I've simulated an antenna with a microstrip feedline. At first, the antenna is excited with a waveguide port. The waveguide port is constructed by selecting the feedline as a face, then the port dimensions are calculated using macro.
After that, I needed to rotate the antenna such that the feedline face wouldn't be aligned with the cartesian coordinate system, and using the waveguide port will not work in this situation in Time Domain Solver. So I decided to use the discrete port and after the end of the simulation, I saw the results of using the discrete port (S11 parameter) is quite different compared with using the waveguide port.
What's the reason for the difference between the two approaches?
The frequency band is 2-18GHz.
In waveguide port, electric and magnetic fields are the inputs. But in discrete port, current is the input from which generated the fields.
The difference in the results obtained using the waveguide port and discrete port could be due to several reasons:
The descriptions above are helpful. The fields around the discrete port are not the same as the fields of the microstrip mode you want, so more microstrip modes are launched than just the one you want. Most of these will be cut-off, so will appear as inductive or capacitive loading to the port. After a short distance only the mode you want will be left, but its power will depend on the reflection caused by the other modes.
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