Multi-Frequency Microwave Radiometer for Medical Thermography

Microwave radiometer systems are an entirely non-invasive, non-toxic, avoiding ionizing radiation, and relatively inexpensive detecting modality. The microwave radiometry technique is based on the measurement of natural electromagnetic noise signals emitted by lossy materials. In medicine, microwave radiometry technique offers a non-invasive thermometry method having the potential advantages of monitoring and producing a full map of the temperature deeply inside the human tissues. The method of diagnosing procedures is safer and more comfortable during the examination. The former microwave radiometer systems require stabilization techniques to eliminate the systematic errors like gain variations, system temperature variations, and reflection variations in the interface between the antenna and the human body. The previous stabilization techniques require passive components (circulator, coupler, or switch) between the antenna and other system components to inject a reference noise signal into the human body. Consequently, the microwave radiometer system has lost the passive property, and this could be risky for the health of the human body. As well as adding passive components between the antenna and the other system components reduces the temperature sensitivity because of an increase in the total noise figure. Unlike to the available microwave radiometer systems in the medical applications, an innovative system design is proposed to build the microwave radiometer system with a passive stabilization technique that does not need to inject noise signals into the human body. To improve the system’s spatial resolution, the proposed system has two radiometric channels which have different operating frequency ranges. The first subsystem channel operates in the frequency range of 1.1 GHz to 1.65 GHz. The second subsystem channel operates in the frequency range of 3.25 GHz to 4.25 GHz. In the proposed system, a novel multi-frequency Archimedean spiral antenna-coupler is proposed to combine two functions in one structure which reduce the complexity of the radiometer system. This design also reduced the total system noise figure, because the antenna is connected directly to the first stage of a low noise amplifier.