Communications: directive radio wave systems and devices (e.g. – Testing or calibrating of radar system – By monitoring
Reexamination Certificate
2003-01-17
2004-06-08
Tarcza, Thomas H. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Testing or calibrating of radar system
By monitoring
C342S372000
Reexamination Certificate
active
06747595
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an array antenna calibration apparatus for use in a radio base station and the like.
2. Description of the Related Art
In order that a digital beam-forming apparatus forms an accurate transmission beam, it is necessary to make the phase characteristics and amplitude characteristics of signals emitted from respective antenna elements uniform.
FIG. 5
is a block diagram of a conventional array antenna calibration apparatus.
The array antenna calibration apparatus according to the conventional art includes beam formers
13
for users
1
to N, respectively, a user signal multiplexing section
12
, multipliers
10
, adders
5
, transmitters
3
, couplers
17
, antennas
1
, a power synthesizer
18
, a receiver
7
, a calibration factor calculation section
9
and a calibration signal generator
4
.
Each beam former
13
forms a beam having a directivity for each user. The user signal multiplexing section
12
multiplexes the beams for the respective users 1 to N and outputs user multiplex signals for six transmitting systems, respectively. Each multiplier
10
multiplies the user multiplexed signal by a corresponding calibration factor. The calibration signal generator
4
generates a calibration signal corresponding to each user multiplexed signal. Each adder
5
adds the corresponding calibration signal to the corresponding user multiplexed signal multiplied by the calibration factor. Each transmitter
3
transmits the corresponding user multiplexed signal which is multiplied by the corresponding calibration factor and to which the corresponding calibration signal is added. The coupler
17
branches a part of each transmission signal and supplies the branched signal to the power synthesizer
18
and the remaining signal to the antenna
1
. Each antenna
1
transmits the signal supplied from the coupler
17
.
The power synthesizer
18
synthesizes the powers of the signals supplied from the six couplers
17
. The receiver
7
receives the power-synthesized signals. The calibration factor calculation section
9
calculates a calibration factor for each user multiplexed signal based on the signal received by the receiver
7
, and supplies the calculated calibration factor to the corresponding multiplier
10
.
The calibration signals have such signal patterns to be orthogonal to one another among the transmitting systems. Due to this, the calibration factor calculation section
9
performs a correlation processing for the signals synthesized and received by the power synthesizer
18
, whereby the phases and amplitudes of the calibration signals for the respective antenna elements can be measured. The calibration factor calculation section
9
also calculates the calibration factors of the respective transmitting systems based on the measured phases and amplitudes.
The above-stated conventional antenna array calibration apparatus has a disadvantage in that fluctuations in the characteristics of the couplers
17
and the antenna elements
1
—
1
to
1
-
6
cannot be corrected. Further, although the conventional array antenna calibration apparatus can measure the characteristics of the couplers
17
and the antenna elements
1
—
1
to
1
-
6
in advance and correct the fluctuations using a table, the apparatus disadvantageously requires high accuracy in measurement and stability in characteristics. In addition, to suppress a fluctuation in the characteristics of cables which connect the couplers
17
to the antenna elements
1
—
1
to
1
-
6
, it is necessary to arrange the couplers
17
in the vicinity of the corresponding antenna elements
1
—
1
to
1
-
6
. To do so, each coupler
17
needs a waterproof structure, with the result that the coupler becomes disadvantageously expensive.
To solve these disadvantages, a method adapted for an apparatus constituted as shown in
FIG. 6
has been conventionally proposed. Namely, a calibration signal-receiving station
19
which includes a receiver
7
and a calibration factor calculation section
9
is disposed within a sight range. The receiver
7
receives calibration signals transmitted from base station array antennas
1
—
1
to
1
-
6
and having signal patterns orthogonal to one another. The calibration factor calculation section
9
calculates calibration factors by measuring the phases and amplitudes of the respective signals. With this configuration, however, it is necessary to notify the obtained calibration factor to the correction factor receiving section
20
of each base station by a cable or radio communication means. As a result, the system becomes disadvantageously complicated and expensive. Further, it is disadvantageously necessary to dispose the calibration signal receiving station
19
within the sight range of the base station. Besides, it is disadvantageously necessary to grasp the accurate positional relationships between the base stations and the signal generating station.
SUMMARY OF THE INVENTION
The present invention has been achieved to solve the above-stated disadvantages. It is an object of the present invention to provide an array antenna calibration apparatus which is simple in configuration and inexpensive while ensuring an accurate calibration of an array antenna, and an array antenna calibration method therefor.
According to the present invention, there is provided an array antenna calibration apparatus comprising: supply means for supplying original calibration signals to a plurality of antenna elements constituting an array antenna, the original calibration signals being orthogonal to one another among the antenna elements; phase and amplitude characteristic calculation means for calculating correlations between calibration signals, emitted from the antenna elements and received by the adjacent antenna elements, and the original calibration signals related to the received calibration signals; relative calibration factor calculation means for obtaining a relative calibration factor among all the antenna elements constituting the array antenna based on phase and amplitude characteristics of the respective antenna elements; and calibration means for calibrating transmission signals to be supplied to the respective antenna elements based on the relative calibration factor.
In the array antenna calibration apparatus according to the present invention, the antenna elements constituting the array antenna may be classified into a first group and a second group, and the relative calibration factor calculation means comprises: first relative calibration factor calculation means for obtaining a relative calibration factor among all of the antenna elements belonging to the first group based on the phase and amplitude characteristics of all the antenna elements of the first group; second relative calibration factor calculation means for obtaining a relative calibration factor among all of the antenna elements belonging to the second group based on the phase and amplitude characteristics of all the antenna elements of the second group; third relative calibration factor calculation means for obtaining a relative calibration factor between the first group and the second group based on the phase and amplitude characteristics of one of the antenna elements belonging to the first group and the phase and amplitude characteristics of one of the antenna elements belonging to the second group; and fourth relative calibration factor calculation means for obtaining a relative calibration factor among all the antenna elements constituting the array antenna based on the relative calibration factor among all the antenna elements belonging to the first group, the relative calibration factor among all the antenna elements belonging to the second group, and the relative calibration factor between the first group and the second group.
The array antenna calibration apparatus according to the present invention may comprise: synthesizing means for synthesizing the calibration signal received by one of the antenna elements belonging to the second group fr
Andrea Brian
Foley & Lardner LLP
NEC Corporation
Tarcza Thomas H.
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