Terahertz time-domain spectroscopy (THz-TDS) systems traditionally operate in a single mode, either in reflection or transmission. In cases where the sample has nonunity permeability, measurements in both reflection and transmission geometries are required. The process of shifting and swapping the samples during an experiment increases the measurement uncertainty. This paper therefore presents a system where both reflection and transmission measurements can be performed simultaneously to reduce both experimental error and acquisition time. The measurement results are validated against findings in literature.