Research Of Terahertz Waveguide Direct Modulator Based On Mode Conversion

With the rapid development of 6G technology,terahertz wireless communication systems have become an integral part of 6G technology by virtue of their high transmission rate,high confidentiality and strong anti-interference capability.As a key component in the communication system,the performance of terahertz modulator directly affects the index of the wireless communication system.Traditional modulation devices face the problems of high insertion loss,low rate and difficulty in integration and systematisation,so how to achieve high rate,low insertion loss and easy integration and systematisation of the device has become a current research hotspot.In this thesis,several devices are designed to achieve low insertion loss,high switching ratio and high transmission rate by using the principle of resonant mode conversion,Schottky diodes,metallic artificial microstructures and standard waveguides.The main research elements of this thesis are:1.By using the principle of resonant mode conversion,a waveguide-loaded differential-fed type of terahertz high-speed modulator in the frequency bands 140 GHz and 108 GHz is proposed.The structures both adopt a four-port differential-feed type structure,and the applied voltage at the IF port is used to control the on and off states of the diode to realize the resonant characteristics of the device in different states,and finally to realize the modulation of terahertz waves.The simulation results show that the insertion loss of 108 GHz I-beam metal structure is 1.9d B and the maximum switching ratio is 19 d B;the lowest insertion loss of 140 GHz parallel double tube core H-type structure is 1.8d B and the maximum switching ratio is 20 d B.2.The waveguide-loaded differential-fed modulators of the two structures were processed in flow and tested experimentally.Firstly,static tests were carried out and the static test results showed a high agreement with the simulated design results.Then,a simple 140 GHz terahertz direct modulation system was built by connecting the 140 GHz parallel diode H-structure modulator to a frequency multiplier,detector and horn antenna.The system dynamic test results show that the parallel diode H-structure modulator can reach a single-tone test rate of 30 G with no significant distortion of the demodulation curve.The eye diagram test shows that when the data transmission rate at the transmitter is 30 Gbps,the demodulated receiver profile is clear with no obvious distortion,indicating that the data transmission rate of the communication system can reach 30 Gbps.3.in the standard waveguide,using Schottky diodes,probe microstructure,based on the principle of coupling resonance,research and design of 140 GHz coupled probe modulator.By feeding a voltage at the IF feed port,the state of the Schottky diode is changed to control coupling characteristics of the structure,thus realising the modulation of terahertz waves.The S-parameter curves of the symmetrically coupled probe structure show that the structure has an insertion loss of 2d B and a switching ratio of more than20 d B in the 140 GHz band.In the tandem structure modulator,the insertion loss is 3d B and the switching ratio is 15 d B at 140 GHz band.