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.

Near-Field Radio Holography of Slant-Axis Terahertz Antennas

A near-field millimeter-wave holography system operating in the 3-mm waveband have been developed as a prototype for DATE5, a 5-m terahertz telescope proposed to be deployed at Dome A, Antarctica. Experimental measurements at 92 GHz have been made on a 1.45-m test antenna. During the night time at which the ambient temperature doesn’t vary rapidly, a 75-minute repeatability (repeating measurement 3 times) of ~2.3 μm rms has been achieved with an aperture resolution of 46 mm. A local surface change of known value is correctly detected. After long-time repeating measurements, thermal-induced feed displacement is also detected with an accuracy of approximately 20 μm. Random error factors of the experiment system are evaluated and their contributions to the derived surface error are also simulated, showing that relative poor pointing of the test antenna is the major factor limiting the measurement repeatability.

Experimental studies on near-field holographic antenna measurement

In this paper the author presents a digital correlation design for the radio holography receiver of DATE5 (the 5-m Dome A Terahertz Explorer). Signal digitization is made at the IF outputs of the receiver and correlation is implemented in time domain. A 4-component algorithm for complex correlation is proposed. With this algorithm, the systematic error is much lower and the SNR is expected to have a 3 dB improvement comparing with the previous 3-component algorithm.

Design Study on the Digital Correlator Using for Radio Holography

The terahertz windows of the 5 meter Dome A Terahertz Explorer (DATE5) are primarily over the wavelengths between 350 and 200 μm. For studying the performance of the DATE5, based on a finite element model of the whole telescope assembly, the Eigen frequencies and Eigen modes of the DATE5 structure at different elevation angles are studied. The obtained results show the ranges of first 3 Eigen frequencies are in [5.73Hz, 6.22Hz], [6.84Hz, 7.60Hz], and [10.20 Hz, 13.30Hz] respectively, and show dependence with elevation angles. All of the Eigen frequencies are larger than 5 Hz, which meet the performance requirements for this telescope.

http://ieeexplore.ieee.org/iel7/7394815/7411336/07411722.pdf

Mode analysis of the 5 meter Terahertz antenna for Dome A, Antarctica

The terahertz windows of 5 meter Dome A Terahertz Explorer (DATE5) are primarily over the wavelengths between 350 and 200 µm. For studying the performance of the DATE5, based on a finite element model of the whole telescope assembly, the deformations of the telescope under gravity load at different pointing are calculated. The obtained results show the ranges of surface RMS errors is in [2.59 µm, 4.11µm]. All of the surface RMS errors are smaller than 5.00µm, which meet the performance requirements for the telescope. Besides, the results show that surface RMS errors due to gravity loading increase as the elevation angle increase. There is a nonlinear dependence of the reflector surface RMS error over the elevation angles. It can be fitted to a sine function.

http://or.nsfc.gov.cn/bitstream/00001903-5/519177/1/1000020821683.pdf

Gravity loading effect analysis of the 5 meter Terahertz antenna for Dome A, Antarctica

The 5m Dome A Terahertz Explorer (DATE5) is a proposed terahertz telescope to be deployed in Dome A, Antarctica, to exploit one of the best observing conditions at terahertz wavelengths on earth. In this paper, a design configuration for the near-field holography of the DATE5 surface measurement is presented. Important factors, such as measurement distance, operating frequency, and signal source location, are discussed. Special efforts have been given to the reduction of truncation errors. Simulation results under typical signal-to-noise ratios and design parameters are also provided.

http://ap-s.ei.tuat.ac.jp/isapx/2013/pdf/121_2_0.pdf

Design study on near-field radio holography of the 5-meter Dome A Terahertz Explorer

Terahertz radiation comes from cold objects in universe. It provides important information of star and galaxy formation. Within these bands, thousands of molecular lines are located, which may reveal important processes in cosmology. In Antarctica, the Dome A area has the best observing windows in the terahertz waveband. In this paper, a 5 meters Dome A Terahertz Explorer (DATE5) telescope concept is provided, which is a fully steerable telescope, working under the harsh Dome A polar environments. It requires a higher surface and pointing accuracies. This paper also discusses major aspects to be taken into consideration in its initial conceptual study.

http://ap-s.ei.tuat.ac.jp/isapx/2013/pdf/122_4_0.pdf

Initial considerations of the 5 meter Dome A Terahertz Explorer (DATE5) for Antarctica

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Design study on near-field radio holography of the 5-meter Dome A Terahertz Explorer

Initial considerations of the 5 meter Dome A Terahertz Explorer (DATE5) for Antarctica