U.S. patent application number 15/907730 was filed with the patent office on 2019-03-14 for antenna device, wireless communication device and signal transmission method.
This patent application is currently assigned to KABUSHIKI KAISHA TOSHIBA. The applicant listed for this patent is KABUSHIKI KAISHA TOSHIBA. Invention is credited to Makoto HIGAKI, Seiya KISHIMOTO, Makoto SANO.
Application Number | 20190081685 15/907730 |
Document ID | / |
Family ID | 65410963 |
Filed Date | 2019-03-14 |
United States Patent
Application |
20190081685 |
Kind Code |
A1 |
SANO; Makoto ; et
al. |
March 14, 2019 |
ANTENNA DEVICE, WIRELESS COMMUNICATION DEVICE AND SIGNAL
TRANSMISSION METHOD
Abstract
According to one embodiment, an antenna device includes a branch
circuit, a first phase shifter, a second phase shifter and a
radiating element. The branch circuit divides an input signal and
generates a first signal and a second signal. The first phase
shifter is capable of shifting a phase of the first signal. The
second phase shifter is capable of shifting a phase of the second
signal. The radiating element transmits a right-hand circularly
polarized wave based on a first output signal of the first phase
shifter and transmits a left-hand circularly polarized wave based
on a second output signal of the second phase shifter.
Inventors: |
SANO; Makoto; (Kawasaki,
JP) ; KISHIMOTO; Seiya; (Tokyo, JP) ; HIGAKI;
Makoto; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KABUSHIKI KAISHA TOSHIBA |
Tokyo |
|
JP |
|
|
Assignee: |
KABUSHIKI KAISHA TOSHIBA
Tokyo
JP
|
Family ID: |
65410963 |
Appl. No.: |
15/907730 |
Filed: |
February 28, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04B 7/0682 20130101;
H01Q 9/045 20130101; H01Q 3/36 20130101; H01Q 9/0407 20130101; H01Q
25/001 20130101; H01Q 21/245 20130101 |
International
Class: |
H04B 7/06 20060101
H04B007/06; H01Q 25/00 20060101 H01Q025/00; H01Q 3/36 20060101
H01Q003/36 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 11, 2017 |
JP |
2017-174236 |
Claims
1. An antenna device comprising: a branch circuit configured to
divide an input signal and generate a first signal and a second
signal; a first phase shifter configured to be capable of shifting
a phase of the first signal; a second phase shifter configured to
be capable of shifting a phase of the second signal; and a
radiating element configured to transmit a right-hand circularly
polarized wave based on a first output signal of the first phase
shifter and transmit a left-hand circularly polarized wave based on
a second output signal of the second phase shifter, wherein
insertion loss of the first phase shifter is substantially equal to
insertion loss of the second phase shifter.
2. (canceled)
3. The antenna device according to claim 1, wherein a sum of
lengths of a transmission line connecting the branch circuit and
the first phase shifter and a transmission line connecting the
first phase shifter and the radiating element is substantially
equal to a sum of lengths of a transmission line connecting the
branch circuit and the second phase shifter and a transmission line
connecting the second phase shifter and the radiating element.
4. The antenna device according to claim 1, wherein a shape of the
branch circuit is substantially symmetrical when seen from a
transmission line supplying the input signal to the branch
circuit.
5. The antenna device according to claim 1, wherein a shape of the
transmission line connecting the branch circuit and the first phase
shifter and a shape of the transmission line connecting the branch
circuit and the second phase shifter are substantially symmetrical
when seen from the branch circuit.
6. The antenna device according to claim 1, wherein amplitudes of
the first signal and the second signal are substantially equal.
7. The antenna device according to claim 1, wherein a range of a
phase shift amount of the first phase shifter is equal to a range
of a phase shift amount of the second phase shifter.
8. The antenna device according to claim 1, wherein the first phase
shifter has the same configuration as the second phase shifter.
9. The antenna device according to claim 1, further comprising a
control circuit configured to, in a state of fixing a phase shift
amount of one of the first phase shifter and the second phase
shifter, cause a phase shift amount of the other to change.
10. The antenna device according to claim 9, wherein the control
circuit is further configured to fix fixes the phase shift amount
of the one of the phase shifters to a maximum or minimum value of a
range of the phase shift amount.
11. A wireless communication device comprising: the antenna device
according to claim 1; and a wireless communication circuit
configured to perform wireless communication using the antenna
device.
