Adaptive array antenna

Details Adaptive array antenna Adaptive array antenna

1998-10-16

2002-01-01

Kincaid, Lester G. (Department: 2682)

Telecommunications

Receiver or analog modulated signal frequency converter

With wave collector

C455S277200, C455S279100, C455S562100

Reexamination Certificate

active

06336033

ABSTRACT:

TECHNICAL FIELD
The present invention relates to an adaptive array antenna for use, for example, in base stations of mobile communications which has a plurality of antenna elements grouped into subarrays that fixedly define the control range of directivity.
PRIOR ART
FIG. 1
depicts the basic configuration of a conventional adaptive array antenna disclosed, for example, in Takeo Ohgane et al., “A Development of GMSK/TDMA System with CMA Adaptive Array for Land Mobile Communications,” IEEE 1991, pp. 172-176. M antenna elements
11
1
to
11
M
are equally spaced, for example, by a distance d, and each have the same element directional pattern
12
of a large beam width, and they are connected to a high-frequency distributor
13
; received signals via the antenna elements
11
1
to
11
M
are each distributed by the high-frequency distributor
13
to channel parts
14
1
to
14
N
, that is, the received signal via each antenna element is distributed to N. The antenna element spacing d ranges from a fraction of to several times the wavelength used.
In each channel part
14
i
(i=1, 2, . . . , N) the received signals from the M antenna elements distributed thereto are applied to M receivers
15
1
to
15
M
, respectively. Baseband signals from the receivers
15
1
to
15
M
are provided via level-phase regulators
16
1
to
16
M
to a baseband combiner
17
, wherein they are combined into a received output; the output is branched to an adaptive signal processing part
18
, then the level-phase regulators
16
1
to
16
M
are regulated to minimize an error of the received baseband signal, whereby the combined directional pattern
19
of the antenna elements
11
1
to
11
M
is adaptively controlled as shown, for example, in
FIG. 1
so that the antenna gain decreases in the directions of interfering signals but increases in the direction of a desired signal. This allows the base station to perform good communications with N mobile stations over N channels. An increase in the number M of antenna elements increases the gain and enhances the interference eliminating performance. At the same time, however, the number of receivers
15
also increases and the amount of signal processing markedly increases.
With a view to solving the abovementioned problems, there is proposed in Japanese Patent Application Laid-Open No. 24702/87 an adaptive array antenna of such a configuration as depicted in
FIG. 2
wherein the array antenna elements are divided into groups (subarrays) each consisting of several antenna elements, the high-frequency received signals are controlled in phase and level and then combined for each subarray and the combined signals are each distributed to the N channels. In the illustrated example, subarrays
21
1
to
21
L
are formed in groups of four antenna elements, and for each subarray, the received signals are combined by one of high-frequency signal combiners
22
1
to
22
L
. Each subarray has high-frequency level-phase regulators
23
1
to
23
4
connected to the outputs of the antenna elements, in which coefficients W
1
to W
4
are set to regulate the levels and phases of the received signals so that the subarrays
21
1
to
21
L
have the same antenna directional pattern
24
. The outputs of the high-frequency signal combiners
22
1
to
22
L
are fed to the high-frequency distributor
13
, from which they are distributed to the channels
14
1
to
14
N
. The subsequent processing is he same as in the case of FIG.
1
.
In this instance, the number of receivers
15
1
to
15
L
in each channel part
14
i
is reduced to L, in this example, M/4, and the number of level-phase regulators
16
1
to
16
L
is also reduced to M/4, that is, the amount of hardware used is reduced; besides, the gain of the overall directivity (combined directivity) of the antenna elements
11
1
to
11
M
increases and interfering signal components are also removed sufficiently. However, the range over which the combined directivity can be controlled is limited only to the range of the subarray directional pattern
24
, and hence it cannot be controlled over a wide range. That is, when the direction of the subarray directional pattern is changed as indicated by the dashed line
26
in
FIG. 2
, for example, by setting coefficients W
5
′ to W
8
′ in the level-phase regulators
23
1
to
23
4
, respectively, the range over which the combined directional pattern
19
can be regulated by the level-phase regulators
16
1
to
16
L
is limited specifically to the range of this directional pattern
26
. The range over which to track mobile stations is thus limited, but a wide angular range could be covered by such an antenna arrangement as depicted in FIG.
3
. That is, a plurality of array antennas
27
1
to
27
5
, each consisting of the subarrays of antenna elements in groups of M shown in
FIG. 2
, are installed with the subarray directional patterns of the array antennas
27
1
to
27
5
sequentially displaced a proper angle apart as indicated by beams
24
1
to
24
5
and the array antennas
27
1
to
27
5
are selectively switched to track mobile stations in any directions over such a wide range as indicated by the beams
24
1
to
24
5
; by this, a wide service area could by achieved. From the practical point of view, however, it is difficult to install such a large number of antenna elements as mentioned above.
A possible solution to this problem is to decrease the number M of antenna elements used and hence enlarge the antenna spacing d. In this instance, as depicted in
FIG. 2
, when the width of the element directional pattern
12
is large, narrow grating lobes
28
of relatively large gains, other than the main beam
19
, develop in plural directions at about the same angular intervals. In the directions of the grating lobes
28
, however, the BER (Bit Error Rate) due to interfering signal components increases, making it difficult to use the antenna. On the other hand, when the directional pattern
12
is narrow as indicated by a brokenline
24
in
FIG. 5
, no grating lobes appear as shown in
FIG. 5
, but the range over which to control the combined directivity
19
is limited by the element directivity
24
and a wide range cannot be covered accordingly.
An object of the present invention is to provide an adaptive array antenna with which it is possible to offer services over a wide range without involving marked increases in the numbers of receivers and processing circuits and in the computational complexity.
DISCLOSURE OF THE INVENTION
The adaptive array antenna according to the present invention comprises:
a plurality of subarrays of antenna elements arranged in groups of at least two, said antenna elements each outputting a high-frequency received signal;
a plurality of high-frequency level-phase regulators for regulating the levels and phases of said high-frequency received signals from said at least two antenna elements of each of said plurality of subarrays, thereby setting the directivity of said each subarray;
a high-frequency signal combiner for combining the regulated high-frequency received signals from said plurality of high-frequency level-phase regulators corresponding to said each subarray and for outputting the combined high-frequency signal;
a receiver for converting said combined high-frequency signal from said high-frequency signal combiner corresponding to said each subarray to a baseband signal and for outputting said baseband signal;
a baseband level-phase regulator for adaptively regulating the level and phase of said baseband signal from said receiver corresponding to said each subarray;
a baseband signal combiner for combining the regulated baseband signals from said baseband level-phase regulators corresponding to said plurality of subarrays, respectively, and for outputting the combined baseband signal; and
an adaptive signal processing part whereby said baseband level-phase regulators corresponding to said plurality of subarrays, respectively, are adaptively controlled based on said combined baseband signal from said baseband signal

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