JP2012023640A - Antenna device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an antenna device coping with a plurality of frequency bands, capable of matching impedance at each of frequency bands.SOLUTION: A GPS radiation electrode 108 radiates electric wave at a GPS frequency. A BT radiation electrode 110 radiates electric wave at a Bluetooth (R) frequency which is higher than the GPS frequency. A feeding electrode 114 supplies the electric power supplied from a feeding point 124 to the radiation electrodes. A matching circuit 126 is inserted between the feeding electrodes 114 and a ground pattern 106. One end of the GPS radiation electrode 108 is connected to the feeding electrode 114 at a first connection point. One end of the BT radiation electrode 110 is connected to the feeding electrode 114 at a second connection point. A connection point between the feeding electrode 114 and the matching circuit 126 is positioned between the first and second connection points.

Description

  The present invention relates to an antenna device, and more particularly to matching of its impedance.

  Many portable terminals have been adapted to a plurality of frequency bands such as GPS (Global Positioning System) and Bluetooth (registered trademark). In order to support a plurality of frequency bands while responding to the demand for miniaturization of portable terminals, it is desirable to generate radio waves in a plurality of frequency bands with a single antenna element. However, such a dual-band portable terminal has a problem that it is difficult to match impedance as compared with a single-band type.

JP 2006-229445 A JP 2002-185238 A

  In order to deal with such a problem, in Patent Document 1, impedance matching is achieved by adjusting the positional relationship between the antenna and the ground pattern on the low frequency band side. The impedance on the high frequency band side is adjusted by a matching circuit while maintaining this matching state. However, in the case of Patent Document 1, since it is necessary to change the ground pattern, it is difficult to finely adjust the impedance. Further, since a duplexer and an antenna switch are required, the circuit scale tends to increase.

  In Patent Document 2, two antenna elements are extended in the separation direction. This is because it is easy to independently adjust the impedance of each antenna element by suppressing the mutual influence of the two antenna elements. However, in the case of Patent Document 2, since the antenna element (radiation conductor) on the low frequency band side becomes too long, it is difficult to reduce the size. In addition, it is difficult to sufficiently suppress the mutual influence only by such arrangement.

  The present invention has been completed in view of the above problems, and a main object thereof is to match impedances in each frequency band in an antenna device capable of dealing with a plurality of frequency bands.

  The antenna device according to the present invention is supplied from a first radiation electrode that radiates radio waves at a first frequency, a second radiation electrode that radiates radio waves at a second frequency higher than the first radiation electrode, and a feed line. A feeding electrode that feeds the power to the first and second radiation electrodes, and a matching circuit that connects the feeding electrode and the ground pattern. One end of the first radiation electrode is connected to the power supply electrode at the first connection point, and one end of the second radiation electrode is connected to the power supply electrode at the second connection point. A connection point between the feeding electrode and the matching circuit is located between the first and second connection points.

  In such a configuration, when the position of the connection point of the matching circuit is changed, the inductance of the first radiation electrode and the inductance of the second radiation electrode are changed in opposite directions, so that the respective impedances can be easily adjusted. What is necessary is just to adjust the impedance of the 1st and 2nd radiation electrode by the distance from the 1st and 2nd connection point of each of the connection point of a matching circuit.

  The first and second radiation electrodes may be formed in an end region of the printed circuit board, and the first radiation electrode may be formed on a side closer to the end of the printed circuit board than the second radiation electrode. According to such a configuration, the impedance characteristics of the first radiating electrode and the impedance of the second radiating electrode are easily brought close to each other, so that the subsequent impedance adjustment is easy.

  The feeding electrode is formed on the printed circuit board, the first and second radiation electrodes are formed on the inner wall of the housing covering the printed circuit board, and the first and second radiation electrodes are interposed via the first and second power feeding pins. May be connected to the power supply electrode. The other end of the first radiation electrode may be connected to the ground pattern via a capacitive coupling element. The other end of the second radiation electrode may be an open end.

