Design, fabrication and characterization of D band two-beam folded waveguide structure

To enhance the output power of Terahertz (THz) Traveling-Wave Tubes (TWT), a new proposal about power combining of multiple signal is presented in the paper. Firstly, the design of D band Two-Beam Folded Waveguide Structure (TBFWS) was completed and the power divider was optimized. Then, a TBFWS was fabricated by micro milling, and its dimensions errors are below the designed values. Lastly, the cold-test and interaction characteristics of TBFWS were analyzed by CST code. The simulation results show theS11of TBFWS is below -20 dB, and the experiment results demonstrate the S11 of TBFWS is about -15 dB. The dispersion characteristics of the TBFWS show the circuit has a broad cold bandwidth of 22 GHz (16%) and 3 dB bandwidth of 12.5 GHz. With the 10 mW input peak power, 10 mA beam current and 15.79 kV beam voltage of each FW circuit, the gain and output power of single beam FW-TWT are 22 dB and 1.58 W at 0.14 THz, respectively, whereas, the TBFWS circuit can produce the combining output power of 2.91 W at 0.14 THz. Power combining efficiency of the circuits is more than 90%. The power combining method can efficiently enhance the output power of THz TWT.