I am starting a new project and would like to use dual circular polarization and transmit using both ports. However before starting, I would like to know how much loss the dual polarization would add to the link budget. Does anyone know a way to calculate that.
You need to make choices before you can weigh the pros and cons.
In which cases do you want to estimate the loss ? Replacing a dipole (or horn or patch array or ??) with a dual polarization antenna (spiral/ sinuous / log periodic toothed or ??)?
Unless you talk specifics, it would not be possible to estimate much.