An A6 relativistic magnetron with quasi-continuous frequency tunability

• Metamaterial Integration for Frequency Tuning in Relativistic Magnetrons: The study demonstrates a novel approach to achieve quasi-continuous frequency tuning in an A6 relativistic magnetron by embedding metamaterial slabs (PTFE substrate with 0.66 cm spaced metal strips) in alternate cavities. Rotation of these slabs around the local z-axis enables precise frequency adjustment. • 57 MHz Tunability via Angular Rotation: By rotating the metamaterial slabs across 21 angles (−10° to 10°), the operating frequency shifted from 4.63 GHz to 4.58 GHz, achieving a 57 MHz tuning range. Stable RF voltage and efficiency were observed for all angles except −1° and −8°, which exhibited prolonged transient behavior. • Breakdown Mitigation with Mylar Insulation: A 0.004 cm Mylar layer was integrated to prevent dielectric breakdown under high electric fields. Simulations confirmed electric fields at critical capacitive points remained below 85.71 MV/m, ensuring reliability in high-power microwave (HPM) operation. • Enhanced Performance via CST Simulations: Simulations revealed stable output power (0.595 GW), anode current (12.6 kA), and electronic efficiency (13.12 %). The system reached steady-state operation within 28 ns, with a resonant frequency of 5.70 GHz for the metamaterial, optimized to avoid overlap with the magnetron’s operational band. • S-Parameter-Driven Permittivity/Permeability Modulation: Angular rotation altered the tangential electric field on the metamaterial, modifying its effective permittivity and permeability via S-parameter shifts. This method provides a non-mechanical, scalable solution for frequency-agile HPM devices, eliminating the need for structural modifications. We numerically demonstrate quasi-continuous frequency tunability of an A6 relativistic magnetron (RM) using alternate cavities loaded with split-ring resonator (SRR) metamaterial slabs. The design employs SRRs fabricated on a dielectric substrate coated with a thin Mylar layer to suppress electrical breakdown at the capacitive points. To minimize the electric field concentration, the resonance frequency of the SRR is deliberately shifted away from that of the bare RM cavity. Full particle-in-cell (PIC) simulations using CST Studio Suite show that inserting the SRR slabs produces an initial frequency shift from 4.63 GHz to 4.58 GHz. The simulation results demonstrate that the orientation of metamaterial slabs significantly influences the S-parameter profile, affecting effective permittivity and permeability. These findings provide a promising framework for the design of high-performance metamaterials (MMs) in tunable frequency applications. By varying the rotation angle of the slabs inside the cavities, the effective permittivity and permeability are modulated, enabling a quasi-continuous frequency tuning. Acceptable RF output power (∼0.595 GW) and efficiencies (∼13 %) are achieved for most rotation angles, except at where mode competition prevents stable oscillation. This work introduces a compact, mechanically adjustable method for frequency tuning without altering the cavity volume, offering promising applications in high-power microwave (HPM) sources, frequency-agile communication systems, and radar.