SpectreRF PSS simulation for harmonic

I have tried a simple circuit to check the harmonic. However, the harmonic is observed for the input port. I have no idea for explain this. Very appreciate for you any help.
The following is the main flow in my work,
(1) Schematic: Only one capacitor 10 pf, Port 1 is set sin source with 50 ohms res, freq=900MHz,Power=30 dBm, Port 2 is set as DC with 50 ohms res.
https://obrazki.elektroda.pl/6263692600_1358861736.png
https://obrazki.elektroda.pl/2469448200_1358861831.png

(2) I have chosen the PSS to meas the output harmonic. Beat freq=900MHz， 5 harmonic.
https://obrazki.elektroda.pl/9116446000_1358861895.png

(3)The input and output harmonic is plotted.
https://obrazki.elektroda.pl/3380132900_1358861930.png

(4)My question is:
(a)The harmonic is observed for the input port. This phenomenon is normal or abnormal? Due to my simulation setting is not right? How do this harmonic signal generate?
(b)Do these input harmonic influence the output harmonic? The output and input harmonic has the same magnitude.

Very appreciate for you kindly help.