JP2009268149A - Antenna device, and communication apparatus using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a multiband enabled antenna device which attains reduction in size/in space, prevents a gain from being reduced, by ensuring isolation even in a plurality of frequency bands, and has a broad bandwidth and a high average gain in each of frequency bands. <P>SOLUTION: The antenna device includes: a mount board having a ground part and a non-ground part; a chip antenna provided with a base, a first radiation electrode formed on the base, and a first feeding electrode connected to one end of the first radiation electrode or not connected thereto; and at least one radiation electrode made of a conductor pattern on the non-ground part of the mount board and formed on a rear side of a chip antenna mounting surface of the mount board, wherein one end of the radiation electrode formed on the rear side of the mount substrate is electrically connected to the first radiation electrode and the other end thereof acts as an open end. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a small-sized and wide-band antenna device that can be used for a multiband, particularly a triple band, used for a mobile phone, a wireless LAN (Local Area Network), and the like.

In response to the demand for miniaturization of communication devices such as mobile phones and personal computers, and electronic devices, it is necessary to miniaturize the antenna device used. Therefore, a chip antenna having a feeding electrode and a radiation electrode provided on the surface or inside of a substrate such as a dielectric or a magnetic material has been used.
On the other hand, mobile phone systems include, for example, EGSM (Extended Global System for Mobile Communications) method and DCS (Digital Cellular System) method, which are popular in Europe, and PCS (Personal Japan Communication System), which is popular in the United States. There are various systems using time division multiple access (TDMA) such as the PDC (Personal Digital Cellular) system. With the rapid spread of mobile phones in recent years, especially in major metropolitan areas in developed countries, it is difficult to connect system users in the frequency bands allocated to each system, making it difficult to connect, or connecting in the middle of a call There are problems such as disconnection. Therefore, it has been proposed that the user can use a plurality of systems to increase the number of frequencies that can be substantially used, and further expand the service area and effectively use the communication infrastructure of each system. For this reason, there is an increasing need for multi-band sharing one or more frequency bands with one antenna. For example, with the need for multi-functionality of mobile phones, cellular (cellular: different in each country, for example, transmission frequency: 824 to 849 MHz, reception frequency: 869 to 894 MHz), which is a communication system, and a function of position detection The resulting GPS (Global Positioning System: central frequency 1575 MHz band) dual band, or EGSM (transmission frequency: 880-915 MHz, reception frequency: 925-960 MHz), and DCS (transmission frequency: 1710-1785 MHz) , Reception frequency: 1805 to 1880 MHz) and PCS (transmission frequency: 1850 to 1910 MHz, reception frequency: 1930 to 1990 MHz), a multi-band capable of supporting triple bands A compatible small antenna device is desired.

  Conventionally, as shown in FIG. 6, a dual-band antenna device has been proposed in which two radiation electrodes are provided and chip antennas corresponding to two resonance frequencies are arranged in parallel (see, for example, Patent Document 1). In FIG. 6, the antenna device 90 includes a substrate 91 and two chip antennas 93 a and 93 b mounted on one main surface 92 a of the substrate 91. A power supply line 94 and a ground electrode 95 are formed on one main surface 92 a of the substrate 91. The ground electrode 95 and the two chip antennas 93a and 93b are arranged close to each other. One end of the power supply line 94 is divided into two parts, which are connected to power supply electrodes 96a and 96b of the two chip antennas 93a and 93b, respectively, and the other end is connected to a high-frequency signal source (not shown). The other ends of the radiation electrodes formed on the bases of the chip antennas 93a and 93b are open ends, and the first radiation electrode 97a and the second radiation electrode 97b are configured to form an antenna device.

  However, the antenna device of Patent Document 1 uses two rectangular chip antennas. In order to reduce the size, it has also been proposed to mount the chip antenna 93b on the other main surface 92b of the substrate 91. However, in this case, the thickness of the mounting substrate is added, which does not meet the needs for thickness reduction. At this time, since the electrostatic capacity increases due to an increase in the area where the ground electrode 95 and the chip antenna 93a face each other, the bandwidth decreases. From the above, Patent Document 1 cannot achieve both a reduction in size, space saving, and a wide band.

