CN1189260A - Portable communication device including an antenna, wherein an artificial mismatch is introduced between the communication device and the antenna within a frequency band - Google Patents

Abstract

The invention relates to a portable communication device (10) having an antenna (11). An artificial mismatch is introduced between the impedance of the antenna (11) and the communication device (10) in the frequency band under consideration. In the method, the transmission loss between the antenna (11) and the communication device (10) is compensated as a function of the distance between the interfering object and the antenna (11). In this way, power may be saved and/or performance of the portable communication device may be improved.

Description

Portable communication devices including antennas, wherein an artificial mismatch is introduced between the communication device and the antenna within a frequency band

The invention relates to a portable communication device comprising an antenna. Such portable communication devices are generally known. Examples of such portable communication devices are handsets and pagers for mobile and cordless telephones.

In prior art portable communication devices, the antenna and portable communication device are matched for free space conditions. This makes the matching between the portable communication device and the antenna poor when interfering objects, such as a human body, are present near the antenna. This effect is known as the proximity effect. Consequently, this effect can generate considerable signal loss at both the transmitting and receiving locations.

In European Patent 0 34-238, some methods are described to avoid the proximity effect. In column 2, lines 1-16, it is described that the antenna and communication device are matched in the position of the antenna "on" the body. The disadvantage of this solution is that the performance is poor under free space conditions. Another solution described in EPO341 238 is to adaptively match the antenna and the communication device. regardless of location. The disadvantage of this solution is that additional equipment is required in order to measure the quality of the match between the antenna and the communication device and to change the impedance of the communication device and/or the antenna when the match is poor. This complicates such a communication device.

It is an object of the present invention to provide a portable communication device with acceptable performance and without complications when interfering objects are in the vicinity of the antenna and in free space conditions.

Therefore, a portable communication device according to the invention is characterized in that the communication device and the antenna are matched in the frequency band of interest in order to compensate for the transmission loss. The transmission loss between the antenna and the communication device can measure the performance of the communication device. Since the transmission loss is compensated as a function of the distance between the interfering object and the antenna, the portable communication device has acceptable performance in the vicinity of such interfering objects and under free space conditions. This means that both the received signal and the transmitted signal must be amplified smaller than in prior art arrangements. This means that the portable communication device of the present invention produces a lower value of power loss than that of prior art communication devices. Therefore, a smaller battery can be used, or if the same battery is used, it will last longer.

An embodiment of the portable communication device of the present invention is characterized in that, where the distance between the antenna and the interfering object is relatively small, the mismatch will be arranged so that the loss between the antenna and the communication device is greater than that of the communication device Low transmission loss when matched with an antenna. In a state where the distance between an interfering object, such as a human body or a person's head, and the antenna is small, it is an extremely important situation for the portable communication device since this is a position that it often senses by itself. When the user is making a call, the portable communication device can feel itself near the user's head. When the user carries the portable communication device with him, it can be felt in the vicinity of the user's body itself. Compared to prior art communication devices, the mismatch of the present invention results in a slightly worse transmission loss under free space conditions. However, satisfactory performance is still maintained under free-space conditions. Satisfactory performance under free space conditions is required for the following reasons:

A communication device is in free space conditions when it is placed on a wooden table or near other objects without much interference. When an incoming call is received, the communication device must have sufficient performance to receive the call. Type approval testing is performed in an anechoic chamber under free space conditions. If the free space performance is too poor, the communication device fails the type approval test.

Another embodiment of the portable communication device of the present invention is characterized in that the ratio between the antenna impedance of the antenna and the impedance of the portable communication device should satisfy the following conditions:

The first of these two impedances is substantially real-valued for the free-space condition,

The second of these two impedances has a real part of a value in the range of 35% to 70% of the value of the first impedance and an imaginary part in the range of 15% to 30% of the value of the second impedance, in the frequency band considered Inside, when the antenna is 0.2λ away from the interfering object, the sign of the imaginary part is opposite to the sign of the imaginary part of the first impedance.

