The paper aims at designing a radiometric thermometer for noninvasively measuring the internal body temperature. The radiometric thermometer consists of an active near-field probe and a radiometer designed in the 1.575 GHz band. The active probe integrated with a LNA is a circular patch antenna with short-pin loading and superstrate to collect the black body radiation under the superficial tissue. The Dicke radiometer was constructed and the probe antenna attached to a phantom was designed and implemented to test. The phantom based on Agar material was developed to emulate the real tissue of skin and muscle for experiments. The radiometer has a system gain of 50 dB, NF of 1.738 dB, 3 dB bandwidth of 90 MHz. The active probe has a noise figure of 1.1 dB and a gain of 13 dB at 1.575 GHz. The transferring rate of the power detector can achieve about 75 mv/dB. The measured DC voltage by the microwave radiometer is 2.676 V as attaching the cold saline water of 25 °C, while the voltage is 2.747 V as attaching to the hot water of 80 °C in the chamber.
