I am trying to calibrate correctly on Network Analyzer but I always see errors at the same frequencies. I want a calibrate between 23-25.5 GHz frequencies. I am using mechanical calibration with Keysight N9918A NA, Keysight 85521A Calibration kit. After calibration, when I check the S11 adn S21, I see that when the calibration kit is connected at the thru port, they are at -30dB and -0.5dB respectively. I think the calibration is good and I take out the calibration kit and when Port1 is empty (open), S11 resonates at 24.2 GHz (S11 is around -30dB @24.2GHz). Why is this happening? How can I fix?