| Terahertz waves are located in the transitional region of electronics and photonics,and have excellent properties such as good penetration,low photon energy,and wide bandwidth.Applying terahertz technology to the communication field can improve the transmission rate and security of the communication system,and make it easier to track and align.In terahertz communication system,the terahertz modulator is an important device to realize the modulation function at the transmitter.Therefore,as one of the key devices in the system,more and more researches have been put into the modulator.Aiming at the challenges of narrow working bandwidth,difficulty in integration,and low speed faced by current modulators,this paper designs four types of modulators,and verifies the performance of the designed modulators through theoretical analysis,simulation and experiment.The following is the content of this article1.By combining HEMT with artificial microstructures,an array modulator with gradual gaps is designed.The two-dimensional electron gas concentration in the HEMT is controlled by voltage to realize the resonance mode in different states.The simulation results show that the modulator has a 100 GHz bandwidth.2.Aiming at the problems of large parasitic parameters,low modulation rate,and difficulty in integration of array modulators,a modulator combining a modulation chip and a rectangular waveguide is proposed.The first is a microstrip modulator.The diode is embedded in the resonant branch.And the state of the diode is controlled by the voltage,which can realize the change of the equivalent length of the resonant branch,so as to achieve the regulation of the terahertz wave amplitude.Simulation results show that the modulator can achieve the insertion loss of 5 dB and modulation depth of 25 dB.The second is a probe-type modulator.The probe structure generates resonance under the influence of the terahertz wave,and the resonance frequency of the probe structure can be adjusted through the combination of the diode and the probe structure.The insertion loss and modulation depth of this modulator are 5.5 dB and 15 dB.The third is a wide Ishaped modulator.Among them,the quartz-based wide I-shaped modulator is designed with two structures,single diode and double diode.This type of modulator can control the terahertz wave by controlling the resonant frequency of the center structure,and has a larger bandwidth.Based on the same principle,a wide I-shaped modulator with GaAs substrate is also designed.This device can change the size of the diode.In the simulation,the device also has a wide bandwidth,the insertion loss is about 4dB,and the modulation depth is higher than 10 dB.3.The probe-type modulator and wide I-shaped modulator are processed and assembled,and the performance of these two types of modulators is verified through experimental tests.First,the performance of the modulator,such as insertion loss,modulation depth and bandwidth,is observed through static test.Then set up two test systems,which are received by the detector and received by the mixer,to test the modulator with sinusoidal signal.In the experiment,the modulator has a good waveform at a sinusoidal signal frequency of 100 MHz-2.5 GHz,and has a good flatness in the range of 1-20 GHz.Finally,AWG is used to provide a modulation signal with a certain bandwidth,and a wireless communication system based on envelope detection is built.The experimental results show that the communication rate of this system is higher than13 Gbps. |
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