A unidirectional wideband printed Quasi-Yagi antenna for microwave breast imaging

Active microwave imaging (MWI) is a promising medical modality for breast cancer detection, and is implemented via ultra-wideband (UWB) microwave imaging and microwave tomography. Regardless of technique, the spearhead of any microwave imaging system is an array of antennas, which illuminate the target and collect the scattered energy. The antenna element is expected to be compact, wideband, efficient and high-gain, ideally focusing all radiated energy inside the target. This paper describes a printed quasi-Yagi antenna, which features a unidirectional driver-reflector pair and two closely-spaced directors. The directors increase the operational bandwidth significantly while maintaining a broadband front-to-back ratio (FBR) above 10 dB. The antenna operates in the 2.0-3.3 GHz range (55% fractional bandwidth), and exhibits a maximum gain of 5 ± 0.5 dBi and high efficiency. The architecture of the antenna is inherently simple and its impedance bandwidth is practically unaffected by the presence of the breast phantom.