At present, the built-in solution algorithms in HFSS include: finite element algorithm (FEM), integral equation algorithm (ie), high frequency algorithm (SBR + Solver), hybrid algorithm (febi, ie region), domain decomposition algorithm (DDM, fa-ddm), time domain algorithm (transient), eigenmode algorithm (CMA), eigenmode solver, etc

https://zhuanlan.zhihu.com/p/113897875  

In fact, most people simulate simple antennas and filters. Using the finite element algorithm of HFSS and the adaptive mesh generation and encryption technology of the software itself, setting the convergent Max MAG delta S (default 0.02) is enough to meet their simulation requirements.

The use of software and the setting of other algorithm solvers will not be described here.

CST just makes up for the short board of HFSS simulation UWB, but its simulation accuracy in small size, circular and other structures is not high. As shown in the figure below, the triangular mesh generation of HFSS is particularly delicate at the edge, especially the circular structure accessories, while the hexahedral mesh generation of CST is too regular.

Although the local mesh of CST can be used to encrypt the local mesh near structures such as gaps and circles, beginners may still be the fool adaptive subdivision of HFSS, which is more humanized.

CST software uses the full wave time-domain simulation algorithm of electromagnetic field - finite integral method (FIT) to discretize and iteratively solve the Maxwell integral equation. Due to the time-domain algorithm fit, it only needs to be solved step by step without matrix inversion. This inherent characteristic determines that its suitable simulation structure covers small, medium and large, and can achieve good performance. The calculation amount of volume moment method, finite element method and finite integration method (reflected in CPU time and required memory) is respectively proportional to the 3rd, 2nd and 1.1 ~ 1.2nd power of the number of grids n. It can be seen that the computational force requirements of finite integration method are lower than those of HFSS finite element method.

For CST software, time domain solver is also commonly used. In addition, it also has frequency domain solver, eigenmode solver, integral equation method, asymptotic calculation and multi-layer medium algorithm.

In the next section, we will compare the simulation accuracy of the two software, mainly focusing on the FEM + automatic mesh generation encryption simulation of HFSS and the time domain solver and frequency domain solver of CST.

Firstly, Rogers 4350b with substrate thickness of 0.762mm is selected, and the resonant frequency is 5.8GHz. (slide left and right to see the complete formula)

According to the above formula, the width and length of the patch antenna are 16.9mm and 13.3mm respectively.

clear;clc;path = mfilename('fullpath');i=strfind(path,'');path=path(1:i(end));cd(path);addpath(genpath(strcat(path,'hfssapi-by-Jianhui Huang')));try    % 填写路径    % tmpPrjFile：生成的aedt或者hfss(安装hfss15以下的后缀名为.hfss)项目文件的路径名    % tmpScriptFile：生成的vbs脚本文件的路径名    tmpPrjFile = 'F:vbsScriptPatch_Probe_Feed.aedt';    tmpScriptFile = 'F:vbsScriptauto_code.vbs';    % hfssExePath：HFSS软件的路径    hfssExePath = 'D:softwareHFSS15AnsysEM18.2Win64ansysedt.exe';    % 创建一个可读写vbs脚本文件.    fid = fopen(tmpScriptFile, 'wt');    %创建一个新的HFSS项目并[敏感词]一个新的设计文件.    hfssNewProject(fid);    Design_name='element';    hfssInsertDesign(fid, Design_name);     Patch_W=16.9;Patch_L=13.3;    Sub_W=35;Sub_L=30;Sub_H=0.762;copper_H=0.035;    Probe_dy=-4;Probe_dx=0;    Inner_R=0.5;Diel_R=exp(50/60*sqrt(1))*Inner_R;Outer_R=1.5;L0=2;    % hfssVariableInsert(fid,DesignName,variableName, value, units,flag)    hfssVariableInsert(fid,Design_name,'Patch_W', Patch_W, 'mm',1);    hfssVariableInsert(fid,Design_name,'Patch_L', Patch_L, 'mm',1);    hfssVariableInsert(fid,Design_name,'Sub_W', Sub_W, 'mm',1);    hfssVariableInsert(fid,Design_name,'Sub_L', Sub_L, 'mm',1);    hfssVariableInsert(fid,Design_name,'Sub_H', Sub_H, 'mm',1);    hfssVariableInsert(fid,Design_name,'copper_H', copper_H, 'mm',1);    hfssVariableInsert(fid,Design_name,'Probe_dx', Probe_dx, 'mm',1);    hfssVariableInsert(fid,Design_name,'Probe_dy', Probe_dy, 'mm',1);    hfssVariableInsert(fid,Design_name,'L0', L0, 'mm',1);    hfssVariableInsert(fid,Design_name,'Inner_R', Inner_R, 'mm',1);    hfssVariableInsert(fid,Design_name,'Diel_R', 'exp(50/60*sqrt(1))*Inner_R', 'mm',2);    hfssVariableInsert(fid,Design_name,'Outer_R', Outer_R, 'mm',1);     % 画基板    % hfssBox(fid, BoxName, Start, Size, Units, Color, Material, Transparency, flag)    hfssBox(fid, 'Sub1', {'-Sub_W/2', '-Sub_L/2', '0mm'}, {'Sub_W', 'Sub_L', 'Sub_H'}, 'mm',...        "(0 128 128)", "Rogers RO4350 (tm)", 0, 2);    % 画贴片    hfssBox(fid, 'Patch', {'-Patch_W/2', '-Patch_L/2', 'Sub_H'}, {'Patch_W', 'Patch_L', 'copper_H'}, 'mm',...        "(255 128 0)", "copper", 0, 2);    % 画GND    hfssBox(fid, 'GND', {'-Sub_W/2', '-Sub_L/2', '0mm'}, {'Sub_W', 'Sub_L', '-copper_H'}, 'mm',...        "(128 128 128)", "copper", 0, 2);     % 画同轴部分    % 画同轴内芯    % hfssCylinder(fid, CylinderName, Axis, Center, Radius, Height, Units, Color, Material, Transparency, flag)    hfssCylinder(fid, 'Inner', 'Z', {'Probe_dx', 'Probe_dy', 'Sub_H+copper_H'}, 'Inner_R','-(Sub_H+copper_H*2+L0)', 'mm',...       "(128 128 128)", "copper", 0, 2);    hfssCylinder(fid, 'Diel', 'Z', {'Probe_dx', 'Probe_dy', '-copper_H'}, 'Diel_R','-L0', 'mm',...       "(0 128 128)", "vacuum", 0, 2);    hfssCylinder(fid, 'Outer', 'Z', {'Probe_dx', 'Probe_dy', '-copper_H'}, 'Outer_R','-L0', 'mm',...       "(128 128 128)", "copper", 0, 2);     % 地板开过孔    hfssCylinder(fid, 'GND_hole', 'Z', {'Probe_dx', 'Probe_dy', '0mm'}, 'Diel_R','-copper_H', 'mm',...       "(255 128 0)", "vacuum", 0, 2);    % 布尔操作    hfssSubtract(fid, {'Outer'}, {'Diel'}, true);    hfssSubtract(fid, {'Sub1','Patch','Diel'}, {'Inner'}, true);    hfssSubtract(fid, {'GND'}, {'GND_hole'}, false);    % 保存项目文件到指定路径    hfssSaveProject(fid, tmpPrjFile,1);    % Close the HFSS Script File.    fclose(fid);    disp('vbs脚本已生成！');catch    disp('程序出现异常！');    fclose(fid);end