© 2014 ACES.In this paper, contribution of spherical conformal ultra-wide band (UWB) bow-tie antenna on enhancement of breast tumor detection capability of a radar-based microwave imaging system is investigated through simulation, demonstrating the potential of the novel antenna element used in a half-spherical antenna array surrounding the breast. The designed conformal antenna operates efficiently across the band from 1 GHz to 8 GHz, and it is immersed in a coupling medium in order to get a good impedance matching with the breast. Images are successfully formed by using delay-and-sum (DAS) algorithm for the detection of a spherical tumor model with 2 mm diameter. The tumor is located at 40 mm depth inside three different breast phantom models with homogeneous fatty breast tissue, quasi-heterogeneous mix of fibro-glandular and fatty breast tissues and homogeneous fibro-glandular tissue, respectively. Fidelity factor, indicating the maximum cross correlation between observed and excitation pulses, of the conformal bow-tie is found to be around 13% more than that of the planar bow-tie at 40 mm depth. The use of the spherical conformal antenna presents an excellent solution to increase tumor responses by at least 2.3 dB, as well as to decrease mutual coupling effects between array elements, compared to the same system with planar bow-tie antennas.