JP2012120001A - Antenna device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inexpensive antenna device enabling volume reduction and having directivity with high gain.SOLUTION: An antenna device comprises on a plane substrate : a radiation element; a waveguide element arranged in parallel with the radiation element and being shorter than the radiation element; a reflective element arranged in parallel with the radiation element and being longer than the radiation element; and a radio communication circuit mounted in a region of the waveguide element or reflective element by using a conductor configuring the waveguide element or reflective element as a circuit pattern.

Description

  The present invention relates to a directional antenna device having a planar shape for ubiquitous communication and wireless communication service.

  In recent years, electronic devices having a small antenna such as a wireless LAN or Bluetooth (registered trademark) have become widespread due to the progress of a ubiquitous society. These small antennas are often built into electronic devices.

  On the other hand, antenna devices (communication modules with antennas) have become widespread and are connected to personal computers through USB terminals and the like. These antenna devices include an antenna, a communication IC, a connection interface with a personal computer, and the like.

  Many antenna devices use a monopole antenna. However, although the monopole antenna is often used because of its small size, there is a problem that current flows through the ground and is greatly affected by the ground.

  In general, the gain decreases when the antenna is built-in.

  The related antenna technology is described in, for example, Patent Document 1 and Patent Document 2. Patent Document 1 and Patent Document 2 describe a Yagi type antenna (Yagi / Uda antenna (so-called Yagi antenna (registered trademark))) using a substrate pattern.

An antenna described in Patent Document 1 is shown in FIG.
Reference numeral 220 shown in FIG. 10 denotes an antenna unit, which is provided on the dielectric substrate 221. Each element of the antenna unit 220 is formed on the dielectric substrate 221 by a copper foil pattern. 223 shown in (a) operates as a radiating element, 222 (a), 222 (b), and 222 (c) operate as a director, and 224 operates as a primary reflector. Reference numeral 226 denotes an antenna holding metal fitting, and the holding portion 231 constituting the end portion operates as a secondary reflector. In the Yagi type antenna shown in FIG. 5B, the reflector 224 is omitted and only the holding portion 231 is used as the reflector. In the Yagi type antenna in the figure, d1 and d2 in the figure are set to about ¼ wavelength, and the holding unit 231 is operated as a reflector. The Yagi antenna is fed from the outside of the antenna by a coaxial line 227 to the radiating element 223. The antenna unit 220 and a wireless communication circuit (not shown) are connected via a coaxial line 227.

  The Yagi type antenna that can obtain a good gain on the substrate pattern with the above configuration can be configured. On the other hand, since the connection between the radio communication circuit and the antenna uses a coaxial line (cable), it cannot be realized in a compact and inexpensive manner. The wireless communication circuit is provided separately from the antenna.

A planar antenna described in Patent Document 2 is shown in FIG.
As shown in FIG. 11, antenna elements (radiating elements, waveguide elements, and reflecting elements) constituting the Yagi antenna are arranged on both sides of the substrate to constitute a planar antenna. In the figure, the solid line indicates the pattern on the front surface and the oblique line indicates the pattern on the back surface. Power supply to the dipole radiating element of the planar antenna is performed by forming a microstrip line using both surfaces of the substrate. Also, the shape of the microstrip line on one side is tapered to function as a balun. It is also described that a part of the wireless communication circuit connected to the end of the microstrip line may be provided on a substrate that forms a planar antenna. However, it is described that the components to be mounted on the substrate are limited to be provided on the microstrip line.

JP 2005-142925 A JP 2009-200719 A

  In providing an antenna, an antenna having good directivity characteristics and gain characteristics is desired. In addition, it is desired that matching can be easily performed for each device even if it is incorporated in each device. In addition, it is desired to be small and inexpensive.

  However, a satisfactory antenna is not provided for the plurality of requirements.

