| Millimeter-wave radiometer acts as a passive receiver which can receive and detect the thermal radiation of objects.It relies on the advantages of millimeter-wave's wide frequency bandwidth,short wavelength,strong penetrability,and its own high sensitivity,good concealment,full-time all-weather work and other characteristics.So it has been widely used in many fields such as resource detection,meteorological observation,environmental monitoring,security imaging and so on.Moreover in recent years,the radiometer system has put forward very high requirements for arraying and miniaturization,so the research of the multi-channel wideband millimeter-wave radiometer in this thesis has important engineering application value.In order to develop a radiometer with wider operating frequency band and higher temperature sensitivity,this thesis first conducts research on high performance wideband millimeter-wave detector.Based on the working principle of the detector,by analyzing the functions and performance requirements of each part of the detector,a high performance low-pass filter with a wider stopband range is designed,and then the broadband matching is realized.In the range of 27?50GHz,the voltage sensitivity of the finally designed detector is higher than 3m V/ ?W,and the highest value is reached8.2m V / ?W.Under the condition of video bandwidth of 3.3k Hz,the tangent sensitivity is about-54 d Bm.Then for the millimeter-wave high-rate demodulation detector used in video transmission,the parallel structure of the detector is determined based on the highpass characteristic of the rectangular waveguide,and then through the detailed calculation process,the simulation index of the low-pass filter is determined,and then the reasonable DC circuit is designed.The demodulation detector finally developed has a demodulation rate of 10 Gbps within the carrier frequency range of 30?40GHz.Then,based on the basic principle of the radiometer,the essence of object resolution and the main factors affecting the temperature sensitivity of the radiometer are analyzed.By comparing the advantages and disadvantages of different structures,the structure of the dual-channel radiometer is determined.The design content includes the selection of the low-noise amplifier chip and the design of video amplifier circuit,the DC power supply,of the low-noise amplifier peripheral bias circuit and the cavity structure to meet the miniaturization and electromagnetic compatibility.The temperature sensitivity of the two channels of the finally developed dual-channel broadband millimeter-wave radiometer reaches 0.058 K and 0.059 K respectively when the transient time is 20 ms.Finally,as for the millimeter-wave switches that are widely used in millimeter-wave systems including millimeter-wave radiometers,starting from the PIN diode principle,switching principle and main technical indicators commonly used in microwave control devices.Then determined the model of the switch chip,designed a reasonable switch drive circuit and a cavity structure that meets the requirements.Finally,a W-band SP3 T was developed.The experimental test results show that the insertion loss of the three channels of the W-band SP3 T is less than 3d B in the range of 88.5?89.5GHz,and the insertion loss of one channel is less than 3d B in the range of 81.5?96.5GHz,the minimum insertion loss is only 1.49 d B;the isolation between the three channels is greater than 25 d B in the range of 88?100GHz. |
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