12. A signal transmission method comprising: dividing an input
signal and generating a first signal and a second signal; adjusting
a phase of the first signal by a first phase shifter; adjusting a
phase of the second signal by a second phase shifter; and
transmitting a right-hand circularly polarized wave based on the
first signal phase-adjusted by the first phase shifter;
transmitting a left-hand circularly polarized wave based on the
second signal phase-adjusted by the second phase shifter, wherein
insertion loss of the first phase shifter is substantially equal to
insertion loss of the second phase shifter.
13. The antenna device according to claim 9, wherein the control
circuit is further configured to fix the phase shift amount of the
one of the first phase shifter and the second phase shifter to 0
degree or 180 degree, and change the phase shift amount of the
other of the first phase shifter and the second phase shifter
between 0 degree and 180 degree.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is based upon and claims the benefit of
priority from the prior Japanese Patent Application No.
2017-174236, filed on Sep. 11, 2017, the entire contents of which
are incorporated herein by reference.
FIELD
[0002] Embodiments described herein relate to an antenna device, a
wireless communication device and a signal transmission method.
BACKGROUND
[0003] Among variable-polarization-plane antennas provided with a
right-hand circularly polarized antenna and a left-hand circularly
polarized antenna, a configuration is known in which a phase
shifter is connected to a feeder of one of the right-hand
circularly polarized antenna and the left-hand circularly polarized
antenna. Thereby, it is possible to change a polarization plane of
a linearly polarized wave only by controlling a phase shift amount
of the one phase shifter.
[0004] However, there is a problem that an amplitude difference
between a right-hand and a left-hand circularly polarized waves
occurs due to insertion loss of the phase shifter, and cross
polarization discrimination deteriorates (a cross polarization
component increases). Further, in order to maximize a variable
range of the polarization plane of the linearly polarized wave (0
to 180.degree.), it is necessary to cause a variable range of the
phase shift amount of the phase shifter to be 0 to 360.degree..
That is, it is necessary to increase the variable range of the
phase shift amount. A phase shifter the phase shift amount variable
range of which is large has such problems that the phase shifter is
physically large, that insertion loss is large, and that
fluctuation of insertion loss caused by change in the phase shift
amount and frequency is large.
[0005] On the other hand, a polarization plane control antenna is
also known which controls a phase of one of a right-hand circularly
polarized wave and a left-hand circularly polarized wave by a phase
shifter and controls amplitudes of both waves by amplifiers,
respectively. According to the polarization plane control antenna,
it is possible to, by compensating fluctuation of insertion loss of
the phase shifter by the amplifiers, the cross polarization
discrimination can be improved.
[0006] However, since the insertion loss of the phase shifter
differs according to frequency, it is necessary to adjust an
amplitude according to frequency for transmission/reception, and
there is a problem that configurations of each amplifier and the
phase shifter are complicated. Further, it is difficult to use a
wide frequency band while maintaining preferable cross polarization
discrimination. In addition, there is also a problem that a
waveform of a transmitted/received high-frequency signal is
distorted by the variable amplifiers, a problem that harmonics
occur, and the like.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 is a diagram showing a schematic configuration of an
antenna device according to an embodiment of the present
invention;
[0008] FIG. 2 is a diagram showing a modification of a radiating
element;
[0009] FIG. 3 is a diagram showing a modification of the radiating
element;
[0010] FIG. 4 is a diagram showing a modification of the radiating
element;
[0011] FIG. 5 is a diagram showing a relationship between phase
shift amounts of a first phase shifter and a second phase shifter
and a polarization plane;
[0012] FIG. 6 is a diagram showing a relationship between an
amplitude difference between a right-hand circularly polarized wave
and a left-hand circularly polarized wave, and cross polarization
discrimination;
[0013] FIG. 7 is a diagram showing a configuration example in which
a control circuit is connected to the antenna device according to
the embodiment of the present invention;
[0014] FIG. 8 is a diagram showing a configuration example in which
the control circuit is connected to the antenna device according to
the embodiment of the present invention;
[0015] FIG. 9 is a diagram showing a modification of the antenna
device according to the embodiment of the present invention;
[0016] FIG. 10 is a diagram showing a modification of the antenna
device according to the embodiment of the present invention;
and
[0017] FIG. 11 is a diagram showing an example of a wireless
communication device provided with the antenna device according to
the embodiment of the present invention and a wireless
communication circuit.
