Patent Application
20100231453
The present invention relates to a steerable array antenna apparatus capable of electrically steering its beam directions. More particularly, the present invention relates to a circuitry for controlling directivity of the array antenna apparatus.
In recent years, devices applying wireless techniques, such as wireless LANs complying with IEEE 802.11a/b/g standards, and Bluetooth, have been rapidly spreading. IEEE 802.11a and IEEE 802.11g specified the data transmission rate of 54 Mbps, and recently, active researches and developments have been done on wireless schemes for achieving higher transmission rates.
As one of techniques for increasing transmission rates of wireless communication systems, a MIMO (Multi-Input Multi-Output) communication system has received wide attention. This is a technique for increasing transmission capacity and improving communication speed by providing both the transmitter and the receiver with multiple antenna elements and having transmission paths spatially multiplexed. This technique is essential not only for wireless LANs, but also for next-generation wireless communication systems such as mobile phone communication systems and IEEE 802.16e (WiMAX).
In the MIMO communication scheme, a transmitter divides and sends transmitting data through multiple antenna elements, the data is transmitted over multiple virtual MIMO channels, and a receiver receives signals through multiple antenna elements and processes the signals to obtain received data. Generally, a wireless device using the MIMO communication scheme is provided with multiple omnidirectional antenna elements such as dipole antennas or sleeve antennas. In this case, there is a problem of degradation in transmission quality caused by increases in the correlations between antenna elements, unless addressing this situation by, e.g., sufficiently separating the antenna elements from one another, or tilting the respective antenna elements in different directions to make a combination of different polarizations.
As a conventional technique available for solving the above problem, for example, there is an array antenna apparatus of Patent Literature 1, which is an adaptive directional antenna. The array antenna apparatus of Patent Literature 1 includes three printed wiring boards arranged so as to surround a half-wave dipole antenna mounted vertically on a dielectric supporting substrate. The half-wave dipole antenna is supplied with a radio frequency signal through a balanced feeder cable. Moreover, on the back side of each printed wiring board, two sets of parasitic elements are provided in parallel with each other, each set including two printed antenna elements (elements each made of a conductor pattern). In each parasitic element, the two printed antenna elements oppose to each other with a space therebetween. A through-hole conductor is provided at one end of each printed antenna element opposing to the other printed antenna element, and is connected to an electrode terminal on the front side of the printed wiring board. In each parasitic element, a variable-capacitance diode is mounted between the two electrode terminals, and these electrode terminals are further connected to a pair of cables through high value resistors for blocking high frequencies, and the pair of cables are connected to bias voltage supply terminals DC+ and DC− of a controller (not shown) for controlling the directivity of the array antenna apparatus. By changing bias voltages supplied from the controller, the respective reactance values of the variable-capacitance diodes connected to the parasitic elements change. In this manner, the electrical length of each parasitic element is changed as compared to that of the half-wave dipole antenna, thus changing the horizontal directivity of the array antenna apparatus.
It is possible to reduce distances between antennas by using, as MIMO communication antennas, adaptive directional antennas such as the array antenna apparatus of Patent Literature 1, and setting the respective antennas' directivities so as to avoid correlations between the antennas.
Furthermore, by using adaptive directional antennas for MIMO communication, two advantages can be expected as follows. As a first advantage, in the case of a low electric field level at the receiver side, it is possible to direct a beam in a direction of arrival of a strong radio wave, thus receiving at a stable electric field level. As a second advantage, when fading occurs due to reflected waves from a wall or ceiling, one antenna receives a direct wave and the other antennas receive the reflected waves with long delay time, thus achieving more effective MIMO wireless communication.
PATENT LITERATURE 1: Japanese Patent Laid-open Publication No. 2002-261532.
By using the adaptive directional antennas of Patent Literature 1 in a MIMO communication system, it is possible to enjoy the above-mentioned three benefits, i.e., a reduction in the correlations between antennas, an improvement in communication quality, and an improvement in received power, and also possible to reduce an area occupied by an antenna apparatus.
However, in the case that the conventional adaptive directional antennas are arranged in close to each other, there is a problem that one of DC voltage supply lines connected to variable-capacitance diodes for controlling parasitic elements affects the directivity of an adjacent antenna, and thus, a desired directivity steering characteristic cannot be expected.
Moreover, the conventional adaptive directional antennas use variable-capacitance diodes with variable reactance, as switching elements for changing directivities. However, in a variable reactance element such as a variable-capacitance diode, there is a problem that its reactance value does not change with respect to the voltage in a centimeter-wave range of several GHz to several tens of GHz, and thus, the directivity can not change.
