This paper presents the results of development of a X-band compact stepped-thickness septum polarizer. All electromagnetic characteristics of the polarizer have been simulated and optimized numerically. A prototype of the polarizer has been designed, fabricated and tested. It has been shown that the use of a stepped-thickness septum instead of a constant-thickness one improves the return loss and XPD of the septum polarizer by 5 and 7 dB, respectively. Measured VSWR of the designed compact septum polarizer is less than 1.4 in the operating frequency band 7.70-8.50 GHz. Tested differential phase shift varies from 83° to 100°. Suggested compact septum polarizer is designed for a quasi-monopulse feed of a dual-polarized ground station antenna system. Measured XPD of the polarizer in an assembled feed system is higher than 30 dB.