magnitude of the SAR value. By automatically changing the shape of the ground routes it is possible to control the location of the hot spots in the device. The electric and magnetic fields created are directed in the device structure to such a place in which the fields are more far off from the user of the device.
In
In the structure as shown in
In the implementation mode as shown in
The disposition of the additional grounds in the cover is in that sense preferable that the cover structure provides a possibility of implementing additional ground leads that are physically even very different and big in respect of their area, and at the same time the hot spots may be directed to the desired place in the device. It is, however, possible to implement the additional ground leads in such a manner that they are wholly disposed on the circuit board. Since there normally is only a little space on the circuit board, they may be disposed in one or more (additional) layers of a multi-layer PC board (FIG. 6). For example, the additional ground lead for each frequency range may be disposed in its own layer. It is advantageous to dispose the actual ground lead wholly on the circuit board, regardless of whether one uses a one-layer or a multi-layer PC board in the device.
The ground plane (ground lead plus additional ground leads) has at each frequency an optimal minimum length, which enables one to achieve sufficient antenna amplification. The decreasing of the SAR value is achieved e.g. in such a manner that the hot spot is moved in the device to such a place in which it is possible to measure for the device a small SAR value. The SAR and VSWR values are not directly dependent on each other. When a good VSWR value is obtained, it is likely that also the antenna amplification increases. In order to achieve good antenna amplification, the antenna coupling has to be good (a small VSWR value), the length of the ground lead has to be optimal and the antenna emitter has to be disposed in a free place as concerns the RF features. If one generalizes a little, it can be said that the length of the necessary ground plane is the bigger the smaller is the frequency. The length of the necessary ground plane is, however, dependent on many factors, e.g. on the location of the ground, its shape and the rest of the device structure.
While the invention has been described above with reference to the examples according to the attached drawings, it should be understood that the invention is not limited to them, instead a person skilled in the art can vary the proposed solutions without departing from the inventive idea. If there are in the device e.g. several antennas, each of them may have at least partly their own ground arrangements, as described above, or there may be common additional ground leads for all antennas.
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| 20011815 | Sep 2001 | FI | national |
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