An object of the present invention is therefore to solve the above-described two problems of the prior art, and provide an array antenna apparatus that is capable of changing between “radiation in an omnidirectional pattern” and “radiation with a beam in a specific direction” even when reducing the distances between antennas or when operating in a centimeter-wave range of several GHz to several tens of GHz, and thus that is suitable for a MIMO communication scheme.
According to an aspect of the present invention, an array antenna apparatus including a plurality of steerable antennas is provided. Each of the plurality of steerable antennas is provided with: an radiating antenna element, at least one parasitic antenna element, at least one pair of rectifier elements provided to the at least one parasitic antenna element, control lines, at least two first inductors. The parasitic antenna element is located at a side of the radiating antenna element so as to be separated from the radiating antenna element in a direction by a distance, and the parasitic antenna element includes a first conductor portion and a second conductor portion. The pair of rectifier elements are provided between the first conductor portion and the second conductor portion, anodes of the rectifier elements are connected to each other, a cathode of a first one of the rectifier elements is connected to the first conductor portion, a cathode of a second one of the rectifier elements is connected to the second conductor portion, and the pair of rectifier elements operate the parasitic antenna element as a reflector when a bias voltage is applied thereto from bias voltage supply means. The control lines connect the rectifier elements to the bias voltage supply means. The at least two first inductors are provided on each of the control lines at predetermined intervals, at portions of the control line being electromagnetically coupled to a steerable antenna other than the steerable antenna including the rectifier elements to which the control line is connected. The intervals for providing the at least two first inductors is set to such a length that substantially no resonance occurs in a section of the control line between the first inductors at an operating frequency of the steerable antenna.
In the array antenna apparatus, the intervals for providing the at least two first inductors are set to a length such that the section of the control line between the first inductors is different from an integral multiple of one-quarter of an operating wavelength of the steerable antenna.
Moreover, in the array antenna apparatus, on each of the control lines, at least one second inductor is further provided at a portion of the control line electromagnetically coupled to the steerable antenna including the rectifier elements to which the control line is connected. A section of the control line between the rectifier elements and the second inductor is set to such a length that substantially no resonance occurs at an operating frequency of the steerable antenna.
Further, in the array antenna apparatus, the array antenna apparatus is patterned on a printed wiring board. Each of the plurality of steerable antennas includes two parasitic antenna elements such that the radiating antenna element is positioned between the parasitic antenna elements.
Furthermore, in the array antenna apparatus, the array antenna apparatus is patterned on a plurality of printed wiring boards. Each of the plurality of steerable antennas includes at least one parasitic antenna element provided on at least one of the plurality of printed wiring boards.
In order to solve the above-described problems of the prior art, an array antenna apparatus of the present invention is configured as follows. Each parasitic antenna element has a space at the middle of the parasitic element, and is provided with a pair of rectifier elements (e.g., PIN diodes) connected in series such that their anode terminals oppose to each other, and the rectifier elements are connected through control lines to bias voltage supply means (controller) such that their anode terminals are connected to an on/off terminal of the bias voltage supply means and their cathode terminals are connected to a GND terminal of the bias voltage supply means. In addition, inductors with a certain inductance are inserted to each control line at predetermined intervals, at portions of the control line that are electromagnetically coupled to a steerable antenna (preferably, inserted at three points in total, i.e., a point on the control line that is closest to an adjacent steerable antenna, and two points on the control line each remote from the closest point by a predetermined distance). The distances between the inductors are preferably set to a length different from an integral multiple of one-quarter of an operating wavelength for communication, e.g., set to a length shorter than one-quarter of the operating wavelength.
When a voltage from the controller is lower than an operating voltage of a diode, the diode is equivalent to a series connected circuit of small capacitance and impedance, and accordingly, the parasitic antenna element does not affect antenna radiation, thus resulting in omnidirectional radiation. On the other hand, when a voltage from the controller is higher than the operating voltage of the diode, the diode becomes conductive, and thus, the parasitic antenna element acts as a reflector. By using this circuitry, even when operating in a high-frequency range where variable reactance elements are not operable, it is possible to change a MIMO antenna's directivity.
Moreover, the inductors inserted to the control lines prevent undesirable resonances in the control lines. By setting the distances between the inductors to be shorter than one-quarter of the operating wavelength, the resonance frequency of the control lines becomes higher than the operating frequency. By using such a configuration, it is possible to prevent that resonances in the control lines affect the directivity of an adjacent antenna.
