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We designed a 7 mm band ambient temperature receiver in the laboratory. The receiver's radio frequency is 30-32 GHz, and the final output after the mixed frequency is 0.8-2.8 GHz signal of intermediate frequency. It is mainly used to carry out atmospheric opacity measurement in the 7 mm band (31.2 GHz), so as to proceed accurate amplitude calibration in the scientific observation of the 7 mm band. The receiver is mainly composed of the feed network and the post-stage microwave link. After the completion of development, the dynamic range of the receiver's intermediate frequency output spectrum is about 30 dB, and the power range is about -38 dBm. Subsequently, combined with the mechanical rotation platform of azimuth and elevation, the 7 mm band receiver can scan and measure in the range of 0-90° elevation, and the atmospheric opacity value of the corresponding band can be obtained through power acquisition and fitting calculation.

The 25-meter radio telescope at Nanshan Observatory of Xinjiang Astronomical Observatory of the Chinese Academy of Sciences has been equipped with four cryogenic receivers in the centimeter band, namely, L, S/X, C and K band receivers. The newly installed Q-band cryogenic receiver (30–50 GHz) is the first millimeter-wave receiver of the 25-meter radio telescope, which is currently in the stage of installation and debugging. In order to better carry out millimeter wave observation at Nanshan Observatory, millimeter wave amplitude calibration is very important, and atmospheric opacity is the key to accurate millimeter wave amplitude calibration. To this end, we use the K-band cryogenic receiver (22–24.2 GHz) in the highest frequency band of the four centimeter wave cryogenic receivers of the existing 25-meter radio telescope to control the antenna to take skydip for elevation scanning in fixed azimuth, and obtain the corresponding power values at 18 elevation angles respectively. The power values are selected as the intermediate frequency signals (100–600 MHz) of the K-band receivers. The atmospheric opacity of K-band is obtained by using Levenberg-Marquette non-linear fitting of the signal power value at 200 MHz frequency point (corresponding radio frequency signal of K-band cryogenic receiver is 22.1 GHz). By comparing the measured data, the maximum error of the three groups of test results is 4.5%, which verifies the feasibility of the fitting method. We intend to apply this method to Q-band cryogenic receiver atmospheric opacity measurement after the installation and debugging of Q-band receiver in the future, so that it can improve the accuracy of millimeter-wave amplitude calibration.

Fast radio bursts (FRBs) are millisecond-duration radio transients of unknown origin. Two possible mechanisms that could generate extremely coherent emission from FRBs invoke neutron star magnetospheres or relativistic shocks far from the central energy source. Detailed polarization observations may help us to understand the emission mechanism. However, the available FRB polarization data have been perplexing, because they show a host of polarimetric properties, including either a constant polarization angle during each burst for some repeaters or variable polarization angles in some other apparently one-off events. Here we report observations of 15 bursts from FRB 180301 and find various polarization angle swings in seven of them. The diversity of the polarization angle features of these bursts is consistent with a magnetospheric origin of the radio emission, and disfavours the radiation models invoking relativistic shocks., Published online in Nature on 29 Oct, 2020

The proposed Qi Tai 110m radio Telescope (QTT) is a fully steerable single-dish radio telescope with an observing frequency coverage from 150 MHz to 115 GHz. The QTT will play an important role for fundamental research fields of radio astronomy, such as pulsars, molecular spectral lines, active galactic nuclei, and VLBI observations [1]. In order to mitigate the potential interference in the buildings at the QTT site, a low-cost shielding scheme is proposed for the buildings, to mitigate medium and low level RFIs. The measured shielding effectiveness shows that the scheme achieves our design goal.

We present our piggyback search for fast radio bursts using the Nanshan 26m Radio Telescope and the Kunming 40m Radio Telescope. The observations are performed in the L-band from 1380 MHz to 1700 MHz at Nanshan and S-band from 2170 MHz to 2310 MHz at Kunming. We built the \textsc{Roach2}-based FFT spectrometer and developed the real-time transient search software. We introduce a new radio interference mitigation technique named \emph{zero-DM matched filter} and give the formula of the signal-to-noise ratio loss in the transient search. Though we have no positive detection of bursts in about 1600 and 2400 hours data at Nanshan and Kunming respectively, an intriguing peryton was detected at Nanshan, from which hundreds of bursts were recorded. Perytons are terrestrial radio signals that mimic celestial fast radio bursts. They were first reported at Parkes and identified as microwave oven interferences later. The bursts detected at Nanshan show similar frequency swept emission and have double-peaked profiles. They appeared in different sky regions in about tens of minutes observations and the dispersion measure index is not exactly 2, which indicates the terrestrial origin. The peryton differs drastically from the known perytons detected at Parkes, because it appeared in a precise period of $p=1.71287\pm 0.00004$ s. Its origin remains unknown., 17 pages, 13 figures

