A 10-GHz quasi-optical grid amplifier using integrated HBT differential pairs

The authors report the fabrication and testing of a 10-GHz grid amplifier utilizing 16 GaAs chips each containing an HBT (heterojunction bipolar transistor) differential pair plus integral bias/feedback resistors. The AlGaAs-GaAs HBT material was grown by molecular-beam epitaxy. The amplifier exhibits a peak gain of 12 dB at 9.9 GHz, with a 3 dB bandwidth which extends from 9.55 and 10.3 GHz. The peak gain and bandwidth are sensitive to polarizer position, indicating that the polarizers provide good matching to free space. Output power is linear with input power, indicating that the grid operates as an amplifier rather than as an injection-locked oscillator. Gain saturation can be observed at low DC bias and high-input RF levels.