JP2013046141A - Radio communication terminal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a radio communication terminal capable of preventing decline of a communication performance of an antenna.SOLUTION: An antenna system of a radio communication terminal 1 includes a main antenna 2 and a sub antenna 3 for diversity. The main antenna 2 is a λ/4 ground antenna and is connected at a connection point 23 with a ground plane provided on a circuit board 20, and the sub antenna 3 is connected to the ground plane through a matching element 32 having an inductance value between an open end of a parallel conductor 31 arranged in parallel with the ground plane and a feeding point 34. The inductance value of the matching element 32 is 1.0 nH which is a half or less of 5.6 nH to be impedance matched for the sub antenna 3. Thus, the parallel conductor 31 functions as an extension part of the ground plate, and an electric length on the ground side is extended to λ/4.

Description

  The present invention relates to a wireless communication terminal, and more particularly to prevention of deterioration in communication performance of an antenna accompanying downsizing.

The λ / 4 grounded antenna, which is often used in wireless communication terminals such as cellular phones, is also located across the feed point because current flows through the ground plane provided on the circuit board and the board itself operates as part of the antenna. The antenna element and the ground plane of the circuit board are required to have an electrical length of λ / 4 corresponding to the radio frequency used.
In recent years, the case of a wireless communication terminal has been increasingly reduced in size and thickness, and the circuit board needs to be downsized. Therefore, a desired electrical length may not be secured for the ground plane provided in the circuit board. In this case, the communication performance of the antenna deteriorates.

  For this reason, as disclosed in Patent Document 1, a chip coil is provided between the feeding point and the ground plane to extend the apparent electrical length, or a metal rod is connected to the ground plane to increase the electrical length. It is extended.

JP-A-2005-229212

However, in the above case, there is a problem that a metal rod or a chip coil is required for the purpose of extending the electrical length, and the number of parts increases, resulting in an increase in cost and an increase in mounting area.
In view of the above problems, an object of the present invention is to provide a wireless communication terminal capable of preventing a decrease in antenna communication performance without increasing cost and mounting area even if a circuit board is downsized. To do.

  In order to solve the above problems, the present invention is a wireless communication terminal having a main antenna and a sub-antenna, wherein the main antenna is a λ / 4 ground type and is connected to a ground plane provided on a circuit board. The sub-antenna includes an antenna element connected to a feeding point, and a matching element for connecting the antenna element and the ground plane for impedance matching, and when the main antenna is used, the impedance of the matching element Is lowered to the mismatch region to stop the function of the antenna element as an antenna and to function as an extension of the ground plane.

  By providing the above-described configuration, the wireless communication terminal of the present invention can prevent a decrease in antenna communication performance.

It is a figure which shows the structure of the radio | wireless communication terminal which concerns on one embodiment of this invention. 1 is an external perspective view of an antenna system according to an embodiment of the present invention. It is a figure for demonstrating the antenna system which concerns on one embodiment of this invention from a functional surface. It is a figure which shows the measurement result of the communication efficiency for every aspect of ground extension. (A) is a figure which shows a measurement result, (b) is a schematic diagram of a structure. It is a figure which shows the result of having measured the communication efficiency of the subantenna, changing the inductance value. (A) is a measurement result, (b) is a structure of a matching element, (c) is a graph which shows a measurement result. It is an external appearance perspective view of the antenna system which concerns on the modification of this invention. It is a figure for demonstrating the antenna system which concerns on the modification of this invention from a functional surface.

A wireless communication terminal according to an embodiment of the present invention includes a main antenna that is a λ / 4 ground antenna and a sub-antenna that is an inverted F-type antenna. By arranging a matching circuit that is smaller than the impedance matching value as the inductance value of the sub antenna in parallel with the ground plane, the sub antenna functions as an extension of the ground plane during operation of the main antenna. Even when the electrical length of λ / 4 cannot be secured only by the ground plane, the electrical length on the ground side of the main antenna is extended to secure λ / 4. Hereinafter, it demonstrates concretely using drawing.
1. Configuration A wireless communication terminal 1 according to an embodiment of the present invention includes, as an example, a CDMA EVDO Rev. A wireless communication terminal corresponding to A (Code Division Multiple Access Evolution Data Only Revision A) and performing wireless communication by a diversity method.

