分类： 天文学 >> 天文学 分类： 地球科学 >> 大地测量学 提交时间： 2024-02-05
摘要： LR polarization is commonly used for the corresponding geophysical parameters retrieval in GNSS#2; R(Global Navigation Satellite System-Reflectometry) or SoOP-R (Signal of Opportunity-Reflectometry) . However, the other polarization of the reflected signals has attracted more and more attention with the development . The popular used equation for RR polarization demonstrates that it decreases as the soil moisture content increase and this is in contradiction with the experiment data. Here, three new models have been developed: Spec4PolR (Specular reflectivity model for polarization GNSS#2; R), SPM4Pol (small perturbation model for polarization GNSS#2; R), and Umich4Pol (Umich model for polarization GNSS-R). The Mueller matrix of these three models has been presented and the wave synthesis technique is employed to calculate the reflectivity at RR polarization. Spec4polR employs only three elements in the Mueller matrix for the final reflectivity, while five elements for Umich4polR participate in the calculation and although all the elements of the SPM4Pol have constructed the Mueller matrix and only nine elements have been employed for calculation. Each elements' effects on the soil moisture content are presented and the final reflectivity at RR polarization has been illustrated. However, due to the simple formulations of Spec4Pol, its reflectivity at RR polarization still decreases as the soil moisture content increase. while the results of SPM4Pol and Umich4Pol are consistent with the measured data and the reflectivity at RR polarization increase as the soil moisture content increase. The accurate forward calculation of RR polarization is crucial for the subsequent retrieval algorithm of polarization GNSS-R/SoOP-R.
分类： 地球科学 >> 空间物理学 提交时间： 2017-03-10
摘要： The W-band full-polarization radar detection system is in need of a new type of antenna feed with good performance. The waveguide slot array antenna, has the advantages of low profile, high radiation efficiency, easy access to high gain. It has been become the research emphasis in the field of millimeter wave detection. In order to satisfy the need of developing complete polarization radar detection system, a W-band four-channel dual-polarization waveguide slot antenna is designed. The results of the simulation and optimization tests show that, the antenna has outstanding technical characteristics in double polarization. The antenna gain is higher than 13dB, and the cross-polarization level lower than -34dB. The bandwidth below VSWR 1.5 is better than 2.8GHz. High isolation of over 50dB is achieved between different polarization input ports.
分类： 地球科学 >> 空间物理学 提交时间： 2017-03-10
摘要： Two single-layer X/Ku dual-band dual-polarization reflectarray antennas of different sizes with double parallel dipole elements are presented. Elements of the two bands are set to two orthogonal linear polarizations and placed in interlaced grid. The proposed reflectarrays operate in two frequency-bands within X-band centered at 10 GHz and Ku-band centered at 13.58 GHz. The smaller size reflectarray with elements arranged in a 13 �13 grid for X-band and in a 12 �12 grid for Ku-band is designed and simulated first. Based on the excellent dual-band performance of the small size reflectarray, then a larger size prototype has been designed, manufactured and measured. Measured results demonstrate the maximum gain of 28.54 dB with 50.93% aperture efficiency at 10 GHz and 31.06 dB with 51.34% aperture efficiency at 13.58 GHz, which show desirable dual-band dual-polarization radiation performance.
分类： 地球科学 >> 空间物理学 提交时间： 2017-03-10
摘要： In this paper, a novel X-band broadband single-layer unit cell with attached phase-delay lines for reflectarray antennas is proposed to surmount the limitation of the reflectarray bandwidth. The unit cell is composed of three circular rings, each with a pair of gaps which are mutually placed orthogonally, and two identical circular phase-delay lines are attached to the outer ring to provide the required reflection phase. After the simulation for the unit cell carried out, a large reflecting phase range of about 600�and almost linear phase curve are achieved at the center frequency of 10 GHz. Parallel phase curves of different frequencies ranging from 9 GHz to 12 GHz are also obtained. To validate the broadband performance of the proposed unit cell, a 9 �9 center-fed reflectarray antenna operating at X band is designed and simulated. Simulation results show that the designed antenna has 34% 1-dB gain bandwidth, which demonstrates that an obvious improvement on the bandwidth has been achieved compared to the previous works. Besides, the cross-polarization level is decreased to -40 dB by a mirror symmetric element arrangement.
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