From experience, the 8481A series does not perform up well beyond 18 GHz. The response drops very quickly towards 19/20 GHz, and at 26.5 GHz, the response difference is more than 3 to 4 dB. The N connector is not responsible for this poor performance, as 85025A detectors easily perform up to 40 GHz with only a few glitches due to VSWR beyond 18.6 GHz. Conversely, an 8485A often performs up to 30 or even 33 GHz.