FIG. 1 is a diagram showing a configuration of a wireless communication terminal 1 according to an embodiment of the present invention.
The wireless communication terminal 1 includes a main antenna 2, a sub-antenna 3, a communication unit 4, a control unit 5, an operation unit 6, a display unit 7, an audio unit 8, and a memory unit 9.
The communication unit 4 includes a transmission / reception unit 11, a reception unit 12, and a baseband unit 13, and communicates with a base station (not shown) or the like in a predetermined frequency band (for example, 2 GHz band, 800 MHz band, etc.). The communication unit 4 communicates using only the transmission / reception unit 11 for voice communication and data transmission, which are processes other than data reception, and for data reception, the transmission / reception unit 11 and the reception unit 12 are switched in a diversity manner. connect.

The transmission / reception unit 11 transmits / receives signals to / from the base station using the main antenna 2. Specifically, the transmission / reception unit 11 transmits the signal supplied from the baseband unit 13 to the base station 20 using the antenna 2, receives the signal supplied from the base station, and receives the received signal. Output to the baseband unit 13.
The receiving unit 12 receives a signal from the base station using the sub-antenna 3 and outputs the received signal to the baseband unit 13.

The baseband unit 13 demodulates the signals received by the transmission / reception unit 11 and the reception unit 12 to generate an audio signal and a video signal, and supplies the audio signal to the audio unit 8 based on the control of the control unit 5. The video signal is supplied to the display unit 7. The baseband unit 13 modulates the audio signal received from the audio unit 8 and supplies the modulated audio signal to the transmission / reception unit 11.
The control unit 5 performs overall control of the wireless communication terminal 1.

Specifically, the control unit 5 includes a CPU (Central Processing Unit), a RAM (Random Access Memory), a storage device that stores a program executed by the CPU, and the like.
The operation unit 6 is an input device such as a keypad or a touchpad for inputting instructions by a user operation. The operation unit 6 notifies the control unit 5 of the input instruction (user instruction).

The display unit 7 is a display device such as a liquid crystal display, and displays images, characters, moving images, and the like according to control by the control unit 5.
The audio unit 8 includes an audio processing unit, a speaker, a microphone, and a receiver (these are not shown).
The audio processing unit performs predetermined audio processing on the signal supplied from the baseband unit 13 and supplies the signal to the receiver. The receiver receives the voice signal generated by the voice processing unit, converts the received voice signal into voice, and amplifies the voice.

The audio processing unit supplies an audio signal generated by processing a signal input from the microphone to the baseband unit 13. The voice processing unit also performs processing related to voice other than the call and data communication, such as outputting a ringtone to a speaker when a call is received for a call or mail.
The memory unit 9 is a memory device, and stores audio data used for calculation, data used by the control unit 5 for overall control, and the like.

Next, the antenna system in the wireless communication terminal 1 will be described in more detail.
FIG. 2 is a perspective view showing an external appearance of the antenna system.
FIG. 3 is a diagram for explaining the antenna system from the functional aspect.
The main antenna 2 is a λ / 4 grounded antenna, and a parallel conductor 21 is connected to the circuit board 20 at a feeding point 22 as shown in FIG. As shown in FIG. 3, the feeding point 22 is connected to a ground pattern (not shown) of the circuit board 20 at a connection point 23.

  The sub-antenna 3 is an inverted F-type antenna, and a parallel conductor 31 as an antenna element is connected to the circuit board 20 at a feeding point 34. A connection point 35 in the vicinity of the feeding point 34 between the open end of the parallel conductor 31 and the feeding point 34 is connected to the ground pattern at the connection point 33 via the matching element 32. The sub-antenna 3 can be used as a diversity antenna.

Here, conventionally, the inductance value of the matching element 32 in the sub-antenna 3 matches the impedance between the parallel conductor 31 and a coaxial cable or a circuit that supplies a signal to the coaxial cable via the feeding point 34 in the 800 MHz band communication. A value of about 5.6 nH (nanohenry) is used.
However, in the present embodiment, as the inductance value of the matching element 32, a value of about 1.0 nH, which is a value less than half of the impedance matching value (5.6 nH), is used. With this configuration, since the impedance of the matching element 32 is reduced, the portion from the matching element 32 to the open end of the parallel conductor 31 regarding the sub-antenna 3 functions as an extended portion of the ground plane. As a result, the electrical length on the ground side of the main antenna 2 is extended by the electrical length of the portion serving as an extended portion of the ground plane for the sub antenna 3 in addition to the electrical length of the ground pattern on the circuit board. That is, for the main antenna 2, the electrical length from the ground-side terminal of the feeding point 22 to the open end of the parallel conductor 31 via the connection point 23, the connection point 33, the matching element 32, and the parallel conductor 31 is This is the electrical length of the main antenna 2 on the ground side. Here, the length of the parallel conductor 31 of the sub-antenna 3 is adjusted so that the total electrical length on the ground side of the main antenna 2 is λ / 4.

