In this paper, a novel design of broadband coaxial to substrate integrated waveguide (SIW) transition has been implemented. The difficulties to get impedance matching between SIW and excitation port especially for thin substrate has been investigated and design steps to overcome the problem has been discussed. A two port SIW section using back-to-back configuration of the proposed transition is designed to operate at X-band (8-12 GHz) and fabricated. The measured result shows a broad bandwidth (30%) and an insertion loss of 1.2 dB in the operating band. © 2013 IEEE.