This paper presents a breakthrough methodology for overcoming the intrinsic suppression limitations of mixers in low-order in-band spurious suppression within frequency conversion chains, including innovative design methodologies, circuit architectures, and comprehensive simulation and experimental validation results. Currently, in complex microwave frequency conversion systems operating under predetermined frequency planning schemes, the suppression of in-band low-order spurious components remains a persistent technical challenge that significantly impacts system performance and operational reliability. This study introduces an innovative approach where harmonic signals are extracted through LO signal path splitting. These LO-generated harmonics are then phase/amplitude-conditioned to produce cancellation signals, which undergo vector synthesis cancellation with intrinsic low-order in-band spurious components, thereby achieving a significant enhancement in spurious suppression capability beyond conventional mixer limitations. Currently, the spaceborne Ka/Ka-band frequency converters achieve an in-band spurious suppression capability of 32 dBc for the − RF + 6LO mixing component under room temperature conditions. Through the implementation of LO harmonic mixing to generate cancellation signals and their subsequent vector synthesis cancellation, the suppression capability has been enhanced to 70 dBc, achieving an improvement of approximately 40 dB compared to conventional methods. In contrast, the comparable spurious suppression capability of similar systems developed by Thales Alenia remains at approximately 20 dBc. Therefore, the low-order spurious suppression capability demonstrated in this study achieves internationally leading performance, surpassing existing state-of-the-art solutions by a significant margin.