DETAILED DESCRIPTION
[0018] According to one embodiment, an antenna device includes a
branch circuit, a first phase shifter, a second phase shifter and a
radiating element. The branch circuit divides an input signal and
generates a first signal and a second signal. The first phase
shifter is capable of shifting a phase of the first signal. The
second phase shifter is capable of shifting a phase of the second
signal. The radiating element transmits a right-hand circularly
polarized wave based on a first output signal of the first phase
shifter and transmits a left-hand circularly polarized wave based
on a second output signal of the second phase shifter.
[0019] An embodiment of the present invention will be described
with reference to drawings.
[0020] FIG. 1 shows an example of a schematic configuration of an
antenna device according to the embodiment of the present
invention.
[0021] The antenna device in FIG. 1 is provided with a radiating
element 100, a first phase shifter 101a, a second phase shifter
101b and a branch circuit (hereinafter referred to as a two-branch
circuit) 102.
[0022] The radiating element 100 is connected to the first phase
shifter 101a via a transmission line 104a. The radiating element
100 is connected to the second phase shifter 101b via a
transmission line 104b. The first phase shifter 101a is connected
to the two-branch circuit 102 via a transmission line 105a. The
second phase shifter 101b is connected to the two-branch circuit
102 via a transmission line 105b. The two-branch circuit 102 is
connected to an input/output terminal 107 of a high-frequency
circuit via a transmission line 106.
[0023] The radiating element 100 transmits and receives a
right-hand circularly polarized wave and a left-hand circularly
polarized wave. The radiating element 100 is provided with an
input/output terminal 103a for the right-hand circularly polarized
wave and an input/output terminal 103b for the left-hand circularly
polarized wave. By using the right-hand circularly polarized wave
input/output terminal 103a, the right-hand circularly polarized
wave can be transmitted/received. By using the left-hand circularly
polarized wave input/output terminal 103b, the left-hand circularly
polarized wave can be transmitted/received. By using the right-hand
circularly polarized wave input/output terminal 103a and the
left-hand circularly polarized wave input/output terminal 103b at
the same time, the right-hand circularly polarized wave and the
left-hand circularly polarized wave can be transmitted/received at
the same time. More specifically, at the time of transmission, a
linearly polarized wave is transmitted from the radiating element
100 by combining right-hand and left-hand circularly polarized
waves. At the time of reception, a linearly polarized wave received
by the radiating element 100 is separated into a right-hand
circularly polarized wave and a left-hand circularly polarized
wave, and a high-frequency signal of the right-hand circularly
polarized wave and a high-frequency signal of the left-hand
circularly polarized wave are outputted from the input/output
terminals 103a and 103b, respectively. As a specific example of the
radiating element 100, a patch antenna provided with perturbation
elements can be used.
[0024] A modification of the radiating element 100 will be
described with reference to FIGS. 2, 3 and 4. As shown in FIG. 2,
the radiating element 100 may be configured with two radiating
elements, a radiating element 200a configured to radiate a
right-hand circularly polarized wave and a radiating element 200b
configured to radiate a left-hand circularly polarized wave.
Further, the radiating element 100 may be configured by connecting
an external circuit 301, such as a 90.degree. hybrid coupler, to a
dual linearly polarized antenna 300 for generating two orthogonal
linearly polarized waves as in FIG. 3. In this case, by giving a
phase difference of .+-.90.degree. to the two orthogonal linearly
polarized wave signals which are inputted, by the external circuit
301, the right-hand circularly polarized wave and the left-hand
circularly polarized wave are generated by the dual linearly
polarized antenna 300. Further, the dual linearly polarized antenna
300 in FIG. 3 may be divided into two. FIG. 4 shows a configuration
example in this case. Linear polarization antennas 310a and 310b
corresponding to two orthogonal linearly polarized waves,
respectively, are connected to the external circuit 301. By the
external circuit 301 giving the phase difference of .+-.90.degree.
to high-frequency signals of the two orthogonal linearly polarized
waves which are inputted, a right-hand circularly polarized wave
and a left-hand circularly polarized wave can be generated by the
linear polarization antennas 310a and 310b, respectively. In
addition, a sequential array which generates a circularly polarized
wave by giving phase differences to a plurality of antennas for
linearly polarized waves to excite the antennas may be used as the
radiating element 100.
