Simulations of the Antenna-shielding Effect of the Daocheng Solar Radio Telescope (DSRT)
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摘要: 稻城太阳射电望远镜（DSRT）由313面6 m直径抛物面天线组成。天线接收信号幅值和相位的精确修正是决定DSRT成像质量的关键因素。然而DSRT阵列可能会出现邻近天线相互遮挡的问题，从而改变接收信号的幅值和相位，影响其成像质量。利用电磁仿真软件计算了接收频率为300 MHz（波长λ=1 m）时的相邻两单元与相邻三单元两种情况。三元系统中遮挡效应的影响仅比双元系统中相关影响略为显著。在本文考虑的最严重的遮挡情况（天线边缘的投影间距D = –1λ）下，对于双/三元系统，相对于单天线系统水平和垂直增益分别降低了0.6/0.6 dB和 0.3/0.4 dB，相位偏差分别为–3.3º/–3.871º和–1.744º/–2.244º。此外还分析了其他遮挡情况。研究表明DSRT系统中的天线遮挡效应分析可由双元系统充分描述，在后期数据处理时应适当考虑该效应，尽量提升DSRT数据的利用效率和成图质量。Abstract: The Daocheng Solar Radio Telescope (DSRT) is a next-generation solar radio telescope funded by the Chinese Meridian Project–Phase II. DSRT is composed of 313 parabolic antennas with a diameter of six meters. The antennas are evenly distributed in a circle with a diameter of one kilometer. With the synthetic aperture imaging techniques, key factors determining the DSRT imaging quality are accurate calibrations of amplitude and phase of the received signals. Yet, under some circumstances, adjacent antennas of DSRT may shield each other, which will affects the amplitude and phase of the received signals and thus deteriorate imaging quality. In this study, such shielding effects of three- or two-antenna using the electromagnetic simulation software at frequencies of 300 MHz (λ=1 m) were simulated. The shielding effect in the three-antenna system is slightly worse than that in the two-antenna system. When the projected distance of adjacent antennas is taken to be –1λ, i.e., the most serious effect of shielding considered here, the horizontal and vertical gains of the system with two/three antennas decline by 0.6/0.6 dB and 0.3/0.4 dB, respectively, and the horizontal and vertical phase deviations are –3.3º/–3.871º and –1.744º/–2.244º, respectively, compared to the system with one antenna. Other situations with different projected shielding distances are also investigated. The results show that the two-antenna system can sufficiently describe the shielding effect associated with DSRT. Such effect should be properly taken into account when processing the future DSRT data so as to improve the data usage efficiency and imaging quality.
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图 1 不同时刻DSRT中被遮挡天线位置分布（蓝点为未遮挡天线位置，红点为被遮挡天线位置）
Figure 1. Distributions of antennas in the DSRT array at different local time (Blue and red dots represent unshielded and shielded antennas respectively)
图 2 不同时刻DSRT剔除可视遮挡基线的uv分布
Figure 2. uv excluding baselines consisting of shielded antennas
图 3 双线极化对数周期天线馈源(a)和6 m抛物面天线结构(b)
Figure 3. Feed of the dual polarization log periodic antenna (a) and the 6-meter parabolic antenna (b)
图 4 仿真计算的天线回波损耗S11 (a)及不同频率的天线主方向增益分布(b)
Figure 4. Return loss S11 of the simulated antenna (a) and antenna gain along the main direction at different frequencies (b)
图 5 双元系统的侧视(a)前视(b)及三元系统俯视(c)图
Figure 5. (a) Side view of the two-antennas system; (b) front view of the two-antenna system; (c) side view of the three-antenna system
图 6 仿真计算的单元、双元和三元系统中不同遮挡情况下水平极化接收天线在300 MHz频率的增益方向图（灰色竖线表示单天线的主方向）
Figure 6. Simulated gain pattern of the horizontal polarization at 300 MHz under different shielding conditions (The gray vertical line is the main direction of the single-antenna system)
图 7 仿真计算的单元、双元和三元系统中不同遮挡情况下垂直极化接收天线在300 MHz频率的增益方向图（灰色竖线表示单天线的主方向）
Figure 7. Simulated gain pattern of the vertical polarization at 300 MHz under different shielding conditions (The gray vertical line is the main direction of the single-antenna system)
图 8 仿真计算的单元、双元和三元系统中不同遮挡情况下水平极化(a)(b)和垂直极化(b)(d)的相位方向图
Figure 8. Simulated phase patterns of (a)(c) horizontal polarization and (b)(d) vertical polarization under different shielding conditions
图 9 双元 (实线) 和三元 (虚线) 系统中，不同遮挡情况下接收天线的辐射相位
Figure 9. Radiation phase of receiving antenna under different shielding conditions in the two-antenna system (solid line) and three-antenna system (dotted line)
表 1 双/三元系统中不同遮挡情况水平极化接收天线的辐射性能比较
Table 1. Comparison of radiation characteristics of horizontal polarized antennas under different shielding conditions in the two/three-antenna system
双/三元系统主方向增益/dBi 双/三元系统旁瓣水平/dB 双/三元系统主波束指向/(°) 单天线 23.8/23.8 19.0/19.0 0/0 D=1λ 23.8 /23.8 19.2/19.1 0/0 D=0.5λ 23.8/23.8 19.9/19.4 0/0.5 D=0λ 23.8/23.8 19.8/19.0 0.5/0.5 D=–0.5λ 23.6/23.6 17.0/18.7 1.0/1.0 D=–1λ 23.2/23.2 17.7/16.2 1.5/1.5 
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表 2 双/三元系统中不同遮挡情况垂直极化接收天线的辐射性能比较
Table 2. Comparison of radiation characteristics of vertical polarization under different shielding conditions in the system with two/three-antenna system
双/三元系统主方向增益/dBi 双/三元系统旁瓣水平/dB 双/三元系统主波束指向/(°) 单天线 23.8/23.8 19.0/19.0 0/0 D=1λ 23.8/23.8 19.1/19.1 0/0 D=0.5λ 23.8/23.8 19.4/19.4 0/0.5 D=0λ 23.8/23.8 19.0/19.0 0.5/0.5 D=–0.5λ 23.6/23.7 17.9/18.7 1.0/1.0 D=–1λ 23.5/23.4 15.6/16.2 1.5/1.5
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表 3 双/三元系统中不同间距遮挡下接收天线的主方向相位比较
Table 3. Comparison of radiation phase along the main direction of the receiving antenna under different shielding distance in the two/three-antenna system
主方向相位变化 双/三元系统水平极化/(°) 双/三元系统垂直极化/(°) 单天线 0/0 0/0 D=1λ –0.279/–0.309 –0.079/–0.093 D=0.5λ –0.767/–0.819 –0.089/–0.137 D=0λ –1.289/–1.545 –0.393/–0.490 D=–0.5λ –1.983/–2.096 –1.085/–0.490 D=–1λ –3.300/–3.871 –1.744/–2.244
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