A Sheet Beam-Operated Gridless Inductive Output Tube With Metamaterial-Inspired Cavity

Metamaterial-based structures offer the potential to significantly miniaturize vacuum electron devices. This property is desirable for the gridless inductive output tube (IOT), due to its primary application as a compact high-power amplifier. This article presents a novel sheet beam-driven gridless IOT with a metamaterial-inspired cavity. The 922-MHz rectangular cavity is loaded with four complementary split-ring resonator (CSRR) cells. Power is extracted with a loop coupled to the magnetic field of the TM<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> mode. The analytical model of the cavityand CSRR cells is derived using an equivalent circuit, and compared to the simulation results. Eigenmode and time-domain simulations show <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\pi $</tex-math> </inline-formula>-mode operation, double negative behavior, and an external quality factor (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${Q}_{e}$</tex-math> </inline-formula>) of 96.6. A cold test of the cavity is performed to experimentally verify the scattering parameters. The 45-kV, 16.8-A electron beam is focused with a 0.35-T magnetic field and density-modulated using a 1-kV sinusoidal signal. Particle-in-cell simulations of the IOT show an average output of 250kW and 27-dB gain. Compared to a cavity of standard waveguide dimensions at 922 MHz, the metamaterial-based design offers a 73.9% reduction in cross-sectional area.