  On the other hand, in Patent Document 2, a chip antenna including a radiation electrode formed on a base, a feeding electrode to which one end of the radiation electrode is connected, and a terminal electrode to which the other end of the radiation electrode is connected, and this chip There has been disclosed an antenna device including an antenna and a mounting substrate having a radiation conductor formed on the surface thereof. According to this antenna device, since the radiation electrode of the chip antenna and the radiation conductor of the mounting substrate are connected, the effective length of the conductor can be increased. As a result, the radiated electric field of the antenna device is strengthened, resulting in high gain and wide bandwidth. It can be realized.

  Furthermore, in the antenna device disclosed in Patent Document 3, it has been proposed to provide a notch-shaped slit in the ground portion between the chip antenna mounted on the mounting substrate and the high-frequency circuit adjacent thereto. In the case of this antenna device, the notch slit suppresses the flow of high-frequency current flowing from the chip antenna to the high-frequency circuit side, and as a result, radiation characteristics can be improved.

Japanese Patent Laid-Open No. 11-4117 Japanese Patent Laid-Open No. 11-330830 JP 2001-274719 A

Japanese Patent Laid-Open No. 2003-228867 proposes a wide band, but cannot cope with multiband only by suppressing the deterioration of the bandwidth in the low frequency band. In addition, the antenna device disclosed in Patent Document 3 is said to have improved radiation characteristics due to the notch slit. However, by limiting the path of the high-frequency current flowing through the ground electrode due to the notch slit, it is possible to increase the bandwidth and It cannot cope with banding. Therefore, the conventional antenna device has a problem that it cannot satisfy all of downsizing, space saving, and wide band.
In addition, when a plurality of radiation electrodes are formed on a conventional antenna base to form a multiband, it is difficult to maintain isolation due to the capacitance generated between the radiation electrodes. Specifically, as the capacitance between the radiation electrodes increases, the amount of high-frequency current flowing in the opposite direction increases. As a result, the radiation of electromagnetic waves weakens each other and the gain (sensitivity) decreases. is there. In a multiband antenna device, it is desirable that each of a plurality of frequency bands has a wide bandwidth and a high gain. However, Patent Document 1 and Patent Document 2 do not make such studies.
In recent years, it has become important to reduce the influence of electromagnetic waves radiated from a mobile phone or the like on the human body (head) from the health aspect, and an antenna having a low specific absorption rate (SAR) SAR (Specific Absorption Rate). An apparatus is desired.

  Therefore, the present invention achieves miniaturization and space saving, maintains isolation in a plurality of frequency bands to prevent gain reduction, and supports a wide band with a wide bandwidth and high average gain in each frequency band. It is an object of the present invention to provide an antenna device and a communication device using the antenna device.

  The present invention provides a mounting substrate having a ground portion and a non-ground portion, a base, a first radiation electrode formed on the base, and a first connected to or disconnected from one end of the first radiation electrode. And at least one radiation electrode (third radiation electrode) formed in a conductor pattern on the non-ground portion of the mounting substrate and formed on the back surface of the chip antenna mounting surface of the mounting substrate. ), And the radiation electrode formed on the back surface of the mounting substrate is an antenna device having one end electrically connected to the first radiation electrode and the other end being an open end.

