Hi, Chettri

please, show the following links

https://www.cst.com/Products/CSTMWS/TechnicalSpecification

http://www.ansys.com/Products/Electronics/ANSYS+HFSS/Features/#1

With my best regards

CST has many solver modules.. the time domain solver uses Finite Integration Technique (FIT)

HFSS predominantly uses Finite Element Method (FEM).. HFSS-IE uses integral equation based approach.. Uses Method of Moments

CST is based on finite integral method

HFSS is based on finite element method

FEKO is based on method of moments ((by solving Integral equations) as well as ((by solving Differential equations) FEM.

For more information please read Numerical techniques in EM by sodiku....

Hi Dhanu

Nowadays all packages employ a variety of different methods, some with fancy names. To summarize:

CST- uses FIT  (finite integration technique, a relative of FDTD) for its transient solver; FEM for its Frequency domain solver, MoM for its Integral equation solver. It has also an optical simulation tool, for large structures, based on the SBR Shooting and bouncing rays method (Physical Optics)- its called A solver in their lingo.

HFSS - main solver is FEM, but it also uses a time domain solver, and a MoM solution. 

It has become impossible to packages to cover all different applications with just one solver, therefore they are picking different numerical methods and integrating them. 

HFSS in do optimization based on Quasi newton technique and it is design based on FEM for 3D full EM solver .

HFSS in FEM (finite element method)

CST- uses a relative of FDTD i.e. finite integration technique but HFSS uses finite element method and FEKO also uses moments finite element method.

FEM AND FIT respectively 

HFSS uses Finite Element Method

CST based on FIT (finite integration technique)

CST based on FITD (finite integration time domain)

CST uses the Finite Integration Time Domain method (FITD)

HFSS uses the Finite Element Method (FEM)