Relativistic BWO With Gaussian Radiation Radially Extracted Using an Electromagnetic Bandgap Medium

The importance of the Gaussian microwave beam is the concentration of maximum energy density along its axis. At the open-ended corrugated waveguide, the hybrid mode, HE
$_{\mathrm { {11}}}$
, couples to the fundamental free-space Gaussian mode with almost no loss over wide bandwidths. Even though the backward wave oscillator is typically known to radiate circular waveguide TM
$_{\mathrm { {0n}}}$
modes, an asymmetric mode can also be generated in these devices. Unfortunately, a cutoff-neck reflector is the only means to effectively reflect an asymmetric wave for radiation. The disadvantage of the cutoff-neck reflector is its proximity to the electron beam, which leads to beam scrape-off and alignment difficulty. In this paper, the novel idea of combining a periodic slow wave structure with an electromagnetic bandgap medium for coupling and extracting a Gaussian radiation pattern is presented.