JPH0723450A - Cordless phone - Google Patents

Abstract

(57) [Abstract] [Purpose] To obtain a cordless telephone that can maintain a stable call by ensuring impedance matching between the antenna and the internal circuit even when the human body is in close contact with the slave. [Structure] The cordless handset 2 is provided with a rod-shaped antenna 1,
An internal circuit 5 including a wireless transmission / reception circuit and a control circuit connected to the antenna 1 is provided in the case 2a, and the stub 3 is connected to the antenna 1 via a changeover switch 4. Depending on the usage state of the slave unit 2, the changeover switch 4 is contacted and separated, the stub 3 and the antenna 1 are connected, and impedance matching between the antenna 1 of the slave unit 2 and the internal circuit 5 is performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cordless telephone composed of a base unit and a handset, and more particularly to a cordless telephone capable of impedance matching between an antenna of the handset and an internal circuit.

[0002]

2. Description of the Related Art A base unit conventionally connected to a telephone line,
There is known a cordless telephone including a slave connected to the master via a wireless line.

FIG. 10 is a block diagram showing a configuration of a base unit of a conventional cordless telephone.

The base unit 11 includes a microphone 15, a speaker 16, an input section 17 such as a switch, a display section 18,
Antenna 19 and line connection unit 22 connected to a telephone line
Etc., and the microphone 1 is provided in the case 11a.
5, a call circuit 20 connected to the speaker 16 and the line connection unit 22, and a C connected to the input unit 17 and the display unit 18.
A control circuit 12 including a PU and a modem is provided. Further, an incoming call detection circuit 21 is provided between the line connection unit 22 and the control circuit 12, and a wireless transmission circuit 14 is provided between the control circuit 12 and the call circuit 20 and the antenna 19.
Is provided, and a radio receiving circuit 13 is provided between the antenna 19 and the control circuit 12 and the communication circuit 20.

FIG. 11 is a perspective view showing an external appearance of a cordless telephone of a conventional cordless telephone, and FIG. 12 is a block diagram showing a configuration of a cordless telephone of a conventional cordless telephone.

The slave unit 2 includes a speaker 33, a microphone 34, an input section 36 such as a switch, a display section 37, and an antenna 1. The case 2a has a radio signal received by the antenna 1. A radio receiving circuit 38 for receiving the signal is provided, a low frequency amplifying circuit 31 for amplifying the received signal is connected to the radio receiving circuit 38, and the low frequency amplifying circuit 31 is connected to a speaker 33. . Further, the microphone 34 is connected to a low-frequency amplifier circuit 32 that amplifies an audio signal, the low-frequency amplifier circuit 32 is connected to a wireless transmission circuit 39, and the wireless transmission circuit 39 is connected to the antenna 1. Has been done. Further, the input unit 36 and the display unit 37 include a control circuit 35 including a CPU and a modem.
Are connected, and the control circuit 35 controls the low frequency amplifier circuit 3
1. The wireless receiver circuit 38 and the wireless transmitter circuit 39 are connected.

FIG. 13 is a diagram showing a general data format of a control signal exchanged between the master unit 11 and the slave unit 2, and 131 is a bit synchronization signal for synchronizing each bit. , 132 is a frame synchronization signal for synchronizing each frame, 133 is a calling signal (ID data) for connecting a communication line only to the master unit 11 and the slave unit 2 forming a pair, and 134 is a call And command data including information exchanged between the base unit 11 and the handset 2 in order to realize other functions.

Next, the operation will be described with reference to FIGS.
This will be described using the flowchart of FIG.

The base unit 11 is connected to the base unit 11 by a button of the input section 17 or the like, an extension instruction, an external line transfer instruction, or whether or not an incoming call is received from an external line through the line connection unit 22 connected to a telephone line. Whether or not to make a call is determined (step 1), and when it is determined to make a call to the handset, a control signal having a data format as shown in FIG. 13 is transmitted as a call request signal to the handset 2 ( Step 2). On the other hand, the handset 2 is performing the intermittent reception which repeats the waiting state and the carrier sense state when on-hook. Then, the transmission of the control signal is repeated several times in consideration of the intermittent reception interval of the slave unit 2 so as not to be unable to be received depending on the transmission timing.

