Research And Design Of LDMOS RF High Power Solid-state Source

Human life needs many kinds of energy,the emergence of electric energy provides more choices for human life.As a kind of electric energy,RF energy not only brings great convenience to families,but also opens up new applications in industry,medical treatment and even national defense.RF e nergy generator mainly includes magnetron and RF solid-state source.However,RF solid-state source is gradually replacing magnetron in the field of RF energy because of its advantages such as controllable power,high efficiency,small size and safety.Hig h power and high efficiency RF solid-state source is in urgent need in industrial medical applications,so it is of great significance to design a high-power RF solid-state source.Based on a large number of research,this paper has done the following work :1.Aiming at the high-power solid-state source in industrial application,a 3 00 W power amplifier is designed.The amplifier has the advantages of miniaturization and high efficiency.It is composed of crystal oscillator circuit,driving stage circuit and final stage circuit.The circuit realizes the maximum power transmission through the conjugate impedance matching;the bias circuit is designed as high impedance in the high frequency case,which prevents the RF signal from leaking into the DC power supply and improves the efficiency of the power amplifier;for the working stability of the power amplifier,the stable circuit is designed;in order to meet the high efficiency,the impedance point with high efficiency is selected while the output impedance is considered as the output power.The output power of the power amplifier is 300 W and the efficiency is 75%.2.In order to improve the efficiency,a harmonic suppression low-pass filter is designed,which has the advantages of high rectangular coefficient and w ide stopband,and can effectively suppress the high-order harmonics of the power amplifier.The second and third harmonics of the power amplifier are effectively reduced and the efficiency is increased to 77%.3.Based on the 300 W power amplifier,in order to achieve a higher output power of the solid-state source.A four channel power combiner composed of lumped devices is designed It can achieve k W level power integration.Compared with the power synthesizer composed of coaxial balun and waveguide,it has the advantages of being suitable for working in the short wave band and high efficiency and consistency.In order to improve the isolation degree of the input port of the combiner,by adopting the way of parallel isolation capacitor at both ends of the isolation resistance,finally the isolation degree is increased by 10 d B.The insertion loss of the test results is 6.2d B,the isolation degree is greater than 30 d B,and the return loss is greater than 17.8d B.The test results can meet the requirements of the four-way combiner of 1000 W.