Radio communication apparatus with retractable antenna and its impedance matching method

• US 6,738,603 B1
• Filed: 06/09/2000
• Issued: 05/18/2004
• Est. Priority Date: 06/10/1999
• Status: Expired due to Fees

• Current Assignee: NEC Corporation
• Original Assignee: NEC Corporation
• Inventors: Saito, Tetsuya
• Primary Examiner(s): Maung, Nay
• Assistant Examiner(s): Gantt, Alan T.
• Application Number:
  US09/590,844
• Time in Patent Office: 1,439 Days
• Field of Search: 455/90, 455/550, 455/128, 455/351, 455/90.1, 455/550.1, 455/129, 455/575.7, 343/702, 343/895, 333/124, 333/17.3, 333/32, 333/173
• US Class Current: 455/90.1
• CPC Class Codes: H01Q 1/244 extendable from a housing along a given path

Abstract

A radio communication apparatus is provided, which realizes a desired impedance matching state between a retractable antenna and a circuit connected thereto in both a situation where the antenna environment is similar to a free space and a situation where the antenna environment is dissimilar from a free space. The apparatus comprises (a) a casing; (b) a retractable antenna having first and second elements joined together; the second element being connected to an internal, circuit provided in the casing; (c) a terminal matching circuit for matching an impedance of the antenna to that of the internal circuit in a first situation where an environment of the antenna is similar to a free space and a second situation where an environment of the antenna is dissimilar from a free space; the terminal matching circuit being configured to provide at least two terminal impedance values for the antenna; and (d) a control circuit for controlling an operation of the terminal matching circuit corresponding to whether the apparatus is placed in the first situation or the second situation; the control circuit controlling the terminal matching circuit in such a way that a first one of the at least two terminal impedance values is selected when the apparatus is placed in the first situation and a second one of the at least two terminal impedance values is selected when the apparatus is placed in the second situation.

Claims

1. A radio communication apparatus comprising:

(a) a casing;

(b) an antenna retractable into said casing;

said antenna having a first element and a second element joined together;

said first element being placed outside even when said antenna is retracted;

said second element being retracted into said casing when said antenna is retracted;

said second element being connected to an internal circuit provided in said casing;

(c) a terminal matching circuit for matching an impedance of said antenna to that of said internal circuit in a first situation where an environment of said antenna is similar to a free space and in a second situation where an environment of said antenna is dissimilar from a free space;

said terminal matching circuit being configured to provide at least two terminal impedance values for said antenna both in the extended state and in the retracted state; and

(d) a control circuit for controlling an operation off said terminal matching circuit corresponding to whether said apparatus is placed in said first situation or said second situation;

said control circuit controlling said terminal matching circuit in such a way that a first one of the at least two terminal impedance values is selected when said apparatus is placed in said first situation and a second one of the at least two terminal impedance values is selected when said apparatus is placed in said second situation.

2. The apparatus according to claim 1, wherein said terminal matching circuit comprises a first termination subcircuit, a second termination subcircuit, and a switch for switching said first and second termination subcircuits by a control signal from said control circuit.

3. The apparatus according to claim 2, wherein said first termination subcircuit is connected to said second element of said antenna when said apparatus is said the first situation, and said second termination subcircuit is connected to said second element of said antenna when said apparatus is in said second situation.

4. The apparatus according to claim 2, wherein said first termination subcircuit is connected to said second element of said antenna when said apparatus is in said first situation, and said first and second termination subcircuits are connected to said second element of said antenna when said apparatus is in said second situation.

5. The apparatus according to claim 1, wherein said first situation includes a stand-by state and a data communication state of said apparatus and said second situation includes a voice message exchange state.

6. The apparatus according to claim 1, further comprising an earphone detection circuit outputting an earphone detection signal to said control circuit;

and wherein said control circuit controls said terminal matching circuit responsive to said earphone detection signal in such a way that said first one of the at least two terminal impedance values is selected.

7. The apparatus according to claim 1, wherein said control circuit is designed to receives an operation selection signal;

and wherein said control circuit controls said terminal matching circuit responsive to said operation selection signal in such a way that the first one of the at least two terminal impedance values is selected when said apparatus is placed in said first situation and the second one of the at least two terminal impedance values is selected when said apparatus is placed in said second situation.

8. The apparatus according to claim 7, wherein the first one of the at least two terminal impedance values is selected when said operation selection signal is a signal ending voice message exchange or a disconnection signal sent from a remote apparatus, and the second one of the at least two terminal impedance values is selected when said operation selection signal is a signal starting voice message exchange.

9. The apparatus according to claim 7, wherein a signal indicating an operation state of said apparatus generated from said reception data is used.

10. An impedance matching method of a radio communication apparatus, said apparatus comprising:

(i) a casing;

(ii) an antenna retractable into said casing;

said antenna having a first element and a second element joined together;

said first element being placed outside even when said antenna is retracted;

said second element being retracted into said casing when said antenna is retracted;

said second element being connected to an internal circuit provided in said casing;

(iii) a terminal matching circuit for matching an impedance of said antenna to that of said internal circuit; and

(iv) a control circuit for controlling an operation of said terminal matching circuit;

said method comprising the steps of;

(a) providing at least two terminal impedance values for said antenna to said terminal matching circuit so as to match said impedance of said antenna to that of said internal circuit in a first situation where an environment of said antenna is similar to a free space and in a second situation where an environment of said antenna is dissimilar from a free space,

said at least two terminal impedance values being provided for both the first and second situations both in the retracted state and in the extended state; and

(b) operating said control circuit in such a way that a first one of the at least two terminal impedance values is selected when said apparatus is placed in said first situation and a second one

of the at least two terminal impedance values is selected when said apparatus is placed in said second situation.

11. The method according to claim 10, wherein said terminal matching circuit is configured to comprise a first termination subcircuit, a second termination subcircuit, and a switch;

and wherein a control signal is sent from said control circuit to switch said first and second termination subcircuits.

12. The method according to claim 11, wherein said first termination subcircuit is connected to said second element of said antenna when said apparatus is in said first situation, and said second termination subcircuit is connected to said second element of said antenna when said apparatus in said second situation.

13. The method according to claim 11, wherein said first termination subcircuit is connected to said second element of said antenna when said apparatus is in said first situation, and said fist and second termination subcircuits are connected to said second element of said antenna when said apparatus is in said second situation.

14. The method according to claim 10, wherein said first situation is set to include a stand-by state and a data communication state of said apparatus and said second situation is set to include a voice message exchange state.

15. The method according to claim 10, wherein an earphone detection circuit outputting an earphone detection signal to said control circuit is provided;

wherein said control circuit controls said terminal matching circuit responsive to said earphone detection signal in such a way that the first one of the at least two terminal impedance values is selected.

16. The method according to claim 10, wherein said control circuit receives an operation selection signal;

and wherein said control circuit controls said terminal matching circuit responsive to said operation selection signal in such a way that the first one of the at least two terminal impedance values is selected when said apparatus is placed in said first situation and the second one of the at least two terminal impedance values is selected when said apparatus is placed in said second situation.

17. The method according to claim 16, wherein the first one of the at least two terminal impedance values is selected when said operation selection signal is a signal ending voice message exchange or a disconnection signal sent from a remote apparatus, and the second one of the at least two impedance values is selected when said operation selection signal is a signal starting voice message exchange.

18. The method according to claim 16, wherein a signal indicating an operation state of said apparatus generated from said reception data is used as said operation selection signal.