[0025] The radiating element 100 and the antennas 200a, 200b, 300,
301, 310a and 310b are not limited to those illustrated above. Any
antenna is possible if the antenna can transmit/receive a
right-hand circularly polarized wave and a left-hand circularly
polarized wave, or one of them. For example, a dipole antenna, a
helical antenna, a spiral antenna, a loop antenna, a dielectric
resonator antenna, an antenna using a waveguide provided with a
septum polarizer or an orthogonal mode transducer, a slot antenna,
a reflector antenna, a lens antenna, an antenna using a
meta-surface and the like are possible, and a combination thereof
is also possible. An array antenna in which a plurality of these
antennas are arrayed is also possible.
[0026] The right-hand circularly polarized wave input/output
terminal 103a is electrically connected to the transmission line
104a. The left-hand circularly polarized wave input/output terminal
103b is electrically connected to the transmission line 104b. As an
example, the input/output terminal 103a has a structure enabling
the transmission line 104a to be attached to or detached from the
radiating element 100 like a coaxial cable connector or a wave
guide connector. Otherwise, the transmission line 104a and the
radiating element 100 may be, for example, fixedly combined or
integrally formed (that is, in a configuration in which the
transmission line 104a cannot be attached to or detached from the
radiating element 100). In this case, an arbitrary point on the
transmission line 104a may be defined as the right-hand circularly
polarized wave input/output terminal 103a. The input/output
terminal 103b is similar to the input/output terminal 103a.
[0027] The first phase shifter 101a is a phase shifter capable of
changing a phase of a high-frequency signal to be transmitted from
the transmission line 104a to the transmission line 105a or a
high-frequency signal to be transmitted from the transmission line
105a to the transmission line 104a. Similarly, the second phase
shifter 101b is a phase shifter capable of changing a phase of a
high-frequency signal to be transmitted from the transmission line
104b to the transmission line 105b or a high-frequency signal to be
transmitted from the transmission line 105b to the transmission
line 104b. The first phase shifter 101a adjusts a phase of an
inputted high-frequency signal, and the second phase shifter 101b
adjusts a phase of an inputted high-frequency signal. To adjust a
phase includes the case of maintaining the same phase in addition
to the case of shifting a phase.
[0028] Insertion losses of the first phase shifter 101a and the
second phase shifter 101b are substantially equal when the
frequencies of the inputted high-frequency signals are the same,
and phase shift amounts are the same. Being substantially equal
includes both of the case of being equal and the case of being
almost equal. As an example of the case of being almost equal, a
case where an insertion loss difference is within a predetermined
error range is given. The predetermined error range can be, as an
example, specified according to quality or performance required for
communication. A configuration of the first phase shifter 101a may
be the same as the second phase shifter 101b. Specifically, the
first phase shifter 101a and the second phase shifter 101b may be
products with the same model number. Further, the first phase
shifter 101a and the second phase shifter 101b may be devices
having the same pattern.
[0029] The first phase shifter 101a and the second phase shifter
101b may be analog phase shifters the phase shift amount of which
can be continuously changed or may be digital phase shifters the
phase shift amount of which can be discretely switched. The first
phase shifter 101a and the second phase shifter 101b may be phase
shifters configured to switch a line length with a PIN diode, an
FET or MEMS switch or the like or may be ferrite phase shifters or
MEMS phase shifters, or may be reflective phase shifters in which a
variable impedance element such as a varactor diode or a
transmission line the line length of which can be switched, and a
90.degree. hybrid coupler are combined.
[0030] The transmission lines 104a, 104b, 105a, 105b and 106 are
transmission lines for transmitting high-frequency signals, such as
microstrip lines, coplanar lines, strip lines, parallel two-wire
lines, coaxial lines and wave guides. As an example, the
transmission line 104a and the transmission line 104b are
transmission lines with the same structure, and the transmission
line 105a and the transmission line 105b are transmission lines
with the same structure. Types of the transmission lines 104a, 105a
and 106 may be different from one another. Similarly, types of the
transmission lines 104b, 105b and 106 may be different from one
another.
[0031] Further, a circuit element attached to the first phase
shifter 101a may be connected to the transmission lines 104a and
105a. Similarly, a circuit element attached to the second phase
shifter 101b may be connected to the transmission lines 104b and
105b. Further, a circuit element attached to the two-branch circuit
102 may be connected to the transmission line 106.