The third radiating electrode is formed so that its open end is close to the first feeding electrode, so that it is easy to obtain the two resonance modes. Furthermore, it is possible to increase the bandwidth by providing a slot between the chip antenna and the ground portion of the mounting substrate.
Moreover, it is preferable that the longitudinal direction of the first radiation electrode and the third radiation electrode are arranged substantially in parallel.
The antenna device includes a self-inductance of the first radiation electrode, a capacitance between the first radiation electrode and a ground electrode of the mounting substrate, and a back surface of the first radiation electrode and the mounting substrate. A first resonance mode can be obtained by an LC resonance circuit composed of a capacitance between the radiation electrode and the self-inductance of the radiation electrode formed on the back surface of the mounting substrate, and A capacitance between the radiation electrode and the ground electrode formed on the back surface of the mounting substrate; a capacitance between the first radiation electrode and the radiation electrode formed on the back surface of the mounting substrate; and The second resonance mode can be obtained by an LC resonance circuit including an open end of the radiation electrode formed on the back surface of the mounting substrate and a capacitance between the feeding electrode.
The first radiation electrode preferably has a helical structure or a meander structure.
Further, it is desirable that the chip antenna on the chip antenna mounting surface and the third radiation electrode formed on the opposing surface are connected through a through hole.

In the antenna device of the present invention, it is important to provide a predetermined interval for ensuring isolation between the first radiation electrode and the second radiation electrode provided on the chip antenna. For example, the dielectric constant of the substrate of the chip antenna is Er, the resonance frequency of the first radiation electrode 12 and the second radiation electrode 16 is fh [Hz], and the first radiation electrode 12 and the second radiation electrode 16 are When the length of the interval (isolation securing portion) 10 is Wa [m], the following equation is obtained. Wa> (3 × 10 ⁸ ) / fh × √Er / 100, where the highest frequency band fh = 1.9 [GHz] used in North American mobile phones, and the chip antenna substrate Er = 8, Substituting into the above equation, Wa> 4.5 [mm] is obtained. Thus, it is preferable to set the isolation ensuring part. In addition, it is preferable that an independent power supply circuit is provided for each of the first feeding electrode and the second feeding electrode.

  The present invention is a communication device such as a mobile phone, which is equipped with any of the antenna devices described above.

In the antenna device according to the present invention, since the third radiation electrode is formed on the back surface, the conductor pattern of the base functions as a radiation electrode through the substrate. Therefore, the first radiation electrode and the third radiation pattern are formed by the thickness of the substrate. The geometric distance to the radiation electrode increases, and the capacitance between them decreases. As a result, the coupling between the two is weakened, so that isolation can be secured and the bandwidth is increased at the same time. In addition, the board space can be effectively used, and the size can be further reduced.
The third radiating electrode is formed so that its open end is close to the first feeding electrode, so that it is easy to obtain the two resonance modes.
Further, if the first and second radiation electrodes are provided side by side on the antenna base and the third radiation electrode is provided on the mounting substrate, this can achieve a wider band and a smaller size. At this time, an antenna device corresponding to a multiband with isolation can be obtained by arranging each radiation electrode provided on the substrate with an appropriate interval.
In the antenna device of the present invention, since the radiation electrode is also provided on the mounting substrate side, the concentration of the electric field distribution close to the human head is reduced. As a result, a communication device such as a mobile phone having a small SAR value can be provided.

It is a perspective view which shows one Example of the antenna device which concerns on this invention. It is a top view of FIG. 1 which shows the antenna apparatus which concerns on this invention. It is a perspective view which shows the other example of the chip antenna used for the antenna apparatus which concerns on this invention. It is a frequency-VSWR characteristic curve figure in one Example of the antenna apparatus which concerns on this invention. It is an isolation characteristic figure in one Example of the antenna device which concerns on this invention. It is a perspective view which shows an example of the conventional antenna device. "

  1 and 2 show an antenna device 100 according to an embodiment of the present invention. The mounting substrate 2 includes a ground portion 21 having a ground electrode pattern (a ground portion 21a provided on the chip antenna mounting surface and a ground portion 21b provided on the opposite surface (back surface) of the chip antenna mounting surface), and a ground electrode pattern Is formed of a non-ground portion 22 (a non-ground portion 22a provided on the chip antenna mounting surface and a non-ground portion 22b on the opposite surface of the chip antenna mounting surface). The non-ground portion 22a of the mounting substrate 20 is formed with the chip antenna 1 and the third radiation electrode 3 made of a linear conductor pattern provided on the mounting surface of the chip antenna 1, and thereby the antenna The apparatus 100 is comprised.

