Abstract
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 ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\rho $ </tex-math></inline-formula> ), instrument electronic noise ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\boldsymbol {T}_{ \boldsymbol {rec}}$ </tex-math></inline-formula> ), amplifier noise ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\boldsymbol {T}_{ \boldsymbol {A}}$ </tex-math></inline-formula> ), and system gain ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\boldsymbol {G}$ </tex-math></inline-formula> ). Design of a self-balanced dual frequency band Dicke radiometer is reported in this work with real time calibration to eliminate the influence of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\rho $ </tex-math></inline-formula> , <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${ \boldsymbol {T}}_{ \boldsymbol {rec}}, \boldsymbol {T}_{ \boldsymbol {A}}$ </tex-math></inline-formula> and gain ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\boldsymbol {G}$ </tex-math></inline-formula> ) on the unknown source temperature ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\boldsymbol {T}_{ \boldsymbol {S}}$ </tex-math></inline-formula> ). 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.
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