Active Surface Compensation for Large Radio Telescope Antennas
Table 2
Modern antenna surface measurement methods.
Measurement methods
Characteristics
Remarks
Theodolite method
Less than 20 m under the accuracy 0.2 mm
The measurement process of large antennas is slow.
Total station method
Less than 120 m under the accuracy 0.2 mm
Compared with the former, it possesses lower cost, easier operation, faster construction of the coordinate system, and faster maintenance time.
Photogrammetric method
Less than 125 m under the accuracy 0.2 mm
It utilizes object images to reconstruct 3D shapes.
Laser tracking method
Less than 400 m under the accuracy 0.2 mm
It needs to be recalibrated when the instrument tilts, and dense sampling is slow.
Phase retrieval method
Tianma 65 m adopts this method to obtain the surface precision 510 μm.
It uses a single receiver and an astronomical source to measure the beam at a couple of different secondary focus positions.
Tower holography method
ALMA telescope, which is a reflector antenna array made up of antennas with the aperture of 12 meter and 7 meter, adopts this method to obtain the surface precision better than 20 μm.
It is a near-field measurement method using a tower transmitter.
Radio holography method
GBT adopted this method to obtain the surface precision 0.46 mm.
It requires a second reference telescope or receiver system, and both the telescope and receivers must have good phase stability.
Edge sensor method
Good stability and sensitivity on the order of 10 mm and CCAT use this method
It measures the real-time changes of panel-to-panel in the surface to implement real-time closed-loop control of the surface during astronomical observations.