The chip antenna 1 has a helical monopole antenna formed in one end region of a substantially rectangular parallelepiped base 11, and an inverted F type monopole antenna formed in the other end region. The helical monopole antenna has a first radiating electrode 12 whose other end is an open end 15 (see FIG. 3) and a feeding electrode 13 to which one end of the first radiating electrode 12 is connected. A first power supply 51 is connected to the electrode 13 via a connection electrode 41. The terminal electrode 14 (see FIG. 3) provided on the side surface of the base 11 is used when the first radiation electrode 12 formed on the chip antenna 1 is connected to the third radiation electrode 3. In this case, the open end 15 of the first radiation electrode 12 and the terminal electrode 14 may be directly connected by soldering or the like, or may be capacitively coupled as disconnected. Similarly, the terminal electrode 14 and the third radiation electrode 3 may be connected or not connected. If not connected, the capacity increases and the radiation electrode can be shortened.
On the other hand, the inverted F type monopole antenna has a second radiating electrode 16 whose other end is an open end 18 and a feeding electrode 17 to which one end of the second radiating electrode 16 is connected. A second power supply 52 is connected to the power supply electrode 17 via a connection electrode 42. Here, the non-ground portion 22a on the open end 18 side of the second radiation electrode 16 has a ground electrode 43 connected to the ground portion 21a.

An interval (isolation securing portion) 10 for securing isolation is provided between the first radiation electrode 12 and the second radiation electrode 16 so that interference between these resonance circuits does not occur. Yes. Capacitance is generated between the radiation electrode 12 and the radiation electrode 16 or the power supply electrode via the isolation securing unit 10, and the isolation decreases as the capacitance increases. Therefore, in order to reduce the capacitance and increase the isolation, it is sufficient to make the securing portion 10 long, but it is not preferable because the antenna becomes large. In order to solve this problem, the inventors have found the conditions for the isolation securing section as described below. That is, since the first radiating electrode and the second radiating electrode are coupled in series via the isolation securing unit 10, the series resonance frequency fo is different from the resonance frequency of the antenna having each radiating electrode. What is necessary is just to adjust the length of the securing part 10. Further, in the case of a multiband antenna provided with a plurality of radiation electrodes on or inside the substrate, the electrostatic coupling between the radiation electrodes becomes stronger with high frequency, so that the isolation is likely to deteriorate. Furthermore, due to the wavelength shortening effect due to the dielectric constant of the chip antenna substrate, the larger the relative dielectric constant, the shorter the radiation electrode and the smaller the size. However, the capacitance between the radiation electrodes increases, but the isolation deteriorates. It became clear by experiment that it became easy to do. In order to solve this problem, it is desirable to increase the distance between the radiation electrodes and increase the isolation, but there are limitations due to the limited antenna volume. Therefore, in order to solve the problem of the trade-off between isolation and miniaturization, the present invention of the antenna structure as shown in the present embodiment has been reached, and the optimum conditions for the isolation securing unit 10 have been obtained. For example, as described above, the dielectric constant of the substrate of the chip antenna is Er, and the first radiating electrode 12 and the second radiating electrode 16 are selected with the relatively high resonance frequency as the target for fh [Hz]. It has been found that the following equation is obtained when the length of the distance (isolation securing portion) 10 between the first radiation electrode 12 and the second radiation electrode 16 is Wa [m].
Wa> (3 × 10 ⁸ ) / fh × √Er / 100
For example, if the highest frequency band fh = 1.9 [GHz] used in North American mobile phones and Er = 8 of the chip antenna base are substituted into the above equation, Wa> 4.5 [mm] is obtained. . Here, as an example, the length Wa of the isolation securing portion 10 is set to 5 mm.