The length of the intermittent reception waiting state of the slave unit 2 is timed by the control circuit 35, and it is judged whether or not it is time to change to the carrier sense state (step 11). When it is determined that the radio reception circuit 38 is turned on, the control circuit 35 turns on the power of the wireless reception circuit 38 (step 12) and checks whether or not the radio wave from the master device 11 is coming (step 13). Then, if no radio wave is detected for a predetermined time, it is judged whether or not it is the timing for ending the intermittent reception (step 14). When the timing for ending the intermittent reception is reached, the control circuit 35 causes the wireless reception circuit 38 to operate.
Turn off the power to change to the waiting state (Step 1
5).

On the other hand, when the radio wave from the base unit 11 is detected, continuous reception is performed (step 16), and the bit synchronization signal 131,
The frame synchronization signal 132 and the calling signal 133 are confirmed, and it is judged whether or not the signals are correct signals from the parent device 11 of its own (step 17). If it is determined that the signal is a correct signal from the parent device 11 of its own, the contents of the command data 134 are checked (step 18), and if it is a signal for a call (step 19), it is determined according to the contents of the command data 134. A response signal is transmitted (step 20), and the procedure required for a call is performed (step 21). At this time, the user of the child device holds the child device 2 and talks.

If the signal is not a signal for a call in step 19, the designated process is performed (step 22) and the process returns to step 11.

Then, the base unit 11 judges whether or not the response signal is received (step 3), and if the response signal is correctly received, after the procedure necessary for the call such as ringing the bell or confirming the on-hook (step 4). , Between the base unit 11 and the handset 2,
Alternatively, the child device 2 communicates with the outside line via the parent device 11 (step 5). When the mobile phone 2 is on-hook after the end of the call, the slave unit 2 performs intermittent reception again.

When the response signal is not received in the above step 3, the control circuit 12 measures a preset predetermined time limit and determines whether or not the time limit for waiting the response signal has elapsed (step 6) If the response signal is not received within the time limit or the response signal is not correct, the call failure is displayed on the display unit 18 or a voice is notified through the speaker 16 (step 7).

[0015]

The conventional cordless telephone is constructed as described above. Then, the master unit and the slave unit are provided with a matching circuit (stub circuit) for the impedance mismatch generated between the antenna and the internal circuit (including the wireless transmission circuit, the wireless reception circuit, etc.), and as a cordless telephone, It is set so that impedance matching is always maintained.

However, the slave unit is usually used while being held by hand or in close contact with the head, and when used in this manner, the impedance changes due to contact with the human body,
There is a problem that the impedance mismatching occurs between the antenna of the slave and the internal circuit, which deteriorates the communication performance.

Further, when the slave unit uses an electric field antenna such as a whip antenna, there is a problem that the radiation pattern of the radio wave changes when the human body approaches and the gain deteriorates.

With respect to such deterioration of communication performance of the cordless telephone, Japanese Patent Laid-Open No. 184429/1993 proposes the first and second communication methods in order to secure the best reception characteristics with respect to the communication characteristics which change depending on the use condition. Provide a second RF connector,
A configuration of a mobile wireless telephone device capable of connecting an arbitrary antenna is disclosed.

However, the reception characteristics of cordless telephones mainly used indoors do not change remarkably unlike those of portable radio telephones. Further, the change in impedance changes with each use depending on how the human body is in close contact with the slave unit. In addition, communication between the base unit and the handset is performed regardless of the contact / separation of the human body of the handset, and quick impedance matching suitable for the usage state of the handset is required. Therefore, it is not practical to change the antenna connected to the cordless telephone like a portable radio telephone device.

