Matching, if is well done and tuned, will decrease the insertion loss of the mixer.
If is not designed well the mixer may have higher insertion loss compared with no matching at all.
The matching circuit will make the mixer narrowband, when with no matching the mixer has broader bandwidth.
Thank you vfone. Do you know how to simulate diode in CST? Problem is I have 2 spice files - for diode and for package, how to make one file from that?