Design Of Coupled Microwave Power Sensor Based On GaAs MMIC Process

In recent years,microwave technology has developed into a more systematic discipline and has been widely used in many fields,such as communications,radar,electronic information countermeasures,and electronic navigation.Microwave power is one of the important parameters that characterize the characteristics of microwave signals.The detection of microwave power is indispensable in the generation,transmission and reception of microwave signals.Microwave power sensors are widely used in the detection of microwave power in microwave equipment,circuit protection and gain control.At present,microwave power sensors are mainly divided into thermoelectric MEMS microwave power sensors and capacitive MEMS microwave power sensors.The thermoelectric MEMS microwave power sensor is based on the principle of thermoelectric conversion,which has the advantages of high sensitivity,good linearity and good microwave performance.Capacitive MEMS microwave power sensors can measure microwave signals online,and their sensitivity depends on the change in output capacitance.However,when the MEMS beam is sensitive to the input power,the output capacitance changes greatly,and the large capacitance change will increase the reflection coefficient,resulting in the deterioration of microwave performance.The linearity of this system will be poor,and it will affect the detection accuracy of the sensor.It can be found that one of the main problems for capacitive MEMS microwave power sensors is the contradiction among sensitivity,dynamic range and microwave performance.The reason is that the two steps of microwave signal power extraction and measurement are performed simultaneously.Therefore,a coupled MEMS microwave power sensor is proposed in this paper.This sensor divides the extraction and measurement of microwave signal power into two steps.In the first step,a MEMS cantilever beam is used as a coupler to online-couple a certain percentage of microwave power.In the second step,a thermoelectric power detection system is used to detect the coupled microwave power.The coupled MEMS microwave power sensor fundamentally solves the contradiction among the sensitivity performance,dynamic range and microwave performance of the capacitive microwave power detection system.The main content of this paper includes the following parts:(1)In the first part,the application fields of MEMS microwave power sensors and the development status of various types of MEMS microwave power sensors are introduced,and the advantages and disadvantages of different types of microwave power sensors are sumed up.The contradiction among its sensitivity,dynamic range and microwave performance of online capacitive MEMS microwave power sensors is revealed.In order to solve this contradiction,a coupled MEMS microwave power sensor is proposed in this paper.(2)In the second part,the working principle and theory of the coupled MEMS microwave power sensor is introduced.Firstly,the microwave characteristics of the coplanar waveguide structure in the sensor are analyzed,and then the scattering parameter model of the coupled MEMS microwave power sensor is established,and the relationship of the microwave power extraction ratio with the coupling capacitance is derived.Then,the influence of the cantilever beam structure on the microwave performance of the microwave power sensor is analyzed.Finally,the microwave power detection model of the sensor is established,and the relationship of relevant parameters with sensor sensitivity is analyzed and discussed.(3)In the third part,three coupling degree MEMS microwave power sensors are designed.The design method of the coupling MEMS microwave power sensor with a specific coupling degree is studied.The coupling MEMS microwave sensor is analyzed by finite element simulation software.The microwave performance of the sensor is further optimized to improve its microwave performance.The structure of the power detection part of the coupled MEMS microwave power sensor is improved.The optimized structure can reduce the area of the microwave power sensor and save the manufacturing cost.(4)In the fourth part,the coupled MEMS microwave power sensors with coupling rates of 1%,10%,and 20% are fabricated.Due to some errors in the manufacturing process,the sensor with a coupling degree of 1% failed.According to the final test results,the sensitivities of the microwave power sensor with a coupling degree of 10% are 1.2m V/W@9GHz,1.4m V/W@10GHz and 0.8m V/W@11GHz,respectively.The sensitivities of the microwave power sensor with a coupling degree of 20% are 2.4m V/W@9GHz,2.4m V/W@10GHz and 1.3m V/W@11GHz,respectively.Finaly,the content of the research of this paper is summarized,and some innovations and some improvement in the future are proposed.