Transmission line for 258 GHz gyrotron DNP spectroscopy

We report the design and test of the transmission line for DNP spectrometer with 258GHz gyrotron. The 16 meter line includes mode converter, HE11 waveguides, 5 mitre bends, variable attenuator, directional couplers, calorimeter and switch. Transmission is 70 ± 15% with 15Watt in the pure HE11 mode.