The present invention has been made in order to solve the above problems, and even if the human body of the user is in close contact with the slave unit, the impedance can be matched between the antenna and the internal circuit, and the stability is always stable. The purpose is to obtain a cordless telephone that can make a call.

[0021]

First, a cordless telephone according to the present invention is a cordless telephone including a master unit connected to a telephone line and a slave unit connected to the master unit via a wireless line. And a stub for impedance matching between an antenna of the slave unit and an internal circuit, and a changeover switch for connecting and disconnecting the stub and the antenna to the slave unit. In a cordless telephone, a stub group consisting of a plurality of types of stubs for impedance matching between an antenna of a cordless handset and an internal circuit, and at least one of selecting a desired stub from the plurality of types of stubs and connecting / disconnecting the stubs And a selection switch for performing the above-mentioned operation.

Thirdly, in a cordless telephone, a stub group consisting of a plurality of types of stubs for impedance matching between an antenna of a slave unit and an internal circuit, and the strength of a received signal from the master unit are detected and received. A reception signal strength detection circuit for sequentially switching the plurality of types of stubs to connect to the antenna when the signal strength is smaller than a predetermined threshold value; As a cordless telephone, a stub group consisting of a plurality of types of stubs for impedance matching between an antenna of a child device and an internal circuit, and the intensity of a received signal from the parent device are detected, and the intensity of the received signal is a predetermined threshold. If the value is smaller than the value, the received signal strength detection circuit that sequentially switches the plurality of types of stubs and connects to the antenna, and the contact / separation of the stub and the antenna It is characterized in further comprising a changeover switch for performing, to the slave unit.

Furthermore, as a fifth aspect, in the cordless telephone, the cordless telephone is provided with a slidable stub with respect to a rod-shaped antenna of a slave unit, and when the stub is moved to the uppermost portion of the rod-shaped antenna, a loop antenna is provided. And a sixth feature is that
In the cordless telephone, the slave unit includes a minute loop antenna that receives radio waves from the master unit, and a metal plate that contacts the minute loop antenna and impedance-matches the minute loop antenna and the internal circuit. To do.

[0024]

In the cordless telephone of the present invention, the cordless telephone is provided with the stub for impedance matching between the antenna and the internal circuit, and the changeover switch for connecting and disconnecting the stub and the antenna. Since they can be connected, impedance matching between the antenna and the internal circuit can be easily performed if necessary.

Since the stub group having a plurality of types of stubs is provided and the stubs are sequentially switched to perform impedance matching, the best impedance matching can be easily performed. Further, since the received signal strength detection circuit for sequentially switching a plurality of types of stubs and connecting to the antenna is provided, the best impedance matching can be automatically performed.

Further, the stub is slidably provided on the rod-shaped antenna, and when the stub is moved to the uppermost part of the antenna,
Since the loop antenna is formed, it functions as a magnetic field antenna and the radiation pattern of the radio wave becomes large when the human body approaches, so that the gain deterioration due to the human body can be suppressed even if the human body is in close contact.

Furthermore, since the metal plate for impedance matching which is slidable with respect to the minute loop antenna is provided on the minute loop antenna provided in the slave unit, impedance matching between the minute loop antenna and the internal circuit is achieved, Even when the human body comes into contact with the child device, impedance matching between the antenna and the internal circuit can be easily achieved.

[0028]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic configuration diagram showing a cordless telephone of a first embodiment according to the present invention. The cordless handset 2 includes the rod-shaped antenna 1, and the antenna 1 is provided in the case 2a.
An internal circuit 5 including a wireless transmission / reception circuit and a control circuit connected to is provided. A feature of this embodiment is that the antenna 1 is connected to a stub 3 for impedance matching via a switch 4 opened and closed by a slider (not shown) provided on the surface of the case 2a. The stub 3 is adjusted so that the user can perform impedance matching when the user holds the child device 2 or makes it closely contact with the head of the user's body to bring it into contact with the human body.

