In this paper, a design of Substrate Integrated Waveguide (SIW) cavity backed slot antenna for polarization diversity application is presented. The proposed design uses a pair of slots placed at right angle with respect to each other at the top metallic plate of the cavity to generate two linear orthogonally polarized radiation pattern at same frequency to implement polarization diversity technique. The antenna interchanges between two separate feed line to excite either of the two orthogonal modes TE120 and TE210 respectively at same frequency and as a result, the proposed antenna exhibits a radiation pattern switching between Vertical (VP) and Horizontal Polarization (HP) at 9.98 GHz. The simulated result of the proposed design shows an isolation better than 20 dB between two input port and a gain of 4.2 dBi at broadside direction. © 2015 IEEE.