Further, the antenna device of the present invention combines, for example, a chip antenna mounted on a mounting substrate and a third radiation electrode formed on the same mounting surface as the chip antenna or on the surface facing the chip antenna. The resonance electrode is configured to resonate in the first frequency band (high band side), and further, the second frequency is generated by the resonance current flowing from the first radiation electrode via the third radiation electrode on the mounting substrate. Dual band support can be achieved by resonating in the band (low band side). Further, the second radiation electrode formed on the other side of the chip antenna is caused to resonate in the third frequency band (high band side). Therefore, it can be used for a triple band.
Here, for the dual-band resonance mode, the self-inductance of the first radiation electrode, the capacitance between the first radiation electrode and the ground electrode of the mounting substrate, the first radiation electrode, and the third radiation. A first resonance mode is obtained by an LC resonance circuit composed of a capacitance between the electrode and the electrode, while the self-inductance of the third radiating electrode and between the third radiating electrode and the ground electrode. , A capacitance between the first radiation electrode and the third radiation electrode, and a capacitance between the open end of the third radiation electrode and the feeding electrode. The second resonance mode is obtained by the LC resonance circuit. It is preferable to bring the open end of the third radiating electrode closer to the feeding electrode because two resonance modes can be obtained with certainty. At this time, in order to achieve isolation between the two resonance modes, the third radiation electrode is preferably provided on the back surface of the mounting substrate. This is because when the third radiating electrode is formed on the back surface, the conductor pattern functions as a radiating electrode through the substrate. Therefore, the geometrical relationship between the first radiating electrode and the third radiating electrode is equal to the thickness of the substrate. The distance increases and the capacitance between them decreases. As a result, the coupling between the two is weakened, so that isolation can be secured and the bandwidth is increased at the same time. For example, when a chip antenna having a thickness of about 3 mm is mounted on a substrate having a thickness of about 0.6 mm (a copper-clad laminate having a relative dielectric constant εr = 5), the distance between the electrodes forming the capacitance is 3. 6mm. As a result, the coupling between the third radiating electrode and the first radiating electrode is weakened, and the bandwidth is further increased.

Now, the antenna device 100 according to the present embodiment mounts the chip antenna 1 on the non-ground portion 22a of the mounting substrate 20 to cause resonance, for example, in the PCS (1.9 GHz) band by the first radiation electrode 12, and The antenna is configured to transmit and receive a dual band that covers a resonance band of a cellular (0.8 GHz) band, for example, by one radiation electrode 12 and the third radiation electrode 3. On the other hand, the second radiation electrode 16 of the inverted F type is not an antenna that receives a single band, for example, GPS (1.5 GHz band), and constitutes a triple band antenna together. Therefore, the dual-band antenna part resonates in the frequency band covering the cellular and PCS by supplying power from the first power supply 51, and the radiation resistance is radiated from the antenna into the air. Conversely, the received wave is converted into a voltage via the resonance circuit. On the other hand, the single-band antenna part is dedicated to GPS reception, and the received wave is converted into a voltage via a resonance circuit. In this example, a dual power supply structure is used in which the respective power supplies function in parallel. In addition to this, it is conceivable to provide a switch circuit for switching between transmission and reception of both antennas and share them with one power source. However, in this case, it is necessary to separate the cellular, PCS, and GPS carrier signals using a switch or antenna duplexer, so that power loss and signal distortion (spurious) occur and the circuit configuration is complicated. There is. In this respect, the dual power supply system is desirable in that it can reduce circuit elements for frequency separation, and can realize a highly reliable and highly efficient wireless device by simplifying the circuit configuration.
In addition, a dual band transmission signal, in particular, a PCS close to the GPS band or a part of a harmonic transmission signal emitted from a cellular may cause an isolation failure that leaks to the GPS side. In an antenna having a multiband, a higher resonance frequency is generally targeted for improvement of isolation, but isolation may be improved in accordance with a dedicated reception frequency band like the GPS antenna. At this time, in order to obtain sufficient isolation characteristics, it is first necessary to secure a predetermined amount of the space between the first radiation electrode and the second radiation electrode as described above. Furthermore, an avoiding means of dividing the power supply into two parts to avoid interference is also effective. In this case, a two-power supply system is preferable.