[0032] At the time of transmission, the two-branch circuit 102
divides a high-frequency signal (an input signal) inputted from the
transmission line 106 into two and outputs them to the transmission
lines 105a and 105b. Further, at the time of reception, the
two-branch circuit 102 combines high-frequency signals inputted
from the transmission lines 105a and 105b and outputs the combined
high-frequency signal to the transmission line 106. As examples of
the two-branch circuit 102, a Wilkinson divider, a T junction, a
magic Tee, a 90.degree. hybrid, a rat-race coupler are given.
[0033] The input/output terminal 107 is, as an example, a connector
or the like capable of attaching or detaching the transmission line
106 to or from a high-frequency circuit (for example, an
amplifier). Otherwise, the transmission line 106 and the
high-frequency circuit may be fixedly combined or integrally formed
(that is, in a configuration in which the transmission line 106
cannot be attached to or detached from the high-frequency circuit).
In this case, an arbitrary point on the transmission line 106 may
be defined as the input/output terminal 107 of the high-frequency
circuit.
[0034] According to the antenna device in FIG. 1, it is possible
to, only by changing a phase shift amount of at least one of the
first phase shifter 101a and the second phase shifter 101b to
adjust a relative phase difference between a right-hand circularly
polarized wave and a left-hand circularly polarized wave,
preferably maintain cross polarization discrimination over a wide
frequency band and change a polarization plane of a linearly
polarized wave.
[0035] An operation principle of the antenna device in FIG. 1 is
shown below. An electric field "E.sub.RHCP" of a right-hand
circularly polarized wave and an electric field "E.sub.LHCP" of a
left-hand circularly polarized wave are expressed as blow.
E RHCP = 1 2 ( E x + jE y ) E LHCP = 1 2 ( E x - jE y ) [ Formula 1
] ##EQU00001##
Here, "E.sub.x" and "E.sub.y" indicate "x" and "y" components of
each electric field. When a phase shift amount of the first phase
shifter 101a is indicted by ".psi..sub.1", and a phase shift amount
of the second phase shifter 101b is indicted by ".psi..sub.2", an
electric field "E" obtained by combining "E.sub.RHCP" and
"E.sub.LHCP" with equal amplitudes is expressed as:
E = E RHCP exp ( - j .psi. 1 ) + E LHCP exp ( - j .psi. 2 ) = 1 2 [
exp ( - j .psi. 1 ) + exp ( - j .psi. 2 ) ] E x + j 1 2 [ exp ( - j
.psi. 1 ) - exp ( - j .psi. 2 ) ] E y [ Formula 2 ]
##EQU00002##
[0036] For example, when ".psi..sub.1"=".psi..sub.2"=0.degree. is
satisfied, the following formula is satisfied:
E= {square root over (2)}E.sub.x [Formula 3]
A linearly polarized wave the polarization plane of which is an
"xz" plane (".phi."=0; ".phi." is a rotation angle from an "x"
axis) is obtained.
[0037] When ".psi..sub.1"=90.degree. and ".psi..sub.2"=0.degree.
are satisfied, the following formula is satisfied:
E = 1 2 ( 1 - j ) ( E x + E y ) [ Formula 4 ] ##EQU00003##
A linearly polarized wave with a polarization plane of
".phi."=45.degree. is obtained.
[0038] When ".psi..sub.1"=180.degree. and ".psi..sub.2"=0.degree.
are satisfied, the following formula is satisfied:
E=-j {square root over (2)}E.sub.y [Formula 5]
A linearly polarized wave with a polarization plane of
".phi."=90.degree. is obtained.
[0039] Thus, by changing ".psi..sub.1" within a range of 0.degree.
to 180.degree. in a state that the phase shift amount of the second
phase shifter 101b is fixed to ".psi..sub.2"=0.degree., a
polarization plane of a linearly polarized wave can be changed
within a range of ".phi."=0 to 90.degree..
[0040] Similarly, when ".psi..sub.1"=0.degree. and
".psi..sub.2"=90.degree. are satisfied, the following formula is
satisfied:
E = 1 2 ( 1 - j ) ( E x + E y ) [ Formula 6 ] ##EQU00004##
A linearly polarized wave with a polarization plane of
".phi."=-45.degree. is obtained.
