Self-Balanced Near-Field Microwave Radiometer for Passive Tissue Thermometry

Medical microwave radiometry is a near-field passive thermometry technique that requires highly sensitive and stable receiver to gather and process the ultra-low power thermal radiation from biological tissues (−174 dBm/Hz). The noise measurements are susceptible to radio frequency interference (RFI) and influenced by variations in power reflection between the near-field antenna and radiometer input (
$\rho $
), instrument electronic noise (
$\boldsymbol {T}_{ \boldsymbol {rec}}$
), amplifier noise (
$\boldsymbol {T}_{ \boldsymbol {A}}$
), and system gain (
$\boldsymbol {G}$
). Design of a self-balanced dual frequency band Dicke radiometer is reported in this work with real time calibration to eliminate the influence of
$\rho $
,
${ \boldsymbol {T}}_{ \boldsymbol {rec}}, \boldsymbol {T}_{ \boldsymbol {A}}$
and gain (
$\boldsymbol {G}$
) on the unknown source temperature (
$\boldsymbol {T}_{ \boldsymbol {S}}$
). The radiometer is designed for operation over 1.2-1.5 GHz (low frequency/LF) and 2.8-3.1 GHz (high frequency/HF) for deep and superficial tissue temperature measurements, respectively. The radiometer measurements are characterized using matched load and ultra-wideband spiral antenna using tissue mimicking phantoms. The linearity of source temperature measurements for the matched load is close to 1 with root mean square error of 0.22 and 0.37 °C in LF and HF bands, respectively. Radiometer noise measurements using UWB antenna in tissue mimicking phantom confirm stable measurements and immunity to ambient RFI.