Triangle and concave pentagon electrodes for an improved broadband frequency response of stripline beam position monitors

Shobuda, Yoshihiro   ; Chin, Y. H.*; Takata, Koji*; Toyama, Takeshi*; Nakamura, Keigo*

The frequency domain performance of a stripline beam position monitor depends largely on the longitudinal shape of its electrode. To attain a good impedance matching along the electrode, it needs to be precisely bent down toward its downstream in proportion to its width. In this report, we first propose a triangle electrode for easy fabrication and set-up. Theoretical and simulation results show that the simple triangle electrode has a remarkably flatter frequency response than the rectangle one. The frequency response, in particular at high frequencies, can be further improved by attaching an "apron" plate, perpendicular to the upstream edge of the electrode. The overshooting of the frequency response at low frequency can be eliminated by replacing the straight sidelines of the triangle by three-point polylines. We found that the concave pentagon electrode achieves a wide and flat frequency response up to about GHz for the J-PARC Main Ring.