【作者】 吴明和；

【导师】 阮成礼；

【作者基本信息】 电子科技大学 ， 无线电物理， 2010， 博士

【摘要】 论文讨论了与光控阵列有源冲激雷达发射样机系统有关的三个方面内容:以光电导半导体开关(Photoconductive Semiconductor Switches,PCSS)为基础的瞬态高功率光电导脉冲源研究;利用点源近似模型,对瞬态电磁脉冲的传输特性进行了研究;以光控脉冲源和瞬态电磁脉冲的传输特性为基础,研制光控阵列有源冲激雷达发射样机系统,并对样机系统作了系统的实验测试。光控脉冲源是以半绝缘GaAs材料制作PCSS为核心的高功率纳秒脉冲源,完成了四个方面与PCSS的物理机制有关的工作。第一,根据Fermi-Dirac统计,研究了半绝缘GaAs中电离EL2浓度,计算了半绝缘GaAs对于1064nm激光的吸收系数;第二,讨论了EL2中心在电场作用下对电子捕获系数的加强效应,利用这一效应解释了高功率纳秒脉冲产生的机制。第三,采用连续性方程,考虑载流子的产生、漂移、复合等机制,以532nm和1064nm激光激励为例,数值计算了这两种波长激光激励下线性PCSS的输出电脉冲波形参数;考虑了储能电容大小对PCSS进入非线性模式阈值电场的影响,并对PCSS的输出脉冲进行了数值计算;数值计算结果表明:在储能电容很小的情况下,如果高电压偏置的PCSS快速而充分地导通,PCSS有可能处于线性工作模式。第四,重点研究了半绝缘GaAs PCSS非线性模式中的Lock-on模式。在PCSS研制与实验测试方面,主要完成了以下三方面工作:第一,分别采用解析与仿真计算方法,给出了PCSS机械结构及绝缘封装设计的一般方法;第二,探索了PCSS Pd/Ge/Ti/Pt/Au等金属系统的耐高温欧姆电极研制工艺,并研制了在50Ω负载上产生峰值功率超过2MW、触发抖动约65ps、使用寿命超过3.6×106次、脉冲宽度1ns、重复频率1kHz的高功率PCSS近1500只;第三,设计了准直流馈电和脉冲电源馈电PCSS直接测试电路,并完成了线性、非线性以及临界条件下的系列实验测试任务。在瞬态电磁脉冲传输特性的研究方面,主要完成了以下两个方面的工作:第一,利用点源近似模型,研究了阵列PCSS产生的瞬态电磁脉冲在轴线的传输特性、高效合成特性和波束聚焦特性;第二,用Laplace变换讨论了匹配负载的Blumlein传输线输出,计算了有阻情形下,Blumlein传输线的传输效率。在光控有源冲激雷达发射样机系统研制与实验测试方面,独立承担了小型化脉冲电源的设计、研制和测试;参与研制了光纤分束器、光电同步控制仪、集成Blumlein传输线和槽天线的一体化天线,以及样机系统的安装、调试及实验测试工作;实验测试结果验证了瞬态电磁脉冲的能量传输特性、阵列瞬态电磁脉冲的高效合成、波束聚焦等原理性概念,较好完成了项目研究任务。更多还原

【Abstract】 Three topics are discussed for ultra-wide band Radar sample transmitter in this dissertation: firstly, high power electric pulse source is developed which is based on Photoconductive Semiconductor Switches (PCSS); some research work has been done on the transmission properties of transient pulses according to a simplified model; finally, ultra-wide band Radar transmitter system is set up on basis of such pulse sources and transmission properties.When PCSS made from semi-insulating (SI) Gallium Arsenide (GaAs) is illuminated by laser pulse with its 1064 nanometers wavelength, the parameters of output pulse from the load can be calculated if absorption coefficient of GaAs and capture coefficient are given. Firstly, in terms of Fermi-Dirac statistics approximation, the density of unionized EL2 center is calculated and absorption coefficient of SI GaAs for sub-gap laser pulse was determined. Secondly, it is the enhancement of capture coefficient by electric field via EL2 centers that leads to output pulse with a nanosecond rise-time. Thirdly, three cases are discussed when PCSS is operated under linear mode: the wavelength of laser pulse is 532, 1064 nanometers, respectively, and the capacitance from Blumlein transmission line is 27.2 pF with a biased high voltage. The last section of this topic is related to the nonlinear mode of PCSS. In this section, a proposal is given: PCSS is operated under the nonlinear mode if electric field is higher than 3.5kV/cm when the laser pulse turned off, on the contrary, PCSS is still in linear mode.As for PCSS fabrication and the test of PCSS, research work has been done as follows.First, mechanic structure and insulation package of PCSS are developed for PCSS excellent performance. Second, the layers of refractory Ohmic electrode consist of Pd/Ge/Ti/Pt/Au for longetivity of PCSS.1500 PCSSes have been fabricated by such electrode layers.When 50? load is used for measurement of the output power and pulse width (more than 2MW, less than 1 nanosecond), each PCSS lasts more than 3.6×106 shots if repetitition frequency of the triggering signal is set to 1kHz.Third, two types of test circuit are designed for the research of differences between linear and nonlinear mode of PCSS. One of test circuits is charged by direct current voltage module, while another is charged by pulse charged module.Some research on properties of transient electromagnetic pulse has been done as follows: the z-axis properties of transient pulse coming from PCSS array such as transmission, power combination and beam formation are simulated by a model where each antenna is at its own location; the ouput efficiency of Blumlein transmission line is discussed by Laplace technique when the resistance of PCSS is taken into account.The impulse radar system is made up of some modules such as pulse charged module, laser generation and optical fibre transmission module, the module for the control of time sequence between two triggering signals, the antenna package module integrated with Blumlein transmission line and antenna.Among those modules,the pulse charged module is independently designed,developed and tested by the author.Other modules are designed,developed and tested by the collaboration of our research group.After the impulse radar system is completed, properties of transient electromagnetic pulse such as transmission, power combination and beam formation are explained and verified when simulation results and experimental results are in their comparison.更多还原