feko仿真偏置单反面天线与自己编的程序在交叉极化上有较大不同，求解释，多谢，

用feko仿真一个单偏馈发射面天线，馈源是喇叭，馈源部分默认算法，反射面部分用po（illuminate only from front ）    频率是8g 反射面投影口径是260mm。
   
之前对整体天线进行仿真需要4个小时左右，但是面的算法可能选的是    po 全照射
最近使用 po illuminate only from front  对天线整体仿真一次 最多只要10几分钟， 馈源是默认算法
请问 这2种方法为了什么仿真时间差别这么大?

 
3d 图
同时我用书上的 口径场法 ，编了一个软件，用hfss 仿真喇叭，导出方向图，作为软件的输入，用口径场法计算面天线的 交叉极化，
然后将计算结果和po   illuminate only from front   比较   结果比较结果是 e h 面主极化 曲线基本相同，但是e 的交叉极化2者相差好多， 而且轴向交叉极化 相差数值也略大，
下面是归一化的 2d图 图下半部分的2条曲线就是 e面的交叉极化曲线，从图中看 相差大多，
请教大家，po  illuminate only from front    计算交叉极化用的是什么算法?还有仿真这个整体天线只要10几分钟，这样的结果可信吗?

求懂的人，多多指教，

USING CADFEKO 3-112 (User’s Manual Suite 6.1)
3.9.7 Setting solution parameters on faces
Physical optics (PO): The high frequency physical optics method is used when calculating the currents on the face.
1. full ray-tracing :
With this method, a significant fraction of the solution time is spent on ray tracing (determining which elements are visible from each non-PO radiating element).
The advanced PO options (see section 3.9.6) allow manual optimisation of ray tracing.
2. always illuminated :
This option is applicable when the model is such that the entire surface will always be illuminated (such as for a basic reflector antenna analysis). Shadowing is not analysed, and non-PO or large element PO surfaces are considered transparent for this purpose.
3. only illuminate from front :
This option is applicable to all closed bodies, but the normal vector must point outward (away from the closed body) from each face. Smaller mesh elements are required close to the shadow boundaries.
Large element PO:
The high frequency large element physical optics method is used for large smooth areas when calculating near and far fields. This method is only to be used when there are no discontinuities in the incident fields (e.g. close to a point source). If the large element PO is used together with the MoM method, the MoM and PO regions are to be de-coupled. Note that the same options as given above for PO (full ray-tracing, always illuminated etc.), are also valid for large element PO.
Geometrical optics (ray launching):
The geometrical optics (ray launching) method is used.
This method is applicable to the simulation of thin dielectric or metallic objects, such as radomes and dielectric lenses. The use of ray-launching GO is also supported for thin dielectric sheets, coatings and anisotropic media. Note that the use of plane wave as an excitation is also supported (required for RCS requests).
GEOMETRY CARDS 11-82
The physical optics (PO) approximation can only be used for certain structures. Structures where the antenna is situated in front of a reflector are well suited. Then PO can be used for the triangles that form the reflector. This results in a large reduction in computational time and memory for electrically large objects.
Note that the ray tracing options and the number of reflections can be specified on a per label basis, by using multiple PO cards. All other parameters can only be specified once. For the global parameters, the values of the last PO card will be used.
Using Full ray tracing, illumination only from outside has two main applications:
1. Acceleration of the PO ray tracing with closed bodies (the normal vector must then point outward), since the dot product of the normal and propagation vectors can be used to quickly determine if a triangle is to be used in the ray tracing. In this case the closed model must be constructed with the normals pointing outward.
2. In, for example the MoM/PO hybrid method on a closed body, the MoM region (such as an antenna) can be prevented from illuminating the PO region from inside.
A basis function that has been assigned to an edge between two triangles will only be solved with the PO, if the PO approximation has been declared for the labels of both triangles.
The metallic PO region must be perfectly conducting, i.e. no losses are allowed. Dielectric coatings (see CO card) and thin dielectric sheets (see SK card) can, however, be treated with the PO approximation.

粗略的读了你贴的 资料， 是不是 illuminate from front 只能用于封闭 结构， 我建立的模型不能?