  The first and second radiation electrodes are formed on the upper surface of a substantially rectangular parallelepiped dielectric, the dielectric is attached to a mounting region formed at the end of the printed circuit board, and a ground pattern provided on the periphery of the mounting region by a matching circuit And the feeding electrode may be connected. The other end of the first radiation electrode may be capacitively coupled to the ground pattern via a gap formed on the side surface of the dielectric. The other end of the second radiation electrode may be an open end.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes easy to match an impedance in each frequency band in the antenna device which can respond to a some frequency band.

It is a schematic diagram which shows the mounting area | region of the antenna element in a printed circuit board. It is a perspective view which shows the structure of the antenna device formed in the mounting area periphery. It is a figure which shows typically the positional relationship of the radiation conductor and matching circuit in this embodiment. It is a Smith chart which shows the impedance characteristic of a GPS radiation electrode and a BT radiation electrode. 5 is a Smith chart showing impedance characteristics when the matching circuit is moved from the state of FIG. 4 to the first connection point side in the present embodiment. In this embodiment, it is a graph which shows the VSWR characteristic of a GPS radiation electrode. In this embodiment, it is a graph which shows the VSWR characteristic of a BT radiation electrode. It is a figure which shows typically the positional relationship of the radiation conductor and matching circuit in a comparative example. 5 is a Smith chart showing impedance characteristics when the matching circuit is moved from the state of FIG. 4 to the feeding point side in the comparative example. In a comparative example, it is a graph which shows the VSWR characteristic of a GPS radiation electrode. In a comparative example, it is a graph which shows the VSWR characteristic of BT radiation electrode. It is a Smith chart which shows the impedance characteristic before setting a matching circuit. It is another example of the structural drawing of an antenna apparatus. It is an expanded view of the antenna element shown in FIG.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. In each embodiment, an antenna element built in a mobile phone will be described as a theme. An antenna device is formed as a mobile phone incorporating an antenna element.

  FIG. 1 is a schematic diagram showing a mounting position of an antenna element on a printed circuit board 100 of a mobile phone. In FIG. 1, the x-axis is set in the short side direction of the printed circuit board 100, the y-axis is set in the long-side direction, and the z-axis is set in the direction from the paper surface to the front side. The same applies to the subsequent drawings. In FIG. 1, a mounting region 102 is provided at the upper right end portion of the printed circuit board 100. The mounting area 102 is a position where an “antenna device” is formed.

  FIG. 2 is a perspective view showing the structure of the antenna device 112. A part of the printed circuit board 100 is covered with a ground pattern 106, and various electronic circuits (not shown) are mounted thereon. The printed circuit board 100 and the electronic circuit are sealed by a housing 104. At the end of the printed circuit board 100 (a part of the mounting region 102), the ground pattern 106 is cut out, and the power supply electrode 114 is printed thereon.

  A GPS radiation electrode 108 (first radiation electrode) and a BT radiation electrode 110 (second radiation electrode) are printed on the inner wall of the housing 104. The GPS radiation electrode 108 radiates radio waves in the GPS frequency band (around 1.5 GHz). The BT radiation electrode 110 radiates radio waves in a Bluetooth (registered trademark) frequency band (near 2.4 GHz). As shown in FIG. 2, the GPS radiation electrode 108 is formed closer to the end of the printed circuit board 100 than the BT radiation electrode 110, in other words, formed outside the printed circuit board 100.

  One end of the GPS radiation electrode 108 is connected to the power supply electrode 114 via the first power supply pin 116. The other end of the GPS radiation electrode 108 is connected to the capacitive coupling element 122 via the connection pin 120. The capacitive coupling element 122 is a capacitor installed on the ground pattern 106. A connection point between the first power supply pin 116 and the power supply electrode 114 is referred to as a “first connection point”.

  One end of the BT radiation electrode 110 is connected to the power supply electrode 114 via the second power supply pin 118. The other end of the BT radiation electrode 110 is an open end. A connection point between the second power supply pin 118 and the power supply electrode 114 is referred to as a “second connection point”.