The K-band cryogenic receiver of the 26m radio telescope at Nanshan Station, Xinjiang Astronomical Observatory, Chinese Academy of Sciences is mainly used for the observation of molecular spectral lines, active galactic nuclei and very long baseline interferometry. The calibration method of receiver takes noise injection mode, which is to inject standard noise into the rear stage of the feed to calibrate the amplitude response of the received signal. After replacing the low noise amplifiers, the K-band cryogenic receiver is calibrated in five typical frequency bands again. By comparing with the previous calibration results, the latest test results could satisfy the calibration requirements, and the latest calibration parameters can be further applied to the radio source amplitude calibration.

The Nanshan radio telescope (NSRT) is a fully steerable radio telescope with a diameter of 26 meters, located in Urumqi, Xinjiang, China. The NSRT currently operate in the frequency range from 1.4 GHz to 22.4 GHz。In order to reduce effect of gravity-induced structural deformations on antenna efficiency and pointing accuracy, the subreflector adjustment system has been used to adjust subreflector position in 6 degree-of-freedom to correct subreflector defocusing and reflectors misalignment. The Stewart platform is used as the adjustment mechanism to perform translation -50/+50 mm (along x, y, z axis) and rotation -5/+5 degree (with respect to x, y axis) with repeated positioning accuracies of 0.07 mm (translation) and 0.01 degree (rotation). The paper will mainly introduce an overview of the NSRT subreflector adjustment system, including Stewart platform and control system, performance testing, and position adjustment of subreflector.

Industrial Ethernet is widely used in automation and control system because of its high reliability and good communication performance. There are several protocols for Industry Ethernet. In different applications, it is necessary to select a appropriate protocol standard according to different needs. In order to apply industrial Ethernet in the active surface system of QTT, the control network requirements of active surface system were summarized. The period and jitter of three protocol standards, Ethernet/IP, Profinet RT and EtherCAT, were tested by evaluation hardware. The differences between network configuration and ring redundancy settings are analyzed. The results show that EtherCAT is more suitable for the network application requirements of active surface system of QTT.

The proposed 110-m fully movable radio telescope (Qi Tai Radio Telescope, QTT) in Xinjiang province has extremely high system sensitivity. A good radio environment of QTT site is of importance for QTT scientific output. In order to ensure that all kinds of electromagnetic interference can be monitored effectively during QTT construction stage, an automatic and high reliability radio environment monitoring system was developed. According to the design requirements, the extremelty high compact microwave device integration scheme was employed for radio frequency receiver model to improve the system sensitivity. System performance measured results show that the system gain is more than 40 dB below 6 GHz and the system noise figure is less than 2 dB. The measurement uncertainty is less than 1.49 dB below 7 GHz based on the analysis. Meanwhile, outdoor protection, lightning and electromagnetic compatibility designs were taken into account for high reliability. In addition, we developed an automatic spectrum measurement and performance monitor software and a data processing and mapping software based on HDF5 format, realizing automatic spectrum monitoring and high effective data processing.

In order to achieve the function of active adjustment of primary reflector for the QiTai radio Telescope (QTT), a kind of high precision positioning actuator is designed and some performances of the prototype are tested. The actuator scheme adopts the stepping motor, angle sensor, ball screw and worm gear. The detail design and simulation for the key components are made, and their accuracy, electromagnetic compatibility and environmental adaptation are especially studied. Accuracy tests of prototypes are carried out, and the result indicates that the actuator can meet the requirement of positioning accuracy (15 μm). Moreover, the field test of environmental adaptability of actuator prototype has been carried out in Xinjiang for more than a year, and during the test the prototypes go well without any faults, they can meet the requirement of environmental suitability.

The large-diameter radio telescope has extremely high system sensitivity; however, various electronic devices will be equipped at the constructing and operating process, which will generate electromagnetic interference impacting on radio astronomical observations. Therefore, it is necessary to investigate effective Electromagnetic Compatibility (EMC) control approach. This paper based the EMC requirements of radio astronomy, analyzing the deficiencies and adaptability of the EMC evaluation standards available, considering the feasibility of engineering process and operating management as well, on which an EMC control method for large-diameter radio telescope was proposed, including quantified interference level limits for the electronic equipment, EMC measurement method and shielding effectiveness testing method. This method will be applied to the proposed steerable 110-m aperture radio telescope (Qi Tai Radio Telescope, QTT) in Xinjiang, ensuring that QTT has good EMC performance.

