Low-frequency noise and passive imaging with 670 GHz HEMT low-noise amplifiers

Abstract

We combine newly developed InP HEMT amplifiers operating at 670 GHz with a zero-bias diode (ZBD) in order to investigate limits on passive imaging performance possible with fully uncooled, direct-detection technology. Noise-equivalent temperature difference (NETD) values under 2 K are found for reference conditions (30 Hz modulation). However, noise spectra continue to fall approximately as 1/f out to 'knee' frequencies of several hundred hertz (Hz) and spectral densities of ∼0.12 K/Hz1/2 for the current, somewhat gain-starved, amplifiers. The amplifier alone contributes 0.043 K/Hz1/2. These results indicate that modest-sized, rapidly scanned arrays should provide real-time, passive imaging - desired for standoff security screening and other applications - with the same image quality as cryogenic bolometer arrays.