Harmonic components measurement of TWT with rectangular waveguide output structure

The results of output harmonic components measurements show great disagreement where rectangular waveguide is used as output port in hundred watts CW-TWT operating above X-band. Typical error of X-band TWT is larger than 12dB. This paper advanced a quasi-direct measurement method using signal spectrum analyzer (SSA), which measured harmonic components under pulse mode. The error is less than 3.5dB and can be improved by applying matched coax-waveguide convertor.