JP2007235635A - Multi-frequency resonant antenna and mobile terminal using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a multi-frequency resonant antenna capable of solving a problem of antenna characteristics being narrowed owing to its miniaturization. <P>SOLUTION: An antenna electric length viewed from a switch (#1) 6 forms a λa/4 antenna at a frequency fa, and an antenna electric length viewed from a switch (#2) 7 forms a λb/4 antenna at a frequency fb. In operation of the λb/4 antenna the switch (#1) 6 makes an antenna element 5 and a matching circuit (#1) 2 electrically non-conductive to permit a matching circuit (#2) 3 to be selected at a switch (#2) 7 and a switch (#3) 8. In operation of the λa/4 the switch (#1) 6 makes the antenna element 5 and the matching circuit (#1) 2 electrically conductive to permit an impedance adjusting circuit 4 to be selected at the switch (#2) 7 and the matching circuit (#1) 2 to be selected at the switch (#3) 8. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a multi-frequency resonant antenna and a mobile terminal using the same, and more particularly to an antenna mounted on a mobile terminal such as a mobile phone.

  In recent years, antennas for mobile terminals have been required to be built in a casing of a mobile terminal and support multiple frequencies from the viewpoint of design. In other words, this type of antenna is required to be miniaturized with the miniaturization of the casing of the portable terminal (incorporation in the casing). However, generally, when the antenna is downsized, the resistance becomes low, so that the antenna efficiency is deteriorated and the usable frequency band is narrowed.

  On the other hand, mobile terminals are required to support not only communication with base stations but also various uses such as reception of television broadcasts. In this case, antennas corresponding to a plurality of frequency bands are required. (Multiple frequency support) (see, for example, Patent Documents 1 and 2).

JP 2004-172714 A Japanese Patent Laid-Open No. 11-163620

  In the conventional antenna for a portable terminal described above, it is generally necessary to reduce the size of the antenna in order to incorporate the antenna in the housing. Become.

  Accordingly, an object of the present invention is to provide a multi-frequency resonant antenna and a mobile terminal using the same, which can solve the above-mentioned problems and can solve the narrowing of antenna characteristics due to downsizing.

The multi-frequency resonant antenna according to the present invention has first and second feeding paths for one antenna element, and the antenna element has a λ / 4 element at a different frequency depending on each of the first and second feeding paths. A multi-frequency resonant antenna capable of selecting an electrical length by selecting the first and second feeding paths,
First and second matching circuits provided corresponding to the first and second feeding paths and for impedance matching;
The first power supply path is selected by electrically connecting one of the first and second power supply paths and non-conductive the other of the first and second power supply paths. A switch,
A second switch for selecting conduction or non-conduction between the antenna element and the first matching circuit in the first feeding path;
A short stub including a circuit for adjusting impedance in the second feeding path;
A third switch for selecting connection between the antenna element and any of the second matching circuit and the short stub in the second feeding path;

  A portable terminal according to the present invention is characterized by using the multi-frequency resonant antenna.

  That is, the multi-frequency resonant antenna of the present invention is characterized by providing means for solving the narrowing of the antenna characteristics due to the miniaturization by multi-frequency resonance in the multi-frequency resonant antenna.

  More specifically, in the multi-frequency resonant antenna of the present invention, the antenna electrical length viewed from the first switch is λ / 4 antenna (hereinafter referred to as λa / 4 antenna) at the frequency fa and viewed from the second switch. An antenna electrical length forms a λ / 4 antenna (hereinafter referred to as a λb / 4 antenna) at a frequency fb.

  In the multi-frequency resonant antenna of the present invention, the antenna electrical length can be selected according to the frequency used, and the first switch eliminates the influence of the first matching circuit of the λa / 4 antenna when the λb / 4 antenna is operated. In order to do so, the second switch and the second switch select the second matching circuit. When the λa / 4 antenna operates, the first switch is turned on (ON), the second switch selects the impedance adjustment circuit, and the third switch selects the first matching circuit.

