A compact design of phased array Vivaldi antenna for channel sounding applications is proposed. 64-elements of low-profile 22 GHz Vivaldi antennas with coaxialto-SIW feeds and well-defined end-fire radiation patterns have been used to form an 8×8 planar array design. The antenna elements are designed on 1.6 mm Arlon AD-320 substrates (ε=3.2 and δ=0.0038). The structure of SIW is composed of two rows of cylinders between metal plates which can improve the radiation performance of the elements. The proposed phased array antenna has compact size with frequency response of 21-23 GHz. It has good features in terms of impedance-matching, gain and efficiency characteristics. More than 22 dB realized gain, 23 dBi directivity, and -0.5 dB (90%) total efficiency have been obtained. In addition, the performance of the planar array with different numbers of the radiators has been investigated.