Ultra-wideband microwave imaging for breast tumor screening using step recovery diode-based pulse generator

The feasibility of a multistatic imaging system built on step recovery diode (SRD)-based pulse generator for microwave breast cancer detection is investigated to develop a low-cost and portable non-invasive screening device in the future. The system consists of a pulse generator, an antenna array, and a sampling oscilloscope, in which the pulse generator generates monocycle pulse with a frequency bandwidth from 510 MHz to 6.1 GHz. Experiments are performed on a breast phantom made up of a breast model using 3D printing technology and soybean oil as internal filler, without the usage of any coupling medium. Four identical omnidirectional antennas sequentially transmit ultra-wideband (UWB) signal and collect signals scattered inside the breast phantom, and then, the interior image of the phantom is reconstructed by background subtraction method and delay and sum (DAS) imaging algorithm. The system can successfully detect and distinguish a variety of test scenarios including cancerous breast phantom containing target with different size and different depth made by iron ball and bacon and healthy breast phantom. The smallest detectable target is 3 mm bacon, with signal to clutter ratio (SCR) and signal to mean ratio (SMR) metrics of 1.63 and 7.79 dB, respectively, and positioning error and relative error of 2.2 mm and 1.7%, respectively. It proves that the proposed time-domain imaging system is promising for scaling up the detection range of early breast cancer.