Passive noninvasive deep tissue thermometry is needed for detecting, monitoring, and diagnosing several clinical ailments. Existing clinical thermometry techniques are not suited for routine use by non-skilled healthcare workers. Microwave radiometry (MR) is a near-field passive technique that employs an antenna and low noise receiver to gather ultra-low power thermal radiation (−174 dBm/Hz at 298 K) from biological tissues deep inside the body. However, the measurements are very sensitive to variations in system temperature, amplifier temperature, gain drift, and impedance mismatch between the antenna and receiver.

In this thesis, stable switch circulator Dicke radiometers operating over 1.2-1.5 GHz (low frequency/LF) and 2.8-3.1 GHz (high frequency/HF) were designed and fabricated to compensate the influence of system parameters on source brightness temperature measurements. The root mean square error (RMSE) of the temperature estimated by the LF and HF single reference Dicke radiometers was 0.21 and 0.19 ℃, respectively.

Passive near field microstrip antennas operating in LF and HF bands fabricated for radiometer measurements had return loss >10 dB over 1.2 to 1.4 GHz and 2.75 to 3 GHz, respectively in tissue mimicking phantoms. A high-gain (30 dB) monolithic microwave integrated circuit (MMIC) low-noise amplifier was integrated with near-field multi-layered microstrip patch antenna to enhance the received thermal noise. Noise measured using active antennas indicate improved measurement accuracy and resolution compared to passive antennas in LF and HF bands. The feasibility of using microwave radiometer for detecting the progression of diabetic foot ulcer was investigated in the HF band.

Radiometer measurements in HF band have limited penetration depth of about 20 mm. Measurements in LF band has deeper penetration but suffer from ambient EM interference. Thus, a 2x2 array of near-field active antenna (48 mm x 48 mm) was realized in HF band to enhance the sensing depth in the HF band. The active antenna array showed increased measurement resolution of 0.18 ℃, deeper depth of detection and increased field of view (FOV) (45 mm with FOV of 41663