In this letter, a numerical short-open-calibration (SOC) technique is developed to be directly integrated with the commercial electromagnetic software for accurate extraction of propagation constant of substrate integrated waveguide (SIW) with longitudinally periodic metallic posts. Short- and open-end circuits can be exactly realized by means of electric and magnetic wall in software respectively. After three distinctive equivalent circuit networks are described for SOC de-embedding procedure. The propagation constants of SIW with different dimensions are extracted. Comparison between our extracted and those reported propagation constant is made to validate our SOC technique. In final, the phase and attenuation constants of SIW are derived to demonstrate the propagation and leakage characteristics of SIW. © 2015 IEEE.