  The Yagi antenna described in Patent Document 1 has good characteristics but has not been miniaturized. In addition, the Yagi antenna described in Patent Document 2 has good characteristics and some components are mounted on the microstrip line, but many other mounting components related to the wireless communication circuit need to be mounted on another substrate. is there. In addition, although matching is performed between the antenna and the microstrip line, it is not possible to perform matching in consideration of mounted components. That is, the Yagi type antennas described in Patent Document 1 and Patent Document 2 still have problems regarding volume reduction and matching.

If the antenna used for ubiquitous communication is described with regard to the reduction in volume, the volume allocated to the antenna device incorporated in the terminal device is reduced due to the downsizing of each terminal device (node). At this time, if the volume of the wireless communication circuit cannot be reduced and is fixed, it means that the volume that the antenna can use is reduced. On the other hand, it is very difficult to take measures to maintain characteristics such as gain while reducing the volume used by the antenna.
As a measure for maintaining the communication distance in addition to the miniaturization of the terminal device, it is necessary to reduce the volume as the communication module while maintaining the performance as the antenna.
In the terminal device used as a sensor node, individual terminal devices are arranged in a wide range, and the communication distance with the server tends to be long. In particular, when the 2.4 GHz band is used as the use frequency band, the communication distance is shorter than the 900 MHz band used in the United States and the like, and therefore, an expensive high gain antenna is used on the server side. For this reason, the appearance of a small and inexpensive high gain antenna while having good gain on the server side and the terminal device side has been expected.

  A patch antenna may be used as a high gain antenna. However, since the patch antenna has a characteristic that a high gain cannot be obtained if the thickness is thin, it is not practical to use a pattern on the substrate as an antenna element.

  In addition, it is also desired to perform matching after the fact that the capacitance around the antenna changes due to the arrangement of the housing with the antenna or other components.

  An object of the present invention is to provide an antenna device having directivity and high gain, low volume, low cost, and easy matching.

  An antenna device according to the present invention includes, on a flat substrate, a radiating element, a waveguide element that is arranged in parallel with the radiating element and shorter than the radiating element, and is arranged in parallel with the radiating element and longer than the radiating element. A reflection element; and a wireless communication circuit mounted in the region of the waveguide element or the reflection element by using a conductor constituting the waveguide element or the reflection element as a circuit pattern.

  According to the present invention, it is possible to provide an antenna device having directivity and high gain, low volume, low cost, and easy matching.

It is a mimetic diagram showing antenna device 1 concerning a 1st embodiment. It is a schematic diagram which shows the antenna apparatus 1 concerning 1st Embodiment. It is a schematic diagram which shows the gamma match modification of the antenna device 1 concerning one Embodiment. It is a schematic diagram which shows the antenna apparatus 1 concerning one Embodiment. It is a schematic diagram which shows the gamma match modification of the antenna device 1 concerning one Embodiment. It is a block diagram which shows the antenna apparatus 101 concerning an Example. It is explanatory drawing which shows the relationship between the antenna apparatus 101 concerning Example, and the case 120 made from polycarbonate. It is a figure which shows the actual measurement return loss of the antenna apparatus 101 concerning an Example. It is a figure which shows the antenna apparatus 101 concerning an Example, and measured radiation characteristics. It is a block diagram which shows the antenna described in patent document 1. It is a block diagram which shows the planar antenna described in patent document 2.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a configuration diagram illustrating an antenna device 1 according to a first embodiment.
The antenna device 1 according to the present embodiment uses a pattern antenna having directivity configured using a substrate pattern as an antenna.

  In the antenna device 1, a radiating element 3, a waveguide element 4, a reflecting element 5, and a feed line 6 are formed on a printed board 2 using a substrate pattern. In addition, the reflective element 5 is also used as a mounting area for the wireless communication circuit 7. The feed line 6 is a parallel two-wire line, and feeds the radiation element 3 thereby.

  The wireless communication circuit unit 7, that is, the RF unit is configured by an RFIC and a matching circuit, and is connected to a feed line. A balanced signal is output from the output port 10 of the RFIC toward the feed line 6 which is a balanced parallel two-line line, and further output to the feed line 6 via the matching circuit to be fed to the radiation element 3.