[0041] When ".psi..sub.1"=0.degree. and ".psi..sub.2"=180.degree.
are satisfied, the following formula is satisfied:
E=j {square root over (2)}E.sub.y [Formula 7]
A linearly polarized wave with a polarization plane of
".phi."=-90.degree. is obtained.
[0042] Therefore, by changing ".psi..sub.2" within the range of
0.degree. to 180.degree. in a state that the phase shift amount of
the first phase shifter 101a is fixed to ".psi..sub.1"=0.degree., a
polarization plane of a linearly polarized wave can be changed
within a range of ".phi."=0 to -90.degree..
[0043] Here, as shown in FIG. 5, ".phi."=90.degree. and
".phi."=-90.degree. indicate the same polarization plane. From the
above, when both of phase shift amount ranges of the first phase
shifter 101a and the second phase shifter 101b are 0 to 1800, it is
possible to, by adjusting the phase shift amounts of the first
phase shifter 101a and the second phase shifter 101b, realize a
linearly polarized wave with an arbitrary polarization plane.
[0044] A variable-polarization-plane antenna according to a
related-art technique will be described. In this antenna device
according to the related-art technique, a phase shift amount is
given only to a right-hand circularly polarized wave (or a
left-hand circularly polarized wave) by a phase shifter as
indicated by the following formula:
E=E.sub.RHCPexp(-j.psi..sub.1)+E.sub.LHCP [Formula 8]
In this case, in order to realize an arbitrary polarization plane,
it is necessary to set a phase shift amount of the phase shifter to
be 0 to 360.degree.. When the phase shift amount of the phase
shifter is increased, there are problems such as that the phase
shifter is physically large-sized, that insertion loss is increased
and that fluctuation of insertion loss when at least one of the
phase shift amount and frequency changes is increased. By the
insertion loss of the phase shifter or the fluctuation of the
insertion loss, a large amplitude difference occurs between the
right-hand circularly polarized wave and the left-hand circularly
polarized wave in the antenna device of the related-art technique,
and the cross polarization discrimination deteriorates.
[0045] FIG. 6 shows an example of a graph of a relationship between
an amplitude difference between a right-hand circularly polarized
wave and a left-hand circularly polarized wave, and the cross
polarization discrimination.
[0046] When insertion loss of a phase shifter is 0 dB, amplitudes
of the right-hand circularly polarized wave and the left-hand
circularly polarized wave become equal, and the cross polarization
discrimination becomes infinite. Actually, however, it is not
possible to realize a phase shifter the insertion loss of which is
0 dB. When the insertion loss of the first phase shifter 101a is,
for example, 6 dB and the insertion loss of the second phase
shifter 101b is 1 dB, the right-hand circularly polarized wave is
lower than the left-hand circularly polarized wave by 5 dB, and the
cross polarization discrimination deteriorates to 12.9 dB. Though
the amplitude difference between the right-hand and left-hand
circularly polarized waves can be reduced by using an amplitude
adjustment circuit such as a variable amplifier, it is necessary to
adjust gain of the amplitude adjustment circuit according to the
phase shift amount and frequency of the phase shifter, and,
therefore, a problem occurs that a control circuit for performing
such control is complicated.
[0047] On the other hand, in the antenna device according to the
present embodiment, both of a right-hand circularly polarized wave
transmission line and a left-hand circularly polarized wave
transmission line are provided with phase shifters the insertion
losses of which are substantially equal (the first phase shifter
101a and the second phase shifter 101b), respectively. When the
phase shift amounts of the first phase shifter 101a and the second
phase shifter 101b are the same, amplitude difference between the
right-hand and left-hand circularly polarized waves are decreased,
and the amplitudes become substantially equal. That is, an
amplitude difference between the right-hand and left-hand
circularly polarized waves does not occur or included within a
predetermined error range. When the phase shift amount of one of
the first phase shifter 101a and the second phase shifter 101b is
changed, the insertion loss of the phase shifter for which the
phase shift amount has been changed fluctuates, and the insertion
losses of the phase shifters become different from each other.
However, if the fluctuation of the insertion loss is 0.5 dB or
less, that is, the insertion loss difference is 0.5 dB or less, the
cross polarization discrimination is 30.8 dB or more. Further, even
if the fluctuation of the insertion loss is 1.0 dB or less, the
cross polarization discrimination is 24.8 dB or more. Therefore,
even if the phase shift amount of any one of the phase shifters is
changed, preferable cross polarization discrimination can be
obtained.
