PASSIVE MILLIMETER-WAVE imaging is experiencing a surge in popularity. Given its potential to detect thermal radiation, it can reduce public-health and security concerns for both medical patients and the military. Imaging has gained such capabilities with the evolution of monolithic millimeter-wave integrated-circuit (IC) technologies. At the University of California at Irvine, for example, a W-band receiver chipset for passive, millimeter-wave imaging in 65-nm standard CMOS has been presented by Lei Zhou, Chun-Cheng Wang, Zhiming Chen, and Payam Heydari.
Essentially, their system is a direct-conversion receiver front end with an injection-locked tripler and an analog back end for a Dicke radiometer. To lower the phase-locked-loop (PLL) frequency, the designers propose a local-oscillator (LO) scheme that uses a frequency tripler. The receiver's noise performance is further improved through optimum biasing of the detector's transistors.
The chipset exhibits measured peak gain of 35 dB with a 3-dB bandwidth of 12 GHz. It shows a noise figure of 8.9 dB while consuming 94 mW. Peak responsivity was 6 kV/W with noise-equivalent power (NEP) of 8.54 pW/Hz0.5. The calculated Dicke noise-equivalent temperature difference (NETD) is 1 K with integration time of 30 ms. See "A W-band CMOS Receiver Chipset for Millimeter-Wave Radiometer Systems," IEEE Journal Of Solid-State Circuits, Feb. 2011, p. 378.