  One end of each of the first and second power supply pins 118 and 120 is fixed to the printed circuit board 100, and the other end is in contact with the GPS radiation electrode 108 and the BT radiation electrode 110. Each power supply pin is preferably inserted into a through-hole conductor provided on the printed circuit board 100 and mechanically fixed, and is electrically connected to the power supply electrode 114 via the through-hole conductor. In order to ensure contact with the radiation electrode, the tip of the power feed pin may have elasticity (spring property).

  The feeding electrode 114 is connected to the feeding point 124. The AC power supplied from the feeding point 124 is supplied from the first connection point to the GPS radiation electrode 108 via the first feeding pin 116, and from the second connection point to the BT radiation electrode via the second feeding pin 118. 110. As shown in FIG. 2, the second connection point is closer to the feeding point 124 than the first connection point.

  Further, the power supply electrode 114 is also connected to the ground pattern 106 via the matching circuit 126. The matching circuit in the present embodiment is an impedance matching element that includes both or one of an inductor and a capacitor and is connected to a feed line. The impedances of the GPS radiation electrode 108 and the BT radiation electrode 110 are adjusted by the inductance of the matching circuit 126 and the insertion position thereof. In the present embodiment, the connection point between the feeding electrode 114 and the matching circuit 126 is located between the first contact and the second contact.

  FIG. 3 is a schematic diagram showing the positional relationship between each radiation electrode and the matching circuit 126 in the present embodiment. When the inductance of the matching circuit 126 itself is increased, the inductances of the GPS radiation electrode 108 and the BT radiation electrode 110 are both increased. When the matching circuit 126 is brought closer to the first connection point side, that is, the GPS radiation electrode 108 side, the inductance of the GPS radiation electrode 108 decreases and the inductance of the BT radiation electrode 110 increases. On the other hand, when the matching circuit 126 is close to the second connection point side, that is, the BT radiation electrode 110 side (feeding point 124 side), the inductance of the GPS radiation electrode 108 increases and the inductance of the BT radiation electrode 110 decreases. Thus, by adjusting the position of the matching circuit 126 between the first connection point and the second connection point, the inductances of the GPS radiation electrode 108 and the BT radiation electrode 110 can be changed in the opposite directions.

  FIG. 4 is a Smith chart showing impedance characteristics of the GPS radiation electrode 108 and the BT radiation electrode 110. The center point indicates 50Ω. The purpose of impedance adjustment is to bring both the BT radiation electrode 110 and the GPS radiation electrode 108 as close as possible to the center point. In the case of FIG. 4, the center point is located outside the locus indicating the impedance characteristic of the BT radiation electrode 110 and inside the locus of the GPS radiation electrode 108. A state where the center point is outside the locus as in the BT radiation electrode 110 is referred to as undercoupling, and a state where the center point is inside the locus as the GPS radiation electrode 108 is referred to as overcoupling. In general, overcoupling is more preferable because it has a wider band than undercoupling.

  FIG. 5 is a Smith chart showing impedance characteristics when the matching circuit 126 is moved to the first connection point side from the state of FIG. 4 in the present embodiment. When the matching circuit 126 is moved to the first connection point side, the inductance of the GPS radiation electrode 108 is reduced, so that the loop size of the locus of the GPS radiation electrode 108 is reduced. As a result, the locus and the center point come closer. On the other hand, the inductance of the BT radiation electrode 110 increases, and the loop size of the locus of the BT radiation electrode 110 increases. As a result, the locus of the BT radiation electrode 110 also approaches the center point.

  Thus, if the matching circuit 126 is moved to the first connection point side, the locus of the overcoupling GPS radiation electrode 108 is reduced and the locus of the undercoupling BT radiation electrode 110 is enlarged. At the same time, it can be close to the center point. In FIG. 5, as a result, both the GPS radiation electrode 108 and the BT radiation electrode 110 are overcoupled.

  FIG. 6 is a graph showing the VSWR (Voltage Standing Wave Ratio) characteristics of the GPS radiation electrode 108 in the present embodiment. The dotted line indicates the VSWR characteristic of the GPS radiation electrode 108 before adjustment (state of FIG. 4), and the solid line indicates the VSWR characteristic after adjustment (state of FIG. 5). As shown in FIG. 6, even if the matching circuit 126 is moved, the characteristics of the GPS radiation electrode 108 are hardly changed.

