Near-Field Power Density Mapping of Close-to-Body Low-Power mmWave Devices

This letter introduces a method for power density (PD) measurement of low-power millimeter-wave devices, accounting for antenna/body coupling. This technique employs a thin solid absorbing structure with equivalent scattering properties used to convert the absorbed power into a heat pattern measured by an infrared (IR) camera. The measured IR pattern is then used to reconstruct the PD distribution. The lock-in technique is used to enhance the signal-to-noise ratio. It consists in filtering the ambient IR noise as well as removing the parasitic heat conduction effect. The reduction of noise enables achieving a measurement sensitivity of the order of 1 mW/cm
$^{2}$
, substantially overcoming the sensitivity without lock-in (
$> $
10 dB). The proposed approach is experimentally validated for a conical horn antenna at 60 GHz. For the first time, this study demonstrates the sensitivity of IR-based measurements sufficient enough to assess the compliance of medium- and low-power wireless devices above 6 GHz.