JP2006310995A - Antenna system and mobile wireless communication equipment employing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a dual band antenna system that eliminates degradation of a radiation efficiency due to interference between two elements adopted by prior arts, can be downsized, and reduces a loss caused by an operating frequency changeover switch to the utmost extent. <P>SOLUTION: The dual band antenna system includes: a single antenna element 1; first and second matching circuits 4, 5 respectively connected to first and second feeding parts 2, 3 located at both ends of the element 1 and compatible with first and second operating frequency bands; and a single switch 6 for alternatively connecting either of the matching circuits 4, 5 to a wireless circuit 7, and the matching circuits 4, 5 are configured such that the second feeding part 3 is almost opened when the switch 6 selects the first matching circuit 4, and the first feeding part 2 is almost opened when the switch 6 selects the second matching circuit 5. Thus, the dual band antenna system (antenna system compatible with dual band) can be realized by having only to use the single element and the single switch so as to prevent degradation in the radiation efficiency due to the interference between the two elements adopted by prior arts and increase in the switch loss caused by adoption of two switches by prior arts. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an antenna device and a portable wireless communication device using the antenna device, and more particularly to improvement of a dual-band antenna device that can handle different frequency bands.

  2. Description of the Related Art In recent years, with mobile phones, which are one of portable radio devices, with the increase in subscribers, the number of call channels has been insufficient with only the frequency of the 800 MHz band that has been conventionally used. Subscription to frequencies above 9 GHz is also recommended. Conventionally, mobile phones have models for each frequency band, and when making a call using different frequency bands, it is necessary to purchase multiple models corresponding to those frequency bands, the telephone number can not be shared, There is an inconvenience of having to carry a plurality of mobile phones.

  In view of this, a dual band machine has been developed in which two frequency bands can be used with one mobile phone. For example, there are ones that can be used in two frequency bands, an 800 MHz band and a 1.5 GHz band that is about twice that, and ones that can be used in two frequency bands, an 800 MHz band and a 1.9 GHz band. In such a dual-band machine, it is required that not only the radio circuit unit but also the antenna be configured to operate in two frequency bands.

  On the other hand, in recent mobile phones, models with an antenna built in a housing are mainstream, but the housing size tends to be smaller than the conventional one, and the volume of the antenna is also becoming smaller.

  A dual-frequency antenna in such a dual band machine will be described with reference to FIG. Such a dual-frequency antenna is configured using a first antenna element 10 that operates in a low frequency band and a second antenna element 20 that operates in a high frequency band, and approximately λ in each frequency band. The electrical length is adjusted to / 4. As these antenna elements, since the volume of the antenna is made as small as possible by using a coil-shaped or meander-shaped element, the radiation resistance of the antenna becomes small. Therefore, since the antenna alone cannot be matched with the radio circuit, a matching circuit 40 is provided between the antenna power supply unit 30 and the radio circuit 50, and the first frequency band and the second frequency band are provided. Each of them is designed to be consistent.

  However, since the impedance elements constituting the matching circuit 40 differ in impedance depending on the frequency, when the matching between the first frequency band and the radio circuit is optimally adjusted, the matching with the second frequency band is reduced. In contrast, when the matching with the second frequency band is optimally adjusted, there is a problem that the matching with the first frequency band cannot be achieved. Therefore, as shown in FIG. 13, there is a configuration in which two matching circuits 40 and 41 are provided, and band matching switches 60 and 61 are used to select optimum matching circuits for the two antenna elements 10 and 20 respectively. .

  In addition, referring to Patent Document 1, instead of using two antenna elements, one antenna element is used, and the electric length of the element is changed by two feeding parts so as to correspond to two frequency bands. Technology is disclosed. Also in this case, for each of the two frequency bands, two matching circuits are provided in order to optimize the matching with the radio circuit, and these two matching circuits are switched simultaneously with the switching of the power feeding unit. It has become.

JP 2004-172714 A

  In the configuration shown in FIG. 13, in order to select the matching circuits 40 and 41, two switches are required before and after these matching circuits, which increases the power passing loss and deteriorates the radiation efficiency of the antenna. In addition to the drawbacks, the two antenna elements 10 and 20 are required, which is one of the factors that prevent the miniaturization of the apparatus. Further, there is a drawback that an unused antenna element interferes with the used antenna element and causes deterioration in radiation efficiency.

  The technique of Patent Document 1 also has a problem in that a switch is provided before and after the matching circuit for switching the power feeding unit and switching of the matching circuit, resulting in an increase in power transmission loss.

  In addition, when changing the electrical length of one antenna element, an antenna element having a length corresponding to a long electrical length corresponding to a low frequency band is prepared, and corresponding to a short electrical length corresponding to a high frequency band. In some cases, the power feeding unit is switched to the intermediate point, and as a result, as shown in FIGS. 12 and 13, it is the same as using two antenna elements, which reduces the size of the device. Has the problem of not contributing.