  FIG. 7 is a graph showing the VSWR characteristics of the BT radiation electrode 110 in the present embodiment. The dotted line indicates the VSWR characteristic of the BT radiation electrode 110 before adjustment (state in FIG. 4), and the solid line indicates the VSWR characteristic after adjustment (state in FIG. 5). As shown in FIG. 7, even if the matching circuit 126 is moved, the minimum value of the VSWR value hardly changes. However, in the case of the BT radiation electrode 110, since the undercoupling is changed to the overcoupling, a practical frequency is used. The band is widened and the characteristics are improved.

  FIG. 8 is a schematic diagram showing the positional relationship between each radiation electrode and the matching circuit 126 in the comparative example. In the present embodiment, the matching circuit 126 is installed between the first connection point and the second connection point. However, in the comparative example shown in FIG. 8, the matching circuit 126 is provided between the second connection point and the feeding point 124. Is installed. When the matching circuit 126 is moved to the first connection point side, the inductances of the GPS radiation electrode 108 and the BT radiation electrode 110 are both reduced. On the other hand, when the matching circuit 126 is moved to the feeding point 124 side, the inductances of the GPS radiation electrode 108 and the BT radiation electrode 110 both increase. In the comparative example, by adjusting the position of the matching circuit 126, the inductances of the GPS radiation electrode 108 and the BT radiation electrode 110 change in the same direction.

  FIG. 9 is a Smith chart showing impedance characteristics when the matching circuit 126 is moved to the feeding point 124 side from the state of FIG. 4 in the comparative example. When the matching circuit 126 is moved to the feeding point 124 side, the inductances of the GPS radiation electrode 108 and the BT radiation electrode 110 both increase, and the locus of both expands. As a result, the trajectory of the BT radiation electrode 110 that was under-coupled approaches the center point, but the trajectory of the GPS radiation electrode 108 that was originally over-coupled moves away from the center point.

  In FIG. 9, as a result, both the GPS radiation electrode 108 and the BT radiation electrode 110 are overcoupled, but the locus of the GPS radiation electrode 108 is moved away from the center point by the adjustment. As a result, the minimum value of VSWR becomes large and reflection loss becomes large, which is not preferable.

  FIG. 10 is a graph showing the VSWR characteristics of the GPS radiation electrode 108 in the comparative example. The dotted line indicates the VSWR characteristic of the GPS radiation electrode 108 before adjustment (state of FIG. 4), and the solid line indicates the VSWR characteristic after adjustment (state of FIG. 9). As shown in FIG. 10, when the matching circuit 126 is moved, the minimum value of the VSWR of the GPS radiation electrode 108 is increased, the reflection loss is increased, and the VSWR characteristic is deteriorated.

  FIG. 11 is a graph showing the VSWR characteristics of the BT radiation electrode 110 in the comparative example. The dotted line indicates the VSWR characteristic of the BT radiation electrode 110 before adjustment (state of FIG. 4), and the solid line indicates the VSWR characteristic after adjustment (state of FIG. 9). As shown in FIG. 11, even if the matching circuit 126 is moved, the minimum value of the VSWR characteristic hardly changes. However, in the case of the BT radiation electrode 110, since the undercoupling is changed to the overcoupling, a practical frequency is used. The band is widened and the VSWR characteristics are improved.

  As described above, in the case of the comparative example, if the impedance characteristic of the BT radiation electrode 110 is improved by adjusting the position of the matching circuit 126, the impedance characteristic of the GPS radiation electrode 108 may be deteriorated. On the other hand, in the case of the present embodiment, by setting the insertion position of the matching circuit 126 between the first and second connection points, the impedance characteristics of the GPS radiation electrode 108 and the BT radiation electrode 110 are reversed. There is an advantage that both can be easily brought close to the center point.

  FIG. 12 is a Smith chart showing impedance characteristics before setting the matching circuit 126. The solid line indicates the impedance characteristic when the GPS radiation electrode 108 is arranged on the end side (outside) of the BT radiation electrode 110 as shown in FIG. On the other hand, dotted lines indicate impedance characteristics when the GPS radiation electrode 108 is disposed on the inner side and the BT radiation electrode 110 is disposed on the outer side.