Preferred embodiments for implementing the present invention will be described below with reference to the drawings. Note that components having similar functions are denoted by the same reference numerals throughout the specification and drawings, and are not explained repeatedly.
The steerable antenna 100 includes one half-wave dipole antenna element 101 as an radiating antenna element, and two parasitic antenna elements 111 and 112. The dipole antenna element 101 includes two strip radiating conductor elements 101a and 101b, each formed as a conductor pattern on the printed wiring board 1. The radiating conductor elements 101a and 101b oppose to each other with a space therebetween, and are located along a straight line. Feeding points 102a and 102b are respectively provided at opposing ends of the radiating conductor elements 101a and 101b, and connected to a wireless communication circuit (not shown) through a balanced radio frequency cable (not shown), thus transmitting and receiving radio signals through the dipole antenna element 101. Each of the parasitic antenna elements 111 and 112 is located on a line parallel to the straight line of the dipole antenna element 101 so as to be separated from the straight line by one-quarter of an operating wavelength for communication, such that the dipole antenna element 101 is positioned between the parasitic antenna elements 111 and 112. The parasitic antenna element 111 also includes two strip parasitic conductor elements 111a and 111b, each formed as a conductor pattern on the printed wiring board 1. The parasitic conductor elements 111a and 111b oppose to each other with a space therebetween, and are located along a straight line. A pair of PIN diodes 121a and 121b are respectively provided at opposing ends of the parasitic conductor elements 111a and 111b. A cathode terminal of the PIN diode 121a is connected to the parasitic conductor element 111a, a cathode terminal of the PIN diode 121b is connected to the parasitic conductor element 111b, and anode terminals of the PIN diodes 121a and 121b are connected to each other. The anode terminals of the PIN diodes 121a and 121b are connected through a control line 131a to a bias voltage supply terminal (DC terminal) of a controller (not shown) for controlling the directivity of the array antenna apparatus by applying a control voltage (i.e., a bias voltage). The cathode terminals of the PIN diodes 121a and 121b are connected through a control line 131b to a ground terminal (GND terminal) of the controller. Thus, the control lines 131a and 131b are a DC voltage supply line and a GND line for controlling the parasitic antenna element 111, respectively.
A radio frequency choke inductor (coil) 141a having, e.g., an inductance of about several tens of nH is provided on the control line 131a so as to be close to the anode terminals of the PIN diodes 121a and 121b. On the control line 131a, a current control resistor 151 of about several hundreds of ohms is further provided. In addition, radio frequency choke inductors 141c and 141d having, e.g., an inductance of about several tens of nH are provided on the control line 131b so as to be close to the cathode terminals of the PIN diodes 121a and 121b. In this case, the inductors 141a, 141c, and 141d serve to prevent a radio-frequency signal exciting at the parasitic antenna element 111 from leaking to the control lines 131a and 131b. On the control lines 131a and 131b, inductors having, e.g., an inductance of about several nH are further provided at predetermined intervals for preventing the control lines 131a and 131b from resonating with a radio wave radiated from the steerable antenna 100 or the other steerable antenna, and thus for avoiding the resonation affecting radiations of the steerable antennas.
Furthermore, the parasitic antenna element 112 is also configured in a similar manner as that of the parasitic antenna element 111. The parasitic antenna element 112 includes parasitic conductor elements 112a and 112b, which are configured and located in a similar manner as that of the parasitic conductor elements 111a and 111b of the parasitic antenna element 111. At opposing ends of the parasitic conductor elements 112a and 112b, a pair of PIN diodes 122a and 122b is provided in a similar manner as that of the PIN diodes 121a and 121b connected to the parasitic antenna element 111. The PIN diodes 122a and 122b are connected to the controller of the array antenna apparatus through control lines 132a and 132b. On the control lines 132a and 132b, inductors 142a to 142e and a resistor 152 are provided in a similar manner as that of the inductors 141a to 141e and the resistor 151 on the control lines 131a and 131b.
