Passive deep tissue thermometry is needed for detection, monitoring, and diagnosis of inflammation in tissues. Existing clinical thermometry techniques have shallow measurement depths. Techniques based on magnetic resonance and ultrasound principles are not suited for regular clinical examination. Microwave radiometry (MR) is a near-field passive technique that employs an antenna and a low noise receiver to gather ultra-low power thermal radiation (−174 dBm/Hz at 298 K) from biological tissues deep inside the body. A microwave radiometer is very sensitive to system temperature and impedance mismatch between the antenna and receiver. In this thesis, stable switch circulator Dicke radiometers operating at 1.3 GHz (LF band) and 2.9 GHz (HF band) were designed and fabricated to compensate the influence of system parameters on source brightness temperature measurements. A high-gain (30 dB) 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 accuracy and resolution better than 0.24 ℃ compared to passive antennas in LF and HF bands. A 22 near-field active antenna array was realized in HF band (48 mm  48mm) to enhance the sensing depth to several cm. The measurement resolution of HF band active array probe improved to 0.18 ℃ with sensing depth of 45 mm. The ability to detect localized thermal anomalies were assessed in phantoms for detection of early stage breast cancer and progression of diabetic foot ulcer. The outcomes of this research suggest that MR could be an affordable alternative for clinical deep tissue thermometry