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

Abstract

The frequency domain performance of a stripline beam position monitor depends largely on the longitudinal shape of its electrode. Some shapes other than a conventional rectangle have been proposed and tested. To attain a good impedance matching along the electrode, they need to be precisely bent down toward their downstream in proportion to their width. This is a considerable task, and a failure to comply with it will result in a large distortion of the frequency-domain transfer function from the ideal one due to unwanted signal reflections. In this report, we first propose a triangle electrode for easy fabrication and setup: it only requires that a triangularly cut flat electrode will be placed in a chamber while being obliquely inclined toward the downstream port. 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 (with a result that the triangle is transformed to a concave pentagon). The concave pentagon electrode needs to be bent only once at the middle point of the polylines for a good impedance matching and thus its fabrication and setup remain to be easy. Rf measurements for the various electrode shapes have been carried out. We found that the concave pentagon electrode achieves a wide and flat frequency response up to about 4 GHz for the J-PARC Main Ring (MR).

Titanium nitride-coated ceramic break for wall current monitors with an improved broadband frequency response

“…We theoretically and experimentally associate the time domain analysis with the frequency domain analysis based on the electric circuit theory. Consequently, we find that the wall current monitor utilizing the ceramic break with the TiN coating has a better frequency characteristic of up to a few GHz and can be another candidate against the bunch shape monitor utilizing the triangle and concave pentagon electrodes, previously investigated by the authors [12], because the frequency response of the bunch shape monitor utilizing the electrodes at low frequencies maps the derivative of the bunch shape with time in the time domain, instead of the bunch shape itself.…”

“…The uniqueness of the amplitude and the linearity of the phase were good until around 2.5 GHz. The authors previously investigated the characteristic of triangle and concave pentagon electrodes [12] and the exponential electrode until a few GHz [26]. The characteristic of this monitor utilizing a TiN-coated ceramic is better than that of the cases at a low frequency extreme because the amplitude of S from that of the triangle and concave pentagon electrodes and the exponential electrode.…”