Transmission Spectra in RF module

Hi,

I'm a beginner in COMSOL. I am using the COMSOL scripting in MatLab. I would like to know how I can get the transmission spectra as shown in Fig 4 of the file attached below. I am looking to plot transmission vs wavelength. I have used scattering boundary conditions and obtained the field distribution in the waveguide. But I do not know how to obtain the transmission plot. Any help will be highly appreciated. Thank you