A miniaturized frequency scanned leaky wave antenna (LWA) based on half mode substrate integrated waveguide (HMSIW) with open stop-band suppression is proposed. The modified cross-slot is etched on the top of HMSIW as the radiating element. The folded and unfolded ground plane designs of the proposed HMSIW LWA are compared and analyzed with respect to their Bloch impedance characteristics and it is found that further miniaturization and gain improvement at broadside by ~ 2 dBi are achieved for folded ground plane design. The proposed LWA scans a region from -40° to +24° as the frequency range increases from 12 to 17 GHz with broadside at 15.5 GHz. The HMSIW LWA with folded ground plane is fabricated and its performance is experimentally measured showing the close agreement between the simulation and the measured results. KeywordsMiniaturization, folded ground plane, half mode substrate integrated waveguide, broadside gain enhancement, leaky wave antenna