[0048] In the antenna device according to the present embodiment, a
phase shift amount required to realize an arbitrary polarization
plane of a linearly polarized wave is 180.degree., and this is
smaller than 360.degree., a phase shift amount required by the
antenna device of the related-art technique. Further, it is
relatively easy to design a phase shifter with a small phase shift
range the insertion loss of which fluctuates less. Therefore,
according to the present embodiment, it is possible to realize a
variable-polarization-plane antenna having preferable cross
polarization discrimination without using an amplitude adjustment
circuit. Further, when the first phase shifter 101a and the second
phase shifter 101b are in the same configuration, variations in
insertion losses at the time when the phase shift amounts change
are equal, and variations in insertion losses at the time when
frequencies change are equal. Therefore, it is possible to realize
preferable cross polarization discrimination in a wider frequency
band.
[0049] FIG. 7 shows a configuration in which a control circuit
configured to adjust the phase shift amounts of the first phase
shifter 101a and the second phase shifter 101b is added to the
antenna device in FIG. 1. A control circuit 400 is connected to the
antenna device in FIG. 1. The control circuit 400 adjusts the phase
shift amounts of the first phase shifter 101a and the second phase
shifter 101b. When the phase shift amount ranges of the first phase
shifter 101a and the second phase shifter 101b are the same, phase
shift amounts of a right-hand circularly polarized wave and a
left-hand circularly polarized wave can be controlled in the same
method, and a control scheme can be facilitated. Therefore, a
configuration of the control circuit 400 can be simplified. The
control circuit 400 may be configured with a dedicated circuit or
may be configured with a processor such as a CPU which executes
software.
[0050] The control circuit 400 may fix the phase shift amount of
one of the first phase shifter 101a and the second phase shifter
101b and continuously change the phase shift amount of the other
phase shifter. Thereby, a polarization plane may be continuously
changed. In this case, only one of the two phase shifters can be a
control target. Thereby, the configuration and control scheme of
the control circuit can be further simplified. FIG. 8 shows a
configuration example in the case of controlling only the phase
shift amount of the second phase shifter 101b. A control circuit
410 controls only the phase shift amount of the second phase
shifter 101b. The phase shift amount of the first phase shifter
101a is fixed to a predetermined value.
[0051] The predetermined value may be a maximum or minimum value of
the phase shift amount range of the first phase shifter 101a.
Thereby, a polarization plane variable range can be maximized. For
example, by using phase shifters with a phase shift amount of 0 to
180.degree. are used as the first phase shifter 101a and the second
phase shifter 101b, fixing the phase shift amount of the first
phase shifter 101a to 00 or 180.degree. and changing the phase
shift amount of the second phase shifter 101b within a range of 0
to 180.degree., the polarization plane variable range is maximized.
Though the second phase shifter 101b is a control target here, the
first phase shifter 101a may be controlled instead of the second
phase shifter 101b. In this case, by fixing the phase shift amount
of the second phase shifter 101b to 00 or 180.degree. and changing
the phase shift amount of the first phase shifter 101a within the
range of 0 to 180.degree., the polarization plane variable range is
maximized.
[0052] Further, when a sum of lengths of the transmission lines
104a and 105a and a sum of lengths of the transmission lines 104b
and 105b are substantially equal, change in a phase and amplitude
of a high-frequency signal of a right-hand circularly polarized
wave by the transmission lines 104a and 105a is substantially equal
to change in a phase and amplitude of a high-frequency signal of a
left-hand circularly polarized wave by the transmission lines 104b
and 105b, and, therefore, the cross polarization discrimination can
be improved. If the sum of the lengths of the transmission lines
104a and 105a and the sum of the lengths of the transmission lines
104b and 105b are substantially equal, a similar effect can be
obtained even if the lengths of the transmission lines 105a and
105b are different from each other.
[0053] FIG. 9 shows a configuration example of an antenna device in
the case where the lengths of the transmission line 105a and the
transmission line 105b are different from each other. The lengths
of the transmission line 105a and the transmission line 105b are
different from each other, and the lengths of the transmission line
104a and the transmission line 104b are also different from each
other. However, the sum of the lengths of the transmission line
104a and the transmission line 105a and the sum of the lengths of
the transmission line 104b and the transmission line 105b are
substantially equal. Therefore, changes in the amplitudes and
phases of high-frequency signals of right-hand and left-hand
circularly polarized waves due to the transmission lines 104a,
104b, 105a and 105b are substantially equal, and the cross
polarization discrimination can be improved.