  Further, when the antenna element is used in a high frequency band, about half of the antenna elements are not used. However, this causes interference with the antenna elements used and also causes deterioration in radiation efficiency.

  An object of the present invention is to provide an antenna device that eliminates switch loss, reduces size, and does not cause deterioration of radiation efficiency, and a portable wireless communication device using the antenna device.

  An antenna device according to the present invention is an antenna device that can be adapted to different first and second frequency bands, and is connected to an antenna element and first and second terminals at both ends of the antenna element, respectively. First and second matching circuits corresponding to the first and second frequency bands, and a switch for selectively connecting the first and second matching circuits to a radio circuit, and The second terminal is substantially open when one matching circuit is selected, and the first terminal is substantially open when the second matching circuit is selected by the switch. It is characterized by comprising a matching circuit.

  Each of the first and second matching circuits has an impedance viewed from each of the first and second terminals when the other matching circuit is selected by the switch. It is characterized by being configured to be large for each of one frequency band.

  The first matching circuit has an impedance element inserted in series and in parallel with the first terminal, and the second matching circuit is inserted in series with the second terminal. Each of the first and second matching circuits includes an impedance element inserted in series and in parallel with each of the first and second terminals; and And a switching element that controls on / off of parallel connection of impedance elements inserted in the.

  A portable wireless communication device according to the present invention uses the antenna device described above.

  The operation of the present invention will be described. In an antenna device adaptable to different first and second frequency bands, the first and second frequency bands are connected to the first and second terminals, which are both ends of a single antenna element, respectively. The first and second matching circuits are provided, and a single switch is provided for selectively connecting the first and second matching circuits to the radio circuit. When the first matching circuit is selected by the switch, the second terminal of the antenna element is substantially open, and when the second matching circuit is selected, the first terminal is substantially open. Thus, these matching circuits are configured.

  Thus, a dual-band antenna can be realized only by using a single antenna element and a single switch, and deterioration of radiation efficiency due to interference between elements and increase in switch loss can be suppressed.

  According to the present invention, even when a single antenna element is used, there is no interference between antenna elements, no switch loss, and the like, and it is possible to optimally adjust matching to two different frequency bands. There is.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing an embodiment of the present invention. Referring to FIG. 1, a dual-frequency antenna device according to the present invention includes a meander antenna 1 as an antenna element, first and second feeding units 2 and 3 at both ends of the meander antenna 1, and these feeding units 2 and 3. The first and second matching circuits 4 and 5 have one end connected to the other end and the other end connected to the switch 6, a band changeover switch 6, and a radio circuit 7 for the antenna 1.

  As shown in the Smith chart of FIG. 2, the meander antenna 1 has an electrical length of about λ / 4 between a first frequency band and a second frequency band higher than the first frequency band. The first and second power feeding units 2 and 3 are connected to both ends of the meander antenna 1. And these 1st and 2nd electric power feeding parts 2 and 3 are connected to the single band change switch 6 via the corresponding 1st and 2nd matching circuits 4 and 5, respectively. The wireless circuit 7 and the first and second matching circuits 4 and 5 are connected through the switch 6.

  A method for adjusting the matching circuit of the antenna device will be described. First, matching in the first frequency band is intended. In this case, the switch 6 is connected to the first power feeding unit 2. A circuit diagram at this time is shown in FIG. 3, and the second feeding unit 3 is opened, so that the first feeding unit 2 serves as a feeding point to the antenna 1, and the second feeding unit 3 serves as an open end. Thus, it operates as an inverted L-shaped antenna.

  In this state, the first matching circuit 4 is adjusted so as to match with the first frequency band. In this example, an inductance L1 is connected in series and an inductance L2 is connected in parallel. 4A shows the input impedance in the first frequency band after matching, and FIG. 4B is a Smith chart thereof. Thus, it can be seen that good characteristics are exhibited in the first frequency band.

  Next, the matching of the second frequency band is adjusted. In this case, the switch 6 is connected to the second power feeding unit 3. Accordingly, since the first power feeding unit 2 is opened, the first matching circuit 4 is equivalent to the inductance L1 and L2 inserted in series in the first power feeding unit 2. Here, if the combined impedance of the inductances L1 and L2 is made sufficiently large in the second frequency band, the first feeding unit 2 is equivalent to an open circuit when viewed from the meander antenna 1, and thus this antenna is The second feeding unit 3 serves as a feeding point, and the first feeding unit 2 serves as a substantially open end, and operates as an inverted L-shaped antenna.

  In this state, the second matching circuit 5 is adjusted to match the second frequency band. In this example, matching is achieved by inserting a capacitor C1 in series. FIG. 6A shows the input impedance in the second frequency band after matching, and FIG. 6B shows the Smith chart. Thus, it can be seen that good characteristics can be obtained even in the second frequency band.