When the ratio of the antenna impedance and the device impedance is set like this, an excellent compensation of the transmission loss as a function of the distance between the interfering object and the antenna is obtained.

The present invention will be further described in conjunction with the accompanying drawings, wherein,

Figure 1 shows a block diagram of a portable communication device,

Figure 2 shows the antenna resistance of a dipole antenna as a function of the distance between the antenna and the interfering object,

Figures 3, 5 and 7 show three implementations of the communication device of the invention compared to the transmission loss of a prior art communication device as a function of the distance between the antenna and the interferer for the case where the antenna and the communication device are matched The transmission loss value between the antenna and the communication device as a function of the distance between the antenna of the example and the interfering object; and

4, 6 and 8 show the difference in transmission loss between the communication device of the present invention and the communication device of the prior art. Wherein for these three embodiments the antenna and the communication device are matched for the free space condition.

Figure 1 shows in a general manner a block diagram of a portable communication device 10, such as a handset for mobile and cordless telephony. The portable communication device includes an antenna 11, a control switch 12, an RF transmitting stage 13, an RF receiving stage 14, a frequency synthesizer 15, first and second mixers 16, 17, a controller 18, a baseband processing unit 19, a codec 20, loudspeaker 21 and microphone 22. Such portable communication devices are well known. Depending on their system (GSM, DECT, etc.), they operate at frequencies ranging from a few tens of MHz to several GHz. If when sending or receiving signal, available control switch 12 is controlled. The first mixer 16 mixes the high-frequency wave generated by the frequency synthesizer 15 with a baseband signal to obtain an RF signal transmitted via the RF transmission stage 13 . The second mixer 17 mixes the high frequency wave with the RF signal received by the RF receiving stage 14 to obtain a baseband signal. The controller 18 and the codec 19 are arranged to process and encode the analog signal input via the microphone 22 to obtain a baseband signal (digital) and to decode the baseband signal, thereby obtaining an analog signal reproduced by the loudspeaker 21.

Figure 2 shows the antenna impedance values of a dipole antenna as a function of the distance between the antenna and an interfering object. The distance between the interfering object and the antenna is expressed in wavelength (λ) belonging to the frequency of the designed dipole antenna. The real part of the antenna impedance is denoted RA and the imaginary part is denoted XA. For large distances between the interfering object and the antenna, the antenna impedance has a real value RA of approximately 73 ohms and an imaginary value XA of approximately zero. When the distance between the interfering object and the antenna is small, the value of the antenna impedance is completely different. In prior art devices, the impedance of the antenna and the communication device are matched for free space conditions, so when the distance between the interfering object and the antenna is small, the transmission loss between the antenna and the communication device is high. This can be clearly seen from the curves of FIGS. 3 , 5 and 7 . Since the communication device is usually carried by the user and since the user's body is an interfering object, this position is quite important in practice.

In the portable communication device of the present invention, an artificial mismatch is arranged between the impedance of the antenna and the impedance of the communication device, which is the output impedance of the transmitting stage 13 at the transmitting position and the receiving position at the receiving position. input impedance of stage 14. This artificial mismatch allows the transmission loss between the antenna and the communication device to be compensated as a function of the distance between the antenna and the interfering object. The transmission loss TL is defined as follows:

TL=-10LogT (1) where $T=1-{\left|\frac{Z_C^x-Z_A}{Z_C-Z_A}\right|}^2$ $T=1-{\left|\frac{Z_C-Z_A^x}{Z_C+Z_A}\right|}^2---\left(3\right)$ in

Zc = impedance of the communication device, which is the output impedance of the RF transmit stage 13 at the transmit position and the input impedance of the RF receive stage 14 at the receive position,

ZA ^* = complex conjugate value of ZA, and

ZA = antenna impedance.

