A novel polarization diverse substrate integrated waveguide (SIW)-based leaky-wave antenna (LWA) is proposed for larger radiation coverage by frequency beam scanning in X-band. For feeding purpose, the SIW-based power divider, the directional coupler, and the 180° power splitter are used in the design. For radiation, +45°/-45° tilted slots are etched on top and bottom faces of the structure such that the radiated quad beam scans all the four quadrants. By varying the means of excitation at two input ports, multiple polarization states are realized. The antenna shows ±45° dual polarization (+45° and -45° are co-existing), horizontal and vertical polarization, and two types of circular dual-polarization (left handed and right handed simultaneously). The proposed antenna is capable of scanning in each of the four quadrants simultaneously with the scanning range of 62° having the maximum gain of 12.6 dBi and an improved cross-polarization level better than -20 dB. The quad beam covers overall scanning range of 248° with different polarization states. The S-parameters, radiation patterns, gain, and axial ratio are calculated and demonstrated. The proposed LWA shows desirable advantages, such as simultaneous four-quadrant frequency beam scanning having polarization diversity capabilities, which leads to a flexible design for practical utilization. © 1963-2012 IEEE.