International Journal of Antennas and Propagation / 2018 / Article / Tab 2

Review Article

Active Surface Compensation for Large Radio Telescope Antennas

Table 2

Modern antenna surface measurement methods.

Measurement methodsCharacteristicsRemarks

Theodolite methodLess than 20 m under the accuracy 0.2 mmThe measurement process of large antennas is slow.
Total station methodLess than 120 m under the accuracy 0.2 mmCompared with the former, it possesses lower cost, easier operation, faster construction of the coordinate system, and faster maintenance time.
Photogrammetric methodLess than 125 m under the accuracy 0.2 mmIt utilizes object images to reconstruct 3D shapes.
Laser tracking methodLess than 400 m under the accuracy 0.2 mmIt needs to be recalibrated when the instrument tilts, and dense sampling is slow.
Phase retrieval methodTianma 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 methodALMA 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 methodGBT 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 methodGood stability and sensitivity on the order of 10 mm and CCAT use this methodIt 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.