A six-port junction based on substrate integrated waveguide technology with high reliability and efficient performance is proposed in a sub-K-band of 21-23.5 GHz. This substrate integrated waveguide (SIW) six-port junction is constructed from three directional couplers and one T-junction power divider as fundamental components in SIW form, where using appropriate via techniques led to -6 dB coupling coefficients and -15 dB return loss. There is good agreement between the simulation and the measurement results.