Communications: radio wave antennas – Antennas – Measuring signal energy
Reexamination Certificate
2002-06-13
2003-12-09
Nguyen, Hoang (Department: 2821)
Communications: radio wave antennas
Antennas
Measuring signal energy
C342S360000, C343S7810CA
Reexamination Certificate
active
06661384
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a mirror surface accuracy measuring device which is applied to a reflector antenna such as a large diameter radio telescope for astronomic observation using a millimeter radio wave or a submillimeter radio wave and in which mirror surface accuracy of the reflector antenna is measured. Also, the present invention relates to a mirror surface control system of the reflector antenna in which the adjustment of a mirror surface of a main reflector composed of a plurality of mirror panels is improved according to the mirror surface accuracy measured by the mirror surface accuracy measuring device.
2. Description of Related Art
A reflector antenna such as a radio telescope is used to perform astronomic observation by reflecting a radio wave radiated from a faraway celestial body on a reflector, converging the reflected radio wave and receiving the converged radio wave in a primary radiator. A radio wave radiated from a celestial body is propagated while spreading like a spherical wave. However, because an observation point is far away from the celestial body, the radio wave of the celestial body is incident like a plane wave on the reflector antenna. In case of the astronomic observation using the radio telescope, to efficiently converge the radio wave incident like a plane wave on the primary radiator, a uniform aperture phase distribution is required. This aperture phase distribution directly depends on the mirror surface accuracy of the main reflector. Therefore, it is very important to heighten the mirror surface accuracy of the reflector antenna for the purpose of improving the observation performance of the reflector antenna.
To measure the mirror surface accuracy of the reflector antenna, a mechanical measuring technique using a private gauge or a range-angle measuring unit and an electrical measuring technique such as a radio holography method have been used as a prior art. In cases where the mechanical measuring technique is used to measure the mirror surface accuracy of the reflector antenna, because a measurement error in the use of a measurement jig depends on the manufacturing accuracy and positioning accuracy of the measurement jig, it is difficult to significantly measure the mirror surface accuracy required of the reflector antenna such as a large diameter radio telescope which is used to perform astronomic observation with a millimeter radio wave or a submillimeter radio wave. Therefore, in a general case, the mechanical measuring technique is used for the initial adjustment of the mirror surface of the large diameter radio telescope used for the astronomic observation with a millimeter radio wave or a submillimeter radio wave, and the radio holography method of the electrical measuring technique is used for the final adjustment of the mirror surface.
FIG. 7
is a constitutional view showing the configuration of a conventional mirror surface control system in which mirror surface accuracy of a reflector antenna is measured and controlled according to a radio holography method. This conventional mirror surface control system is disclosed in “Measurement of Mirror Surface Accuracy of 45m Radio Wave Telescope based on Radio Holography Method”, written by M. Ishiguro, K. Morita, S. Hayashi, T. Masuda, E. Ebisu and S. Betsudan, Technical Report Vol. 62, No. 5, pp. 69-74 of Mitsubishi Electric Corporation, in 1988.
In
FIG. 7
,
1
indicates a reflector antenna.
2
indicates a geostationary satellite.
3
indicates a collimation antenna mounted on the geostationary satellite
2
and functioning as a transmitted wave source.
4
indicates a transmitted radio wave radiated from the collimation antenna
3
.
5
indicates a main reflector of which the mirror surface accuracy is measured.
5
a
indicates each of a plurality of mirror panels composing the main reflector
5
.
5
b
indicates each of a plurality of actuators for changing setting positions and attitudes of the mirror panels
5
a
.
5
c
indicates a backing structure on which the mirror panels
5
a
and the actuators
5
b
are supported.
6
indicates a primary radiator in which a radio wave reflected and converged on the main reflector
5
is received.
7
indicates a receiver to which the radio wave is fed from the primary radiator
6
.
8
indicates each of a plurality of support struts.
9
indicates radiation field distribution data obtained in the receiver
7
.
10
indicates an antenna attitude signal. An attitude of the reflector antenna
1
is changed according to the antenna attitude signal
10
to obtain the radiation field distribution data
9
corresponding to an attitude of the reflector antenna
1
.
11
indicates a radio holography processor in which the Fourier transformation is performed to calculate an aperture distribution from the radiation field distribution data
9
and the antenna attitude signal
10
.
12
indicates a mirror surface accuracy processor in which the mirror surface accuracy of the main reflector
5
is calculated from the aperture distribution obtained in the radio holography processor
11
.
13
indicates a mirror surface control device which controls the actuators
5
b
according to the mirror surface accuracy obtained in the mirror surface accuracy processor
12
to adjust setting positions and attitudes of the mirror panels
5
a
of the main reflector
5
.
14
indicates an actuator control signal.
15
indicates a reference antenna in which a reference of the radiation field distribution data
9
is measured.
Next, an operation of the conventional mirror surface control system will be described below.
To measure the mirror surface accuracy of the main reflector
5
, a radio wave is used for the reflector antenna
1
. Therefore, a transmission source position of the radio wave is placed sufficiently far away from the reflector antenna
1
a
in the same manner as the geostationary satellite
2
. Also, in place of the geostationary satellite
2
, in cases where a certain on-ground position sufficiently far away from the reflector antenna
1
is set as a transmission source position of the radio wave, the on-ground position is determined on condition that the reflection of the radio wave on the earth is reduced due to geographical features. A radiation field distribution of the transmitted wave
4
on the reflector antenna
1
is obtained by receiving the transmitted wave
4
while changing the attitude of the reflector antenna
1
in two dimensions.
Therefore, the radiation field distribution data
9
and the antenna attitude signal
10
indicating the attitude of the reflector antenna
1
are measured in a pair. Because a relationship between the radiation field distribution and the aperture distribution of the transmitted wave
4
on the main reflector
5
is expressed by Fourier transformation, the radiation field distribution data
9
is sent to the radio holography processor
11
, the calculation processing such as fast Fourier transformation is performed for the radiation field distribution data
9
and the antenna attitude signal
10
, and the aperture distribution on the main reflector
5
is calculated. A phase term of the calculated aperture distribution expresses an aperture phase distribution and corresponds to the unevenness of the mirror surface of the main reflector
5
. In the mirror surface accuracy processor
12
, the aperture phase distribution is converted in used wavelength equivalent, and a distribution of degrees of deformation shifted from an ideal shape of the mirror surface is obtained. Therefore, the mirror surface accuracy of the main reflector
5
can be estimated. In addition, the setting positions and attitudes of the mirror panels
5
a
composing the main reflector
5
are corrected by the actuators
5
b
in the mirror surface control device
13
, and the mirror surface accuracy of the main reflector
5
is improved.
In general, in view of antenna gain, it is required that the mirror surface accuracy of the main reflector
5
is equal to or lower than {fract
Mitsubishi Denki & Kabushiki Kaisha
Nguyen Hoang
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