Next, the operation of this embodiment will be described.

Normally, the switch 4 is turned off when the slave unit 2 operates without contact with the user (when communication is performed between the master unit and the slave unit in the on-hook state), and the stub 3 is separated from the antenna 1. Then, the slave unit 2 is in a state where predetermined impedance matching is performed. When the user holds the handset 2 by hand and an impedance mismatch occurs due to the influence of the human body, when the user turns on the switch 4 during a call, the stub 3 and the antenna 1 are connected and the handset The impedance between the antenna 1 of No. 2 and the internal circuit 5 is in a matched state. This makes it possible to prevent deterioration of communication performance.

FIG. 2 is a schematic configuration diagram showing a cordless telephone of the second embodiment according to the present invention. The cordless handset 2 includes the rod-shaped antenna 1, and the antenna 1 is provided in the case 2a.
An internal circuit 5 composed of a wireless transmission / reception circuit and a control circuit connected to the antenna 1 is provided, and a stub 40 for impedance matching is connected to the antenna 1. Then, as shown in detail in FIG.
a is provided, and a plurality of contacts (four contacts 41a to 4a in this embodiment) are provided so as to contact the contact 40a at the position P.
A rotary switch 41 as a selection switch including 1d) is rotatably supported around a shaft 41e.
Contact 4 provided at the edge of the rotary switch 41
1a to 41d include stubs 42a to 42d having different lengths.
Are connected to form a stub group. And
A plurality of types of stubs are configured by connecting one of the stub 40 and the stubs 42a to 42d.

In the second embodiment having such a configuration, when the user holds the handset 2 by hand and the call performance is deteriorated due to impedance mismatch during the call, the user is exposed from the case 2a. A part of the rotary switch 41 is rotated. Then, the contact 40a of the stub 40 is connected to the contact 41
Any of the stubs 42a to 42d is connected via a to 41d, the length of the entire stub changes, and the impedance between the antenna 1 of the handset 2 and the internal circuit 5 is sequentially adjusted. . Then, the rotation of the rotary switch 41 is stopped at the position where the best communication performance is obtained, and the impedance matching state is established. This makes it possible to prevent deterioration of communication performance.

FIG. 3 is a schematic configuration diagram showing a cordless telephone of a third embodiment according to the present invention. The cordless handset 2 has the same structure as the cordless telephone shown in the second embodiment and includes a rod-shaped antenna 1. Inside the case 2a, a wireless transmission / reception circuit and a control circuit connected to the antenna 1 are provided. 2B is provided, and the rotary switch 41 including a plurality of stubs, which is shown in detail in FIG. 2B, is provided. In this embodiment, the antenna 1 and the rotary switch 4
A switch 42 that is opened and closed by a slider (not shown) provided on the surface of the case 2a is provided between the switch 42 and the case 1.

When the slave unit 2 is on-hook, the switch 4 is normally turned off, the stub 40 is separated from the antenna 1, and the slave unit 2 is in a state in which a predetermined impedance matching is performed. When the user holds the handset 2 by hand and impedance mismatch occurs due to the influence of the human body and the call performance deteriorates, the user turns on the switch 42 during a call, and the stub 40 and the rotary switch 41 are switched on. It becomes possible to connect a stub composed of a plurality of stubs provided to the antenna 1, and the best impedance matching can be performed. Therefore, it is possible to perform appropriate impedance matching in the state where the handset 2 is in contact with the human body and the state where it is not in contact with the human body.

FIG. 4 is a schematic configuration diagram showing a cordless telephone according to the fourth embodiment of the present invention. The cordless handset 2 includes the rod-shaped antenna 1, and the antenna 1 is provided in the case 2a.
An internal circuit 5 including a wireless transmission / reception circuit and a control circuit connected to the antenna 1 is provided, and a stub circuit 44 containing a plurality of types of stubs is connected to the antenna 1 via a stub 40 for impedance matching. . The stub circuit 44 is connected to a reception signal strength detection circuit 43 that detects the strength of the reception signal from the master unit, and the reception signal strength detection circuit 43 determines that the reception signal strength is higher than a predetermined threshold value. When the size is small, the stub circuits 44 are sequentially switched and connected.

