Communications: radio wave antennas – Antennas – With coupling network or impedance in the leadin
Reexamination Certificate
2003-01-23
2004-08-17
Nguyen, Hoang V. (Department: 2821)
Communications: radio wave antennas
Antennas
With coupling network or impedance in the leadin
C342S174000, C370S248000, C370S249000
Reexamination Certificate
active
06778147
ABSTRACT:
The present document is based on Japanese Priority Document JP2002-014149, filed in the Japanese Patent Office on Jan. 23, 2002, the entire contents of which being incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an antenna apparatus including an array antenna used in a time division multiple communication system and its signal calibration circuit and particularly to an antenna apparatus capable of calibrating an amplitude of a transmission/reception signal of each antenna element and a phase thereof without having to depend on the outside information.
2. Description of Related Art
In a time division multiple communication system using an array antenna, signals are send to each antenna element during transmission. However, even if the same signals are send to each antenna element, errors are generated in an amplitude and a phase of the signal to be emitted by each antenna element according to variations of a gain characteristic of an amplification circuit for amplifying the output of a transmitter (a transfer function), and an amplitude characteristic and a phase characteristic of a cable for propagating a signal, a filter for controlling a frequency component of the signal and an antenna element. Due to these errors, the control of a transmission beam pattern becomes difficult, so that beam forming can not be correctly realized.
In addition, also during reception, the similar problems may occur. When a signal arrives at each receiver, an output signal of the receiver has errors in the amplitude and the phase of the signal received by each antenna element depending on variations of a filter characteristic, a gain characteristic of the amplification circuit, and further, a character of a cable for propagating the received signal or the like. Thus, there may be a problem such that a direction of arrival (DOA) of the received signal can not be correctly estimated or the like.
Therefore, in an antenna apparatus using the array antenna, a measure is taken that a calibration circuit is provided to obtain a calibration factor for correcting the error of each transmitter-receiver.
FIG. 6
is a configuration example of an entire antenna system including a conventional calibration circuit. As shown in the drawing, this antenna apparatus is constructed of an antenna array including antenna elements
11
,
12
,
13
-
1
L, filters
21
,
22
,
23
-
2
L connected to each antenna element, antenna switches
31
,
32
,
33
-
3
L connected to each filter, a calibration circuit
200
, transmitters
81
,
82
,
83
-
8
L and receivers
91
,
92
,
93
-
9
L.
The calibration circuit
200
is constructed of directional couplers
41
,
42
,
43
-
4
L and SPDT (single pole double through) RF switches (hereinafter, as a matter of convenience, simply referred to as a RF switch)
51
,
52
,
53
-
5
L−1,
62
,
63
-
6
L−1,
71
,
72
,
73
-
7
L.
The directional couplers
41
,
42
-
4
L output the inputted signals to other output terminals with a predetermined amplitude attenuation rate and a predetermined phase difference.
The antenna switch has three terminals and is capable of switching between the transmitting signal and the received signal. For example, the antenna switch
31
has terminals a
1
, a
2
and a
3
, and the terminals a
1
and a
2
are connected during transmission so that a signal is sent from the directional coupler
41
to a filter
21
. In addition, during reception, the terminal a
1
is connected to the terminal a
3
, so that the received signal from the filter
21
is sent to the directional coupler
41
.
In addition, each RF switch also has three terminals, respectively. For example, the RF switch
71
has terminals b
1
, b
2
and b
3
. The terminal b
1
is connected to the terminal b
2
during the reception and the terminal b
1
is connected to the terminal b
3
during calibration.
During the normal transmission, the signal to be sent from the transmitter
81
is inputted to the terminal a
2
of the antenna switch
31
through the directional coupler
41
. In this time, since the terminal a
2
is connected to the terminal a
1
in the antenna switch, the signal is inputted to the filter
21
. Then, a signal component that passed through the filter
21
is transmitted to the antenna element
11
, and emitted in the air.
In addition, in the same way, the signal to be sent from the other transmitter
82
,
83
-
8
L are transferred to the antenna elements
12
,
13
-
1
L, respectively, to be emitted in the air from each antenna element. During the transmission, by controlling the phase of the signal to be transmitted to each antenna element, a predefined beam pattern is formed, namely, a so-called beam forming can be realized.
The beam forming during the transmission can be realized, for example, by outputting a signal to each antenna element, in which the signals from the transmitters
81
,
82
,
83
-
8
L are multiplied by predefined weighting factors for controlling an amplitude and a phase, respectively. In addition, the weighting processing, which multiplies the transmitting signal by this weighting factor, can also be realized, for example, by a multiplier provided between the antenna element and the filter, or between the filter and the antenna switch.
During the normal reception, the signal received by the antenna element
11
is transmitted to the filter
21
and then, the signal component that passed through the filter
21
is inputted to the terminal a
1
of the antenna switch
31
. In this time, since the terminal a
1
is connected to the terminal a
3
in the antenna switch
31
, and then the received signal is transmitted to the terminal b
2
of the RF switch
71
. The terminal b
2
is connected to the terminal b
1
in the RF switch
71
, so that the received signal is inputted to the receiver
91
. Further, in the same way, the received signals of the other antenna elements
12
,
13
-L
1
are transferred to the receivers
92
,
93
-
9
L, respectively.
In addition, not only during the transmission but also during the reception, by way of multiplying the received signal from each antenna element by a predefined weighing factor, respectively, the beam forming can be realized. Further, by way of measuring the received signal while sweeping the received beam during the reception, it is also possible to estimate an arrival direction of the received signal.
According to the above described antenna apparatus, when calibrating the device, on the basis of a transmitter and a receiver, it is possible to obtain the calibration factors of respective transmitters and receivers by measuring the amplitudes changes and the phase changes of the transmitting signals and the received signals of the other transmitters and receivers with respect to the above mentioned reference transmitter and receiver.
With reference to
FIG. 7
, a method of the calibration in the antenna apparatus shown in
FIG. 6
will be described below.
FIG. 7
is a conceptual diagram for showing a flow of a signal when calibrating the antenna apparatus. In
FIG. 7
, a transmission/reception set including a transmitter
8
i−
1 (i=2,3-L) and a receiver
9
i−
1 and a transmission/reception set including a transmitter
8
i
and a receiver
9
i
are depicted.
As shown in
FIG. 7
, the calibration for the transmitter
8
i
and the receiver
9
i
is carried out by measuring a received signal T
i−1
R
i
of the receiver
9
i
when transmitting a signal from the transmitter
8
i−
1 and by measuring a received signal T
i
R
i−1
of the receiver
9
i−
1 when transmitting a signal from the transmitter
8
i.
A principle of the calibration and how to obtain the calibration factor will be described below.
According to the antenna apparatus shown in
FIG. 6
, in the receivers
91
to
9
L, the optimum weighting factors are defined as W
01
to W
0L
, such that there is no amplitude difference and no phase difference between the received signals r
1
to r
L
. The output Y
ri
of the receiver
9
i
is represented a
Kohno Ryuji
Sanada Yukitoshi
Nguyen Hoang V.
Sony Corporation
Wolf Greenfield & Sacks P.C.
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