Active Surface Compensation for Large Radio Telescope Antennas

Table 1

Traditional methods of antenna surface measurement.

Methods		Measurement accuracy/mm	Scope of application
Mechanics	Template method	±0.1~0.2	It is only suitable to measure the antenna in elevation and more effective for the installation and detection of small and medium antennas.
	Lathe method	±0.02~0.1	It is only suitable for measuring small antennas (the diameter should be less than or equal to 4 m).
Optics	Theodolite and steel tape method	<±0.2	It is widely used.
	Double pentaprism method	±0.15~0.66	It can measure the surface accuracy of paraboloid at different elevation angles.
Others	Pentaprism and tape method, steel wire ranging method, car measurement method, etc.