On-Chip Radiometer with Miniaturized Near-Field Antenna for Internal Body Thermometry

An on-chip correlation-Dicke hybrid radiometer for internal body thermometry at a frequency of 1.4 GHz is presented. The 3.8mm by 2.3mm GaAs MMIC includes two 90° hybrid couplers, a single-stage LNA in each path, and a switch. The hybrid coupler employs lumped elements instead of transmission lines to reduce chip size. Two single-stage LNAs are between the hybrid couplers to enhance robustness against input impedance mismatch. The circuit shows a gain of 13.4 dB, isolation of 16 dB, and a noise figure of 1.31 dB. Following the switch, an off-the-shelf band-pass filter, an on-chip LNA, and a detector are connected to provide a dc output proportional to the temperature at the antenna port. A 3.5 cm diameter circular near-field antenna is designed, capturing thermal noise from the liquid inside a human mouth. The dc voltage at the output is used to compute the temperature detected by the near-field antenna. In-vivo measurements are conducted using orange juice inside the human cheek, showcasing the ability to non-invasively track internal temperature.