Passive Subcutaneous Microwave Thermometry With Spatial Pattern Diversity

In this letter, we present a dual-feed near-field antenna (NFA) with different sensing depths for noninvasive internal body temperature measurements using microwave radiometry. The two feeds correspond to different spatial power densities in the tissues, providing more information for temperature estimation. An on-chip 1.4-GHz Dicke radiometer with a switch and low-noise, high-gain amplifier is designed using enhancement-mode 0.18- $\mu $ m InGaAs technology. The radiometer shows 45 dB of gain and 1.26-dB noise figure (NF) at 1.4 GHz. The Dicke radiometer includes an SP3T switch connected to a noise source and the two feeds of the NFA. Measurements are performed on a skin-muscle phantom to monitor temperature. The temperature information obtained from the two antenna feeds is used to estimate the temperature of both the skin ( $20~^{\circ } $ C) and muscle ( $34~^{\circ } $ C) phantoms with average errors around $1.58~^{\circ } $ C and $0.7~^{\circ } $ C, respectively. The results show usefulness of spatial pattern diversity for estimating layered tissue temperatures.