【作者】 张英浩；

【导师】 吴文；

【作者基本信息】 南京理工大学 ， 电磁场与微波技术， 2011， 博士

【摘要】 毫米波辐射计能检测物体毫米波辐射信号的强弱,从而根据物体辐射特性的不同对目标进行探测识别及成像,具有区分金属非金属能力强、穿透雨雾烟尘及衣物等能力强、全天时工作等特点,因此在灵巧弹药末制导、地球环境遥感、大气气象研究、导航和安检等领域具有广泛的应用前景。本文主要对毫米波被动探测中利用物体极化辐射信息对虚假目标识别问题、毫米波被动相控阵成像中相位控制波束扫描问题及毫米波辐射计中逆向辐射、温度补偿及稳定性等相关问题进行理论和实验研究,具体工作如下：1.分析了毫米波超外差式辐射计中本振源相位噪声、混频器端口隔离度等参数对逆向辐射噪声及其引起的噪声温度测量误差的影响,给出了分析模型和解析计算公式,为系统设计时关键部件参数选择提供参考依据。2.提出基于四次谐波混频的毫米波辐射计,采用谐波混频抑制了逆向辐射噪声,采用X波段本振源增强了系统稳定性,降低了系统成本。在对逆向辐射抑制原理分析基础上,设计并研制了8mmm波段系统样机,实测温度灵敏度1.1K。3.针对小体积高集成度平台应用需要,对8mm直接检波式辐射计及其关键部件进行了设计与研制,实测系统样机温度灵敏度0.48K。针对毫米波前端增益-温度变化引起系统输出信号幅度变化,直接在毫米波电路中进行补偿难度较大的情况,提出在视频放大器中加入热敏电阻对系统总增益进行补偿的温度补偿方案。理论和实验分析表明,该方案简单有效,在-40℃～50℃温度范围内,实测补偿后幅度变化减小为原来的20%。4.提出双极化被动探测方案,通过两正交极化通道同时探测增大了系统作用距离,利用物体极化辐射特性的不同对虚假目标水塘进行识别。设计了8mm波段双极化直接检波式辐射计,理论分析表明系统最大作用距离为单通道辐射计的1.16～1.19倍；当目标充满天线波束的60%以上时,系统对水塘的识别概率大于99%。5.提出基于DDS-PLL相控源+四次谐波混频器的有源移相方案,对该方案及其关键部件进行了设计、理论分析和实验验证。该方案采用直接数字频率合成(DDS)在低频控制移相,具有技术难度小、精度高、控制方便等优点,避免了使用毫米波移相器和功率分配网络。此外采用四次谐波混频器,降低了DDS-PLL相控源技术难度和系统成本。更多还原

【Abstract】 Millimeter-wave (MMW) radiometer can sense the MMW radiation from objects, and can be used for passive MMW detecting and imaging. It can identify metal from nonmetal easily, can work during the day or night, and can penetrate rain, fog, dust, smoke, and cloths. So it is widely used in fire-and-forget weapons, remote sensing, weather forecasting, guidance, and public security. In this dissertation, the study of false target identification by polarized radiation measurement in passive MMW detecting, the phase control in phased array for passive MMW imaging, and some practical problems in MMW radiometer such as inverse radiation, temperature compensation, and system stabilization has been carried out. The main work is shown as follows.1. The effect of system parameters, such as LO noise and LO-RF port isolation of mixer, on the inverse radiation in MMW superheterodyne radiometer and the error in MMW radiation measurement was analyzed. The analysis model and analysis function were given, which can be used as a rule to choose parameters of key components to suppress the inverse radiation in radiometer design.2. MMW radiometer with fourth harmonic mixer was analyzed, in which the inverse radiation is suppressed by harmonic mixer. And the system is more stable and has a lower cost for X-band LO is used. Based on the analysis of the principle of inverse radiation suppression, a system demo at 8mm-band was designed and developed. And the measured temperature sensitivity is 1.1K.3. For compact radiometer is needed in application, the 8mm direct detecting radiometer and its key components were analyzed, designed, and developed. And the measured temperature sensitivity of the system is 0.48K. The gain of the MMW front end varies with the ambient temperature, and affects the amplitude of the output signal of the system. As it is difficult to do temperature compensation in millimeter-wave circuits directly, a thermistor was added to the video amplifier as temperature compensation to keep the total gain of the receiver constant. The analysis and the experimental results show that this temperature compensation method is easy and works well. The output variation of the compensated system is reduced to 20% of the variation of the uncompensated system, when the temperature varies from -40℃to 50℃4. A dual-polarization MMW radiometer was proposed to identify the pool from metal target, for pool has different radiation between vertical and horizontal polarization. An 8mm dual-polarization direct detection radiometer was designed. The analyzed results show that the largest sensing range is increased by 16%～19%, compared with the single-channel radiometer. And the probability of the pool identification is as large as 99%, when more than 60% of the antenna beam is filled with the target.5. A novel active phase control based on DDS-PLL phased source and fourth subharmonic (SH) mixer was proposed. The phase control and the key components were analyzed and designed. And an experiment was carried out to verify the idea. In this phase control, the phase shift is controlled by direct digital synthesizer (DDS) at low frequency. So it is easy to implement with high precision and low cost, and the MMW phase shifter and power divider are omitted. The fourth SH mixer use LO at low frequency, and so the cost of DDS-PLL phased source and system is reduced.更多还原