Next, the operation of this embodiment will be described with reference to the flowchart of FIG.

When the user holds the handset 2 by hand during a call,
If the call performance deteriorates due to impedance mismatch,
The reception signal strength detection circuit 43 determines whether or not the strength of the reception signal is lower than a predetermined threshold value set in advance (step 31). Switch 44 (step 3
2) Connect to the stub 40. At this time, the stub number and the reception level are stored (step 33).

Next, it is again judged whether or not the reception level of the reception signal is lower than a predetermined threshold value set in advance (step 34). If it is lower, the reception signal strength detection circuit 43
The stub circuit 44 is sequentially switched to sequentially compare the corrected reception level with the threshold value. Then, when all the stubs of the stub circuit 44 are switched without the corrected reception level becoming larger than the threshold value (step 3
5) Connect to the stub with the highest reception level (step 36).

As a result, the impedance between the antenna 1 of the handset 2 and the internal circuit 5 is automatically brought into a matched state, and deterioration of communication performance can be prevented.

FIG. 6 is a schematic configuration diagram showing a cordless telephone of the fifth embodiment according to the present invention. The cordless handset 2 has substantially the same configuration as that of the fifth embodiment. That is, the rod-shaped antenna 1 is provided, and in the case 2a, an internal circuit 5 including a wireless transmission / reception circuit and a control circuit connected to the antenna 1 is provided.
Is provided, and a stub circuit 44 containing a plurality of types of stubs is connected to the antenna 1 via a stub 40. The stub circuit 44 is connected to a reception signal strength detection circuit 43 that detects the strength of the reception signal from the master unit, and the reception signal strength detection circuit 43 determines that the reception signal strength is higher than a predetermined threshold value. Stub circuit 44 when small
To switch and connect. In this embodiment,
A switch 42 that is opened and closed by a slider (not shown) provided on the surface of the case 2a is provided between the antenna 1 and the stub circuit 44.

When the slave unit 2 is on-hook, the switch 4 is normally turned off, the stub 40 is separated from the antenna 1, and the slave unit 2 is in a state in which a predetermined impedance matching is performed. When the user holds the slave unit 2 by hand and impedance mismatch occurs due to the influence of the human body and the call performance deteriorates, the user turns on the switch 42 during a call, and the antenna 1 is stub 40, stub 40 Circuit 44
Also, it becomes possible to connect to the received signal strength detection circuit 43, and as described above, the best impedance matching can be performed and the deterioration of communication performance can be prevented. When the handset 2 is on-hook (when it is not in contact with the human body)
Does not require impedance adjustment and does not require stub adjustment. Therefore, the switch 4 is turned off to disconnect the stub 40 from the antenna 1, and the received signal strength detection circuit 4
It is possible to stop the operation of No. 3 and prevent the battery from being wasted due to the impedance matching operation when not in contact with the human body.

7 and 8 are schematic configuration diagrams showing a cordless telephone according to a sixth embodiment of the present invention.

The cordless handset 2 is provided with a rod-shaped antenna 6, and in the case 2a, an internal circuit 5 composed of a radio transmitting / receiving circuit and a control circuit connected to the antenna 6 is arranged. In addition, the antenna 6 has a stub 7
When the stub 7 is slidably engaged with the stub 7 to the upper end of the antenna 6 as shown in FIGS. 7A to 7C, the loop antenna is formed by the antenna 6 and the stub 7. Can be formed. That is, the loop antenna functions as a magnetic field antenna, and the radiation pattern of radio waves increases as the human body approaches, and the antenna gain can be improved. Therefore, by making the antenna a loop antenna when the handset touches the human body,
It is possible to recover the communication performance that has deteriorated due to the approach of the human body when the antenna 6 was functioning alone.

