Polarization manipulation and management are important for 4H-silicon carbide (SiC) integrated photonics, as 4H-SiC has material-based birefringent properties. In this Letter, we propose a low-birefringence polarization beam splitter (PBS) based on asymmetric directional coupler (ADC) mode converters with overall high performances. We numerically and experimentally demonstrate the ADC mode conversion based PBS on a 4H-SiC chip. The experimental results show that the device exhibits high transmittance of -0.6 dB and -1.3 dB for the transverse-electric (TE) and transverse-magnetic (TM) polarized light, respectively, and broad operational bandwidth over 130 nm. The polarization extinction ratio of >25 dB and >17 dB covering the whole C band for the TE and TM polarized light, respectively, and an ultra-large polarization extinction ratio of >32 dB for both polarizations at approximately 1560 nm are achieved.