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In this letter, we present a dual-feed near-field antenna (NFA) with dierent sensing depths for noninvasive internal body temperature measurements using microwave radiometry. The two feeds correspond to dfferent 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-um 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 deg C) and muscle (34 deg C) phantoms with average errors around 1:58 deg C and 0:7 deg C, respectively. The results show usefulness of spatial pattern diversity for estimating layered tissue temperatures. 

This paper addresses microwave radiometry for passive non-invasive subcutaneous temperature measurements at a few centimeter depth in tissues. A correlation radiometer is designed in the quiet 1.4-GHz band and tested on aqueous phantoms. The radiometer is designed from off-the-shelf components and first tested with a matched load, and then with a near-field planar compact probe antenna, both with two temperature-controlled water phantoms of different volumes. The measurement resolution, sensitivity and long-term stability is quantified in terms of integration time for a simple three-point calibration. The lowest measured absolute error compared to a ground-truth thermocouple measurement is 0:25K over one hour of data collection with a single calibration. Measurements show that an integration time of > 1 s results in an absolute error limited by the radiometer gain fluctuations.