Microwave Power Devices and Amplifiers for Radars and Communication Systems

Abstract: SiC MESFETs and GaN HEMTs posses an enormous potential in power amplifiers at microwave frequencies due to their wide bandgap features of high electric field strength, high electron saturation velocity and high operating temperature. The high power density combined with the comparably high impedance attainable by these devices also offers new possibilities for wideband power microwave systems. Similarly Si-LDMOS being low cost and lonely silicon based RF power transistor has great contributions especially in the communication sector.The focus of this thesis work is both device study and their application in different classes of power amplifiers. In the first part of our research work, we studied the performance of transistors in device simulation using physical transistor structure in Technology Computer Aided Design (TCAD). A comparison between the physical simulations and measured device characteristics has been carried out.  We optimized GaN HEMT, Si-LDMOS and enhanced version of our previously fabricated and tested SiC MESFET transistor for enhanced RF and DC characteristics. For large signal AC performance we further extended the computational load pull (CLP) simulation technique to study the switching response of the power transistors. The beauty of our techniques is that, we need no lumped or distributive matching networks to study active device behavior in almost all major classes of power amplifiers. Using these techniques, we studied class A, AB, pulse input class-C and class-F switching response of SiC MESFET. We obtained maximum PAE of 78.3 % with power density of 2.5 W/mm for class C and 84 % for class F power amplifier at 500 MHz. The Si-LDMOS has a vital role and is a strong competitor to wideband gap semiconductor technology in communication sector. We also studied Si-LDMOS (transistor structure provided by Infineon Technologies at Kista, Stockholm) for improved DC and RF performance. The interface charges between the oxide and RESURF region are used not only to improve DC drain current and RF power, gain & efficiency but also enhance its operating frequency up to 4 GHz.In the second part of our research work, six single stage (using single transistor) power amplifiers have been designed, fabricated and characterized in three phases for applications in communications, Phased Array Radars and EW systems. In the first phase, two class AB power amplifiers are designed and fabricated. The first PA (26 W) is designed and fabricated at 200-500 MHz using SiC MESFET. Typical results for this PA at 60 V drain bias at 500 MHz are, 24.9 dB of power gain, 44.15 dBm output power (26 W) and 66 % PAE. The second PA is designed at 30-100 MHz using SiC MESFET. At 60 V drain bias Pmax is 46.7 dBm (~47 W) with a power gain of 21 dB.In the second phase, for performance comparison, three broadband class AB power amplifiers are designed and fabricated at 0.7-1.8 GHz using SiC MESFET and two different GaN HEMT technologies (GaN HEMT on SiC and GaN HEMT on Silicon substrate). The measured maximum output power for the SiC MESFET amplifier at a drain bias of Vd= 66 V at 700 MHz the Pmax was 42.2 dBm (~16.6 W) with a PAE of 34.4 %. The results for GaN HEMT on SiC amplifier are; maximum output power at Vd = 48 V is 40 dBm (~10 W), with a PAE of 34 % and a power gain above 10 dB. The maximum output power for GaN HEMT on Si amplifier is 42.5 dBm (~18 W) with a maximum PAE of 39 % and a gain of 19.5 dB.In the third phase, a high power single stage class E power amplifier is implemented with lumped elements at 0.89-1.02 GHz using Silicon GaN HEMT as an active device. The maximum drain efficiency (DE) and PAE of 67 and 65 % respectively is obtained with a maximum output power of 42.2 dBm (~ 17 W) and a maximum power gain of 15 dB.