Near-Field Radio Holography of Slant-Axis Terahertz Antennas

Near-field radio holography has been successfully applied to the slant-axis terahertz antenna, which features a unique rotational-mechanism. Corrections of residual path length errors and parallax effect caused by the noncoincidence of the aperture center and rotational center of the antenna are analyzed in detail for high precision near-field holographic measurement conducted at very short distances. Particular discussions are also provided about nonuniform sampling and polarization mismatch errors resulted from the beam rotation of the slant-axis mount system. Precise surface measurement and alignment have been demonstrated on a 1.2 m diameter slant-axis antenna, designed as the scaled model of the 5 m Dome A Terahertz Telescope. Experimental results with a root mean square of measurement repeatability better than 2.0 μm has been obtained.