Coaxial-Fed Circular Dipole Array Antenna With Ferrite Loading for Thin Directional Borehole Radar Sonde
Coaxial-Fed Circular Dipole Array Antenna With Ferrite Loading for Thin Directional Borehole Radar Sonde
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DOI：
10.1109/tgrs.2014.2349921
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发表时间：
2015-04-01
影响因子：
8.2
通讯作者：
Choshi, Hiroyuki
中科院分区：
文献类型：
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作者：
Ebihara, Satoshi;Kimura, Yuta;Choshi, Hiroyuki
在本文中，我们提出了一种在钻孔中安装铁氧体负载的同轴馈电偶极子阵列天线，以实现薄型定向钻孔雷达探空仪（直径为 54 mm）。该雷达的工作频率约为 20 至 150 MHz。当先前提出的偶极子阵列用于薄型雷达探空仪时，该天线会受到来自中心导电圆柱体 (CCC) 的散射波的影响。这会干扰 100 MHz 以下的波达方向 (DOA) 估计。为了克服CCC的干扰，在CCC中添加了商用铁氧体磁芯。矩量法分析表明，我们可以利用铁氧体磁芯的电感特性将 CCC 的谐振频率降低到 20 MHz 以下。这加宽了天线的频率带宽。土壤现场实验表明，铁氧体磁芯加载的 CCC 工作可靠，并证实我们可以估计 20 至 150 MHz 之间的 DOA。在岩石中检查直达波功率谱的其他测量发现，铁氧体磁芯拓宽了雷达系统的工作频率带宽。
In this paper, we propose a coaxial-fed dipole array antenna in a borehole with ferrite loading to achieve a thin directional borehole radar sonde (diameter of 54 mm). This radar works between about 20 and 150 MHz. When the dipole array, proposed previously, is used for the thin radar sonde, this antenna suffers from scattered waves from the centered conducting cylinder (CCC). This disturbs the estimation of the direction of arrival (DOA) below 100 MHz. To overcome the interference of the CCC, commercial ferrite cores were added to the CCC. A method-of-moment analysis showed that we may decrease the resonant frequency of the CCC to below 20 MHz, making use of the inductive characteristics of the ferrite cores. This widens the frequency bandwidth of the antenna. Field experiments in soil showed that the ferrite core-loaded CCC works reliably and confirmed that we can estimate the DOA between 20 and 150 MHz. Other measurements in rock which examined the power spectrum of a direct wave found that the ferrite cores widened the operating frequency bandwidth of the radar system.