Fig. 1. Schematic diagram of transmission loss test of waveguide samples （the insert figures show the methods for creating high and low temperature environments respectively）

Fig. 2. Microscopic morphology of the silver reflective layer：（a），（c） ABS structural tubes have been plasma treated before depositing the silver layer； （b），（d） ABS structural tubes have not been plasma treated before depositing the silver layer

Fig. 3. Experimental diagram for testing the bonding strength of silver coating by tape test：（a），（c） ABS panels have been plasma treated before depositing the silver layer； （b），（d） ABS panels have not been plasma treated before depositing the silver layer

Fig. 4. （a） The bending transmission losses of the 3.2 mm and 4.2 mm- waveguides at 0.1 THz； （b） the bending transmission losses of the 3.2 mm and 4.2 mm- waveguides at 0.3 THz

Fig. 5. Transmission stability of the two waveguide samples with and without plasma treatment in hot and cold environments

Fig. 6. （a） The variation curve of the transmission loss of the waveguide sample with the hydrothermal aging time； （b） the variation curve of the transmission loss of the waveguide sample with the number of high and low temperature cycle aging tests