  Between the radiating element 3 and the feed line 6 that is a parallel two-line line, a matching circuit 11 called a T match that feeds a balanced antenna with a balanced line is inserted. The T match has the adjustment capacitor 12 symmetrically.

  In addition, you may match not by T match but by the delta match (it is also called Y match) which does not have a matching capacitor.

  The radiating element 3, the waveguide element 4, and the reflecting element 5 are arranged in parallel on the printed circuit board 2 as shown in the drawing, and each element length is such that the waveguide element length <the radiating element length <the reflecting element length.

  The distance between the radiating element 3 and the reflecting element 4 is set to approximately 1/4 of the effective wavelength or slightly smaller than that. The distance between the radiating element 3 and the reflecting element 5 is configured to be approximately 1/4 of the effective wavelength or slightly smaller than that.

  A wireless communication circuit 7 (RF unit), a control circuit 8 (control unit), and an input / output interface are mounted in the pattern area of the reflective element 5. The wireless communication circuit 7 includes an RFIC, a matching circuit configured by LC, and the like.

The matching circuit is used for subsequent matching. The ground (circuit pattern) that is a part of the electric circuit of the wireless communication circuit 7 uses a conductor constituting the reflective element 5. Further, patterns (not shown) such as other signal lines are also appropriately formed using the conductors that constitute the reflective element 5. The implementation has gained insight that it is less likely to affect antenna characteristics.
The mounting may be double-sided mounting using vias or the like. The RFIC feeds power to the feed line 6 through a matching circuit. A control MCU is mounted on the control circuit 8 and is connected to an input / output interface (A / D port, serial, USB standard, etc.).

  The mounting area may be shared with the waveguide element 4 instead of being shared with the reflective element 5.

  The antenna device 1 may be provided with a matching circuit in the vicinity of the radiating element 3. The matching method is preferably a delta match (Y match) or a T match in which a balanced antenna can be fed by a balanced line.

  In this way, a patterned antenna is formed on a substrate, and a radio communication circuit, a control circuit, etc. are mounted on a reflective element or a waveguide element as an antenna element, thereby obtaining directivity and good gain. On the other hand, an antenna device having a low volume and a low price can be realized. In addition, since the radiating element, waveguide element, reflecting element, and feed line serving as antenna elements can be integrally formed on a single circuit mounting board, a compact and high gain and directivity antenna can be configured at low cost. In addition, an antenna device that is less affected by the mounting of a wireless communication circuit or the like can be realized.

  Further, by providing the matching circuit, in addition to matching between the antenna and the feed line, matching can be performed by combining the effects of mounting the wireless communication circuit and mounting on the housing. The radiating element 3 having the configuration shown in FIG. 1 is a single conductor, but the same applies when the radiating element 3 is replaced with a dipole antenna that feeds two conductors at the center.

  Next, a second embodiment will be described. In the second embodiment, for easy adjustment, the balanced signal from the RFIC is once converted into an unbalanced system, connected to a microstrip line, passed through a matching circuit, and further converted into a balanced system for radiation. Power is supplied to the element.

  A balanced signal is output from the output port 10 of the RFIC in FIG. This balanced signal is output to the unbalanced microstrip line via the balun and fed to the radiating element 3 via the matching circuit. Feeding to the radiating element 3 is performed via a feeding line 6 (microstrip line) and a matching circuit 11 (gamma match). The gamma match converts an unbalanced signal into a balanced signal and simultaneously performs matching adjustment. In the matching circuit 11 that performs gamma matching, the ground portion 9 of the microstrip feed line and the radiating element 3 are connected via a matching chip capacitor 12 and a through-hole via 13. The ground portion 9 of the microstrip line 6 is tapered to reduce the influence of the ground on the radiating element 3.

  As in the first embodiment, the antenna device 1 includes an antenna element, an RF unit (wireless communication circuit unit), a control unit (control circuit), and an input / output unit (input / output interface) on a flat substrate. The control unit has a control MCU.

  Further, as in the third embodiment shown in FIG. 3, the gamma match may be modified. In FIG. 3, the matching circuit 11 (gamma match) and the antenna element are on the opposite side of the substrate from FIG. Even in this configuration, a gamma match is obtained, and a similar antenna device is obtained.

