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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. 

In this paper, we present a compact calibrated radiometer for measuring internal body temperature. The radiometer architecture combines the benefits of a correlation and a Dicke radiometer. The sensitivity to load impedance variations is reduced through a balanced topology, while the pre-detection switch reduces sensitivity to gain fluctuations of all components in the receive chain that follows. The radiometer is designed to operate in the 1.4-1.427 GHz quiet band using off-the-shelf components on a 10cm×7.6cm printed circuit board. Two types of temperature estimation methods are compared and the errors analyzed using resistors at known controllable temperatures at both input ports. One of the ports is then connected to a near-field antenna probe matched to tissue layers of the cheek. When water of variable temperature is in the mouth, an independent thermocouple verifies the radiometric temperature of the water measured by the probe placed on the skin.