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Small antennas have been widely investigated and reported in various medical applications for some times. It is interesting to note that small ultra wideband (UWB) antennas are also demanded for some medical applications recently. One of the medical applications which require the UWB antennas is the microwave imaging of breast cancer. This imaging modality transmits lower power short microwave pulses (tens picoseconds to nanoseconds) into the body and detects the differentiated scattering due to the dielectric contrast between malignant and health tissues. A UWB compact antenna array is employed to conduct a 3D scanning through a so-called digital beamforming in space-time domain. In order to achieve high detection resolutions and good clutter rejection, the antennas with an impedance bandwidth 4-10GHz are usually employed as the elements in a condensed antenna array. So, small and low profile directional UWB antennas are desirable for this application. In addition, the antenna needs to have good radiation characteristics, i.e. consistent patterns over the entire operating bandwidth and good time-domain characteristics - minimal pulse distortion. Therefore, it still remains as an engineering challenge to design suitable UWB antennas for this application.