Design of Small-sized and Low-cost Front End to Medical Microwave Radiometer.

We have investigated the possibility of building a Dicke radiometer that is inexpensive, small-sized, stable, high sensitivity and consists of readily available microwave components. The selected frequency band is at 3-4 GHz and can be used for breast cancer detection, with sufficient spatial resolution. We have found microwave components that are small (< 5mm × 5 mm) and provide sufficient sensitivity. We have built two different Dicke radiometers: One is of conventional design with Dicke switch at front end to select antenna or noise rererence and the other with a low noise amplifier before the Dicke Switch. We have tested this concept with simulations and built prototypes. The two designs provide a gain of approximately 50 dB, and bandwidth of about 500 MHz. One of the designs has a stability μ > 1 and the other design provide instability μ < 1 for a part of the pass band. The prototypes are tested for sensitivity after calibration in two different known temperature waterbaths. The results show that the design with the low noise amplifier before the Dicke switch has 36% higher sensitivity than the other design with Dicke switch in front.