Subjects: Astronomy submitted time 2024-01-31 Cooperative journals: 《天文学报》
Abstract： Radio telescopes usually conduct continuous observation across a wide frequency range, but traditional phased array antenna designs struggle to meet the requirements of both wide band and large scanning volume. The development of tightly coupled antennas offers a novel approach for addressing these challenges. Accordingly, a wideband dual-polarized Vivaldi phased array feed has been designed. Firstly, a theoretical analysis of the tightly coupled principle is conducted, incorporating Wheeler's concept of continuous current and equivalent circuit. It reveals that the strong coupling between the antenna elements effectively expands the operational bandwidth of the Vivaldi phased array. Based on this, a wideband Vivaldi phased array feed composed of 8$\times$9 Vivaldi antenna elements with a operational frequency ranging from 2 to 8 GHz is designed. Furthermore, the phased array enables $\pm$45$^\circ$ scanning characteristics in both E-plane and H-plane. Finally, a prototype of the phased array is fabricated and measured. The measurement results are in good agreement with the simulated ones.
Subjects: Astronomy >> Astrophysical processes submitted time 2023-11-24 Cooperative journals: 《天文研究与技术》
Abstract： VHF (Very High Frequency) band is one of important observation bands in Radio astronomy field. In this band, we usually use the array to form phased array telescope. In another hand, sparse array has more space resolution and lower side lobe level comparing with the regular array. Furthermore, based on array integrated optimization algorithms, we can effectively form the main beam and reject the Maximum side lobe levels and far side lobe levels. In this paper, at first, we review the development and research status of VHF sparse array in radio astronomy filed and analyze difficulties. The second, we promote a pipeline for sparse array building. The first step is constructing the optical elements configuration based on some optimization algorithms. And then, we promote a signal processing structure based on high performance computing severs and FPGA (Field Programmable Gate Array) SOPC (System On Programmable Chip) platform. In this platform, taking advantage of strong computing capability, in the GPU embedded in severs can compute the weighting parameters of different elements and different frequency channels. And then, transmitting these parameters through the high-speed bus and delivery them to each element in FPGA SOPC. We also analyze the data rate with multi-beams that can transmit the weighting parameters in real-time. This work can provide a technical base for future large-scale VHF array building.
Subjects: Astronomy >> Astrophysical processes submitted time 2023-10-20 Cooperative journals: 《天文研究与技术》
Abstract： Radio astronomical telescope is a key system in astronomical observation, deep space exploration and other researches. It is of great significance to improve its sensitivity and reduce the system noise temperature. However, because the frequency band allocated to radio astronomy research is limited and often shared with other businesses, radio astronomy telescopes are vulnerable to strong radio frequency interference. After these interferences enter the RF receiver, intermodulation interference, amplifier saturation and other problems will occur in the low-temperature amplifier, raising its noise background and reducing the detection sensitivity of the radio telescope to weak signals. The filtering metasurface technology can effectively suppress radio astronomy radio frequency interference, but the additional introduced noise needs to be controlled. In this paper, we propose a method to reduce the noise temperature of filtering metasurface in radio astronomical telescope. We study the relationship between the dissipative loss and reflection loss of filtering metasurface and its noise temperature, and minimize the noise temperature by restricting the direction of mismatched reflections. Using the method proposed in this paper, the system noise temperature can be reduced by 35.4%. If the filtering metasurface is set in the cooling chamber, an additional noise temperature of only 0.11K can be achieved.
Subjects: Astronomy submitted time 2023-08-02 Cooperative journals: 《天文学报》
Abstract： As the key component of radio astronomy receiver system, the noise and gain performance of Low Noise Amplifier (LNA) have important influence on the sensitivity of receiver system. In this paper, a broadband LNA which can cover the C-band (4--8\;GHz) is developed by using the 100\;nm gallium arsenide (GaAs) pseudomorphic High Electron Mobility Transistor (pHEMT) technology. The amplifier adopts three-stage common source cascade amplifier topology and dual power supply structure. Measured results show that the average noise temperature of the amplifier is 60\;K in the frequency range of 4--8\;GHz with the lowest noise temperature of 50\;K being achieved at 5\;GHz. The gain is (31$\pm$1.5)\;dB in the whole bandwidth and the input and output return loss is better than 10\;dB. The chip area is 2.1$\times$1.1\;mm$^2$. This designed LNA can be used in the C-band radio astronomy receiver and satellite communication system.
Subjects: Biology >> Botany >> Applied botany submitted time 2021-05-27 Cooperative journals: 《广西植物》
Abstract： To reveal the causes of low seed-setting rate of Pseudosasa viridula, the process of megasporogenesis and microsporogenesis and the development of female and male gametophyte of P. viridula were studied using traditional paraffin section and microscopy techniques. The results were as follows: Each flower contained three anthers (rarely 6) and an anther with four pollen sacs. The anther wall belonged to the basic type with the typical glandular tapetum, which composed of four layers of cells, which were epidermis, endothecium, middle layer and tapetum from outside to inside. The cytokinesis was the successive forming the medianly zygomorphic tetrads. Mature pollen grains were 2-cell type or 3-cell type, and some abortions occured. Mature pollen grains were 2-cell type or 3-cell type, and some abortions had occurred, which mostly occurred in the mononuclear stage of microspores. Its ovary was unilocular, with parietal placenta was anatropous, double integument and crassinucellate. The embryo sac was the polygonum type composed of an egg organ, a polar nucleus and three antipodal cells. The pistil structure was complete with embryo sac normal development, and the microspore abortion occurs in the single nuclear pollen stage. It is the typical male sterility and pollen abortion may be the main reasons for the low seed-setting rate of P. viridula. This study clarified the process of megaspogenesis, microsporogenesis and the development of female and male gametophyte of P. viridula, and initially revealed the reasons for the low seed setting rate of this species, which provides basic information for the development of cross breeding of P. viridula.
Subjects: Astronomy >> Astrophysical processes submitted time 2021-03-30 Cooperative journals: 《天文研究与技术》
Abstract：脉冲星周期跃变是一种罕见的现象，是研究其内部结构的探针。针对2019年2月至12月，国家授时中心昊平观测站40米射电望远镜在脉冲星计时观测中，监测Crab脉冲星的数据，采用脉冲星计时方法，用TEMPO2拟合程序进行分析。结果表明Crab脉冲星在2019年7月23日（MJD58687）附近发生了一次周期跃变现象，该跃变自转增量为 ∆vg = 5.33（4）×10-7 Hz，自转变化量为 ∆vg /v = 17.9（1）×10-9 ，并伴随着恢复系数Q ~ 0.88的指数恢复过程。此次Crab脉冲星周期跃变的监测及处理，证实了国家授时中心40米射电望远镜对脉冲星的监测性能，同时为研究周期跃变的产生机理积累了样本。
Hits
YES
Hits
Downloads
Comment