The Qi Tai telescope (QTT) is a steerable 110 m radio aperture telescope that will be built in Xinjiang province, China. In this paper, we calculate the interference level limits, dB(Wm−2Hz−1) at the feed aperture relevant for the science requirements and the technical parameters of the QTT. These flux densities are converted into field strength units, in dBμV/m, for evaluation of the actual emission levels. Additionally, the side lobe gains of the receiver system will be determined from these key site locations. Based on high-resolution terrain data, a terrain model was constructed for the preliminary layout of the QTT site, in order to analyze the expected propagation losses from key locations to the telescope using the Longley Rice and Two Ray propagation models. Finally, the interference level limits for key activity areas are quantified accurately based on the limits of the feed aperture, the side lobe gains, and the propagation losses.

This paper reports on polarimetric radiation properties based on the switching modes of normal PSR B2020+28 by analysing the data acquired from the Nanshan 25-m radio telescope at 1556 MHz. With nearly 8 hours quasi-continuous observation, the data presented some striking and updated phenomena. The change of relative intensity between the leading and trailing components is the predominant feature of mode switching. The intensity ratio between the leading and trailing components are measured for the individual profiles averaged over 30 seconds. It is found that there is an excess of high ratios over the normal distribution, which indicates that two modes exist in the pulsar. The distribution of abnormal mode has a narrower width indicating that the abnormal mode is more stable than the normal mode. A total of 76 mode switching events are detected in our data. It spends 89\% in the normal mode and 11\% in the abnormal mode. The intrinsic distributions of mode timescales are constrained with power-law distributions. The significant difference in the index of the duration distribution between normal and abnormal modes possibly indicates that the timescale for the abnormal mode to get stable is shorter than that for the normal mode. The frequent switching between both modes may indicate that the oscillations between different magnetospheric states are rapid.

Backend system, as a part of the radio telescope, receives the radio signal which is amplified by the receiver, lays its emphasis on signal digitization and processing, and sends the processed data into storage system. Digital backend as a standard facility of radio telescope takes the place of analog backend, and multi-functional backend system is on its way to perfection. The backend hardware platforms, such as FPGA, GPU, CPU, and MIC, and they can be chosen when designing radio telescope backend system. The 110 m radio telescope (QTT), which is proposed to be built in Xinjiang Qitai, is planned with L, S, C, K wide/ultrawide band single pixel receivers, L band PAF and Q, W band conventional multibeam receivers, and the adaptive ultrawide band digital backend system will also be designed. Based on development of radio telescope backend system and introduction of worldwide research frontiers, we discussed and designed the digital backend plan and roadmap for QTT.

Scintillation of pulsar radio emission provides information about the interstellar medium along the path to the pulsar and the velocities of pulsars. It also affects the precision of pulse timing observations. Using a pulsar timing system developed at the Urumqi Astronomical Observatory 25 m telescope, we observed diffractive scintillation dynamic spectra for several strong northern pulsars. This paper introduces the observing system and discusses the observational results.

The application of an LQG controller in antenna servo system is presented in this work, using Nanshan 25-m antenna of Xinjiang Astronomical Observatory. A linear quadratic optimal controller is designed, based on establishing controlled object model and according to the quadratic performance index. Meanwhile, taking into account the actual situation of the antenna work, the Gaussian noise signal is added to simulate the actual interference signal. Then a Kalman filter is designed for the noise. A traditional PI (Proportional and Integral) controller is joined in order to further improve control performance. The good simulation results are obtained by repeatedly optimizing the controller. The results indicate that the designed LQG controller achieves desired results in control performance (such as settling time and overshoot) and has good disturbance performance. Besides, the system is relatively stable.

A new square law detector has been developed for digital microwave radiometer. It has a wider dynamic range and a more accurate square law response than has been available in the past. Experimental results show that the voltage sensitivity is higher than 0.9mV/uW and the linearity error is less than 0.3% in the frequency range from 100MHz to 2GHz and power range from −50dBm to −20dBm. Another advantage of the detector is its flatness, by selected a best type of diodes. Detailed detection circuit and measurement system have been given in this paper.

Scintillation of pulsar radio emission provides information about the interstellar medium along the path to the pulsar and the velocities of pulsars. It also affects the precision of pulse timing observations. Using a pulsar timing system developed at the Urumqi Astronomical Observatory25 m telescope, we observed diffractive scintillation dynamic spectra for several strong northern pulsars. This paper introduces the observing system and discusses the observational results.