  Next, a fourth embodiment will be described. In the fourth embodiment, a radio communication circuit mounting area is formed in the waveguide element area.

  FIG. 4 is a configuration diagram illustrating an antenna device 1 according to a fourth embodiment. As shown in FIG. 4, in the antenna device 1, the relationship between the radiating element, the reflective element, and the waveguide element is reversed from that of the antenna device 1 according to the second embodiment.

  In the antenna device 1, the reflective element 5 is not accompanied by mounting of the wireless communication circuit 7 or the like. On the other hand, mounting components such as the wireless communication circuit 7 and the control circuit 8 are mounted on both surfaces on the waveguide element 4 region. A matching circuit 11 is provided so as to face the radiation element 3 with the substrate 2 interposed therebetween.

  The matching circuit 11 employs a gamma match, and connects the feeder line 9 and the radiating element 3 via the matching chip capacitor 12 and the through-hole via 13. By appropriately replacing the matching chip capacitor 12, it is possible to change the capacitance of the matching line and perform characteristic matching. The matching circuit 11 has a pattern on which a mounting component whose capacity is changed is placed on the matching line, so that matching can be performed afterwards.

  When the antenna device 1 feeds power to the feed lines 6 and 9 from the wireless communication circuit 7 (waveguide element 4 side), a current standing wave is distributed to the radiating element 3. Thereafter, the radiating element 3 excites the waveguide element 4 and the reflecting element 5, and directivity is generated on the waveguide element 4 side as a result of their interaction.

  Even in the configuration of the present embodiment, as in the second embodiment, even if a wireless communication circuit is mounted in the waveguide element region as an antenna device using a planar substrate, directivity and good gain are achieved. Can be maintained. In addition, low volume, low cost, and easy matching can be realized.

  Similarly, radiating elements are arranged with two conductors of approximately effective wavelength / 4 length, and a communication circuit, a control circuit, an input / output port, etc. are placed on one side to operate as a monopole. Even if a reflective element is placed, it similarly functions as a directional antenna device. Further, as shown in FIG. 5, the gamma match may be modified.

  Next, an Example is shown and this invention is demonstrated.

  The following description will be made with an antenna apparatus having the same shape as that of FIG.

  The antenna device 101 shown in FIG. 6 is a 2.4 GHz band antenna-integrated sensor node antenna device. The antenna device operates as a Zigbee (registered trademark) module with an external interface such as a control unit or USB.

  The antenna device 101 forms a pattern antenna and mounts a wireless communication circuit 107 on an FR4 (Flame Retardant Type 4) substrate 102 of 60 × 60 × 0.8 mm.

  A mounting area such as a chip also serves as the reflective element 105 and secures 60 × 20 mm, and an antenna area excluding the reflective element 105 is 60 × 40 mm.

  The pattern of the reflective element 105 functions as an antenna element and is used as a mounting area for the RF unit, control unit, and input / output unit of the Zigbee module.

  The radiating element 103 is supplied with power from the mounted radio communication circuit 107 for zigbee communication via the microstrip lines 106 and 109.

  The distance d1 between the radiating element 103 and the reflecting element 105 is about 0.15 to 0.25λe, where the effective wavelength is λe. The distance d2 between the radiating element 103 and the waveguide element 104 is about 0.1 to 0.25λe.

  The microstrip lines 106 and 109 are arranged so as to face one side of the substrate 102 and extend from the center of the end of the mounting area of the reflective element 105 to the radiating element 103.

  The ground 109 of the microstrip line is narrowed so as to reduce the influence on the radiating element 103 as it approaches the radiating element 103.

  A matching circuit 111 is provided at the tip of the microstrip line 106.

  The matching circuit 111 employs gamma matching, has a matching chip capacitor 112 and a through-hole via 113, and is formed so that matching can be adjusted by adjusting the matching chip capacitor 112.

  As a matching method, another matching method such as an omega match may be used. Gamma match and omega match are used when a balanced antenna is fed by an unbalanced feed line.

