A microwave imaging system is considered a viable alternative to X-ray mammography and breast MRIs due to its several advantages such as cost and insignificant side-effects. Microwave imaging involves the propagation of very low levels of microwave energy through the breast tissue. The basis for tumor detection and location is the difference in the electrical properties of normal and malignant breast tissue. Normal breast tissue is largely transparent to microwave radiation, while the malignant lump contains more water and blood, resulting in microwave signal backscattering. This scattered signal can be picked up by a microwave antenna (ultra-wideband antenna elements preferably in the planar format) and can be analyzed using a computer An alternative ultra-wideband UWB planar antenna element, which finds use in radar applications, is a uniplanar or antipodal Vivaldi antenna.The present designs of these antennas do not make them straightforwardly applicable to microwave imaging applications. In the recently reported microwave imaging systems for breast cancer detection, resistively loaded monopoles [3, 5] and miniature pyramidal horn antennas [5, 6] have been used. The proposed antenna element is in the form of a planar tapered slot made of a high dielectric constant substrate material to achieve its compact size. It features a very low loss across the desired band, and its radiation efficiency exceeds 90% with a relatively high gain. The design of the UWB antenna as proposed in this report is accomplished using simple design formulas. This is an advantage with the previously reported UWB antenna designs [8 –11] relying on a trial and error method and simulation tools and the design presented in this report offers a compact antenna size.Although worldwide, breast cancer is the second most common type of cancer after lung cancer but in Australia breast cancer is the most common cause of cancer-related death amongst women.