Design of a Novel Reverse Magnetic System for Planar Three-Beam Array

Planar multibeam vacuum electron devices (VEDs) offer enhanced output power in the terahertz (THz) band by increasing total beam current while maintaining appropriate current density. Their associated planar high-frequency interaction circuits also facilitate simplified microfabrication. However, the stable transmission of planar multibeam array remains a critical challenge, primarily due to the reliance on bulky uniform permanent magnet focusing systems, which constrain further device miniaturization and integration. To overcome this limitation, a planar single-reversal permanent magnet focusing system is proposed for a narrow-separation three-beam array. The impact of magnetic field drop in the reverse region on beam transmission stability is analyzed, and a compensation principle and corresponding design methodology are established. Simulations are conducted to verify the proposed approach, demonstrating stable transmission of the three-beam array over a 70-mm distance with 100% transmission efficiency.