  As shown in FIG. 12, when the GPS radiation electrode 108 is disposed on the inner side, the locus of the GPS radiation electrode 108 and the BT radiation electrode 110 is different from that when the GPS radiation electrode 108 is disposed on the outer side. Before the impedance matching is performed by the matching circuit 126, both impedance characteristics are greatly different, and subsequent adjustment becomes difficult. Therefore, as shown in FIG. 2, it is easier to adjust the impedance by arranging the GPS radiation electrode 108 on the outer side and the BT radiation electrode 110 on the inner side.

  In designing the antenna device 112 that can handle a plurality of frequency bands, it is important to make the initial positions on the Smith chart of the high frequency side and the low frequency side as close as possible before inserting the matching circuit 126. If the GPS radiation electrode 108 on the low frequency side is on the inside and the BT radiation electrode 110 on the high frequency side is on the outside, the BT radiation electrode 110 is more easily radiated, so the radiation resistance of the BT radiation electrode 110 is Becomes higher. As a result, the locus of the impedance goes further inward, and the initial impedance position of the BT radiation electrode 110 on the Smith chart deviates from the initial impedance position of the GPS radiation electrode 108.

  On the other hand, as shown in the present embodiment, the radiation resistance of the BT radiation electrode 110 can be suppressed if the GPS radiation electrode 108 on the low frequency side is on the outside and the BT radiation electrode 110 on the high frequency side is on the inside. As a result, since the locus of the impedance of the BT radiation electrode 110 is suppressed from moving inward, the initial impedance position of the BT radiation electrode 110 on the Smith chart approaches the initial impedance position of the GPS radiation electrode 108. That is, by forming the GPS radiation electrode 108 on the low frequency side on the outside and the BT radiation electrode 110 on the high frequency side on the inside, one common matching circuit 126 is provided for both the high frequency side and the low frequency side. This facilitates impedance matching.

  FIG. 13 is a structural diagram of an antenna device 113 in another example. In FIG. 13, an antenna element 128 having a radiation block and the like printed on the surface of a dielectric block is used. The antenna device 113 is formed by installing the antenna element 128 in the mounting region 102 of the printed circuit board 100. In the printed board 100, the mounting area 102 is surrounded by the ground pattern 106. The antenna element 128 is formed by printing a GPS radiation electrode 108, a BT radiation electrode 110, etc. on the surface of a substantially rectangular parallelepiped dielectric. FIG. 14 is a development view of the antenna element 128. The structure of the antenna element 128 will be described with reference to FIGS.

  The antenna element 128 is fixed to the printed circuit board 100 by bonding the rectangular bottom surface 130 of the antenna element 128 to the mounting region 102. The four side surfaces of the antenna element 100 are defined as a first side surface 132 (y × z), a second side surface 134 (x × z), a third side surface 136 (y × z), and a fourth side surface 138 (xx × z), respectively. . The mounting region 102 is formed by cutting out a part of the ground pattern. The base of the antenna element 128 is formed of ceramic or the like.

  The GPS radiation electrode 108 is printed in a band shape from a part of the bottom surface 130 to the third side surface 136, the top surface 140, and the first side surface 132. The GPS radiation electrode 108 is capacitively coupled to the ground electrode 142 via the gap 144 on the first side surface 132.

  The BT radiation electrode 110 is printed in a band shape from a part of the bottom surface 130 to the top surface 140 via the third side surface 136. On the bottom surface 130, the GPS radiation electrode 108 and the BT radiation electrode 110 are connected to the feeding electrode 114. Also in this example, the feeding electrode 114 and the ground pattern 106 are connected by the matching circuit 126 provided between the first connection point and the second connection point.

  The antenna devices 112 and 113 have been described based on the embodiments. According to the present embodiment, the impedance of the GPS radiation electrode 108 and the BT radiation electrode 110 can be easily adjusted by providing the matching circuit 126 between the first connection point and the second connection point. Further, by arranging the GPS radiation electrode 108 on the end side (outside) of the printed circuit board 100, the impedance characteristics of the GPS radiation electrode 108 and the BT radiation electrode 110 can be brought close to each other.

