Novel Low-Loss 0.65-THz Multisectional Folded Waveguide High-Frequency Circuit

A low-loss and high-effective-output-power terahertz (THz) folded waveguide (FWG) high-frequency circuit is proposed, fabricated, and tested. The circuit consists of several slow wave sections connected by a single period transition structure, in which the odd number sections are with the same slow wave unit cells and the even ones are with another same slow wave unit cells. To increase fabrication accuracy and reduce the circuit losses, both slow wave unit cells are designed to operate with phase shifts greater than 600°. The circuit, fabricated from oxygen-free copper (OFC) by using nano computer numerical control (nano-CNC) milling technology, exhibits excellent transmission characteristics in the cold test experiment, achieving a transmission loss of less than 1 dB/mm, corresponding a recorded equivalent conductivity of $3.7\times 10^{{7}}$ S/m above 0.6 THz. The simulations with modified structural dimensions based on the fabricated sample indicate that the machining errors are below $2\mu $ m, resulting in the frequency shift within 12 GHz. In addition, the low loss enables the saturated input power to be as low as 0.5 mW, while the maximum output power reaches 2.86 W with a 3-dB bandwidth of approximately 8 GHz.