Design Of Embedded Intelligent Microwave Precision Attenuator

Microwave attenuators are often used in radio frequency circuits such as microwave signal sources and microwave testing.Its function is to attenuate the microwave input level.At the same time it will not affect other characteristics of the signal.To achieve the target that control the output power of attenuator,design a system based on programmed control attenuator.And people realized the importance of precision for Measuring element day by day.So design of attenuator with automatic level control function is also a trend.The most important is how to ensure the precision about output power,so automatic level control is used for the element to adjust power in real time.Then we should know the requirement of this system.Automatic level control could adjust the output of attenuator.And PID control is used for logic to raise precision about the system.After the contrast,choose a design scheme which has wide work frequence and lager attenuation dynamic range.The feasibility of this scheme is also convinced by software simulation.PID parameters is also important for the result.So do a optimization for them by Particle Swarm Optimization.The next step is to complete the circuit of design.For each unit,compared different elements the choose the most suitable to meet the requirement.So we should know the function of every unit and the premise for work together and normally.According to the overall design block diagram and design index of the system,the specific circuit design of attenuator unit,power detector unit,power distributor unit,electric source unit and analog-to-digital conversion unit is completed.For the control part,we choose STM32F103 microprocessor to control the attenuator because it's very convenient and easy to programming.Software include storage program,AD acquisition program and PID control program.It's completed based on analyze of control process.Finally,the attenuator system is tested.We make a test for each unit before the test of the circuit.Then make a decision that if this unit is satisfactory.Judge the advantages and disadvantages about the circuit and discuss how can do better in the future.According to the test results,the design of attenuator system has a wide working bandwidth within 300 MHz ~ 3GHz.Under normal circumstances,the output power of the system can step by 0.5dB,and the power flatness is less than 0.5dB.The system can achieve-30 dBm ~ 0dbm dynamic range signal output,which meets the expected design goal.