A GaAs MMIC Correlation-Dicke Radiometer With Compact Antenna for Internal Body Thermometry

In this paper, we present a 1.4 GHz on-chip correlation-Dicke hybrid radiometer designed for internal body thermometry. The GaAs Monolithic Microwave Integrated Circuit (MMIC) measures 3.8 mm by 2.3 mm and includes two 90° hybrid couplers, a single-stage Low-Noise Amplifier (LNA) in each path, and a switch. The radiometer input is connected to a planar compact near-field circular slot-patch antenna placed on the skin and designed to receive noise power from subcutaneous tissues. To enhance robustness against input impedance mismatch, two single-stage LNAs are positioned between the two hybrid couplers. The circuit demonstrates 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 3-stage LNA, and a detector are connected to provide a dc output proportional to the received thermal noise from the near-field antenna. Performance is evaluated through both phantom and in-vivo measurements. The 2-layer phantom measurement shows an average error of 0.35 °C, while in-vivo measurements show an average 0.72 °C error, demonstrating the device's ability to track internal temperature accurately. Additionally, repeatability tests are conducted on multiple human cheeks multiple times and on multiple days.