The steerable antenna 200 also includes one dipole antenna element 201 and two parasitic antenna elements 211 and 212, in a similar manner as that of the steerable antenna 100. The parasitic antenna element 211 is connected with PIN diodes 221a and 221b, and the parasitic antenna element 212 is connected with PIN diodes 222a and 222b. The PIN diodes 221a and 221b are connected to the controller of the array antenna apparatus through control lines 231a and 231b, and the PIN diodes 222a and 222b are connected to the controller of the array antenna apparatus through control lines 232a and 232b. On the control lines 231a and 231b, inductors 241a, 241e, and 241f and a resistor 251 are provided in a similar manner as that of the inductors 141a, 141c, and 141d and the resistor 151 on the control lines 131a and 131b. Furthermore, in a similar manner as that of the inductors 141b and 141e on the control lines 131a and 131b, inductors are provided on the control lines 231a and 231b at predetermined intervals for preventing the control lines 231a and 231b from resonating with a radio wave radiated from the steerable antenna 200 or the other steerable antenna, and thus for avoiding the resonation affecting radiations of the steerable antennas.
In the case of the configuration of
In the steerable antennas 100 and 200 of the array antenna apparatus configured as above, when the control voltage from the controller is off, a voltage is not applied from the DC terminal thereof, and thus, each of the PIN diodes 121a, 121b, 122a, 122b, 221a, 221b, 222a, and 222b is equivalent to a series connected circuit of small capacitance and impedance. Accordingly, the parasitic antenna elements 111, 112, 211, and 212 are not excited, and thus do not affect the directivities of the steerable antennas 100 and 200. On the other hand, when the controller turns on a control voltage to, e.g., the parasitic antenna element 111, the controller applies bias voltages from the DC terminal to the anodes of the PIN diodes 121a and 121b through the control line 131a such that the applied bias voltages are higher than an operating voltage of the PIN diodes 121a and 121b, e.g., about 0.8 V, and thus, the PIN diodes 121a and 121b become conductive. At this time, the parasitic antenna element 111 is excited by a radio wave radiated from the dipole antenna element 101, and re-radiates a radio wave. Since the separation between the dipole antenna element 101 and the parasitic antenna element 111 is one-quarter of an operating wavelength, the radio wave re-radiated from the parasitic antenna element 111 has a phase delayed by 90 degrees with respect to the radio wave radiated from the dipole antenna element 101. As a result of superposition of these two radio waves, radio waves propagating in +X direction relative to the parasitic antenna element 111 are cancelled, and radio waves propagating in −X direction relative to the dipole antenna element 101 are increased. As such, when a bias voltage is applied to the parasitic antenna element 111, the parasitic antenna element 111 operates as a reflector for the dipole antenna element 101, and thus, the directivity of the steerable antenna 100 can be changed so as to steer its beam in −X direction. Moreover, when other parasitic antenna elements 112, 211, and 212 are turned on, directivities can be similarly controlled.
Meanwhile, when antennas are arranged to avoid their correlations as in the present embodiment, the control lines 232a and 232b for the steerable antenna 200 are laid close to the steerable antenna 100, and thus, the steerable antenna 100 and the control lines 232a and 232b are electromagnetically coupled to each other. When a conductor line is laid near an antenna, the conductor line is often excited by a radio wave radiated from the antenna, and thus acts as a reflector to change the antenna's directivity. The inductors 242b to 242d and 242g to 242i respectively provided on the control lines 232a and 232b serve to prevent this phenomenon. As an example, an explanation is shown below based on the control line 232a and the inductors 242b to 242d provided thereon. The inductors 242b to 242d are provided on the control line 232a at portions of the control line 232a that are electromagnetically coupled to the steerable antenna 100. The inductors 242b to 242d are preferably inserted at three points in total, i.e., a point on the control line 232a that is closest to the adjacent steerable antenna 100, and two points on the control line 232a each remote from the closest point by a predetermined distance. A radio wave radiated from the steerable antenna 100 excites the control line 232ab between the inductors 242b and 242c on the control line 232a, and the control line 232ac between the inductors 242c and 242d on the control line 232a. If the frequency at which the control lines 232ab and 232ac are excited is the same as the operating frequency of the steerable antenna 100 for communication, then the control lines 232ab and 232ac act as reflectors at that frequency, thus affecting the directivity of the steerable antenna 100. In this case, undesirable resonances in the control line 232a are prevented by setting the distances between the inductors 242b, 242c, and 242d to be such a length that substantially no resonance occurs at the operating frequency of the steerable antenna 100. Specifically, the distances between the inductors are set to be a length different from an integral multiple of one-quarter of an operating wavelength λ(nλ/4), e.g., a length longer or shorter than nλ/4 by at least 10%. Preferably, the distances between the inductors are set to be a length different from nλ/4, and further set to be a length of less than λ/2 or less than λ/4 relative to the operating wavelength λ, and thus, the resonant frequency of the control lines 232ab and 232ac becomes higher than the operating frequency of the steerable antenna 100, thus preventing undesirable resonances in the control line 232a. By using the configuration described above, it is possible to reduce the influence exerted on the directivity of the steerable antenna 100 by the control line 232a of the steerable antenna 200. The control line 232b and the inductors 242g to 242i provided thereon are configured in a similar manner, thus preventing undesirable resonances in the control line 232b. Also on each of other control lines 131a, 131b, 132a, 132b, 231a, and 231b, undesirable resonances in the control line are prevented by providing inductors on the control line at predetermined intervals at portions of the control line which are close to and electromagnetically coupled to its adjacent steerable antenna (not shown).
