| THz is between microwave and infrared wave.Due to its unique properties,the THz wave has become an important development direction of future information systems such as radar and wireless communications.Universities and research institutes at home and abroad are putting more energy into the research on terahertz technology.It has shown great potential in near field imaging,material detection and high data volume communications.Due to the lack of high efficiency and high power frequency source in the THz band,the sensitivity of the detector is low,and the loss of passive transmission devices is large,which limits the wide application of terahertz wave technology.Therefore,research and development of high-performance terahertz devices appear extremely urgent.In wireless systems,transmitters generally work at ultra-high power while receivers operate at ultra-low power.When the transceiver needs to send and receive information at the same location,it should be guaranteed that the transmitter power does not enter into the receiver,or the receiver will be destroyed.Duplexers are commonly used in communications and radar systems to accomplish this function.And the signal-to-noise ratio and receiver dynamic range are increased when use duplexer.For the terahertz band of electromagnetic waves,the wavelength goes into the millimeter,sub-millimeter range,because of processing technology and materials limitations,the traditional method of making duplexers have a bigger power loss and greater cost.Based on the 340 GHz atmospheric window frequency as the working center frequency,a quasi-optical broadband duplexer with a working bandwidth of more than 25 GHz is presented in this thesis.The basic working principle and structure of the duplexer are also described.The main innovations of this thesis are as follows:1.For the first time to apply flexible film as the base and use photolithography process to produce a diameter of 100 mm ultra-thin metal wire grid polarizer which works in the terahertz band.The width of the metal wire grid is only 10?m and the base thickness of the polarizer is 10?m.The simulation shows that the electromagnetic wave transmission loss of the polarizer in the direction of polarization perpendicular to the metal wire grid is less than0.1d B within 200-400 GHz,The direction of polarization parallel to the direction of the metal wire grid electromagnetic isolation is greater than 35 d B.And it can work in broadband.2.A new type of polarization converter operating at 340 GHz is designed.The polarization converter is a transmission line type metamaterial with a double-layer periodic metal structure.For the first time,we utilize the transmission line principle and the Smith chart to explain how the variation of the thickness between the two metal patterns affects the transmission loss and the phase characteristics of the polarization converter.For the first time,the phase modulation formula of multilayer phase modulation metamaterial was proposed.The influence of double-layer structure alignment error on the performance of the designed polarization converter is analyzed from the optical point of view.The simulation results show that the transmission loss of the polarized converter in the 325-350 GHz band is less than 2d B and the phase difference is 80°-100°,and the calculated emission wave axis ratio is less than 3d B.3.The the method of cutting off the opening of the metal wire grid in the traditional reflective polarization converter and increasing the width of the metal wire grid is proposed to introduce the equivalent capacitance and inductance effect of the metal pattern of the polarization converter on the mutually orthogonal electromagnetic fields in the two polarization directions,which makes it possible to expand the working bandwidth by modulating the phase of incident wave on different polarizations.The simulation results show that when the polarization converter operates in the 500 GHz frequency band,the thickness of the polyimide as the intermediate medium is 34?m.When the axial ratio is less than 3d B,the bandwidth is about 140 GHz.4.Soft film photolithography processing is proposed to increase the processing accuracy of terahertz devices and reduce the transmission loss caused by the substrate materials.Explore the process of photolithography processing with solid state film and processing with liquid polyimide,and compare and advantages and disadvantages.Processing step and microscopic images show that although the use of liquid polyimide solution made of self-made film will increase the processing time,especially when the film is thick.However,the process of processing the device to save the metal pattern is more complete,finished film surface roughness is better,and most importantly,the thickness of the dielectric substrate can be controlled by processing.5.A vacuum adsorption alignment assembly system is designed which is for the alignment assembly of the polarizer double diaphragm.The system achieves the effect of reducing the alignment errors of the double-layer periodic metal patterns of the polarization converter by strictly controlling the initial positions of the two layers of films to be the same and strictly controlling the movement tracks of the two layers of films.Based on the above works,a 340 GHz quasi-optical broadband duplexer is assembled.The test results show that the device in the 325-350 GHz frequency band transmission loss less than 3d B,isolation greater than 42 d B,the outgoing circular polarization characteristic is good.Besides,the processing tech is simple and with high accuracy. |
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