Abstract: In applications such as precise near field antenna measurements and plane wave generator, the operating frequency is often limited by the bandwidth of the near-field scanning probe. To overcome the bandwidth limitation of open-ended waveguide probes, Ultra-Wideband (UWB) small aperture antennas based on Vivaldi antennas have been developed. However, their cross polarization performance is poor due to their common asymmetric structure. To address this issue, a miniature UWB antenna with low cross polarization is proposed in this paper. A 5-layer symmetrical structure is used to improve the traditional asymmetric Vivaldi antenna, and a Bezier curve is employed to design the gradient slot radiation structure. Loading resistance, patch, and etching rectangular chutes are also used to reduce the antenna standing wave and improve radiation directivity. The proposed antenna has an aperture width of 70 mm and a length of 201 mm. In the 0.9-6 GHz frequency band, the simulated cross polarization ratio of the antenna is better than 40.9 dB, and the gain is between −5.5 dBi to 9.53 dBi. The port reflection coefficient amplitude is less than −10 dB, and the radiation pattern is smooth, symmetrical, and without pits across the entire frequency bandwidth.