Dielectric constant measurement using resonant frequencies for minimizing the reflection of pillbox RF windows

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

In the case of the RF window operated with the standing-wave cavity coupled to waveguides using coupling apertures, the reflection of the RF window affects the total coupling factor (voltage standing wave ratio, VSWR) consisted of the RF window and the cavity. Hence, the reflection (VSWR) of the RF window should be minimized not to change the cavity VSWR optimized separately, and to prevent standing waves between the RF window and the cavity. For minimizing the VSWR of the pillbox-type RF window, this report proposes that the dielectric constant of the ceramic is measured directly using the resonant frequency in the fabrication process of the RF window. In this work, three RF windows are fabricated additionally using the same type ceramic (NTK HA95), the small VSWR could be achieved using this procedure. This result also shows that the dielectric constant increases linearly with increasing the density.