AlGaN/GaN-based variable gain amplifiers for W-band operation

In this paper three versions of a variable gain amplifier (VGA) monolithic millimetre-wave integrated circuit (MMIC) are presented. They make use of 100 nm gate-length AlGaN/GaN-based high electron mobility transistors (HEMTs) grown on SiC. The MMICs operate in the 75 to 110 GHz band and have a centre-frequency of 94 GHz. Different phase compensation techniques, which are proposed in literature are applied and their suitability for millimetre-wave (mmW) frequency application is evaluated. We propose an additional phase compensation means leading to our best VGA version providing a gain tuning range from -17.2 to 7 dB with a phase variation of only 12.6 °.