Holographic Measurement System of Nanshan 26m Telescope in Xinjiang Astronomical Observatory

The upgrade work of Nanshan 25m telescope has been completed after more than one year with great efforts. The diameter of main reflector is increased to 26 meter. And to ensure the high observational efficiency of Q band receiver, we have to measure and adjustment the antenna penal elaborately. Microwave holography is the first choice for initial and periodical measurement of antenna surface due to the high precision of this method. So we build a holography system based on the new 26m antenna, which includes reference antenna, receiver, correlator, transmission link, time and frequency reference, antenna control software and holographic processing software. Some techniques have been used for simplify the hardware and promote the performance of this system. We use band pass sampling theorem for IF signal direct digitization, which can save the hardware device of baseband converter and decrease the phase fluctuation due to microwave signal mixing, filtering and amplification. To get a better phase stability of the system, we use a high performance Phase-locked Dielectric Resonator Oscillator(PDRO) for satellite signal mixing, which can support a very stable phase by lock the 10MHz reference signal from a hydrogen mazer. All parts of this system have been designed and tested, the result shows that the whole system works very well and meets the needs of application.