Current Issue : October-December Volume : 2022 Issue Number : 4 Articles : 5 Articles
This work investigates the effects of the surface errors of the satellite antenna on the detection performance of the space VLBI system. First, the relationship between the surface errors and the antenna gain loss is analyzed, and then the influence of the gain loss on the detection performance of the VLBI system is analyzed. Both the uniform and nonuniform distributions of errors are studied, and the second-order Taylor expansion is performed on the errors to simplify the calculation. When the errors distribute nonuniformly, the solver SCIP is adopted to solve the corresponding distribution, which leads to the maximum gain loss of the antenna. Taking the VLBI system with two base stations as the object, and each station’s radio telescope is a hoop truss deployable antenna with 30 m aperture, the effects of antenna gain loss on the detection capability of the radio telescope and the delay error of the VLBI system are studied. The study of extreme working conditions will have a higher guiding significance for the overall link analysis of practical projects....
Radar antennas in the open air are affected by dynamic wind loading during azimuthal scanning. In this state, the acquisition and prediction of the aerodynamic load is the focus of the structure design for the antenna. We performed wind tunnel force tests on flat plate antennas with different aspect ratios. The changes in mean, maximum, and root mean square values of the aerodynamic coefficients relative to the antenna aspect ratio and reduced frequency are given for the first time. The effects of the antenna aspect ratio and reduced frequency on aerodynamic characteristics are analyzed. The experimental results indicate that the magnitude of the azimuthal moment is related to the antenna aspect ratio and the reduced frequency. It is worth noting that the antenna aspect ratio has a significant impact on the mean, maximum, and root mean square values of dynamic aerodynamic coefficients. The mean, maximum, and root mean square values of the rolling moment coefficient, azimuth moment coefficient, and pitching moment coefficient monotonously decrease with the increase in aspect ratio. In addition, the influence of reduced frequency on the dynamic aerodynamic coefficient is closely related to the antenna aspect ratio. Under the same antenna aspect ratio, increasing the reduced frequency will increase the mean, maximum, and root mean square values of the aerodynamic coefficient. For flat plate antennas with different aspect ratios, at the condition of increasing the aspect ratios, the mean, maximum, and root mean square values of aerodynamic coefficients do not change significantly with the change of reduced frequency....
The difference between the space and the earth environment has significantly influenced the shape accuracy of the antenna reflector surface. With the increasing demand for the aperture of the antenna reflector, gravity has become one of the main factors that restrict the accuracy. In this paper, a new method for pretension design considering the effect of gravity is proposed. The design surface can be well restored to the ideal surface in orbit. Meanwhile, this method can avoid flipping antenna reflectors or extensive experiments for modification during ground adjustment. Then, the feasibility and effectiveness of the design method are validated by several numerical simulations. Moreover, the results are compared with the previous method and the differences have been discussed in detail. Finally, the effects of cable radius, cable length, and elastic modulus of the mesh reflector have been researched, respectively....
The paper deals with stochastic-deterministic modelling of radiated electric field by base station antennas (BSAs) operating in GSM frequency range. Within the framework of deterministic analysis, the total electric field above a two-layered lossy ground is obtained by considering the incident and reflected ray in the far field zone. The influence of nonhomogeneous lower medium is taken into account via two approaches: Fresnel plane wave reflection coefficient (FRM) and simplified reflection coefficient stemming from Modified Image Theory (MIT). Antenna height, relative conductivity, and permittivity of each ground layer, as well as the thickness of the upper ground layer, are considered as input parameters with inherent uncertainty. To quantify the uncertainty of output electric field, deterministic models are treated as black boxes by two stochastic methods, Monte Carlo (MC) and Stochastic Collocation (SC), respectively. Stochastic mean and standard deviation of the output are computed, and sensitivity analysis is carried out in order to analyze the impact of input parameters’ variations on the resulting electric field variance. The presented results expose weakness and strength of the two stochastic methods, particularly identifying the cases when the preferred SC method fails to converge. Furthermore, sensitivity analysis reveals that despite the smallest variation around its respective average value, the antenna height has the highest impact on the output variance at observation points in the vicinity of the antenna. However, as the distance from the antenna increases, the 1st layer depth and its relative electric permittivity become the most significant parameters....
In this paper, a wideband 8 × 8 MIMO antenna is proposed. The proposed antenna can realize the low profile of 4mm and the 3.18–4.40 GHz broadband coverage only by adjusting the ground edge structure of the deformed inverted-F antenna. Based on the original antenna, the 5G new radio (NR) band n77 (3.3–4.2 GHz) can be covered without adding any structure. In addition, the coupling between the antenna elements has also been improved, decreasing from −9.7 dB to −13.37 dB. A dual-element IFA pair is simulated, fabricated, and measured, the results show the bandwidth of 3.07–4.43 GHz, and the isolation of −13.89 dB can be achieved. An eight-element MIMO antenna is formed by placing four sets of antenna pairs along the two long edges of the substrate. The experimental results show that the bandwidth is 3.18–4.40 GHz, the isolation between any two ports is better than −12.25 dB, and the total efficiency is 61.14%–93.97%. By placing the planar antenna vertically, the ground clearance of the antenna can be reduced to zero, and the performances are similar to the planar MIMO antenna. The proposed MIMO antenna has a good profile and efficient radiation performance compared with the other works, so it has an important application value in ultrathin 5G smartphones....
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