Communications: directive radio wave systems and devices (e.g. – Directive – Utilizing correlation techniques
Reexamination Certificate
2000-05-30
2003-09-23
Phan, Dao (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Directive
Utilizing correlation techniques
C342S372000, C342S383000
Reexamination Certificate
active
06624784
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an adaptive array antenna and a method for calculating a calibration amount of a receiving system of the adaptive array antenna and a method for calibration.
BACKGROUND ART
Generally, the adaptive array antenna is used for beam control of array antennas. There are two kinds of algorithms for the beam control, which are an interference suppression tracking type and a maximum gain tracking type. In the interference suppression tracking type, tracking is performed having a null point to interference waves and having strong directivity to desired waves. In the maximum gain tracking type, tracking is performed such that the receiving level of the antenna is maximized. In each of the types, a mobile station can be tracked by a main beam. At the current time, the spacing between elements of the array antenna is usually &lgr;/2 as shown in FIG.
12
. The reason for this is that a grating lobe may occur when the spacing is more than &lgr;/2 as shown in FIG.
13
. The grating lobe may increase interference since the main lobe can be distracted to an unnecessary direction. Although the width of the beam narrows, gain increase by this is not obtained.
Because the spacing between elements of the array antenna shown in
FIG. 12
is narrow, the correlation between the elements is very high. Therefore, when the receiving level deteriorates due to fading, the deterioration influences all elements
1
-
8
which are included in the array antenna so that the deterioration can not be compensated for. Especially, the phenomenon is remarkable for a small sized array antenna which has about 4 elements. In addition, in the interference suppression tracking type algorithm, when there are interference waves coming from near the direction of desired waves, the interference suppression capability deteriorates remarkably since the interference waves exist in the main lobe.
That is, in the narrow element spacing adaptive signal processing, correlation of envelope and signal between elements is extremely strong and the phase deviation is less than a wave length. In the interference suppression tracking type algorithm, wait (phase and amplitude) of each antenna element is obtained such that the interference waves cancel each other out and the desired waves do not cancel each other out. Interference waves which come from a direction different enough from the desired waves are input into the antenna as a signal having strong envelope and signal correlation like the desired waves. However, since the arriving angle is different, the phase difference of the interference waves between elements is different from the phase difference of the desired waves. As a result, the desired waves are not necessarily in opposite phase for a wait in which the interference waves are in opposite phase. In many cases, the desired waves operate as in phase. On the other hand, when the arriving direction of the interference waves is close to the desired waves, the amount of phase shift of the desired waves and the interference waves is almost the same. Therefore, the attempt to cancel the interference waves may result in canceling the desired waves so that the interference suppression capability deteriorates.
On the other hand, since a diversity antenna is designed such that the correlation between elements becomes small, the spacing between elements
21
-
28
is large as shown in FIG.
14
. Since the correlation is small, when the receiving level of an element declines, the receiving level of another element may be high. Generally, a maximal ratio combining (MRC) algorithm is applied. According to the maximal ratio combining algorithm, receiving waves of each of the antenna elements
21
-
28
are synthesized after assigning weights of envelop level of the receiving waves after placing the receiving waves in phase. According to this algorithm, the concept of beam control is not applied because the spacing between elements is large, thus, many ripples exists in the envelope which is the beam of each element. Therefore, tracking is not performed since too many main beams exists. Thus, the gain increase by narrowing the beam can not be expected. According to the algorithm, when there are the interference waves, the influence is directly exerted. Because, as mentioned above, in the synthesizing method, amplitude and phase are controlled such that signals of all elements can be received at maximum gain, and the interference waves and the desired waves are treated without distinction. Accordingly, the method of the maximum ratio synthesizing diversity shown in
FIG. 14
is effective for improving receiving characteristics of a desired station that has deterioration due to fading. However, the method does not contribute to improved interference characteristics.
As mentioned above, the narrow element spacing adaptive array antenna of the interference suppression tracking type is effective in suppressing interference waves other than from main beam. However, the antenna has no effect for suppressing interference waves in the main beam and fading. On the other hand, although the diversity antenna which has the wide element spacing can compensate for deterioration of characteristics of the desired waves due to fading, the diversity antenna has no effect pertaining to interference waves.
In addition, there are two more combinations of antenna placements (narrow element spacing, wide element spacing) and algorithms (maximum ration synthesizing, interference suppression). First, the combination is the maximum gain tracking type which uses the narrow element spacing as shown in FIG.
15
and the maximum ratio synthesizing algorithm. Second, the combination is the interference suppression type which uses the wide element spacing as shown in FIG.
16
. In the method shown in
FIG. 16
, the antenna is set for diversity configuration and the algorithm is the interference suppression type. According to the method, capability of interference wave suppression is kept as the basic characteristic of the algorithm. In addition, fading can be compensated for since the correlation between elements is small in the diversity configuration. Especially, the characteristic is remarkable when the angle of spreading of arriving waves is large. A wait (phase and amplitude) can be determined such that many coming element waves of the interference waves are statistically canceled out because phase differences due to the arriving angle are different. Therefore, even if the arriving angles are the same, a wait can be generated such that the desired waves become inphase and the interference waves become opposite phase.
However, according to the combination method of the maximum gain tracking type which uses the narrow element spacing shown in FIG.
15
and the maximum ratio synthesizing algorithm, high gain can be obtained and the desired waves can be tracked with an antenna similar to the adaptive array antenna shown in FIG.
12
. However, the method has no effect on interference waves and fading. In addition, according to the combination method using the wide element spacing and the interference suppression type shown in
FIG. 16
, gain increase can not be obtained because the wideness of the element spacing prevents tracking by the main beam.
DISCLOSURE OF THE INVENTION
One of the objects of the present invention is to solve the above-mentioned problems. The object is to provide an adaptive array antenna which has diversity effects such as fading compensation or the like, eliminates the interference waves from the same direction and increases gain by main beam tracking.
In order to obtain effects which are diversity effects such as fading compensation or the like, removing interference waves from the same direction and increasing gain by main beam tracking, the adaptive array antenna needs to be accurately calibrated. In the following, the calibration will be described.
In the adaptive array antenna, it is necessary that amplitude ratio and phase difference in a high frequency band occurring between element antennas are m
NTT Mobile Communications Network Inc.
Phan Dao
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