  The wireless communication circuit 107 (RF unit) includes an RFIC, a chip capacitor, a balun, an LC matching circuit, and the like that operate the antenna device 101 as a Zigbee module.

  The wireless communication circuit 107 is mounted in the pattern area of the reflective element 105 and operates as an electric circuit using a circuit pattern that is a power source or a ground provided in the pattern area used as the reflective element 105. Also, a wiring pattern between components for causing the wireless communication circuit 107 to function is appropriately formed as a circuit pattern in the reflective element 105 region.

  Here, the influence of the housing and the like will be described. For the sake of explanation, a state in which the antenna device 101 is put in a polycarbonate case 120 is illustrated. The dimensions of the antenna device 101 are appropriately adjusted in consideration of the dielectric constant of the housing and the mounting parts around the antenna.

  The polycarbonate case 120 is made of polycarbonate having a thickness of 1.5 mm and covers the entire surface of the antenna device 101. FIG. 7 shows the relationship between the polycarbonate case 120 and the antenna device 101. Illustration of the wireless communication circuit 107 is omitted.

  The size of the conductor pattern adjusted in a state where the antenna device 101 is mounted on the polycarbonate case 120 of FIG. 7 is as follows.

  The size of the radiating element 103 is 5 × 41 mm, the size of the waveguide element 104 is 5 × 36 mm, and the size of the reflecting element 105 is 20 × 60 mm which is the size of the circuit mounting area.

  The distance between the radiating element 103 and the waveguide element 4 is 13.4 mm, and the distance between the reflecting element 105 (mounting region end) and the radiating element 103 is 14 mm. That is, the distance from the center of the radiating element 103 to the center of the waveguide element 104 is 18.4 mm.

The length L1 of the radiating element 103 is about ½ of the effective wavelength. The effective wavelength for the antenna element is shorter than the free space wavelength due to the influence of the dielectric constant of the substrate 102 and the dielectric constant of the polycarbonate case 120. Therefore, the element length of the radiating element 103 may be shorter than ½ of the free space wavelength.
Similarly, the length L2 of the waveguide element 104 and the length L3 of the reflection element 105 are set shorter than the length in free space in consideration of the influence of the case and the like.
The relationship between the element lengths is that the length L2 of the waveguide element 104 <the length L1 of the radiating element 103 <the length L3 of the reflecting element 105.

  The polycarbonate case 120 has a thickness tc = 1.5 mm and a gap g1 = 0.3 mm with respect to the substrate 102 (see FIG. 7). Further, the gap g2 on the antenna pattern side of the substrate 102 is 2.5 mm, and the gap g3 on the back side is 2 mm (see FIG. 7).

FIG. 8 and FIG. 9 show the evaluation measurement results when the antenna device 101 in which the wireless communication circuit 107 is mounted on the polycarbonate case 120 of FIG. 7 is evaluated. The value of the matching chip capacitor 112 as a result of the matching was 4.7 pF.
FIG. 8 shows measured return loss, and FIG. 9 shows measured radiation characteristics.
Referring to FIG. 8, it can be confirmed that an extremely wide matching characteristic with a return loss of -15 dB or less is obtained for the 2.4-2.5 GHz band.
In addition, referring to FIG. 9, it can be confirmed that the radiation characteristic has a maximum gain of 6.3 dBi in the waveguide element direction.

  As described above, according to the embodiment, it was confirmed that the antenna device 101 having a low volume and a low price can obtain good directivity characteristics and a high gain.

  In addition, matching was achieved by changing the matching chip capacitor of the matching circuit 111 (gamma match portion) and the matching circuit provided in the RF portion, and it was confirmed that the matching could be easily performed with respect to the environment where the antenna device 101 is placed.

  That is, even when a wireless communication circuit is mounted in the reflective element region as an antenna device using a flat substrate, it was possible to confirm the wisdom that maintains directivity and high gain.

  In addition, low volume, low cost, and easy matching were realized.

