<p>This paper introduces a new design technique for Gysel power dividers (PDs) in substrate-integrated waveguide (SIW) technology, suitable for both equal and unequal power division. The method tackles the usual challenges linked to the cutoff frequency and line-width constraints, which often prevent direct application of standard Gysel formulas in SIW-based designs. By deriving new equations, we can achieve any power split while keeping the line width and cutoff frequency constant. Analytical models at Ku-band frequencies confirm this approach for both equal and unequal splits, and two SIW-based PDs operating at 15 GHz are designed and simulated. Moreover, we fabricated a prototype for the equal-power case to validate the design. Measured results show an isolation above 22 dB at 15 GHz, a return loss better than 10 dB at each port, and a 2.44 dB insertion loss, all closely matching the simulated data. This demonstrates the effectiveness of the proposed design approach.</p>