Design Of An S-Band Broadband Power Amplifier Based On GaN HEMTs

With the development of modern communication technology,communication systems with wider bandwidth are more preferred.As an important component of transmitter,operation bandwidth and efficiency of power amplifier(PA)determine the performance of the communication systems.Due to the properties of the semiconducting material,GaN HEMTs have more potential than the devices made of the second generation semiconducting materials in increasing efficiency and extending operation bandwidth.An S-band power amplifier(PA)with high efficiency and wide bandwidth is designed in this work.This thesis describes the design process of the DC power supply circuit,RF circuit and the PA cavity in details.A two-stage cascade structure is applied to realize this design.To achieve the predefined specifications,commercial amplifier TGA2597-SM is used at the first stage and amplifier CGH40010 F is used as the last stage.Several methods of impedance matching are compared to achieve the best matching solution.Based on this matching network,an equilibrium network is achieved by optimizing the width of the microstrip lines.The DC supply circuit is designed through analyzing the DC-DC module,and an effective solution is proposed to achieve timing control.This paper takes fully consideration of the chip structure and applies a back-feeding structure to design the cavity.The resonant frequency of the cavity is calculated by full-wave simulation to eliminate the resonant frequency contained in the operation bandwidth of the amplifier.Finally,this thesis not only summarizes the problems encountered in the measurement of PA such as self-excitation and mismatching,but also analyzes the reason leading to self-excitation.The solutions to inhibit self-excitation are also proposed.Characters of each part of the microstrip line of the RF circuit are found through circuit simulations and the best position for impedance matching is also determined.The measured operation bandwidth of the proposed PA is 2-3.7 GHz and the 1 dB compression point is above 40.5 dBm.The PA exhibits an efficiency between 50% to 71%.