Generation of millimeter-wave radiation by means of a Smith-Purcell free-electron laser

Millimeter-wave radiation in the band from 53 to 73 GHz has been generated by means of a Smith-Purcell free-electron laser. Power levels of approximately 100 mW were observed with beam currents of 90 to 100 mA; the threshold currents ranged from 35 to 82 mA. The electronic tuning transconductance and the linewidth were also measured, yielding $\frac{\mathrm{df}}{\mathrm{dV}}=0.25\mathrm{}$ MHz/V and $\Delta f<~0.4$ MHz, respectively. The measured results agree well with predictions based on a linear theory.