As the inductance value of the matching element 32 is reduced from 5.6 nH, the impedance of the sub-antenna 3 is not matched, and the communication efficiency of the sub-antenna 3 is deteriorated. Since the communication efficiency improvement of the main antenna 2 accompanying the electrical length extension of the sub antenna 3 and the maintenance of the communication efficiency of the sub antenna 3 are in a trade-off relationship, how much the inductance value related to the sub antenna 3 is reduced, It must be determined by simulation, experiment, etc.
2. Experiments related to inductance value determination 2-1. Fig. 4 shows the advantages of using a sub-antenna for extension of electrical length. Fig. 4 shows how ground planes are extended (1) when a metal rod is added, (2) when neither a metal rod nor a sub-antenna is added, 3) The measurement result of the communication efficiency (dB) when each sub antenna is added (L = 1.0 nH) is shown. The configuration in each case of (1) to (3) is schematically shown in FIG.

  FIG. 4A lists the measurement results of the communication efficiency of the main antenna for each frequency (816, 837, 848, 870, 882, 893 MHz) for each configuration of (1) to (3). FIG. Here, the antenna system in this experiment is mounted on a foldable mobile phone as a wireless communication terminal. The indications “open” and “closed” in FIG. 4A indicate whether the mobile phone is in a folded state (closed) or in an open state (open). The target value of communication efficiency is a design item, but is set to −4.5 dB as an example.

  Referring to FIG. 4A, when the metal rod and sub-antenna of (2) are not used, the communication efficiency becomes significantly smaller than the target value compared to the case of adding the metal rod of (1). Yes. For example, when the frequency is 816 MHz and the housing state is “open”, the communication efficiency is −3.7 dB in (1), which exceeds the target value, whereas the communication efficiency is −8 in (2). .8 dB, which is below the target value.

On the other hand, when the sub-antenna (3) is added, the communication efficiency is as good as when the metal rod (1) is added. For example, in the case where the frequency, which is the same condition as described above, is 816 MHz and the housing state is “open”, in (3), the communication efficiency is −3.7 dB, which exceeds the target value.
As for the other frequencies and housing states in FIG. 4A, the above-described result that the communication efficiency is good in the cases (1) and (3) and the communication efficiency is lowered in the case (2). The result is the same.

As described above, when the sub-antenna of (3) is added, the same good communication efficiency as when (1) the metal rod is added to extend the electrical length is obtained, and (2) As compared with the case where no metal rod and sub-antenna are used, the communication efficiency is greatly improved.
Next, experiment 2-2. For determining an optimum inductance value 2-2. Experiment on Determination of Inductance Value FIG. 5 is a diagram showing a result of measuring the communication efficiency of the sub-antenna while changing the inductance value.

The configuration of the matching element 32 used in the experiment is shown in FIG. The matching element 32 includes a 3.0 pF capacitive load, a 0Ω resistor, and an LnH inductive load.
FIG. 5A shows a list of results obtained by changing the value of L between 0.0 nH and 5.6 nH and measuring the communication efficiency of the sub-antennas. FIG. In the table of FIG. 5A, the measurement results in the closed state at 863 MHz are shown in a graph format. The descriptions of “open” and “closed” in FIG. 5A are the same as those in FIG.

  Referring to FIG. 5C, when the value of L is 1.0 nH to 5.6 nH, the communication efficiency of the target value can be over −14 dB, and when it is below 1.0 nH, the target value of −14 dB is reduced. Below. From 2.7 nH to 5.6 nH, the communication performance of 5.6 nH is deteriorated compared to 2.7 nH due to impedance mismatch. On the other hand, as shown in FIG. 5A, in the “open state”, the communication performance of 5.6 nH is improved compared to 2.7 nH.

From the above, it can be seen that the value of L may be at least half or less of the impedance matching value (5.6 nH).
Note that if L is 1.0 nH or more, the communication efficiency of the sub-antenna exceeds the target value. However, if L is less than 1.0 nH, this does not mean that communication is not possible. The value of L is a design matter and should not necessarily be limited to need to exceed 1.0 nH.