Preferably, on each control line, in order to prevent the control line from affecting the radiation of a steerable antenna to which the control line is connected, at least one inductor is provided at a portion that is close to and electromagnetically coupled to the steerable antenna. For example, on the control line 131a, the inductor 141b is provided such that the length of the control line 131a from the inductor 141b to the PIN diodes 121a and 121b (or the length of the control line 131a from the inductor 141b to the inductor 141a or the resistor 151) is a length different from nλ/4 (e.g., a length of less than λ/4). By using this configuration, the length of a portion of the control line 131a that is close to and electromagnetically coupled to the steerable antenna 100 is such a length that substantially no resonance occurs at the operating frequency of the steerable antenna 100, thus preventing undesirable resonances in the control line 131a. Also on each of other control lines 131b, 132a, 132b, 231a, 231b, 232a, and 232b, undesirable resonances in the control line are prevented by providing at least one inductor on the control line at a portion of the control line that is close to and electromagnetically coupled to a steerable antenna to which the control line is connected.
Although the present embodiment shows the case of using the dipole antenna elements 101 and 201 as radiating antenna elements, any antenna element can be used as long as having a horizontal directivity which is nearly omnidirectional. Accordingly, even when sleeve antennas or collinear antennas are used, it is possible to implement an array antenna apparatus operable in a similar manner as that of the present embodiment. In addition, although the present embodiment shows examples in which the two steerable antennas 100 and 200 or the three steerable antennas 100, 200, and 300 are arranged on the printed wiring board 1, four or more steerable antennas may be arranged.
As described above, the array antenna apparatus of the present embodiment is provided with pairs of PIN diodes each pair being connected to each other at their anodes, and further provided with inductors on each control line at predetermined intervals. Thus, it is possible to provide an array antenna apparatus with a circuitry for controlling directivity, capable of changing between “radiation in an omnidirectional pattern” and “radiation with a beam in a specific direction” even when operating in a centimeter-wave range of several GHz to several tens of GHz or when reducing the distances between steerable antennas, and thus suitable for a MIMO communication scheme.
As shown in
The operation of the array antenna apparatus according to the present embodiment will be explained with reference to
Similarly, by changing a combination of parasitic antenna elements to be excited (i.e., to be operated as reflectors), the beam can be steered in any one of eight directions.
As can be seen from
Each of the steerable antennas 100A and 200A is not limited to including only four parasitic antenna elements, and may include one to three parasitic antenna elements or five or more parasitic antenna elements such that the parasitic antenna elements are provided on at least one of a plurality of printed wiring boards.
As described above, the array antenna apparatus of the present embodiment is provided with pairs of PIN diodes each pair being connected to each other at their anodes, and further provided with inductors on each control line at predetermined intervals. Thus, it is possible to provide an array antenna apparatus with a circuitry for controlling directivity, capable of changing between “radiation in an omnidirectional pattern” and “radiation with a beam in a specific direction” even when operating in a centimeter-wave range of several GHz to several tens of GHz or when reducing the distances between steerable antennas, and thus suitable for a MIMO communication scheme.
Although the above-described embodiments show an example in which both of the radiating antenna element and the parasitic antenna elements are configured as dipole antenna elements, these elements may be configured as monopole antenna elements provided on a ground conductor. Moreover, each inductor is not limited to be mounted on electrode terminals of
A wireless communication card connection structure according to the present invention can prevent a conductor near an antenna from being excited and from affecting directivity, and accordingly, this is useful to mount multiple steerable antennas close to each other.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2007-272537 | Oct 2007 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2008/002914 | 10/15/2008 | WO | 00 | 4/19/2010 |
