Bai, J. Chen, Q.S. Fan, K. JACoW Publishing Geneva, Switzerland 2226-0366 978-3-95450-194-6 10.18429/JACoW-LINAC2018-THPO082 English 872-874 THPO082 Contribution to a conference proceedings 2019 2019-01 https://doi.org/10.18429/JACoW-LINAC2018-THPO082 http://jacow.org/linac2018/papers/thpo082.pdf Cylindrical deflectors which are now widely used for bunch length measurement suffer from the degeneration of polarization, while rectangular deflectors can separate polarization mode easily. This paper is focused on the study of a one-cell rectangular deflector, which is considerably different from cylindrical structure or multi-cell structure. A one-cell structure is free of π mode restriction and can achieve higher deflection efficiency per unit length. The proposed scheme is expected to achieve time resolution better than 200fs with the driving power less than 1MW. Cavity optimization and beam dynamic simulation are introduced in this paper.