Research Of MEMS Self-powered Microwave Receiving Front End For Reflected And Excess Energy Collection

With the rapid development of wireless communication technology,the performance of the microwave receiving front-end as an integral part of RF transceiver components has a vital impact on the wireless communication system.In the process of receiving and processing microwave signals,the detection of the three basic parameters of power,frequency and phase of the signal is indispensable.Microwave detection systems require small size,low power consumption,and high integration detection devices in practical applications.In addition,the microwave receiving front end faces the problem of electromagnetic interference and high power input.These undesired microwave energy will cause a reduction in communication quality,and the microwave energy of the signal is not fully utilized.In order to meet the above requirements and solve the problems,this thesis proposes a program studying MEMS self-powered microwave receiving front end for reflected and excess energy collection based on the research of MEMS microwave devices.The main contents include:1.The need for integrated detection of power,frequency and phase of microwave signals in the microwave receiving front end:By designing a four-port coupler,a MEMS thermoelectric power sensor and a power combiner are integrated to build a microwave signal integrated detector.The four-port coupler divides the input signal into a main path and two coupling branches.The main path is used for power detection,while the branch signals are applied for frequency and phase detection,respectively.The power detection is realized by the MEMS thermoelectric power sensor.The results of simulation and testing show that the output thermal voltage has a good linear relationship with the input power.Through the design of the coupling capacitor,the coupling coefficient of the branch is approximately linearly changed with frequency at 8-12 GHz to execute frequency detection.The phase detection employs a power synthesizer to synthesize the reference signal generated by VCO controlled by the output voltage of frequency detection and the other branch signal,the output result is normalized and has a cosine relationship with the phase.Finally,ADS is introduced for system-level simulation to verify the effectiveness of the design.The outcomes prove that the detection of power and phase are related to the frequency,which illustrates the necessity of integrated detection.2.Above the problem of electromagnetic interference in the microwave receiving front-end:A MEMS filter network with reflected energy collection is proposed.By designing a bandpass filter and a band rejection filter with complementary frequency bands,the useful signal is propagated to the latter stage through the bandpass filter,and the interference signal is reflected by the bandpass filter and shunted by the band-stop filter,which can be collected by rechargeable battery.The simulation results of the designed filter structure are presented.For the bandpass filter,the insertion loss S₁₂>-1.3 dB in the range of 4-8 GHz,and the return loss is less than-10 dB in the range of 4.3-8 GHz.For the band rejection filter,the insertion loss is less than-10 dB in the range of 4.1-7.4 GHz,and greater than-3 dB below 3.4GHz and above 8.1 GHz.3.On the problems of high power input in the microwave receiving front-end:A MEMS limiter with excess energy collection is proposed.A MIM capacitor is devised to couple part of the microwave signal for on-line power detection.The detected output controls the pull-down displacement of the MEMS suspended beam,thereby changing the coupling capacitance of the branch to achieve amplitude limiting on the output signal.The excess energy coupled to the branch is collected by a given rechargeable battery via RF/DC conversion.The test result shows that the reflection coefficient S₁₁ is lower than-10 dB in the range of 4-8 GHz.The performance of online power detection is approximately linear,and the detection sensitivities are 0.56 mV/W,0.89 mV/W and 1.25 mV/W at 4 GHz,6 GHz and 8GHz,respectively.The error is controllable within 1%.Through the simulation of the suspended beam structure,the coupling capacitance has a value in the range of 27-1350 fF,and the limit on the output can reach below-3.75 dB.4.The thesis is finalized with the circuit simulation of the proposed MEMS self-powered microwave receiving front end for reflected and excess energy collection is carried out,and the functions of filtering,limiting and energy harvesting are simulated and verified.In the case where the input useful signal is 6GHz and the interference signals are 1 GHz and 9 GHz,respectively,the output interference signal is suppressed below 5%.The energy of interference signal that can be collected after being reflected and passed through the band rejection filter has an efficiency of up to 80%at 1 GHz,and up to 60%at 9 GHz,separately.The amplitude limit for the signal at 6 GHz increases with increasing power.At an input power of 300 mW,the output is limited to 118 mW,and the energy coupled to the branch can be collected up to80 mW.