An example of engagement between the antenna 6 and the slidable stub 7 is shown in FIG. In FIG. 8A, the tip 7a of the stub 7 has a ring shape, the tip 7a is externally fitted to the antenna 6, and the tip 7a of the stub 7 slides along the antenna 6. There is. Further, the stub 7 has a tip portion 7a, a central portion 7b bent at a substantially right angle, and a lower end portion 7a.
The lower end portion 7c is slidable with respect to the vertically arranged gland 8. Therefore, when the stub 7 is moved to the uppermost part, a loop antenna can be easily formed by the rod-shaped antenna 6 and the stub 7. In addition, as shown in FIG. 8B, a long groove 6a in which the tip of the stub 7 is formed in the antenna 6
May be engaged with and slid along.

FIG. 9 is a schematic configuration diagram showing a cordless telephone of the seventh embodiment according to the present invention. The cordless handset 2 includes a loop antenna 9, and an internal circuit 5 including a wireless transmission / reception circuit and a control circuit connected to the loop antenna 9 is arranged in the case 2a. The antenna 6 is in contact with a substantially U-shaped metal plate 10 which is supported so as to be able to move up and down, and the metal plate 10 rises when the human body holds the slave unit 2 and comes into contact with the antenna 9, It is selected so that impedance matching between the antenna 9 and the internal circuit 5 can be performed. In addition, although the metal plate 10 has a substantially U-shape in the above-described embodiment, the present invention is not limited to this.
It may be flat.

[0047]

As described above, according to the cordless telephone according to the present invention, the slave unit is provided with the stub for impedance matching between the antenna and the internal circuit, which can be brought into and out of contact with the changeover switch as needed. So
It is possible to easily bring an impedance matching state into an impedance mismatch caused by the handset touching the human body during a call.

Further, since impedance matching can be performed by providing a stub group having a plurality of types of stubs and sequentially switching the stubs, it is possible to easily perform the best impedance matching according to the usage state. . Further, since the received signal strength detection circuit for sequentially switching a plurality of types of stubs and connecting to the antenna is provided, the best impedance matching can be automatically performed. Further, even when the received signal strength detection circuit is provided, the stub is switched only when necessary by the changeover switch, so that the waste of the battery due to the automatic changeover can be prevented.

Further, the stub is slidably provided on the rod-shaped antenna, and when the stub is moved to the uppermost part of the antenna,
Since the loop antenna is formed, it functions as a magnetic field antenna and the radiation pattern of the radio wave becomes large when the human body approaches, so that the gain deterioration due to the human body can be suppressed even if the human body is in close contact.

Furthermore, since a metal plate for impedance matching which is slidable with respect to the minute loop antenna is provided on the minute loop antenna provided in the slave unit, impedance matching between the minute loop antenna and the internal circuit is achieved. Even when the human body comes into contact with the child device, impedance matching between the antenna and the internal circuit can be easily achieved.

Therefore, the characteristic deterioration of impedance can be prevented and stable communication can be performed.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a cordless handset for explaining a first embodiment of a cordless telephone according to the present invention.

FIG. 2 is a schematic view illustrating a second embodiment of the cordless telephone according to the present invention, (A) is a schematic view of a slave unit,
(B) is a schematic diagram of a roller switch.

FIG. 3 is a schematic diagram of a cordless handset for explaining a third embodiment of the cordless telephone according to the present invention.

FIG. 4 is a schematic diagram of a cordless handset for explaining a fourth embodiment of the cordless telephone according to the present invention.

FIG. 5 is a flowchart showing the operation of a received signal strength detection circuit of the fourth embodiment of the cordless telephone according to the present invention.

FIG. 6 is a schematic view of a cordless handset for explaining a fifth embodiment of the cordless telephone according to the present invention.