[0054] Further, FIG. 10 shows a configuration example of a case
where shapes of the transmission lines 105a and 105b are
substantially symmetrical when seen from the two-branch circuit 102
(including a case where the shapes are symmetrical). Being
substantially symmetrical when seen from the two-branch circuit 102
means, as an example, being symmetrical relative to a symmetry axis
430 passing through a center of the two-branch circuit 102 (for
example, a signal branch point or combination point) and a center
of the radiating element 100. The symmetry axis 430 is a virtual
line. At this time, frequency characteristics of amplitude/phase
variation of high-frequency signals of right-hand and left-hand
circularly polarized waves through the transmission lines 105a and
105b are equal, and, therefore, preferable cross polarization
discrimination can be realized in a wider frequency band.
[0055] Further, a shape of the two-branch circuit 102 may be
substantially symmetrical when seen from the transmission line 106.
In this case, since the two-branch circuit 102 becomes wideband,
the antenna device operates in a wider frequency band.
[0056] When dividing a high-frequency signal supplied from the
transmission line 106, the two-branch circuit 102 may divide the
signal with substantially equal amplitudes (including the case of
the same amplitudes). Thereby, more preferable cross polarization
discrimination can be realized. Further, if high-frequency signals
supplied from the transmission lines 105a and 105b have
substantially equal amplitudes, these signals are combined with
substantially equal amplitudes, and, therefore, more preferable
cross polarization discrimination can be realized. The two-branch
circuit 102 does not have to perform distribution/combination with
equal phases.
[0057] FIG. 11 shows a configuration example of a wireless
communication device provided with the antenna device in FIG. 1 and
a wireless communication circuit 120. The wireless communication
circuit 120 performs wireless communication with a counterpart
wireless communication device using the antenna device. The
wireless communication circuit 120 includes a baseband circuit 109,
a DA/AD conversion circuit 110 and a high-frequency circuit 111.
The baseband circuit 109 generates a frame or a packet in
conformity with a communication scheme, specifications and the like
to be used, and encodes and modulates a digital signal of the
generated frame or packet. The DA/AD conversion circuit 110
converts the modulated digital signal to an analog signal. The
high-frequency circuit 111 extracts a signal of a desired band from
the analog signal by band control, converts frequency of the
extracted signal to radio frequency, amplifies the signal after the
conversion (a high-frequency signal) with an amplifier and outputs
the signal to the two-branch circuit 102.
[0058] The amplifier of the high-frequency circuit 111 is connected
to the transmission line 106 via the input/output terminal 107. At
the time of reception, the high-frequency circuit 111 receives a
high-frequency signal from the two-branch circuit 102. The
high-frequency circuit 111 performs low noise amplification of the
received signal with an LNA, extracts a signal of a desired band
from the amplified signal, and performs frequency conversion of the
extracted signal to obtain a baseband signal, and outputs the
baseband signal to the DA/AD conversion circuit 110. The LNA of the
high-frequency circuit 111 is connected to the transmission line
106 via the input/output terminal 107. The DA/AD conversion circuit
110 converts the inputted baseband signal to a digital signal and
outputs the digital signal to the baseband circuit 109. The
baseband circuit 109 demodulates and decodes the inputted digital
signal to acquire a frame or packet.
[0059] The present antenna device is advantageous when a
polarization plane of an antenna of a wireless communication
counterpart, such as an access point, a base station, a radar and a
remote controller of a wireless LAN (Local Area Network), is
unknown or when the communication counterpart is moving. It is
possible to adjust an antenna to the polarization plane of the
antenna of the counterpart without mechanically moving the antenna.
Improvement of communication quality and communication distance,
multi-functionalization of a radar and the like can be
expected.
[0060] While certain embodiments have been described, these
embodiments have been presented by way of example only, and are not
intended to limit the scope of the inventions. Indeed, the novel
embodiments described herein may be embodied in a variety of other
forms; furthermore, various omissions, substitutions and changes in
the form of the embodiments described herein may be made without
departing from the spirit of the inventions. The accompanying
claims and their equivalents are intended to cover such forms or
modifications as would fall within the scope and spirit of the
inventions.
* * * * *