ANTENNA DEVICE

• US 20110134003A1
• Filed: 04/30/2009
• Published: 06/09/2011
• Est. Priority Date: 06/27/2008
• Status: Active Grant

• Current Assignee: Toyota Jidosha Kabushiki Kaisha (Toyota Motor Corporation)
• Original Assignee: Toyota Jidosha Kabushiki Kaisha (Toyota Motor Corporation)
• Inventors: Okada, Hiroki
• Granted Patent: US 9,160,073 B2
• Time in Patent Office: Days
• US Class Current: 343/745
• CPC Class Codes: H01Q 23/00 Antennas with active circuits or circuit elements integrated within them or attached to them
• CPC Class Codes: H01Q 9/0407 Substantially flat resonant element parallel to ground plane, e.g. patch antenna dipole H01Q9/285; monopole H01Q9/40
• CPC Class Codes: H01Q 9/0442 with particular tuning means
• CPC Class Codes: H01Q 9/30 with feed to end of elongated active element, e.g. unipole H01Q9/44 takes precedence
• CPC Class Codes: H03J 3/185 with varactors, i.e. voltage variable reactive diodes
• CPC Class Codes: H03K 17/60 the devices being bipolar transistors bipolar transistors having four or more electrodes H03K17/72
• CPC Class Codes: H04B 1/0458 Arrangements for matching and coupling between power amplifier and antenna or between amplifying stages matching circuits in general H03H

Abstract

An antenna device includes an antenna unit, a power supply terminal and a time constant circuit. The antenna unit includes an antenna element and a variable capacitance element that is variable in capacitance in accordance with a voltage applied to the variable capacitance element, and resonates in such a manner that the antenna element and the variable capacitance element cooperate with each other. The power supply terminal supplies the voltage applied to the variable capacitance element. The time constant circuit gradually increases the voltage applied to the variable capacitance element when a voltage applied to the power supply terminal is changed from an off state to an on state.

Claims

1. An antenna device that performs at least one of transmission of radio waves in a first frequency band and radio waves in a second frequency band that is lower in frequency than the first frequency band or reception of radio waves in the first frequency band and radio waves in the second frequency band, characterized by comprising:

an antenna unit that includes an antenna element and a variable capacitance element that is variable in capacitance in accordance with a voltage applied to the variable capacitance element, and that resonates in such a manner that the antenna element and the variable capacitance element cooperate with each other;

a power supply terminal that supplies the voltage applied to the variable capacitance element; and

a time constant circuit that gradually increases the voltage applied to the variable capacitance element when a voltage applied to the power supply terminal is changed from an off state to an on state.

2. The antenna device according to claim 1, wherein the time constant circuit includes a resistor and a capacitor that are connected in series, one end of each of the resistor and the capacitor is connected to a node of the variable capacitance element and the antenna element, the other end of the capacitor is grounded, and the other end of the resistor is connected to the power supply terminal.

3. The antenna device according to claim 2, characterized by further comprising a discharge unit that discharges electric charge stored in the capacitor when the voltage applied to the power supply terminal is changed from the on state to the off state.

4. The antenna device according to claim 3, wherein the discharge unit includes a PNP transistor, a base terminal of the PNP transistor is connected to the power supply terminal, an emitter terminal of the PNP transistor is connected to a node of the capacitor and the resistor, and a collector terminal of the PNP transistor is grounded.

5. The antenna device according to claim 2, wherein the time constant circuit further includes at least one resistor that is connected in parallel with the capacitor.

6. The antenna device according to claim 1, wherein the time constant circuit has a time constant that is longer than a duration during which the radio waves in the second frequency band are transmitted or received.

7. The antenna device according to claim 1, wherein the voltage applied to the power supply terminal is equal to a voltage applied to a transmitting circuit or receiving circuit connected to the antenna device.

8. The antenna device according to any one of claims 1 to 7, wherein the variable capacitance element is a varicap diode.

9. The antenna device according to claim 3, wherein the antenna device is able to continuously transmit or receive the radio waves in the second frequency band by repeatedly switching between the on and off states of the voltage applied to the power supply terminal.

10. The antenna device according to claim 3, wherein the antenna device is able to continuously transmit or receive the radio waves in the first frequency band in such a manner that the on state of the voltage applied to the power supply terminal is continued for a period of time that is longer than a time constant of the time constant circuit.

11. The antenna device according to claim 3, wherein the antenna device is able to transmit or receive the radio waves in the first frequency band in such a manner that the on state of the voltage applied to the power supply terminal is continued for a period of time that is longer than a time constant of the time constant circuit, and is able to transmit or receive the radio waves in the second frequency band in such a manner that the voltage applied to the power supply terminal is turned off from the on state and is then turned on again.

12. An antenna device characterized by comprising:

an antenna element;

a switching element that is connected between one end of the antenna element and a ground;

a power supply terminal that supplies a voltage applied to the switching element; and

a time constant circuit that gradually increases the voltage applied to the switching element when a voltage applied to the power supply terminal is changed from an off state to an on state, wherein

the switching element blocks a high frequency immediately after the voltage applied to the power supply terminal is changed from the off state to the on state, and passes the high frequency when a period of time that is longer than a time constant of the time constant circuit has elapsed.

13. The antenna device according to claim 12, wherein the antenna element is a half-loop antenna element.

14. The antenna device according to claim 12, wherein the time constant circuit includes a resistor and a capacitor that are connected in series, one end of each of the resistor and the capacitor are connected to a node of the switching element and the antenna element, the other end of the capacitor is grounded, and the other end of the resistor is connected to the power supply terminal.

15. The antenna device according to claim 14, characterized by further comprising a discharge unit that discharges electric charge stored in the capacitor when the voltage applied to the power supply terminal is changed from the on state to the off state.

16. The antenna device according to claim 14, wherein the discharge unit includes a PNP transistor, a base terminal of the PNP transistor is connected to the power supply terminal, an emitter terminal of the PNP transistor is connected to a node of the capacitor and the resistor, and a collector terminal of the PNP transistor is grounded.

17. The antenna device according to any one of claims 12 to 16, wherein the switching element is a pin diode.

18. The antenna device according to any one of claims 12 to 16, wherein the switching element is a switching diode.

19. The antenna device according to claim 13, wherein the voltage applied to the power supply terminal is repeatedly switched between the on state and the off state when the antenna characteristic of an inverse L-antenna or an inverse F-antenna is required.

20. The antenna device according to claim 13, wherein the voltage applied to the power supply terminal is continuously turned on for a period of time that is longer than a time constant of the time constant circuit when the antenna characteristic of a loop antenna is required.