The CCEM international antenna gain comparison CCEM.RF- K23.F was initiated by the Working Group on Radio Frequency quantities (GT_RF) on the Consultative Committee for Electricity and Magnetism. This key comparison report presents results of measurements of on-axis gain of two Ku-band pyramidal horns at 12.4, 15, and 18 GHz. Participants making corrections for mismatch were asked to provide a table of the real and imaginary parts of the reflection coefficients of the antennas. Optionally, participants could measure the swept frequency gain from 12.4 to 18 GHz. Twelve national laboratories participated. The National Institute of Standards and Technology from the United States was the pilot lab. The purpose of the comparison was to evaluate the consistency between the participating laboratories in the measurement of the boresight gain of horn antennas in the WR-62 band. Main text To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCEM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).