Zhao Rongbing

Relative position determination of a lunar rover using the biased differential phase delay of same-beam VLBI

When only data transmission signals with a bandwidth of 1 MHz exist in the rover, the position can be obtained using the differential group delay data of the same-beam very long baseline interferometry (VLBI). The relative position between a lunar rover and a lander can be determined with an error of several hundreds of meters. When the guidance information of the rover is used to determine relative position, the rover’s wheel skid behavior and integral movement may influence the accuracy of the determined position. This paper proposes a new method for accurately determining relative position. The differential group delay and biased differential phase delay are obtained from the same-beam VLBI observation, while the modified biased differential phase delay is obtained using the statistic mean value of the differential group delay and the biased phase delay as basis. The small bias in the modified biased phase delay is estimated together with other parameters when the relative position of the rover is calculated. The effectiveness of the proposed method is confirmed using the same-beam VLBI observation data of SELENE. The radio sources onboard the rover and the lander are designed for same-beam VLBI observations. The results of the simulations of the differential delay of the same-beam VLBI observation between the rover and the lander show that the differential delay is sensitive to relative position. An approach to solving the relative position and a strategy for tracking are also introduced. When the lunar topography data near the rover are used and the observations are scheduled properly, the determined relative position of the rover may be nearly as accurate as that solved using differential phase delay data.

Sub-reflector model depending on elevations and performance evaluation for TM65 m radio telescope

A sub-reflector system of the TianMa 65 m radio telescopes has been installed in order to compensate for the gravitational deformation of the sub-reflector support and the main reflector. The position and attitude of the sub-reflector are variable in order to improve the pointing performance and the efficiency at different elevations. A model has been constructed to determine the position and attitude of the sub-reflector with elevation. Test results show that the sub-reflector model can effectively improve the efficiency of the 65 m radio telescope at both high and low elevations, where the efficiency can be improved by 20% and 15%, respectively. At X band, the aperture efficiency of the radio telescope reaches more than 60% over the entire elevation range. Pointing deviations caused by the sub-reflector model are consistent with the grasp simulation results.

TM65 m radio telescope microwave holography

Microwave holography is a valuable technique used in the diagnostics and adjustment of large antennas. A brief outline of the technique is given first. Then detail simulations for surface deviation and sub-reflectorr offsets solving method that applied on the TianMa 65 m are described. After several rounds of adjustments, a reflector surface accuracy 0.28 mm and repeated measurement error 0.13 mm were achieved for the TM65 antenna. At last the antenna efficiency on Ka band was measured at elevations between 45 and 60 degrees. The efficiency improved from 37% to 56% when the active surface model is loaded that is consistent with the theoretical predictions.

High precision pointing error detection method for large radio telescope

In the paper, the main factors influencing pointing precision of large radio telescopes are discussed. Then the TianMa radio telescope (TM65 m) is selected for demonstration. The methods of detecting and separating the pointing errors which produce in all the segments from the subreflector to the track rail of the telescope are introduced. They includes: (1) half power point tracking to evaluate the overall antenna pointing error; (2) detecting the pointing error due to position changing of the subreflector support; (3) detecting the deviation of the antenna mount due to temperature changing; (4) detecting the asynchronization of the mechanical axis and the encode axis; (5) high precision pointing modeling based on the uneveness of track rail. A few measurement methods and their respective results are discussed.

Antenna performance measurements on Ku and Ka bands for TM65m radio telescope

TM65m radio telescope Ku and Ka-band antenna pointing, subreflector model, efficiency, sensitivity, and system noise temperature performance are reported in this paper. The key indicators of radio astronomy receiving system are introduced firstly. Secondly the band measurement essential points are discussed these are point and sub-reflector model construction and atmosphere influence. The antenna efficiency, sensitivity and system noise temperature of the two bands are described finally. The measurement results show that in the Ku and Ka-band, in the middle of the elevation, Ku-band efficiency can be controlled to 60%, Ka-band can be controlled to 38%. And in the higher and lower elevations, there is a significant decline in the efficiency since the main surface deformation.