FIG. 3 shows the value of the transmission loss in dB between the antenna and the communication device as a function of the distance between the antenna and the interfering object at the wavelength (λ) belonging to the frequency considered. Curve a represents the transmission loss when the impedance of the antenna and the impedance of the communication device match for free space conditions. Curve b represents the transmission loss of a first embodiment of the communication device of the invention, where the free-space antenna impedance is 73 ohms and the impedance of the communication device at the frequency considered is 24-3i ohms. Fig. 4 shows the difference in transmission loss between curve a and curve b of this embodiment. The following conclusions can be drawn from Figures 3 and 4. When the distance is less than 0.2λ, the transmission loss of the communication device of the present invention is smaller than that of the prior art device. The wavelength of 900 MHz in the GSM frequency band is approximately 33 cm, therefore the communication device of the present invention will perform better than prior art devices at distances of less than 4 cm at this frequency. The increased transmission loss over greater distances is only to the extent that the communication device still has acceptable performance at that location, so that the call can be received correctly and will pass the type approval test. In the case according to FIG. 3 , the impedance of the selection communication device is selected so as to achieve a maximum transmission loss TLmax of 2 dB. As already stated, the portable communication device is in the vicinity of interfering objects most of the time, so the added capability is very useful for small distances.

In Figure 5 it is represented for a prior art device where the antenna impedance and the impedance of the communication device are both matched for free space conditions (curve a), and for a prior art device where the antenna impedance has a value of 73 ohms and the communication device has an impedance value of 30- Transmission loss between antenna and communication device of the second embodiment of the communication device according to the invention of 8i ohms (curve b). Figure 6 shows the difference in transmission loss between curves a and b for this embodiment. At distances smaller than 0.147λ, the transmission loss of the communication device according to the invention is smaller than that of the prior art device. However, the difference in transmission loss between this embodiment and the prior art device is smaller than that of the first embodiment. In the case according to FIG. 3 , the impedance of the communication device is chosen to achieve a maximum transmission loss TLmax of 1.5 dB. This can result in less deterioration of transmission loss over large distances.

In Fig. 7 it is shown for a prior art device (curve a) where both the antenna impedance and the impedance of the communication device are matched for free space conditions, and for a device where the antenna impedance has a value of 73 ohms and the impedance of the communication device is 37-10i Ohmic transmission loss between antenna and communication device for the third embodiment of the communication device according to the invention (curve b). Fig. 8 shows the difference in transmission loss between curves a and b for this embodiment. For distances smaller than 0.2λ, the communication device according to the invention has a lower transmission loss than prior art communication devices. The difference in transmission loss between this embodiment and the prior art device is smaller than that of the first and second embodiments. In the case according to FIG. 7 , the impedance of the selected communication device is selected so as to achieve a maximum transmission loss Tlmax of 1 dB. In this way, the deterioration of the transmission loss over a large distance is relatively small.

Figures 3 to 8 show that smaller transmission losses at small distances lead to larger transmission losses at large distances. There is a compromise between them.

In the communication device of the present invention, the impedance of the communication device may be a real number and the impedance of the antenna may be a complex number, or other mismatched impedance combinations may be used.

The invention has been described in connection with a dipole antenna. However, different types of antennas with different types of antenna impedance, eg complex impedance, may also be used. In case the antenna impedance is complex, the impedance of the communication device can also be made complex, which leads to an excellent compensation of the transmission loss as a function of the distance between the antenna and the interfering object.

Claims (3)

1. comprise the Portable Communications Unit of antenna, it is characterized in that communicator and antenna are mismatches in the frequency band of being considered, be used for compensating the loss between antenna and communication device as disturbing distance function between body and the antenna.

2. according to the Portable Communications Unit of claim 1, it is characterized in that, arrange mismatch to such an extent that make and compare the loss that has reduced antenna and communicator when disturbing between the body distance hour to make all to mate with antenna with communicator at antenna.

3. according to the Portable Communications Unit of claim 1 or 2, it is characterized in that the ratio between the impedance of the antenna impedance of this antenna and Portable Communications Unit should meet the following conditions:

First impedance of these impedances is essentially real number value for the free space condition,

Second impedance of these impedances has the real part and the imaginary part in 5%～30% scope of first resistance value of the value in 35%～70% scope of first resistance value, in the frequency band of being considered, when antenna when interfering object is 0.2 λ, the opposite in sign of the symbol of imaginary part and first impedance.

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