Millimeter-wave AlGaAs-GaAs HBT power operation
The AlGaAs-GaAs HBT has demonstrated good power performance up to 18 GHz. Although f/sub max/ is typically above 100 GHz, the power performance limitation and large signal operation at millimeter wave frequencies have not been studied. Power results from two HBT structures at 35 GHz are analyzed based on numerical simulation. The HBT demonstrated 8.5-dB linear power gain, 30% PAE with 7.8-dB gain and 7.5-V V/sub ce/ bias. The power density reaches 1.25 mW/ mu m/sup 2/. A shorter collector (0.4 mu m) is shown to be better suited for 35-GHz operation as a result of shorter collector transit time and smaller residual collector voltage. Improvement can be achieved by reducing the base and collector resistance, and the collector capacitance.<<ETX>>
High-power, high-efficiency cell design for 26 GHz HBT power amplifier
We describe a 6-chip combination HBT power amplifier and a single-cell chip with excellent power-added efficiency (PAE) and power density at 24-26 GHz. The power amplifier, based on our conventional chip design, exhibited 2.2 W output power with 19% PAE and 5 dB linear gain. To further improve the efficiency and power-density, various types of HBT cells were characterized. The optimum cell (184 /spl mu/m/sup 2/) exhibited 740 mW output power equivalent to power density of 4.0 mW//spl mu/m2, while a record high PAE of 42% was obtained. These results compare well with the best data reported at lower frequency bands (<18 GHz), thereby showing great potential for high-power, high-efficiency HBTs in near MM-wave bands.
DESIGN CONSIDERATION TO PPM KLYSTRONS FOR INDUSTRIAL LINAC
Toshiba has been developing the C-band and X-band Periodic Permanent Magnet (PPM) focused klystron in collaboration with KEK and manufactured prototypes for the JLC project. [1] The PPM klystron has an advantage to enhance the total efficiency as a result of eliminating the electric power for the focusing magnet. From experience on the development the PPM focused klystrons for the JLC project, we plan to apply the PPM focused klystron to the medical and industrial linac. The periodic magnet focusing scheme has some technical difficulties such as stop band voltage. To design the PPM klystron for the medical and industrial linac, it is necessary to give heed to electron beam instability; so that the tube parameters of the PPM focused klystrons have some constraints. The size of the accelerator system is substantially reduced if a PPM focused klystron is used. The majority of medical and industrial linacs use frequencies of S-band range. We discuss the availability of the S-band PPM focused klystron in this paper.