Hello,

Obviously you will have this issue, because if you change the frequency range the mesh properties must be also modified, because they depend on the frequency range and implicitly to the central wavelength, and in CST MWS the used reference for gain/directivity is an ideal spherical radiator ( isotropic antenna ) which is a Lambda/2 ( at operating Frequency ) Dipole that has a gain of 2.2 dBi, and you can see, if the wavelength changes, the gain reference will also change.

So to obtain more accurate farfield results, there is so many tips and tricks to do :

1-Check Energy : The accuracy level in the T-solver should be -40dB,

2-Check boundary : you should use open (add space), and ensures that there is a LAMBDA/8 space at the center frequency for PML Boundaries,

3-Check S-Parameters Balance : Farfield values become critical, if S-Parameter balance = 1 ( which means that no power is radiated ), In this case directivity and gain are calculated from dividing 0/0, which is numerically critical,

Good luck,

In general it should increase at higher frequencies, as you know gain is direct function of the effective area. But, you have to analyze higher-order modes properly. Due cancellation of fields due to higher order modes leads reduced gain.

Thank you Said Choukri for your explanation. it helped me.

thanks Arvind Kumar for your explanation

Dear Mr Said Choukri

So I checked and the accuracy level in my T-solver is -40dB and also the S-parameter balance is less than 1 in whole frequency range. and the the boundary is open (add space) but I don't know how to check its LAMBDA/8 space!?

so if I want to report the gain of the antenna at 2.45GHz should I say 1.5dBi or 0.89dBi????? (see the question again, if it's confusing).

thanks again

Hello Maryam Darabi

You could modify PML settings from this window,

thank you Said Choukri

I faced the same problem, the s-parameters also gets completely change as the frequency range changes.

Does changing the frequency range affect the s-parameter in the same way as the gain or it has some other physics?

However, found some reasons what the affect of changing the frequency range. Thanks to Said Choukri Maryam Darabi Arvind Kumar for their conservations.