Matching circuit and antenna apparatus

• US 5,874,926 A
• Filed: 03/10/1997
• Issued: 02/23/1999
• Est. Priority Date: 03/11/1996
• Status: Expired due to Term

• Current Assignee: Murata Manufacturing Co Limited
• Original Assignee: Murata Manufacturing Co Limited
• Inventors: Suga, Yoichiro, Oida, Toshifumi, Tsuru, Teruhisa, Mandai, Harufumi
• Primary Examiner(s): Wong, Don
• Assistant Examiner(s): NGUYEN, HOANG V
• Application Number:
  US08/815,277
• Time in Patent Office: 715 Days
• Field of Search: 343/860, 343/713, 343/861, 343/704, 343/728, 333/17.3, 333/32, 455/115
• US Class Current: 343/860
• CPC Class Codes: H01Q 1/362 for broadside radiating helical antennas
• CPC Class Codes: H01Q 1/38 formed by a conductive layer on an insulating support patch antennas H01Q9/0407; microstrip dipole antennas H01Q9/065; microstrip slot antennas H01Q13/106; transmission line microstrip antennas H01Q13/206; manufacturing reflecting surfaces using insulating material for supporting the reflecting surface H01Q15/142
• CPC Class Codes: H03H 7/40 Automatic matching of load impedance to source impedance
• CPC Class Codes: H04B 1/18 Input circuits, e.g. for coupling to an antenna or a transmission line coupling networks between antennas or lines and receivers independent of the nature of the receiver H03H

Abstract

A matching circuit and an antenna apparatus which, though small-sized, can be used in a radio apparatus which transmits and receives radio waves having a wide range of frequencies. A matching circuit includes an inductance element formed of a chip inductor connected in series with an antenna body, a first capacitance element formed of a trimmer capacitor, and a second capacitance element formed of a chip capacitor, which capacitance elements are connected between respective ends of the inductance element and a ground terminal, and thus in parallel to the antenna body. One end of the inductance element is connected to the power supply terminal of the antenna body, and the other end is connected to a power source for applying a voltage to the antenna body. The first capacitance element is connected between a ground and the connection point of the power supply terminal of the antenna body and the inductance element. The second capacitance element is connected between a ground and the connection point of the inductance element and the power source.

Claims

1. A matching circuit connected to an antenna body, the antenna body comprising a radiation conductor and a power supply terminal and having an equivalent circuit comprising an inductance component, a resistance component and a capacitance component connected in series, said matching circuit comprising an inductance element connected in series with said antenna body, first and second capacitance elements connected to respective terminals of the inductance element in parallel with the antenna body, the first capacitance element comprising a variable capacitance element;

and further wherein the second capacitance element comprises a fixed capacitance element.

2. The matching circuit of claim 1, wherein the resonance frequency of an antenna apparatus comprising the antenna body and the matching circuit can be varied by varying the variable capacitance element.

3. The matching circuit of claim 2, wherein the variable capacitance element can be varied over a range of resonance frequencies of the antenna apparatus.

4. The matching circuit of claim 3, wherein the variable capacitance comprises a varactor diode responsive to an applied voltage thereby to adjust the resonance frequency over the range of resonance frequencies.

5. The matching circuit of claim 1, further comprising a fixed capacitance element in series with said first capacitance element.

6. The matching circuit of claim 1, further comprising a fixed capacitance component in series with said second capacitance element.

7. The matching circuit of claim 1, further comprising a fixed capacitance element in parallel with said first capacitance element.

8. The matching circuit of claim 1, further comprising a fixed capacitance element in parallel with said second capacitance element.

9. An antenna apparatus comprising an antenna body comprising a radiation conductor and a power supply terminal, the antenna body having an equivalent circuit comprising an inductance component, a resistance component and a capacitance component connected in series, and further comprising a matching circuit provided on a power supply terminal side of the antenna body, the matching circuit comprising an inductance element connected in series with the antenna body, first and second capacitance elements connected to respective terminals of the inductance element, the first capacitance element comprising a variable capacitance;

and further wherein the second capacitance element comprises a fixed capacitance element.

10. The antenna apparatus of claim 9, wherein the resonance frequency of an antenna apparatus comprising the antenna body and the matching circuit can be varied by varying the variable capacitance element.

11. The antenna apparatus of claim 10, wherein the variable capacitance element can be varied over a range of resonance frequencies of the antenna apparatus.

12. The antenna apparatus of claim 11, wherein the variable capacitance comprises a varactor diode responsive to an applied voltage thereby to adjust the resonance frequency over the range of resonance frequencies.

13. The antenna apparatus of claim 9, further comprising a fixed capacitance element in series with said first capacitance element.

14. The antenna apparatus of claim 9, further comprising a fixed capacitance component in series with said second capacitance element.

15. The antenna apparatus of claim 9, further comprising a fixed capacitance element in parallel with said first capacitance element.

16. The antenna apparatus of claim 9, further comprising a fixed capacitance element in parallel with said second capacitance element.

17. A matching circuit connected to an antenna body, the antenna body comprising a radiation conductor and a power supply terminal and having an equivalent circuit comprising an inductance component, a resistance component and a capacitance component connected in series, said matching circuit comprising an inductance element connected in series with said antenna body, first and second capacitance elements connected between respective terminals of the inductance element and a ground terminal, the first capacitance element comprising a variable capacitance element;

and further wherein the second capacitance element comprises a fixed capacitance element.

18. The matching circuit of claim 17, wherein the resonance frequency of an antenna apparatus comprising the antenna body and the matching circuit can be varied by varying the variable capacitance element.

19. The matching circuit of claim 18, wherein the variable capacitance element can be varied over a range of resonance frequencies of the antenna apparatus.

20. The matching circuit of claim 19, wherein the variable capacitance comprises a varactor diode responsive to an applied voltage thereby to adjust the resonance frequency over the range of resonance frequencies.

21. The matching circuit of claim 17, further comprising a fixed capacitance element in series with said first capacitance element.

22. The matching circuit of claim 17, further comprising a fixed capacitance component in series with said second capacitance element.

23. The matching circuit of claim 17, further comprising a fixed capacitance element in parallel with said first capacitance element.

24. The matching circuit of claim 17, further comprising a fixed capacitance element in parallel with said second capacitance element.

25. An antenna apparatus comprising an antenna body comprising a radiation conductor and a power supply terminal, the antenna body having an equivalent circuit comprising an inductance component, a resistance component and a capacitance component connected in series, and further comprising a matching circuit provided on a power supply terminal side of the antenna body, the matching circuit comprising an inductance element connected in series with the antenna body, first and second capacitance elements connected between respective ends of the inductance element and a ground terminal, the first capacitance element comprising a variable capacitance;

and further wherein the second capacitance element comprises a fixed capacitance element.

26. The antenna apparatus of claim 25, wherein the resonance frequency of an antenna apparatus comprising the antenna body and the matching circuit can be varied by varying the variable capacitance element.

27. The antenna apparatus of claim 26, wherein the variable capacitance element can be varied over a range of resonance frequencies of the antenna apparatus.

28. The matching circuit of claim 27, wherein the variable capacitance comprises a varactor diode responsive to an applied voltage thereby to adjust the resonance frequency over the range of resonance frequencies.

29. The antenna apparatus of claim 25, further comprising a fixed capacitance element in series with said first capacitance element.

30. The antenna apparatus of claim 25, further comprising a fixed capacitance component in series with said second capacitance element.

31. The antenna apparatus of claim 25, further comprising a fixed capacitance element in parallel with said first capacitance element.

32. The antenna apparatus of claim 25, further comprising a fixed capacitance element in parallel with said second capacitance element.