Adaptive array antenna system

Details Adaptive array antenna system Adaptive array antenna system

2000-06-19

2004-05-11

Ho, Duc (Department: 2665)

Multiplex communications

Duplex

Time division

C370S328000, C370S334000, C342S372000, C455S562100

Reexamination Certificate

active

06735182

ABSTRACT:

TECHNICAL FIELD
The present invention relates to an adaptive array antenna system, in particular, relates to such a system which can automatically calibrate amplitude and phase of each array antenna elements during communication in the system itself used in communication system such as TDD (Time Division Duplex) which carries out transmission and reception on time division basis.
BACKGROUND OF THE INVENTION
Lately, due to rapid expansion of mobile communication such as a portable telephone set and/or PHS (Personal Handyphone System), it becomes essential to have subscribers as many as possible in limited frequency band. Therefore, a multi-channel access system in which a specific channel is shared by a plurality of subscribers is now widely used in mobile communication system. The typical multi-channel access system used in the current mobile communication system such as cellular system and/or PHS, is Time Division Multiple Access (TDMA) system. Further, in a micro-cell system which is excellent in frequency usage efficiency, a Time Division Duplex (TDD) system which shares transmission and reception on the same frequency on time division basis is used.
On the other hand, it is essential to get rid of interference from adjacent cells in order to have high frequency usage efficiency in radio channels. The conventional technique to improve frequency usage efficiency is the use of an adaptive array antenna system. This is described in Monzingo et al, “Introduction to Adaptive Array”, John willy & Sons, New York, 1980. An adaptive array antenna system has an array of antenna elements each having weighted input signals for amplitude and phase so that the antenna system has null directivity on a radiation pattern in the direction of an interference wave to get rid of affection of an interference wave.
FIG. 13
shows a conventional configuration when an adaptive array antenna is used in a TDD system. When an adaptive array antenna is used in a TDD system, it is possible to use a radiation pattern of an antenna in a receive side as a radiation pattern in a transmit side as it is since transmit frequency is the same as receive frequency. Therefore, an adaptive array antenna is suitable to a TDD system considering transmit characteristics.
In
FIG. 13
, numerals
13
-
1
-
1
through
13
-
1
-N show N (N is an integer larger than 2) number of element antennas, each coupled with transmitters
13
-
3
-
1
through
13
-
3
-N or receivers
13
-
4
-
1
through
13
-
4
-N through transmit/receive switches
13
-
2
-
1
through
13
-
2
-N.
A receive signal is applied to a receiver through an antenna element, and a transmit/receive switch. An output of the receiver is applied to a radiation pattern control calculation circuit
13
-
7
(or direction control calculation circuit) which calculates amplitude and phase of each channel. A weight multiplier circuit
13
-
6
multiplies said amplitude and said phase to a signal to be transmitted, and the product is applied to antenna elements through transmitters and transmit/receive switches. The amplitude and the phase of the antenna elements are controlled by the weight multiplier circuit so that a desired shape of an antenna beam is obtained.
Accordingly, when the radiation pattern control calculation circuit provides the amplitude and the phase of each channels, and the weight multiplier circuit provides the product of said amplitude and the phase, and the transmit signal, the transmit radiation pattern is essentially the same as the receive radiation pattern.
However, although an amplitude and a phase of an antenna element should be ideally the same as those in all the antenna elements, they are actually different from one another because of an error of a high frequency circuit including a power amplifier, a connection cable, and/or temperature variation where an apparatus is mounted. The error degrades null and side lobe, so that interference suppression characteristics of an adaptive array antenna are degraded. This is described in J. Litva et al, “Digital Beamforming in Wireless Communications”, Artech House Publishers, 1996.
FIG. 11
shows an example of the degradation.
FIG. 11
shows three elements circularly arranged array antenna. FIG.
11
(
a
) shows the case of ideal amplitude/phase relations, and FIG.
11
(
b
) shows the depth of null in the radiation pattern because of an error of amplitude and/or phase of each antenna element. When it is ideal, a pattern having a null in 180° direction is obtained as shown in FIG.
11
(
a
). However, when an error exists in amplitude and/or phase in each antenna element, a radiation pattern is considerably degraded as shown in FIG.
11
(
b
). Accordingly, when transmit radiation pattern should coincide with receive radiation pattern of an adaptive array antenna in TDD system, amplitude and phase in each branches in an array antenna should be adjusted.
Conventionally, when amplitude and phase of an array antenna is adjusted, a signal from far field, or a signal transmitted by an array antenna in far field is received, and phase of each branches is sequentially rotated. This is called an element field vector rotation method, and is described in “A Method for Measuring Amplitude/Phase of Antenna Element in Phased Array Antenna”, by Mano, and Kataki, in Technical Journal (B), published by Institute of Electronics, Information and Communication in Japan, vol. J-65-B, No.5, pages 555-560.
However, when base stations are not positioned regularly in a micro-cell mobile communication system, but are positioned considering elimination of out-of-service area in a service area, and/or traffic, it is impossible to use above method in each base stations.
Further, when we try that a terminal station transmits a signal for adjustment purpose, said signal must be transmitted during actual communication, and therefore, transmission efficiency of a communication frame is decreased.
Accordingly, in an environment of mobile communication system, it is desired that amplitude and phase of each branch is adjusted by using an actual communication apparatus itself.
A prior proposal to adjust amplitude and phase of each branch by using an actual communication apparatus itself, is that an apparatus has a reference signal for adjustment purpose, and an array antenna is adjusted by using said reference signal. This is described in H. Steyscal et al, “Digital Beamforming for Readers”, Microwave Journal, vol.32, no.1, pp121-136. The configuration of the adjustment circuit in that article is shown in FIG.
12
.
In
FIG. 12
, an array antenna is adjusted as follows.
(1) A reference signal generator
12
-
11
sends a signal which is common to all the branches to a receiver
12
-
3
through a separator
12
-
14
a
. An adjusted value for each receiver is determined based upon a value received in each receiver and a reference value which is a received value by a specific receiver.
(2) A transmitter
12
-
4
sends a signal to a receiver through a switch
12
-
13
, and an attenuator
12
-
12
. The adjusted value is obtained by an output of each receiver, and a reference value of a reference receiver which is defined in said process (1).
(3) The transmit adjustment value is obtained by the difference of said process (1) and said process (2).
Accordingly,
FIG. 12
can adjust amplitude and phase of each branch of an array antenna by using only a communication apparatus.
However,
FIG. 12
carries out the adjustment of a transmitter and a receiver independently, and therefore has the disadvantage that an adjustment can not be carried out during actual communication in TDD system which carries out transmission and reception on time division multiplex system. Therefore, it can not follow the change of environment such as temperature variation during communication and/or change of location of base stations.
An object of the present invention is to provide an adaptive array antenna which can be adjusted during actual communication by using only a communication apparatus itself. The present invention does not use an external signal for adjustment of

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