研究了基于BEPCⅡ直线加速器的腔式束流位置探测系统（CBPM）的设计。本方案给出的CBPM探头工作频率为S波段，束流管道半径23 mm，参考腔TM₀₁₀工作频率和位置腔TM₁₁₀的工作频率一致。由线下测试结果可知，CBPM实物特征参数与仿真结果一致，CBPM水平和垂直方向工作频率分别为2502 MHz和2503 MHz；垂直和水平的四个端口交叉隔离度均优于?44.7 dB；测量线性区域好于10 mm。射频前端电子学负责对CBPM探头的模拟信号进行滤波、放大和下变频等调制。将CBPM探头置于标定平台，对经过CBPM信号进行时域和频域分析，通过计算得到CBPM水平、垂直方向线下分辨率分别为2.87 μm、2.16 μm。

In BEPCⅡ, button BPM and stripline BPM cannot reach sufficient precise resolution for beam transverse displacement. This project aims at the design of cavity BPM for BEPCⅡ linac. Position cavity in cavity beam position monitor (CBPM) is an re-entrant resonator with four rectangular waveguides. TM₁₁₀ mode frequency is chosen in S band, and the radius of beam pipe is 23 mm. TM₀₁₀ mode in reference cavity is almost as same as TM₁₁₀ mode in position cavity. According to the results of offline test, characterized parameters of CBPM coincided with computer simulated data. The frquency of TM₁₁₀ mode are 2502 MHz in horizontal direction and 2503 MHz in vertical direction. Cross-talk isolation for position cavity is better than -44.7 dB. Ratio front circuits included filtration, amplification and down-convertion when signals extracted from CBPM. Offline caliberation test results showed that CBPM has excellent measurement value of linearity area, which is over 10 mm. After frequency spectrum analysis and linear fitting, the position resolution of CBPM is 2.87 μm in horizontal direction and 2.16 μm in vertical direction.