  Further, the mounting components constituting the wireless communication circuit may be mounted so as to be embedded in the flat substrate. If mounted in this way, the thickness corresponding to the height of the chip constituting the wireless communication circuit can be further reduced. Even if the wireless communication circuit is mounted so as to be embedded in the radiating element or waveguide element region, the directivity and high gain as the antenna device can be maintained. In addition, the volume can be further reduced.

  In the above description, only one waveguide element is described, but a plurality of waveguide elements may be appropriately provided. The waveguide element may be provided on both sides.

  In addition, as described above, the dielectric constant (or magnetic permeability) with respect to the antenna element changes depending on the arrangement of the substrate used in the antenna device and the surrounding housing, and the wavelength shortening effect is generated. For this reason, what is necessary is just to adjust the length of each element in consideration of the said effect.

  In addition, as a material used for the antenna device, a wireless communication circuit or the like may be mounted by printing an antenna element on an FPC (Flexible Printed Circuit) instead of a printed wiring board (PWB).

  Alternatively, a multilayer substrate may be used to form antenna elements, microstrip lines, etc. using an inner layer.

  Further, by configuring the antenna device to be detachable with a USB terminal or the like, it is possible to provide an antenna-integrated communication module that is low in volume and inexpensive while obtaining directivity and high gain. The antenna-integrated communication module can be easily matched and is convenient.

  The present invention can be used for a small-volume directional antenna used in, for example, a sensor node and a wireless LAN. The present invention can also be used for an internal antenna of an external wireless module such as Bluetooth.

DESCRIPTION OF SYMBOLS 1,101 Antenna apparatus 2,102 Printed circuit board 3,103 Radiation element (radiator)
4,104 Waveguide element (waveguide)
5, 105 Reflective element (reflector)
6, 9 Feed line 7, 107 Wireless communication circuit 8 Control circuit (control unit)
10 Output port (RFIC power supply port)
11, 111 Matching circuit 12, 112 Matching chip capacitor 13, 113 Through-hole via 106, 109 Microstrip line 120 Polycarbonate case

Claims (12)

On a substrate having a plane,
A radiating element;
A waveguide element disposed in parallel with the radiating element and shorter than the radiating element;
A reflective element arranged in parallel with the radiating element and longer than the radiating element;
An antenna device comprising: a wireless communication circuit mounted in a region of the waveguide element or the reflective element by using a conductor constituting the waveguide element or the reflective element as a circuit pattern.   The wireless communication circuit and a control circuit mounted using a conductor constituting the waveguide element or the reflection element as a circuit pattern is provided in a region of the waveguide element or the reflection element. Item 1. The antenna device according to Item 1. The antenna device according to claim 1, wherein the wireless communication circuit is mounted so that a conductor constituting the waveguide element or the reflective element is used as a ground.   4. The antenna device according to claim 1, wherein power supply to the radiating element is performed from the wireless communication circuit via a power supply line using a conductive pattern provided on the substrate. 5.   The antenna apparatus according to claim 4, wherein the feed line is a microstrip line.   6. The antenna apparatus according to claim 5, wherein a ground pattern width of the microstrip line is provided in a tapered shape constricting the vicinity of the radiating element. A matching provided by electrically connecting a conductor pattern formed on the opposite side of the surface of the substrate having the radiating element so as to face the radiating element to a conductor constituting the radiating element by a via. 7. The antenna device according to claim 5, further comprising a matching circuit connected to a conductor used as the microstrip line.   The antenna device according to claim 7, wherein the matching circuit has a pattern on which a mounting component that changes a capacitance of the matching line is mounted on the matching line.   9. The antenna device according to claim 7, wherein the matching circuit has a shape capable of performing matching using a gamma match or an omega match. The feeding line is a balanced line using two parallel wires,
5. The antenna device according to claim 4, wherein the feed line is matched with the radiating element by T match or delta match.   The antenna device according to any one of claims 1 to 10, wherein mounting components constituting the wireless communication circuit are embedded and mounted in the substrate.   An antenna-integrated communication module, wherein the antenna device according to any one of claims 1 to 11 is configured to be removable with a USB terminal.

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