Communications: directive radio wave systems and devices (e.g. – Directive – Including a steerable array
Reexamination Certificate
2002-09-12
2004-07-13
Phan, Dao (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Directive
Including a steerable array
C342S174000
Reexamination Certificate
active
06762717
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus and method for calibrating an array antenna.
2. Description of the Related Art
To form an accurate receiver beam in a digital beam forming device, it is necessary in beam forming to make uniform the amplitude characteristics and the phase characteristics of the outputs of receivers provided to antenna elements respectively.
An array antenna calibration apparatus is disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2000-151255 (Method and Apparatus for Calibrating Array Antenna) and Jpn. Pat. Appln. KOKAI Publication No. Hei 10-336149 (Array Antenna radio CDMA Communication Apparatus). The configuration of one example of conventional array antenna calibration apparatuses is shown in FIG.
5
.
In this array antenna calibration apparatus, between antenna elements
801
-
2
through
801
-
5
and receivers
802
-
1
through
802
-
4
are provided couplers
821
-
1
through
821
-
4
respectively, so that a calibration signal generated by a calibration signal generator
810
is divided by a divider
809
. Thus divided calibration signals are input from the couplers
821
-
1
through
821
-
4
to the receivers
802
-
1
through
802
-
4
respectively. The calibration signals thus received by the receivers
802
-
1
through
802
-
4
undergo propagation factor estimation at propagation factor estimators
808
-
1
through
808
-
4
of a calibration signal processor
806
respectively, which output propagation factors to a calibration factor calculator
805
. The calibration factor calculator
805
then calculates a calibration factor based on the propagation factors so that the amplitudes and phases of the signals from the receivers
802
-
1
through
802
-
4
may be equal respectively. Thus obtained calibration factor is input to beam former
803
of each user, and the beamformer
803
correct their respective output signals from the receivers
802
-
1
through
802
-
4
according to the calibration factor.
In such a conventional calibration apparatus, the calibration signals do not pass through the antenna elements
801
-
2
through
801
-
5
nor interconnections between them and the couplers
821
-
1
through
821
-
4
, so that it cannot correct fluctuations in characteristics caused by these components, which is a problem. Furthermore, in the conventional calibration apparatus, when the calibration signals are input to the receivers
802
-
1
through
802
-
4
, they must be equal in both amplitude and phase. This necessity gives rise to a problem that the divider
809
and the couplers
821
-
1
through
821
-
4
must have performance of high accuracy and high stability.
To solve these problems, there has been disclosed such a conventional method as shown in FIG.
6
. This conventional method is disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2000-295152 (Array Antenna Radio Communication Apparatus). By this calibration method, a calibration signal generator
810
is installed at a position where there is no obstacle to an array antenna at a base station, in order to transmit a calibration signal therefrom to the base station array antenna. By this calibration method, the calibration signal is received by the antenna elements
801
-
2
through
802
-
5
and the receivers
802
-
1
through
802
-
4
for calibration. The calibration signal can pass through from the antenna elements
801
-
1
through
801
-
5
to the receivers
802
-
1
through
802
-
4
all the way for calibration. The method, however, has a problem that the calibration signal generator must be installed within an unobstructed range of the base station. Furthermore, it has another problem that it is necessary to know an accurate positional relationship between the base station and the signal generator.
SUMMARY OF THE INVENTION
In view of the above, it is an object of the present invention to provide an array antenna calibration apparatus and method which can take into account the characteristics of a propagation factor ranging from an antenna element to a receiver and also which eliminates the necessity of knowing a positional relationship between a base station and a signal generator.
The present invention provides a novel calibration apparatus and method which calibrates the reception characteristics of a linear array antenna used at the base station. A configuration of the apparatus of the present invention is described with reference to FIG.
1
.
The array antenna calibration apparatus of the present invention comprises a plurality of antenna elements
1
-
2
through
1
-
5
which makes up an array antenna, receivers
2
-
1
through
2
-
4
connected to said antenna elements respectively, propagation factor estimators
4
-
1
through
4
-
4
which estimate propagation factors of user signals output from said receivers
2
-
1
through
2
-
4
respectively, antenna elements
1
-
1
and
1
-
6
which send a calibration signal to said array antenna, a calibration signal supplier
30
-
1
which transmits an equi-amplitude/equi-phase calibration signal from said antenna elements
1
-
1
and
1
-
6
, a calibration factor supplier
40
which has means for obtaining a relative phase fluctuation and a relative amplitude fluctuation between said array antenna and said antenna elements, and a beam former
3
which calibrates said user signal received by each of said antenna elements of said array antenna based on said relative phase fluctuation and said relative amplitude fluctuation.
Furthermore, the calibration signal supplier
30
-
1
has a calibration signal generator
10
and a divider
9
for transmitting an equi-amplitude/equi-phase calibration signal, for supplying the calibration signal to the antennas
1
-
1
and
1
-
6
added to the two ends of the array antenna respectively so that the phase characteristics and the amplitude characteristics of outputs of the receivers
2
-
1
through
2
-
4
connected to the antenna elements
1
-
2
through
1
-
5
respectively may be made uniform.
Furthermore, a calibration factor supplier
40
-
1
is comprised of a calibration signal processor
6
which processes the calibration signal received by the antenna elements
1
-
2
and
1
-
5
at the two ends of the array antenna to which the receivers
2
-
1
and
2
-
4
are connected respectively and a calibration factor calculator
5
which calculates a calibration factor using the information of a phase difference of the calibration signal sent from the calibration signal processor
6
and a transmission path estimate value sent from each of the transmission path estimators
4
-
1
through
4
-
4
of each user. In this configuration, the calibration factor supplier
40
-
1
obtains a relative phase fluctuation and a relative amplitude fluctuation between the antenna elements of the array antenna based on the calibration signal received by the antenna element and the user signal received by each of the antenna elements of the array antenna, thus sending the calibration factor to the beam former
3
.
The following will describe a calibration method of the present invention. The calibration signals transmitted from the antenna elements
1
-
1
and
1
-
6
are received by the receivers
2
-
1
and
2
-
4
through the antenna elements
1
-
2
and
1
-
5
, respectively, owing to electromagnetic coupling between the antenna elements. The calibration signals received by the receivers
2
-
1
and
2
-
4
are sent to propagation factor estimators
8
-
1
and
8
-
2
of the calibration signal processor
6
respectively for estimation of their respective propagation factors.
The resulting propagation factors are used by a phase difference calculator
7
of the calibration signal processor
6
to calculate a phase difference between the outputs of the receivers
2
-
1
and
2
-
4
and then send it to the calibration factor calculator
5
.
Furthermore, the user signals are received through the antenna elements
1
-
2
through
1
-
5
and the receivers
2
-
1
through
2
-
4
in this order and sent to the propagation factor estimators
4
-
NEC Corporation
Phan Dao
Sughrue & Mion, PLLC
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