Every physical body produces natural emissions, which may be detected and used for imaging applications. For passive millimeter-wave imaging applications, it is ideal to use broadband millimeterwave receivers that function within atmospheric windows. A heterodyne receiver chipset using the 140-GHz atmospheric window has been presented by Stefan Koch and Shin Saito from Sony Deutschland GmbH together with Marc Guthoerl from Thermo Fisher Scientific, Ingmar Kallfass from Karlsruhe Institute of Technology, and Arnulf Leuther from the Fraunhofer Institute of Applied Solid-State Physics.

At the heart of this chipset are two millimeterwave monolithic integrated circuits (ICs), which make it possible to have different voltage-controlled- oscillator (VCO) millimeter-wave monolithic ICs with the receiver. The receiver includes a low-noise amplifier (LNA), downconversion mixer, frequency multiplier, and local-oscillator (LO) buffer amplifier with an LO distribution network. The other IC is the VCO, which covers a band around 35 GHz to generate the LO signal for the receiver chip. From 120 to 145 GHz, the receiver demonstrates a flat conversion gain from -1 to +2 dB while consuming 120 mW. The VCO is tunable from 31 to 37 GHz with associated output power ranging from -2 to +1 dBm.

To guarantee stable isolation and avoid loadpulling effects, the VCO is decoupled with a VCO buffer amplifier. This single-stage, variable-gain amplifier fine tunes the oscillator's signal power level. In addition, the VCO signal at the output of the buffer amplifier is divided into two equal paths using a folded 35-GHz Wilkinson power divider. See "A 120-145 GHz Heterodyne Receiver Chipset Utilizing the 140 GHz Atmospheric Window for Passive Millimeter-Wave Imaging Applications," IEEE Journal Of Solid-State Circuits, October 2010, p. 1961.