螺旋线仿真问题: 1.rar

我用的是一个半径为２的铜线绕Z轴绕成圆柱形螺旋线．线圈的两头都连接电路。外面用的边界是Radiation,Solution type选择的是Terminal, 激励选择的是Lumped Port。当选用频率是1GHz时，软件正常运行．当选用频率是１MHz时，软件运行一段时间后出错．错误提示为：Port refinement, process abc3d: failed to solve the problem due to lack of precision. The likely  cause is that the frequency is too low. 我需要的频率就是１MHz呀．请问高手，模型怎么改进，才能使软件正常运行起来呀？谢谢！