  Further, in the case of single band support or dual band support that covers a plurality of relatively close bands by one resonance, a surface mount type chip antenna is preferable. 3A to 3C show preferred shapes of the first radiation electrode 12 or the second radiation electrode 16 provided on the chip antenna 1. Although only one radiation electrode is shown in the drawing, it means that such a radiation electrode structure can be provided in parallel. In the above embodiment, the helical monopole antenna of FIG. 3A is used, but instead, an L-shaped (FIG. 3B), U-shaped or crank-shaped radiation electrode, FIG. A meandering radiation electrode as shown in c) or a combination thereof can be used. The radiation electrode may be trapezoidal, stepped, curved or the like. In the case of a helical or meander structure, the radiation electrode becomes long and can cope with a low resonance frequency, or by combining with the third radiation electrode, it can cope with a lower frequency. In the present invention, functional names such as the first and second radiation electrodes, the first and second power supply electrodes, the terminal electrode, and the ground electrode are given. Since these electrodes are integrally formed by pattern printing, they are not distinguished in appearance.

In the antenna device of the present invention, a terminal electrode is provided between the first radiation electrode and the third radiation electrode. At this time, the first radiating electrode and the terminal electrode, and the terminal electrode and the second radiating electrode may be directly connected, or may be disconnected. it can. In the former case, the first radiating electrode and the terminal electrode may be formed of an integral conductor pattern without being distinguished from each other, and may be electrically connected to the third radiating electrode with solder or the like. Further, when the third radiation electrode is provided on the back surface of the substrate, it is simple and reliable to use a through hole. In this case, solder or the like may be filled in the through hole. On the other hand, in the case of the latter non-connection, capacitive coupling is formed and the capacitance between the electrodes increases conversely. The present invention adjusts the amount of capacitive coupling between the radiation electrodes while reducing the size, but in this case, from the viewpoint of miniaturization, the capacitive coupling is increased, the length of the radiation electrode is shortened, and the chip antenna itself is reduced in size. Is intended to be.
In some cases, capacitive coupling can be achieved by forming the first and second radiation electrodes and the respective power feeding electrodes in a disconnected state. The intention in this case is to achieve broadband impedance matching on the power supply side by the capacitance connected in series with the power supply electrode and the radiation electrode. This eliminates the need for an external matching circuit on the antenna feeding side, so that the antenna peripheral circuit can be simplified and power loss can be reduced, so that the efficiency of the entire antenna circuit can be improved.
In addition, if a mounting hole is provided in the mounting substrate between the chip antenna and the ground portion, the coupling between the chip antenna and the ground portion and the coupling between the third radiation electrode and the ground portion are weakened, and the bandwidth is widened. There is.

