Microwave High-Power GaAs FET Amplifiers

Abstract

AB5TACSolid-state power amplifiers(SSPAs) have-been significantly improving in the past years and gradually replacing travellin* wave tube amplifiers (TWTAs) in the area of microwave and mm-wave communication systems such as terrestrial communications equipment and satellite transponders. This paper surveys the recent research and developmental activities on solid state power amplifiers and related key devices in Japan, focussing on device structures,circuit approaches and processing technologies. INTRODUC'IONThe use of SSPA for transmitters in the microwave telecommunication and radar systems provides advantages over conventional TWTAs in light weight, low voltage operation, small phase shift, low intermodulation distortion(IMD), and high reliability.Today, many SSPAs are already being developed and widely used as replacements for the TWT amplifiers in low to medium power applications. Promotion of this replacement depends strongly on efficiency and reliability of the power GaAs FETs used in the SSPA. Therefore, it is indispensable to improve the power capability and efficiency of the power GaAs FETs as well as reliability. In this paper, the status of GaAs power FET amplifier developmental and technological trends in Japan will be covered, including recent topics of internally matched power FETs, MMIC power amplifiers and advanced microwave power transistors. II. INTERNALLY MATCHED POWER FETsIn the frequency range from C-to Ku-band, internal matching topology has been widely applied for power FETs, and higher power capability and higher power-added efficiency have been realized by optimizing the MESFET devices and circuits.At C-band, several types of 10-to-30 W internally matched power FETs have been developed combined with multi-FET chips for the applications of radar and digital communication systems etc.. Mitsubishi reported a 20 W(PldB) MBE-grown FET with 39 % power added efficiency around 4 GHz[1], [2]. Figure 1 shows a schematic cross section of the power FET structure. A stepped recess sate structure combined with the refractory metal Schottky contact was introduced in order to get the high breakdown voltage and the low gate reverse current, with low source resistance. Figure 2 shows Idss dependence o P for the 12.6 mm-wide GaAs FET comparing those of the conventional structure at 615 GHz. Drastic improvement of 1.3 dB(1.4W) in PldB was observed at the same I ss High power-added efficiency of 57 % and a power output of 17 W were also acTleved with a linear power gain of 13.8 dB. By adopting similar configuration, a 6 GHz-band power FET was developed. It exhibited more than 11 W of power output, 9.8 dB of gain and 44 % of a power-added efficiency within 5.9-6.4 GHz on the two chip devices[3].A C-band 25 W linear power FET was developed by Fujitsu [4]. A four-way combiner/divider based on 1/8 wavelength transmission line configuration was applied to the design of the FETs. The total gate width was 72 mm. The resultant FET delivered an output power of 1 dB gain compression point of 25 W with 12 dB linear ga...