Impedance matching of pillbox-type RF windows and direct measurement of the ceramic relative dielectric constant

Ao, Hiroyuki; Asano, Hiroyuki*; Naito, Fujio; Ouchi, Nobuo ; Tamura, Jun  ; Takata, Koji*

Impedance matching of RF windows that minimizes the RF reflection is necessary to prevent localized standing waves between an RF window and a cavity, which may cause thermal and/or multipactoring issues. The present report proposes new procedures for impedance matching as follows: (1) The relative dielectric constant of the ceramic window is directly measured using the resonant frequency of a cavity made by temporarily combining the pillbox part of the RF window and two short-circuiting plates. (2) The dimensions of the pillbox section including the ceramic disk are fixed on the basis of the measured relative dielectric constant. To confirm this procedure, three RF windows were fabricated using the same type of ceramic material, and successful impedance matching of these windows was performed (VSWR 1.05).