With the above configuration, in this embodiment, when the main antenna is used, the antenna element related to the sub-antenna can function as an extended portion of the ground plane.
2. Although the present invention has been described based on the above embodiment, the present invention is not limited to the above embodiment, and various modifications can be made without departing from the gist of the present invention. Of course, it can be added.
(1) In the above-described embodiment, the sub-antenna is configured with an inverted F-type antenna, but is not limited thereto. For example, the sub antenna may have a monopole configuration.

FIG. 6 is a perspective view showing an external appearance of the antenna system when the sub antenna has a monopole configuration.
FIG. 7 is a diagram for explaining the antenna system from the functional aspect when the sub-antenna has a monopole configuration.
The difference from the above-described embodiment is the position where the matching element is connected as shown in FIGS. 6 and 2 and FIGS. 7 and 3. In the monopole configuration, the antenna itself is not grounded by the matching element. However, as shown in FIG. 7, in the vicinity of the feeding element 43 in the conductor connecting the parallel conductor 41 as the antenna element and the feeding point 43 on the circuit board. Is connected to the ground pattern at the connection point 42 via the matching element 44.

Even in the configuration of the present modification, as in the above-described embodiment, the impedance of the matching element 44 is reduced, so that the portion of the sub antenna 3 from the matching element 44 to the open end of the parallel conductor 41 is the main antenna. 2 functions as an extension of the ground pattern. That is, for the main antenna 2, the electrical length from the ground-side terminal of the feeding point 22 to the open end of the parallel conductor 41 via the connection point 23, the connection point 42, the matching element 44 and the parallel conductor 41 is This is the electrical length of the main antenna 2 on the ground side. Here, the length of the parallel conductor 41 of the sub-antenna 3 is adjusted so that the electrical length on the ground side of the main antenna 2 is λ / 4.
(2) In the above-described embodiment, the inverted F-type antenna is configured as a linear antenna. However, the present invention is not limited to this. For example, it may be configured as a flat antenna.
(3) In the above-described embodiment, the wireless communication terminal uses CDMA EVDO Rev. Although it corresponds to A, the present invention is not limited to this, and the present invention can also be applied to devices that perform wireless communication by other methods as long as they communicate using a plurality of antennas.
(4) In the above-described embodiment, the diversity antenna is used as the sub antenna, but an antenna other than the diversity antenna may be used as the sub antenna.
(5) Specifically, the wireless communication terminal is a computer system including a microprocessor, a ROM, a RAM, a display unit, a keypad, and the like. A computer program is stored in the RAM, and the wireless communication terminal achieves its functions by the microprocessor operating according to the computer program.
(6) The above embodiment and the above modifications may be combined.

  The wireless communication terminal of the present invention is suitable for a portable terminal such as a mobile phone that is required to be reduced in size and thickness.

DESCRIPTION OF SYMBOLS 1 Wireless communication terminal 2 Main antenna 3 Sub antenna 4 Communication part 5 Control part 6 Operation part 7 Display part 8 Audio | voice part 9 Memory part 11 Transmission / reception part 12 Reception part 13 Baseband part 20 Circuit board (ground pattern)
21 Parallel conductor 22 Feed point 23 Connection point 31 Parallel conductor 32 Matching element 33 Connection point 34 Feed point 35 Connection point

Claims (6)

A wireless communication terminal having a main antenna and a sub antenna,
The main antenna is a λ / 4 ground type, connected to a ground plane provided on the circuit board,
The sub-antenna includes an antenna element connected to a feeding point, and a matching element that connects between the antenna element and the ground plane for impedance matching,
A wireless communication terminal, wherein when the main antenna is used, the impedance of the matching element is lowered to a mismatching region to stop the function of the antenna element as an antenna and to function as an extended portion of the ground plane. The wireless communication terminal according to claim 1, wherein an inductance value of the matching element is a value equal to or less than half of a value of impedance matching for the sub-antenna. The wireless communication terminal according to claim 2, wherein the inductance value is 1.0 nanohenry or more and 2.7 nanohenry or less. The wireless communication terminal according to claim 1, wherein the sub-antenna is an inverted F-type antenna. The wireless communication terminal according to claim 1, wherein the sub-antenna is a monopole antenna. The wireless communication terminal according to claim 1, wherein the sub-antenna is a diversity antenna.

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