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The Research Of Key Techniques In Passive Millimeter-Wave Dual-Polarization Detecting And Phased Array Beam Steering

Posted on:2012-06-04Degree:DoctorType:Dissertation
Country:ChinaCandidate:Y H ZhangFull Text:PDF
GTID:1118330335986562Subject:Electromagnetic field and microwave technology
Abstract/Summary:PDF Full Text Request
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.
Keywords/Search Tags:millimeter-wave radiometer, inverse radiation, subharmonic mixer, direct detection, temperature compensation, dual-polarization, passive detecting, phased array, DDS-PLL phased source
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