  At this time, the impedance adjustment circuit causes the current to leak from the point A to the second switch during operation of the λa / 4 antenna so that it does not adversely affect the point A to point B (the ground in the impedance adjustment circuit). It plays the role of adjusting the impedance (seeing the grounding point) to open (OPEN) or high impedance close to open.

  With the above configuration, in the multi-frequency resonant antenna of the present invention, it is possible to use an antenna element in which one antenna element is resonated in a plurality of frequency bands, and the frequency used is divided to narrow the antenna by reducing the size of the antenna. It becomes. In addition, optimum design can be made independently for each of the divided frequency bands.

  The present invention has the above-described configuration and operation, so that the effect of narrowing the antenna characteristics due to the miniaturization can be solved.

  Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing the configuration of a multi-frequency resonant antenna according to an embodiment of the present invention. In FIG. 1, a multi-frequency resonant antenna according to an embodiment of the present invention is connected to a radio circuit 1, and an antenna electrical length corresponding to a frequency to be used can be selected. The multi-frequency resonant antenna according to one embodiment of the present invention includes matching circuits (# 1, # 2) 2, 3, an impedance adjustment circuit 4, an antenna element 5, and switches (# 1- # 3) 6-8. It consists of and.

  The switch (# 1) 6 is electrically connected or disconnected between the antenna element 5 and the matching circuit (# 1) 2 by the switching operation. The switch (# 2) 7 electrically connects the antenna element 5 to the matching circuit (# 2) 3 or the impedance adjustment circuit 4 by the switching operation. The switch (# 3) 8 electrically connects the wireless circuit 1 to the matching circuit (# 1) 2 or the matching circuit (# 2) 3 by the switching operation.

  Therefore, in this embodiment, the power supply path # 1 is connected to the antenna element 5 by connecting the wireless circuit 1 → the switch (# 3) 8 → the matching circuit (# 1) 2 → the switch (# 1) 6. The power supply path # 2 is formed by connecting the wireless circuit 1 → the switch (# 3) 8 → the matching circuit (# 2) 3 → the switch (# 2) 7.

  The antenna electrical length viewed from the switch (# 1) 6 forms a λ / 4 antenna (hereinafter referred to as λa / 4 antenna) at the frequency fa, and the antenna electrical length viewed from the switch (# 2) 7 is λ / at the frequency fb. Four antennas (hereinafter referred to as λb / 4 antennas) are formed.

  During operation of the λb / 4 antenna, the switch (# 1) 6 electrically connects the antenna element 5 and the matching circuit (# 1) 2 in order to eliminate the influence of the matching circuit (# 1) 2 of the λa / 4 antenna. And the matching circuit (# 2) 3 is selected by the switch (# 2) 7 and the switch (# 3) 8.

  During the operation of the λa / 4 antenna, the switch (# 1) 6 electrically connects the antenna element 5 and the matching circuit (# 1) 2, selects the impedance adjustment circuit 4 in the switch (# 2) 7, and selects the switch In (# 3) 8, the matching circuit (# 1) 2 is selected.

  At this time, when the λa / 4 antenna is in operation, the impedance adjustment circuit 4 causes the current to leak from the point A on the antenna element 5 to the path from the switch (# 2) 7 to have no adverse effect. It plays the role of adjusting the impedance viewed from [the ground point to the ground (GND) in the impedance adjusting circuit 4] to be open (OPEN) or to have a high impedance close to open.

  With the above configuration, in the multi-frequency resonant antenna according to an embodiment of the present invention, one antenna element 5 is resonated at two frequencies, and impedance matching is independently performed without being influenced by the other circuit at each frequency. It can be performed.