The material of the base 11 of the chip antenna is a dielectric, a magnetic material or a mixture thereof. Alternatively, a dielectric material or a magnetic material may be formed using a mixed material of resin such as plastic and glass. When the substrate 11 is made of a dielectric or magnetic material, the chip antenna 1 can be downsized due to the wavelength shortening effect. For example, an alumina-based dielectric having a relative dielectric constant εr = 8 can be used. The alumina-based dielectric is composed of oxides of Al, Si, Sr, and Ti as main components. The total of the main components is 100% by mass, and 10-25% by mass (in terms of Al ₂ O ₃ ), 25-60. It contains Si by mass% (SiO ₂ equivalent), 7.5 to 50 mass% (SrO equivalent) Sr, 20 mass% or less (TiO ₂ equivalent) Ti, and further contains 0.1 to 10 mass as subcomponents. % (Bi ₂ O ₃ conversion) Bi, 0.1-5 mass% (Na ₂ O conversion) Na, 0.1-5 mass% (K ₂ O conversion) K, 0.1-5 mass% You may contain at least 1 sort (s) of Co of (CoO conversion).
When the substrate 11 is made of a magnetic material, since the inductance is large, the chip antenna 1 can be further reduced in size, and the Q value of the antenna can be reduced, and the bandwidth can be increased.
When the substrate 11 is made of a mixture of a dielectric and a magnetic material, it is possible to reduce the size of the antenna due to the wavelength shortening effect and to increase the bandwidth by reducing the Q value of the antenna.
In this embodiment, the dimensions of the base 11 are, for example, a width of 3 mm, a length of 30 mm, and a thickness of 3 mm. The cell phone antenna having the same characteristics has dimensions of about 12 mm in width, 34 mm in length, and 8 mm in thickness to realize a conventional sheet metal antenna. Thus, the antenna of the present invention can be miniaturized. .
The impedance matching of the chip antenna 10 can be adjusted by inserting a matching circuit (not shown) between the feed line and the chip antenna 1. Impedance matching can also be achieved by adjusting the width and length of the conductor pattern of the third radiation electrode 3 and the distance (substrate thickness) between the second radiation electrode 3 and the mounting substrate 20.
The linear conductor pattern is preferably formed by printing, but the width and length of the line are not limited. The conductor pattern is not limited to a linear shape, and may be various shapes such as a square, a trapezoid, and a triangle according to the required characteristics of the antenna device. The conductor pattern may be formed of a sheet metal or a flexible substrate. When sheet metal is used, the etching process of the copper-clad substrate can be omitted. When a flexible substrate is used, the degree of freedom in mounting design is high.

Next, characteristic evaluation will be described. As the antenna characteristics of the antenna device 100 shown in FIG. 1, VSWR (voltage standing wave ratio) was measured in the frequency range of 0.75 to 2.2 GHz for Example 1 using a signal input from a network analyzer. VSWR is an index representing the magnitude of reflection between the antenna and the transmitter (or receiver). When reflection is the smallest, VSWR = 1, and the power supplied from the transmitter is not reflected at all and sent to the antenna. On the contrary, when the reflection is the largest, VSWR is infinite, and the supplied power is completely reflected and becomes reactive power.
The feeding terminal provided at one end of the mounting board for antenna measurement and the input terminal of the network analyzer are connected via a coaxial cable (characteristic impedance 50Ω), and the scattering parameter (Scattering) of the antenna viewed from the network analyzer side at the feeding terminal. Parameter) was measured and VSWR was calculated.
FIG. 4 shows the relationship between frequency and VSWR (voltage standing wave ratio), with the horizontal axis representing frequency and the vertical axis representing VSWR. The dotted line represents the required bandwidth, and it is sufficient that the bandwidth is satisfied at VSWR = 3. The results in FIG. 4 are slightly inferior in the cellular band, but are sufficiently satisfied in the PCS band and the GPS band, and can be said to have substantially no problem antenna characteristics.
FIG. 5 shows the measurement results of isolation. The port 21 and the port 2 are connected to the feeding electrodes of the two antennas using a network analyzer, and the S21 characteristic is measured. Isolation in the cellular band is good, and the GPS band and PCS band also satisfy the isolation of 10 dB. As a result of conducting a communication test in a state where it was mounted on a wireless device, it was confirmed that there was no practical problem.

