The aim of the present paper is to provide details of the experimental configuration of sub-terahertz transmission spectra of a GaN two-dimensional electron gas. The experimental configuration used in the present investigation consists of mainly an electronic source, a detection device and cooling arrangements. Such a configuration is not only technically demanding but also critical for observing subtle spectral features associated with plasmonic resonances, intersubband transitions, and carrier scattering processes in GaN 2DEGs. By carefully managing vacuum conditions, cryogenic temperatures, and optical alignment, the setup ensures minimal noise and high spectral fidelity. Moreover, the reproducibility of the calibration spectrum of the source provides confidence in extracting meaningful transmission spectra with and without the sample. This methodology complements recent device-oriented advances by establishing a robust experimental foundation for systematic sub-THz investigations.