| Through nearly two decades of development,terahertz dynamic devices have made great progress,especially the quasi-optical dynamic modulation field has sprung out various electromagnetic functional devices based on different materials and meta-structures.However,the lack of integrability in quasi-optical devices is still a difficult problem,while the on-chip devices obtain the advantages of low cost and easy integration.Terahertz dynamic phase shifter has great potential in radar systems and communication systems.In this thesis,the multi-bit loaded-double-branch phase shifter technique,the perturbation unit phase shifter technique and the reflective phase shifter technique are investigated by theoretical analysis,simulation and experiment.We have designed three types of phase shifter here.The first is a 4-bit 360° loaded-double-branch terahertz phase shifter from 90 GHz to 100 GHz.Secondly,high-precision terahertz phase shifters with different accuracy from 2° to 5° can be achieved in the range of 260 to 270 GHz.The last,a reflective terahertz phase shifter that can achieve continuous180° phase shift at 108 GHz.The research work and the results obtained in this thesis are as follows:1.We move the existing low-frequency loaded-double-branch phase shift theory to the high-frequency band firstly.After theoretical analysis and simulation,four different phase-shifting units with 22.5°,45°,90° and 180° in the range of 90 GHz to 100 GHz are obtained.Then,by combining the 3D simulation with the branch size miniaturization technique,a 4-bit loaded-double-branch terahertz phase shifter satisfying the requirements is obtained,in which the switch module is Al Ga N/Ga N heterojunction 2DEG diode.The experiment shows that linear phase shifts of 22.5°,45°,and 90° can be obtained in the range of 90 GHz to 100 GHz,and the insertion loss is less than 6.5 d B.The principle of the loaded-double-branch multi-bit terahertz phase shifter is verified in this thesis.2.We have modeled the Al Ga N/Ga N heterojunction 2DEG diode in detail.Utilizing this model,we have designed a perturbation unit with a large phase perturbation and a small effect on amplitude.The nonlinear phase shifting superposition of the perturbation units and the phase shifts of asymmetric coding sequences are analyzed in the thesis.Based on the above analysis,a high-precision terahertz phase shifter consisting of six perturbation units is finally designed.The simulation results show that 50° phase shifts can be achieved at 265 GHz with insertion loss in the range of 2 d B to 4 d B.The maximum phase shifts are 35° and 60° at 260 GHz and 270 GHz,respectively.In the experiments,we can obtain the phase shifts with the specific code sequences.At 265 GHz,the phase shift accuracy is 5° and the total phase shift is up to50° with an insertion loss in the range of 5.6 d B to 6.6 d B.At 260 GHz,the phase shift accuracy is 2° and the total phase shift exceeds 30°,with an insertion loss in the range of 5.3 d B to 6.7 d B.At 270 GHz,a phase shift accuracy of 4° and a total phase shift of55° is achieved,at which the insertion loss is between 7.5 d B and 8.8 d B.The proposed high-precision terahertz phase shifter based on perturbation unit is a new type of terahertz phase shifter,which can achieve low insertion loss and small amplitude fluctuation at the same time.3.For the demand of continuous and large phase shifting,we have investigated the reflective terahertz phase shifter.Firstly,a 3 d B directional coupler at 102-117 GHz is designed by using impedance transformation.Then,the reflected load is designed using a Ga As single anode-air-bridge varactor,in which the impedance of the whole reflected load is adjusted by connecting a metal branch.The reflective terahertz phase shifter consists of the 3 d B directional coupler and the reflective load,which can achieve continuous phase modulation from 0 to 173° at 108 GHz with S21 greater than-6 d B and S11 less than-13 d B in the simulation.In the experiment,a total phase shift of about 180° and 170°is obtained at 106 GHz and 108 GHz,respectively.The S21 is in the range of-5 d B to-15 d B and S11 is between-11 d B and-23 d B at the same time.To address the increase of insertion loss caused by the characteristic resistance of Ga As single anode-air-bridge varactor,an improved Ga As double anode-air-bridge varactor is proposed,which can achieve higher phase-shifting performance.The above research results can promote the multi-bit terahertz phase shifter technology,improve the feasibility of the practical application of terahertz phase shifter.They possess important significance for the realization of the terahertz radar and communication applications. |
PDF Full Text Request