  Note that when switching to the first frequency band after matching in the second frequency band, the second matching circuit 5 has only a capacitor inserted in series, so the switch Even if 6 is disconnected from the second matching circuit 5, the capacitor is connected to the antenna 1, but the second power feeding unit 3 is open, so that there is nothing for the first frequency band. There is no influence, and good characteristics can be obtained in each frequency band.

  In the above example, the meander antenna is used as the antenna element. However, the present invention is not limited to this. For example, the plate antenna 11 as shown in FIG. 7, the linear antenna 12 as shown in FIG. As shown, a helical antenna 13 or a dielectric loaded antenna 14 formed on a dielectric 15 as shown in FIG. 10 can be used.

  As described above, good matching can be achieved in two different frequency bands. However, when the impedance condition of the first matching circuit 4 cannot be sufficiently large for the second frequency band, The matching circuit 5 requires a parallel impedance element, and when the impedance of the circuit 5 cannot be sufficiently increased in the first frequency band, the configuration shown in FIG. 11 is preferable.

  11, the same parts as those in FIG. 1 are denoted by the same reference numerals. Referring to FIG. 11, in both matching circuits 4 and 5, PIN diodes D1 and D2 are used, respectively, and switching signals are supplied to these PIN diodes D1 and D2 so as to be turned on / off. The impedance of the matching circuit is not large enough.

  That is, in the first matching circuit 4, a switching signal is supplied to the PIN diode D1 using the resistor R1, the capacitor C3, and the choke coil L3. When the first matching circuit 4 is not used, By turning off the PIN diode D1 and turning off the parallel connection state of the parallel connection element X2, the first power feeding unit 2 of the meander antenna 1 is opened. C2 is a DC blocking capacitor, and X1 and X2 are equivalent to L1 and L2 in FIG. 3, and are series and parallel matching impedance elements.

  In the second matching circuit 5, a switching signal is supplied to the PIN diode D2 using the resistor R2, the capacitor C5, and the choke coil L4, and when the second matching circuit 5 is not used. By turning off the PIN diode D2 and turning off the parallel connection state of the parallel connection element X4, the second power feeding unit 3 of the meander antenna 1 is opened. C4 is a DC blocking capacitor, and X3 and X4 are series and parallel matching impedance elements.

  Each of the above-described embodiments is suitable for use in a mobile phone, but is not limited to this, and is clearly applicable to a wide range of portable wireless communication devices such as a PHS and a PDA having a wireless communication function. .

It is a figure which shows the structure of one embodiment of this invention. It is an example of a Smith chart of the antenna device of FIG. It is a figure explaining the adjustment of the matching with respect to the 1st frequency band of the antenna apparatus of FIG. It is a figure which shows the characteristic of the matching result by FIG. It is a figure explaining the adjustment of the matching with respect to the 2nd frequency band of the antenna apparatus of FIG. It is a figure which shows the characteristic of the matching result by FIG. It is a figure which shows other embodiment of this invention. It is a figure which shows other embodiment of this invention. It is a figure which shows another embodiment of this invention. It is a figure which shows another embodiment of this invention. It is a figure which shows other embodiment of this invention. It is a figure which shows an example of the conventional antenna device. It is a figure which shows the other example of the conventional antenna device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Meander antenna 2 1st electric power feeding part 3 2nd electric power feeding part 4 1st matching circuit 5 2nd matching circuit 6 Band change switch 7 Radio circuit 11 Plate-shaped antenna 12 Linear antenna 13 Helical antenna 14 Dielectric loading antenna

Claims (6)

An antenna device adaptable to different first and second frequency bands, wherein the first and second frequencies are respectively connected to an antenna element and first and second terminals at both ends of the antenna element. A first and second matching circuit corresponding to the band, and a switch that alternatively connects the first and second matching circuits to the radio circuit,
When the first matching circuit is selected by the switch, the second terminal is substantially open, and when the second matching circuit is selected by the switch, the first terminal is substantially open. An antenna device characterized by comprising these matching circuits.   Each of the first and second matching circuits has an impedance viewed from each of the first and second terminals when the other matching circuit is selected by the switch. 2. The antenna device according to claim 1, wherein the antenna device is configured to be large for each of the frequency bands.   The first matching circuit has an impedance element inserted in series and in parallel with the first terminal, and the second matching circuit has an impedance inserted in series with the second terminal. The antenna device according to claim 2, further comprising an element.   Each of the first and second matching circuits turns on and off an impedance element inserted in series and in parallel with each of the first and second terminals and a parallel connection of the impedance element inserted in parallel. The antenna device according to claim 2, further comprising a switch element to be controlled.   5. The antenna device according to claim 1, wherein the antenna element is any one of a meander antenna, a plate antenna, a linear antenna, a helical antenna, and a dielectric loaded antenna.   A portable wireless communication device comprising the antenna device according to claim 1.

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