A two-pole filter based on a quarter-wavelength, two-section coaxial stepped-impedance resonator (SIR) in volumetric technology is reported at X-band, targeting scientific and military applications requiring high power handling (PH). Topological limitations of the SIR structure are analyzed across all degrees of freedom for spurious-response suppression. A multipactor (MP) study predicts a PH threshold of 247 W in a radio-frequency (RF) volume of 1.6 cm3, confirming suitability of the proposed design for high-power X-band operation. An aluminum prototype was manufactured in two parts using CNC machining. Simulations and measurements are presented and discussed.