A novel pulsed microwave confocal system for the detection of breast cancer has been proposed by Hagness, Taflove and Bridges (see Proc. of the IEEE Engineering in Medicine and Biology, Society Conference, p.2506-8, Chicago, IL, 1997). An elliptical reflector focuses a microwave signal at a potential tumor site and efficiently collects the backscattered energy by refocusing it at the point of origin of the illumination. This technology is based upon two fundamental dielectric properties of breast tissues at microwave frequencies: (1) the large contrast in ϵr and σ between malignant and normal tissues, which causes tumors to have significantly greater microwave scattering cross sections than normal tissues of comparable geometry; and (2) the low attenuation in normal breast tissue (less than 4 dB/cm up to 10 GHz), which permits constructive addition of wideband backscattered returns using confocal-imaging techniques. We replace the fixed-focus elliptical reflector reported by Hagness et al. with a variable-focus antenna array and extend the range of breast tissue structures modeled to include small tumors obscured by veins and mammary glands and ducts.