Technique Research On Multiple Frequency Induction Material Recognition

With the rapid development of semiconductor ,solid-state devices have been used in radar ,communication ,remote sensing ,space navigation and electronic warfare .Compared with vacuum tube amplifier ,solid-state power amplifier have the advantages of high reliability ,low operating voltage ,graceful failure ,etc. Transmitters are key parts in microwave and millimeter-wave systems .Recently ,duce to the improvements of semiconductor power device technology's and dropping of cost ,more and more solid-state transmitters have been adopted by various microwave systems .There are some power transistor which have been widely used :Bipolar Junction transistor(BJT),GaAs Metal-oxide Semiconductor and Lateral Diffuse Metal-oxide Semiconductor field effect transistor(LDMOS FET).Thanks to the advantages ,such as ,wide frequency ,easy power supply ,good stability so the LDMOS FET has used widely .For the these reason ,we use the LDMOS FET in the last two stages .However ,as a single device usually gives out little RF power ,effective approaches of RF power combing are needed to obtain greater output power for these application systems .In this thesis ,microwave solid-state power(SSPA) is studied and a SSPA with 200W impulse peak power output is developed with push-pull power amplifier ,with considering the current technology and application requirements.The evolved history of SSPA is introduced first ,then some theories and principles used in analysis and design of microwave PAs are presented ,next some common power-combining technologies are introduced ,especially push-pull power-combining approach .Then ,it comes to the key point of the paper ,the SSPA is divided into the microwave power amplifier and the pulse modulator .The drain of the GaAs FET power amplifier chip is used to realized pulsed power output .The SSPA consists of three stages :the first stage amplifier, the drive stage amplifier and the last push-pull amplifier. We researched and analyzed the impedance matching technique of single stage power amplifier ,design of bias circuit ,load-pull technique .It is discovered by applying ADS simulation software of Agilent and Freescale's LDMOS PA software pack .After that ,a layout circuit will be implemented and tested to verify the veracity of design .At last, we analyse deficiency of the circuit and draw a summary.The amplifier with more than 200W pulsed peak output power at 900MHz is simulated and realized. The simulation and tested data of the amplifier show than the pulsed peak output power is more than 200W at 900MHz,the power gain is more than 50dB,and the pulse duration 200us,the duty circle is 1%. Test result shows that the system has achieved the objectives and requirements.