A 48-79 GHz low noise amplifier (LNA) with broadband phase-invariant gain control is proposed for wide-band phased array applications. The proposed IC consists of a three-stage LNA, a phase-invariant attenuator, and an output buffer. A broadband phase-invariant attenuator is implemented with a phase-compensated transmission line periodically loaded with NFETs. The proposed IC was fabricated in a 45-nm CMOS SOI process and occupies an active area of 1.1 mm2. The measured gain is 22.2 dB with 31-GHz bandwidth (49% fractional bandwidth) from 48 to 79 GHz. The measured gain tuning range is higher than 8.9 dB from 63 to 80 GHz with a phase shift variation less than 6. The measured noise figure (NF) is less than 4.8 dB with an average NF of 3.8 dB from 50 to 62 GHz. The measured dc power consumption is 30 mW from a 1.2-V supply.