大型双板导波天线对核电磁脉冲传输损耗和畸变特性

Loss and Distortion Characteristics of Large Two-plate Guided-wave Antennas for Transmitting Nuclear Electromagnetic Pulse

大型导波核电磁脉冲模拟器可为系统级装备试验提供自由空间辐照环境。针对此类模拟器常用的双板导波天线可能存在的传输损耗和波形畸变问题,以电磁仿真软件和算例对比分析研究了3种主要的影响因素,包括土壤的介电损耗及其抑制、前锥板向平行板转折的结构不连续、线栅阵列代替金属板的缝隙泄漏。研究结果表明:对上下极板等宽的情形,土壤损耗可使电压传输效率降低25%以上;适当展开下极板宽度可屏蔽土壤损耗;上极板转折处的结构不连续可导致平行段试验空间内电场呈现双峰交叠、幅度降低、波形畸变等特征;最大线间距0.3 m不会导致前沿显著变化。作为工程应用案例,设计了前锥长度60 m、顶高15 m、下极板拓宽3 m、由100根线栅阵列构成上极板的导波天线,试验空间超过20 m×20 m×10 m,实现了前沿2.5~3.0 ns双指数脉冲的无损耗、无畸变传输。

Large guided-wave nuclear electromagnetic pulse simulators are used to produce a free-space illumination environment for testing system-level equipment.For the two-plate guided-wave antenna usually used in these simulators,there may exist the transmission loss or waveform distortion problems as if the design has not been optimized.Several main influencing factors are analyzed with electromagnetic simulation software and comparisons of series of examples.These factors include the permittivity loss of soil and its suppression,the discontinuity of structure from the front conic plate to the parallel plate,the field energy leakage through the wire gaps for the wire-array upper plate,and so on.It is shown that,for the usual case of equal widths of the upper and ground plates,the dissipation of soil beneath the ground plate shall result in the loss of voltage transmission efficiency greater than 25 percent.And the lower-plate width is properly enlarged to screen the loss of soil,which almost eliminates the transmission efficiency loss of voltage.Secondly,the discontinuity of structure at the turning point of the upper plate shall result in a duplex peak characteristic of E-field waveforms with lowered amplitudes and distorted profiles for most view points in the parallel section.For the wire-gap leakage effect,a maximal wire-gap of 0.3 m may be sufficient to maintain the fast rise time of the exciting pulse.Finally,as an application example,a guided-wave antenna is designed to obtain a test volume greater than 20 m×20 m×10 m,which has a 60-meter-long and 15-meter-high conical section consisting of 100 wires and a ground plate with an enlarging width of 3 meters.The antenna can transmit the double-exponential pulse with 2.5-3 ns rise time fairly well to the main test volume.