Next, when the antenna device is folded and mounted on a mobile phone, it can be placed on a mounting substrate on the liquid crystal display side, or can be mounted on the periphery of a speaker or the periphery of a microphone. However, in any case, it is desirable to dispose on the back side of the mounting substrate. The distance from the head of the human body will be far away, and the mobile phone should be placed away from interference components such as liquid crystal displays, speakers, and microphones, both when the phone is closed and when it is opened. Can reduce the influence on the antenna characteristics.
In addition, a part of the electromagnetic wave is absorbed by the human body when the human head is close to the electromagnetic wave (high-frequency electric field strength) radiated from the mobile phone. Since the electromagnetic wave radiated to the space in the head direction is weakened due to the influence of the electromagnetic wave absorbed by the human body, there is a problem that the gain decreases in this direction. Furthermore, due to the absorption of electromagnetic waves by the human body, there has recently been a concern about adverse health effects, and a specific regulation of specific absorption rate (SAR) has been implemented. In order to suppress the gain reduction due to the electromagnetic wave absorption effect of the human body and reduce the SAR value, it is the most effective means to separate the electric field generated by the chip antenna from the human head as much as possible. It is preferable to mount the antenna on the surface opposite to the human head.

  With the antenna device according to the present invention, an antenna device with a wide bandwidth can be obtained, and it is easy to make it multiband. For example, GSM (0.9 GHz band) + GPS + PCS (1.8 GHz band) + DCS (1.9 GHz band), cellular (0.8 GHz band) + PCS (1.9 GHz band) + GPS (1.5 GHz band) + W-CDMA (2 GHz) Mobile phone, broadband CDMA (Code Division Multiple Access 2 GHz band), 802.11a (5 GHz band) + 802.11b (2.4 GHz band) wireless LAN, digital TV broadcasting, UWB (Ultra Wide Band) It can be used for communication equipment such as.

  With the antenna device according to the present invention, a device with a wide bandwidth can be obtained. Therefore, the antenna device can be used not only for mobile phones but also for various wireless communication devices such as GPS devices and wireless LANs installed in mobile terminals, personal computers, automobiles and the like.

  1: chip antenna, 2: mounting substrate, 3: third radiation electrode, 10: isolation securing part, 11: base, 12: first radiation electrode, 13: first feeding electrode, 14: terminal electrode 15, 18, 30: open end, 16: second radiation electrode, 17: second power supply electrode, 21a, 21b: ground portion of the mounting board, 22a, 22b: non-ground portion of the mounting board, 43: ground Electrode, 41, 42: Connection electrode, 51: First power supply, 52: Second power supply, 100: Antenna device

Claims (7)

A mounting substrate having a ground part and a non-ground part;
A chip antenna having a base, a first radiating electrode formed on the base, and a first feeding electrode connected to or disconnected from one end of the first radiating electrode;
Having a conductive pattern on the non-ground portion of the mounting substrate, and at least one radiation electrode formed on the back surface of the chip antenna mounting surface of the mounting substrate;
One end of the radiation electrode formed on the back surface of the mounting substrate is electrically connected to the first radiation electrode, and the other end is an open end. The antenna device according to claim 1, wherein an open end of a radiation electrode formed on a back surface of the mounting board is disposed at a position close to the feeding electrode. 3. The antenna device according to claim 1, wherein a longitudinal direction of the first radiation electrode and a radiation electrode formed on a back surface of the mounting substrate are arranged substantially in parallel. A self-inductance of the first radiation electrode; a capacitance between the first radiation electrode and a ground electrode of the mounting substrate; and a radiation electrode formed on the back surface of the first radiation electrode and the mounting substrate. The first resonance mode can be obtained by an LC resonance circuit composed of a capacitance between
And the self-inductance of the radiation electrode formed on the back surface of the mounting substrate, the capacitance between the radiation electrode and the ground electrode formed on the back surface of the mounting substrate, the first radiation electrode and the mounting LC resonance composed of a capacitance between the radiation electrode formed on the back surface of the substrate and a capacitance between the open end of the radiation electrode formed on the back surface of the mounting substrate and the feeding electrode. The antenna device according to claim 1, wherein the second resonance mode can be obtained by a circuit. 5. The antenna device according to claim 1, wherein the first radiation electrode has a helical structure or a meander structure. 6. The antenna device according to claim 1, wherein the first radiation electrode and a radiation electrode formed on a back surface of the mounting board are connected by a through hole provided in the mounting board. A communication device comprising the antenna device according to claim 1.

Images