  FIGS. 2A and 2B are diagrams showing examples of selecting frequency bands of a multi-frequency resonant antenna according to an embodiment of the present invention. In the multi-frequency resonant antenna according to one embodiment of the present invention, for example, as shown in FIG. 2A, the frequencies f0 to fA are used in the λa / 4 antenna so as to divide adjacent frequencies, and the frequencies fB to If f0 is used with a λb / 4 antenna) and λa and λb are selected, it is possible to increase the gain even with the antenna element 5 having a narrow specific bandwidth.

  In the multi-frequency resonant antenna according to one embodiment of the present invention, as shown in FIG. 2 (b), if a distant frequency band is selected (frequency f4 to f3 is used as the λa / 4 antenna, frequency f2 to f2 f1 is used with a λb / 4 antenna), and a multi-resonant antenna can be formed.

  As described above, in this embodiment, the power supply path including the switch (# 1) 6, the matching circuit (# 1) 2, and the switch (# 3) 8 for one antenna element 5, the switch (# 2) 7 and By providing two feeding paths called feeding paths by the matching circuit (# 2) 3 and the switch (# 3) 8, the single antenna element 5 can resonate at a plurality of frequencies.

  Further, in this embodiment, when the λa / 4 antenna is operated, the switch (# 2) 7 is grounded to the ground, so that a short stub of λa / 4 is formed from the point A to the point B, and the short as viewed from the point A. The impedance of the stub part is open or close to open, preventing adverse effects due to current leakage from the point A to the switch (# 2) 7 and providing the impedance adjustment circuit 4 in the short stub part. As a result, a degree of freedom can be given to the length design of the short stub portion.

  Furthermore, in the present embodiment, impedance matching can be performed independently in the power supply path to each of the λa / 4 antenna and the λb / 4 antenna without being affected by the other power supply path. Therefore, in this embodiment, it is possible to reduce the size and increase the gain of the multi-frequency resonant antenna.

  In the present invention, the wavelength of the antenna element 5 may be λ / 4 or less or λ / 4 or more. In the present invention, the antenna element 5 may have various shapes such as an inverted L antenna, a helical antenna, and a meander antenna. Furthermore, the present invention can be applied to a portable terminal such as a cellular phone or a PDA (Personal Digital Assistant).

It is a block diagram which shows the structure of the multifrequency resonant antenna by one Example of this invention. (A), (b) is a figure which shows the example of selection of the frequency band of the multifrequency resonant antenna by one Example of this invention.

Explanation of symbols

1 wireless circuit 2 matching circuit (# 1)
3 Matching circuit (# 2)
4 Impedance adjustment circuit 5 Antenna element 6 Switch (# 1)
7 Switch (# 2)
8 switches (# 3)

Claims (5)

The antenna element has first and second feeding paths, and the antenna element forms λ / 4 elements at different frequencies according to the first and second feeding paths, respectively. A multi-frequency resonant antenna capable of selecting an electrical length by selecting two feeding paths,
First and second matching circuits provided corresponding to the first and second feeding paths and for impedance matching;
The first power supply path is selected by electrically connecting one of the first and second power supply paths and non-conductive the other of the first and second power supply paths. A switch,
A second switch for selecting conduction or non-conduction between the antenna element and the first matching circuit in the first feeding path;
A short stub including a circuit for adjusting impedance in the second feeding path;
A multi-frequency resonant antenna, comprising: a third switch for selecting connection between the antenna element and one of the second matching circuit and the short stub in the second feeding path. The first feeding path forms an antenna element with a short electrical length,
The multi-frequency resonant antenna according to claim 1, wherein the second feeding path forms an antenna element having a long electric length.   The multi-frequency resonant antenna according to claim 1 or 2, wherein the wavelength of the antenna element is either λ / 4 or less and λ / 4 or more.   The multi-frequency resonant antenna according to any one of claims 1 to 3, wherein the antenna element has a shape of at least one of an inverted L antenna, a helical antenna, and a meander antenna.   A portable terminal using the multi-frequency resonant antenna according to claim 1.

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