  The present invention has been described based on the embodiments. It will be understood by those skilled in the art that the embodiments are illustrative, and that various modifications and changes are possible within the scope of the claims of the present invention, and that such modifications and changes are also within the scope of the claims of the present invention. By the way. Accordingly, the description and drawings herein are to be regarded as illustrative rather than restrictive.

  In the present embodiment, GPS is exemplified as the low frequency (first frequency) and Bluetooth (registered trademark) is exemplified as the high frequency (second frequency). However, the present invention is not limited to these frequency bands, and is compatible with a plurality of frequency bands. Those skilled in the art will appreciate that the present invention is applicable to impedance adjustment of possible antenna devices.

In addition, the following invention can be recognized based on this embodiment.
A first radiation electrode that radiates radio waves at a first frequency;
A second radiation electrode that radiates radio waves at a second frequency greater than the first frequency;
The first and second radiation electrodes are connected to the first and second connection points, respectively, and electric power supplied from a power supply line is transmitted from the first and second connection points to the first and second radiation points. A power supply electrode for supplying power to the electrode;
In an antenna device comprising: a matching circuit that is installed between the first connection point and the second connection point and connects the feeding electrode and a ground pattern;
When one of the inductances of the first and second radiating electrodes is changed to a large value and the other is changed to a small value, the connection point between the matching circuit and the feeding electrode is changed to a radiating electrode on the side where the inductance is reduced. A method for adjusting the radiation characteristics of an antenna device, wherein the inductances of the first and second radiation electrodes are simultaneously adjusted by bringing them closer.

  100 printed circuit board, 102 mounting area, 104 housing, 106 ground pattern, 108 GPS radiation electrode, 110 BT radiation electrode, 112, 113 antenna device, 114 feed electrode, 116 first feed pin, 118 second feed pin, 120 connection Pin, 122 capacitive coupling element, 124 feeding point, 126 matching circuit, 128 antenna element, 130 bottom surface, 132 first side surface, 134 second side surface, 136 third side surface, 138 fourth side surface, 140 top surface, 142 ground electrode, 144 gap.

Claims (7)

A first radiation electrode that radiates radio waves at a first frequency;
A second radiation electrode that radiates radio waves at a second frequency greater than the first frequency;
A feed electrode for feeding power supplied from a feed line to the first and second radiation electrodes;
A matching circuit for connecting the power supply electrode and the ground pattern,
One end of the first radiation electrode is connected to the feeding electrode at a first connection point,
One end of the second radiation electrode is connected to the feeding electrode at a second connection point,
A connection point between the feeding electrode and the matching circuit is located between the first and second connection points.   The impedance of the first and second radiation electrodes is adjusted according to the distance from the first and second connection points of the matching circuit connection point, respectively. Antenna device.   The first and second radiation electrodes are formed in an end region of the printed circuit board, and the first radiation electrode is formed closer to the end of the printed circuit board than the second radiation electrode. The antenna device according to claim 1 or 2, wherein The power supply electrode is formed on a printed circuit board,
The first and second radiation electrodes are formed on an inner wall of a housing that covers the printed circuit board,
4. The antenna device according to claim 1, wherein the first and second radiation electrodes are connected to the power feeding electrode via first and second power feeding pins. 5. The other end of the first radiation electrode is connected to the ground pattern via a capacitive coupling element,
The antenna device according to claim 4, wherein the other end of the second radiation electrode is an open end. The first and second radiation electrodes are formed on an upper surface of a substantially rectangular parallelepiped dielectric,
The dielectric is attached to a mounting area formed at the end of the printed circuit board,
4. The antenna device according to claim 1, wherein the matching circuit connects the ground pattern provided at a peripheral edge of the mounting region and the feeding electrode. 5. The other end of the first radiation electrode is capacitively coupled to the ground pattern through a gap formed on a side surface of the dielectric,
The antenna device according to claim 6, wherein the other end of the second radiation electrode is an open end.

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