Communications: directive radio wave systems and devices (e.g. – Directive – Including a steerable array
Reexamination Certificate
1999-05-12
2001-06-19
Phan, Dao (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Directive
Including a steerable array
C342S372000
Reexamination Certificate
active
06249249
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an active array antenna system for use in wireless communication and comprising a plurality of element antennas and radio frequency circuits, and more particularly to a variable phase shifter circuit for controlling the phase of a local signal which is supplied to a frequency converting circuit in the radio frequency circuit.
This application is based on Japanese Patent Application No. 10-131982, filed May 14, 1998, the content of which is comprised herein by reference.
In general, the active array antenna system comprises a plurality of element antennas and radio frequency circuits connected to the element antennas. The active array antenna system is an antenna system for imparting an appropriate phase difference or the phase difference and an appropriate gain difference to a received RF signal or an RF signal to be transmitted, of each element antenna. Thus, directional beam scan can be performed or an arbitrary directional beam can be realized.
A conventional beam scan method adapted to the active array antenna system has been disclosed in Japanese Patent Laid-Open No. 7-202548 (hereinafter techniques described in this disclosure are called “conventional techniques”). According to the disclosure, a variable phase shifter circuit is provided for imparting a predetermined phase difference to a local signal in a carrier-wave frequency band which is supplied to each of frequency converting circuits corresponding to the plural element antennas. Since the S/N ratio of the local signal in the carrier-wave frequency band is higher than that of the received RF signal, the conventional technique attains the following advantages:
(1) An influence of deterioration in the S/N ratio caused by the variable phase shifter circuit on the RF signal can be limited as compared with a case where the variable phase shifter circuit is provided for a signal line for the RF signal.
(2) A plurality of variable phase shifters can concentrically be disposed.
(3) The structure of the control system can be simplified.
When the foregoing conventional technique is applied to a wireless communication system which uses a high carrier-wave frequency, such as a microwave or a millimeter wave, the foregoing conventional technique, however, encounters the following problem. That is, the cost of the variable phase shifter circuit for the local signal in the carrier-wave frequency band cannot be reduced. As a result, the overall cost of the active array antenna system cannot be reduced.
According to the conventional technique, the carrier-wave frequency is fixed. When the conventional technique is used to receive or transmit a plurality of carrier-wave frequencies by a single active array antenna system, such as the FDMA system or a multi-carrier TDMA system, there is a disadvantage that the structure of a power supply system becomes complex.
The conventional technique employs a filter or a delay element (for example, a delay line) to serve as the variable phase shifter circuit for the local signal in the carrier-wave frequency band. If the phase shift variation function is provided for the filter or the delay element, the cost cannot be reduced or a variable range for the phase shift is limited in general. As a result, beam scan freedom is narrowed.
As described above, the conventional active array antenna system has the structure that the phase of the local signal in the carrier-wave frequency band for the beam scan is controlled by the variable phase shifter circuit. When the conventional active array antenna system is applied to a wireless communication system using a high carrier-wave frequency, the cost of the variable phase shifter circuit cannot however be reduced. Thus, there arises a problem in that the cost of the active array antenna system cannot be reduced. Since the carrier-wave frequency is fixed, a plurality of carrier-wave frequencies cannot easily be transmitted or received by a single active array antenna system. Since the filter or the delay element is employed as the variable phase shifter circuit, the variable range of the phase shift is limited. As a result, there arises a problem in that beam scan freedom is narrowed.
BRIEF SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide an active array antenna system which is capable of constituting a variable phase shifter circuit for performing beam scan with a low cost and thus realizing the overall system with a low cost.
Another object of the present invention is to provide an active array antenna system which exhibits a wide variable range for the phase shift and which is capable of widening the beam scan freedom.
Another object of the present invention is to provide an active array antenna system which can be used in a communication using a plurality of carrier-wave frequencies without a necessity of employing a complicated power supply system and which is advantageous when an FDMA system or a multi-carrier TDMA system is constituted.
According to the present invention, there is provided an active array antenna system comprising a plurality of element antennas; and radio frequency circuits connected to the plural element antennas and comprising a frequency converting circuit provided for each element antenna and performing a frequency conversion by using an intermediate-frequency band local signal, and a variable phase shifter circuit for controlling phases of the intermediate-frequency band local signals which are supplied to the frequency converting circuits.
The frequency converting circuit comprises a plurality of first frequency converters provided to correspond to the element antennas and converting the frequency between a carrier-wave frequency and the first intermediate-frequency by using a carrier-wave frequency band local signal, and a plurality of second frequency converters provided to correspond to the element antennas and converting the frequency between the first intermediate-frequency and a second intermediate-frequency which is lower than the first intermediate-frequency by using the intermediate-frequency band local signal.
The variable phase shifter circuit comprises a plurality of variable phase shifters for controlling the phases of the intermediate-frequency band local signals which are supplied to the second frequency converters.
According to the present invention, there is provided another active array antenna system comprising a plurality of element antennas; and radio frequency circuits connected to the plural element antennas and comprising a frequency converting circuit provided to correspond to each of the antennas and performing a frequency conversion between a carrier-wave frequency and an intermediate frequency, and a variable phase shifter circuit provided to correspond to each of the antennas and controlling a phase of a received signal or a transmission signal of each of the antennas, the variable phase shifter circuit having a quadrature modulator.
According to the present invention, there is provided a further active array antenna system comprising a plurality of transmission and reception element antennas; a reception radio frequency circuit supplied with a received signal from the transmission and reception element antenna; and a transmission radio frequency circuit for supplying a transmission signal to the transmission and reception element antenna, wherein the transmission and reception radio frequency circuits comprise a frequency converting circuit provided to correspond to each of the antennas and performing a frequency conversion by using an intermediate frequency band local signal, and a variable phase shifter circuit for controlling a phase of the local signal which is supplied to the frequency converting circuit.
Additional objects and advantages of the present invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the present invention.
The objects and advantages of the present invention may be realized and o
Murakami Yasushi
Obayashi Shuichi
Otaka Shoji
Shoki Hiroki
Yamaji Takafumi
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Kabushiki Kaisha Toshiba
Phan Dao
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