Antenna device and communication device

• US 8,472,907 B2
• Filed: 12/01/2010
• Issued: 06/25/2013
• Est. Priority Date: 12/28/2009
• Status: Active Grant

• Current Assignee: Fujitsu Limited
• Original Assignee: Fujitsu Limited
• Inventors: Yamagajo, Takashi, Takano, Takeshi
• Primary Examiner(s): AKINYEMI, AJIBOLA A
• Application Number:
  US12/957,846
• Publication Number:
  US 20110159832A1
• Time in Patent Office: 937 Days
• Field of Search: 452/69, 455/269
• US Class Current: 455/269
• 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: H01Q 5/335 at the feed, e.g. for impedance matching
• CPC Class Codes: H01Q 5/357 using a single feed point
• CPC Class Codes: H01Q 9/145 by varying the electrical length
• CPC Class Codes: H01Q 9/40 Element having extended radiating surface

Abstract

An antenna device includes: a substrate; a radiating electrode formed on the substrate, a ground electrode formed on the substrate and disposed opposite the radiating electrode, a feed line as a distributed constant transmission line connected via a feed point to the radiating electrode, at least one impedance matching element for impedance-matching the radiating electrode at a prescribed signal frequency by being connected in parallel with the radiating electrode to the feed line at a position a prescribed distance away from the feed point, and a switch, interposed between the at least one impedance matching element and the feed line, for connecting or disconnecting the at least one impedance matching element to or from the feed line in accordance with a prescribed control signal.

Claims

1. An antenna device comprising:

a substrate;

a radiating electrode formed on said substrate;

a ground electrode formed on said substrate and disposed opposite said radiating electrode;

a feed line as a distributed constant transmission line connected via a feed point positioned at one end of said feed line to said radiating electrode;

an impedance matching element for impedance-matching said radiating electrode at a prescribed signal frequency by being connected in parallel with said radiating electrode to said feed line at a position a prescribed distance away from said feed point; and

a switch, interposed between said impedance matching element and said feed line, for connecting or disconnecting said impedance matching element to or from said feed line in accordance with a prescribed control signal, wherein

one end of said impedance matching element is connected to said switch and the other end of said impedance matching element is connected to said ground electrode, and wherein

the other end of said feed line is connected to a communication circuit, and wherein

said prescribed distance is determined so that when said impedance matching element is connected to said feed line, combined conductance of said radiating electrode and said feed line becomes equal to the conductance of the communication circuit, and wherein

said prescribed distance is determined by equation

2. The antenna device according to claim 1, wherein only said feed line is interposed between said feed point and said switch.

3. The antenna device according to claim 1, wherein said impedance matching element has an inductance that compensates so as to cancel out a susceptance component that said radiating electrode and said feed line have when said impedance matching element is connected to said feed line.

4. The antenna device according to claim 3, wherein the inductance that said impedance matching element has is determined by equation

5. The antenna device according to claim 1, further comprising:

a second impedance matching element for impedance-matching said radiating electrode at a second signal frequency, which is different from said prescribed signal frequency, by being connected in parallel with said radiating electrode to said feed line at a position a second prescribed distance away from said feed point; and

a second switch, interposed between said second impedance matching element and said feed line, for connecting or disconnecting said second impedance matching element to or from said feed line in accordance with a prescribed control signal, and wherein one end of said second impedance matching element is connected to said second switch and the other end of said second impedance matching element is connected to said ground electrode, and wherein

only one or the other of said impedance matching element or said second impedance matching element is connected to said feed line or both are disconnected from said feed line.

6. The antenna device according to claim 1, wherein said feed line includes a first sub-feed line and a second sub-feed line as distributed constant transmission lines connected in parallel between said feed point and said switch, said antenna device further comprising:

a second switch, interposed between one end of each of said first and second sub-feed lines and said feed point, for connecting said first sub-feed line or said second sub-feed line to said radiating electrode in accordance with a second control signal; and

a third switch, interposed between the other end of each of said first and second sub-feed lines and said switch, for connecting to said switch either said first sub-feed line or said second sub-feed line, whichever is connected to said radiating electrode by said second switch in accordance with said second control signal, and wherein

said first sub-feed line has a length that impedance-matches said radiating electrode at said prescribed signal frequency when said first sub-feed line is connected both to said radiating electrode and to said impedance matching element via said switch, and

said second sub-feed line has a length that impedance-matches said radiating electrode at third signal frequency when said second sub-feed line is connected both to said radiating electrode and to said impedance matching element via said switch.

7. The antenna device according to claim 6, further comprising a third impedance matching element, connected to said switch so as to be in parallel with said impedance matching element, for impedance-matching said radiating electrode at a fourth signal frequency, and wherein

said switch connects said impedance matching element to said feed line when said antenna device transmits or receives a signal having said prescribed signal frequency, and connects said third impedance matching element to said feed line when said antenna device transmits or receives a signal having said fourth signal frequency.

8. An antenna device comprising:

a substrate;

a radiating electrode formed on said substrate;

a ground electrode formed on said substrate and disposed opposite said radiating electrode;

a feed line connected via a feed point to said radiating electrode and having a plurality of sub-feed lines as distributed constant transmission lines connected in parallel at one end to said feed point, wherein said plurality of sub-feed lines have different lengths from each other that impedance-match said radiating electrode at different signal frequencies;

an impedance matching element connected in parallel to each of said plurality of sub-feed lines at the other end thereof;

a first switch, interposed between said feed point and one end of each of said plurality of sub-feed lines, for connecting one of said plurality of sub-feed lines to said radiating electrode in accordance with a prescribed control signal; and

a second switch, interposed between said impedance matching element and the other end of each of said plurality of sub-feed lines, for connecting to said impedance matching element one of said plurality of sub-feed lines that is connected to said radiating electrode by said first switch in accordance with said prescribed control signal, and wherein

wherein said prescribed distance is determined so that when said impedance matching element is connected to said feed line, combined conductance of said radiating electrode and said feed line becomes equal to the conductance of the communication circuit, and wherein

said prescribed distance is determined by equation

9. A communication device comprising:

an antenna which comprises

a substrate,

a radiating electrode formed on said substrate,

a ground electrode formed on said substrate and disposed opposite said radiating electrode,

a feed line as a distributed constant transmission line connected via a feed point positioned at one end of said feed line to said radiating electrode,

an impedance matching element for impedance-matching said radiating electrode at prescribed signal frequency by being connected in parallel with said radiating electrode to said feed line at a position a prescribed distance away from said feed point, and

a switch, interposed between said impedance matching element and said feed line, for connecting or disconnecting said impedance matching element to or from said feed line;

a control unit which generates a control signal for determining whether or not to operate said switch to connect said impedance matching element to said feed line in accordance with a frequency band used by a communication application, and which sends said control signal to said antenna; and

a radio processing unit which receives via said antenna a signal having a frequency falling within the frequency band used by said communication application, and which demodulates said received signal, wherein

one end of said impedance matching element is connected to said switch and the other end of said impedance matching element is connected to said ground electrode, and wherein

the other end of said feed line is connected to said radio processing unit, and wherein

wherein said prescribed distance is determined so that when said impedance matching element is connected to said feed line, combined conductance of said radiating electrode and said feed line becomes equal to the conductance of the communication circuit, and wherein

said prescribed distance is determined by equation