FIG. 7 is a schematic view illustrating a sixth embodiment of the cordless telephone according to the present invention, and (A), (B), and (C) are description of movement states of a slidable stub provided in a child device. FIG.

FIG. 8 is a schematic view illustrating a sixth embodiment of the cordless telephone according to the present invention, and (A) and (B) are examples of engagement between a slidable stub provided in a child device and an antenna. It is a schematic diagram showing.

FIG. 9 is a schematic view illustrating a seventh embodiment of the cordless telephone according to the present invention, in which (A) is a schematic head of a slave unit,
(B) is a perspective view showing a sliding state of the metal plate.

FIG. 10 is a block diagram showing a configuration of a base unit of a conventional cordless telephone.

FIG. 11 is a perspective view showing the external appearance of a slave unit of a general cordless telephone.

FIG. 12 is a block diagram showing a configuration of a slave unit of a conventional cordless telephone.

FIG. 13 is a diagram showing a general data format of a control signal conventionally exchanged between a master unit and a slave unit.

FIG. 14 is a flowchart showing an operation of a parent device of a conventional cordless telephone.

FIG. 15 is a flowchart showing an operation in a slave unit of a conventional cordless telephone.

[Explanation of symbols]

 1, 6 and 9, antenna 2 slave unit 2a case 3, 7, 40, 42a to 42d stub 4, 42 switch 5 internal circuit 10 metal plate 41 rotary switch 43 received signal strength detection circuit 44 stub circuit

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location H04B 1/18 A 9298-5K H04Q 7/38

Claims (6)

[Claims] 1. A cordless telephone including a master unit connected to a telephone line and a slave unit connected to the master unit via a wireless line, wherein impedance matching between an antenna of the slave unit and an internal circuit is performed. A cordless telephone characterized in that the cordless handset is provided with a stub and a changeover switch for connecting and disconnecting the stub and the antenna. 2. A cordless telephone including a master unit connected to a telephone line and a slave unit connected to the master unit via a wireless line, wherein impedance matching between an antenna of the slave unit and an internal circuit is performed. A stub group composed of a plurality of types of stubs, a selection switch for selecting a desired stub among the plurality of types of stubs and at least one of contacting and separating the stub and the antenna, and the slave unit, wherein Cordless phone to do. 3. A cordless telephone having a master unit connected to a telephone line and a slave unit connected to the master unit via a wireless line, wherein impedance matching between an antenna of the slave unit and an internal circuit is performed. A stub group consisting of a plurality of types of stubs, and the strength of the received signal from the master unit is detected, and when the strength of the received signal is smaller than a predetermined threshold value, the plurality of types of stubs are sequentially switched and connected to the antenna. A cordless telephone, comprising: a reception signal strength detection circuit for: 4. A cordless telephone including a master unit connected to a telephone line and a slave unit connected to the master unit via a wireless line, wherein impedance matching between an antenna of the slave unit and an internal circuit is performed. A stub group consisting of a plurality of types of stubs, and the strength of the received signal from the master unit is detected, and when the strength of the received signal is smaller than a predetermined threshold value, the plurality of types of stubs are sequentially switched and connected to the antenna. A cordless telephone, characterized in that the slave unit is provided with a received signal strength detection circuit that performs: and a changeover switch that connects and disconnects the stub and the antenna. 5. A cordless telephone having a master unit connected to a telephone line and a slave unit connected to the master unit via a wireless line, wherein the cordless telephone is slidable with respect to a rod-shaped antenna of the slave unit. A cordless telephone characterized in that a stub is provided and a loop antenna is formed when the stub is moved to the uppermost part of the rod-shaped antenna. 6. A cordless telephone having a master unit connected to a telephone line and a slave unit connected to the master unit via a wireless line, wherein a micro loop antenna for receiving radio waves from the master unit, A cordless telephone, wherein the slave unit is provided with: a metal plate that is in contact with the minute loop antenna to perform impedance matching between the minute loop antenna and an internal circuit.