The Event Horizon Telescope (EHT) has successfully revealed the shadow of the supermassive black hole, M87∗, with an unprecedented angular resolution of approximately 20 μas at 230 GHz. However, because of limited short baseline lengths, the EHT has been constrained in its ability to recover larger-scale jet structures. The extended Korean VLBI Network (eKVN) is committed to joining the EHT from 2024 that can improve short baseline coverage. This study evaluates the impact of the participation of eKVN in the EHT on the recovery of the M87∗ jet. Synthetic data, derived from a simulated M87∗ model, were observed using both the EHT and the combined EHT+eKVN arrays, followed by image reconstructions from both configurations. The results indicate that the inclusion of eKVN significantly improves the recovery of jet structures by reducing residual noise. Furthermore, jackknife tests, in which one or two EHT telescopes were omitted—simulating potential data loss due to poor weather—demonstrate that eKVN effectively compensates for these missing telescopes, particularly in short baseline coverage. Multi-frequency synthesis imaging at 86–230 GHz shows that the EHT+eKVN array enhances the recovered spectral index distribution compared to the EHT alone and improves image reconstruction at each frequency over single-frequency imaging. As the EHT continues to expand its array configuration and observing capabilities to probe black hole physics more in depth, the integration of eKVN into the EHT will significantly enhance the stability of observational results and improve image fidelity. This advancement will be particularly valuable for future regular monitoring observations, where consistent data quality is essential.

Introduction
Imaging Simulation
    Synthetic Data Generation
    Imaging
Results
    230 GHz
    86–230 GHz Synthesis
Discussions and Conclusions
Acknowledgments
eKVN Sites and Their Partial Participation in the EHT
Effective Angular Resolution
EHT+eKVN towards Sgr A*
References

• Ilje Cho(Korea Astronomy and Space Science Institute, Daejeon 34055, Republic of Korea, Department of Astronomy, Yonsei University, Seoul 03722, Republic of Korea, Instituto de Astrofísica de Andalucía-CSIC, Glorieta de la Astronomía s/n, E-18008 Granada, Spain) Corresponding author
• Jongho Park(School of Space Research, Kyung Hee University, Yongin-si, Gyeonggi-do 17104, Republic of Korea, Institute of Astronomy and Astrophysics, Academia Sinica, Taipei 10617, Taiwan, R. O. C.)
• Do-Young Byun(Korea Astronomy and Space Science Institute, Daejeon 34055, Republic of Korea, University of Science and Technology (UST), Gajeong-ro 217, Yuseong-gu, Daejeon 34113, Republic of Korea)
• Taehyun Jung(Korea Astronomy and Space Science Institute, Daejeon 34055, Republic of Korea)
• Lindy Blackburn(Center for Astrophysics | Harvard & Smithsonian, Cambridge, MA 02138, USA, Black Hole Initiative, Harvard University, Cambridge, MA 02138, USA)
• Freek Roelofs(Department of Astrophysics, Institute for Mathematics, Astrophysics and Particle Physics (IMAPP), Radboud University, 6500 GL Nijmegen, The Netherlands)
• Andrew Chael(Princeton Gravity Initiative, Princeton University, Jadwin Hall, Princeton, NJ 08544, USA)
• Dominic W. Pesce(Center for Astrophysics | Harvard & Smithsonian, Cambridge, MA 02138, USA, Black Hole Initiative, Harvard University, Cambridge, MA 02138, USA)
• Sheperd S. Doeleman(Center for Astrophysics | Harvard & Smithsonian, Cambridge, MA 02138, USA, Black Hole Initiative, Harvard University, Cambridge, MA 02138, USA)
• Sara Issaoun(Center for Astrophysics | Harvard & Smithsonian, Cambridge, MA 02138, USA)
• Jae-Young Kim(Department of Physics, Ulsan National Institute of Science and Technology (UNIST), Ulsan 44919, Republic of Korea, Max Planck Institute for Radio Astronomy, D-53121 Bonn, Germany)
• Junhan Kim(Department of Physics, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, Republic of Korea)
• José L. Gómez(Instituto de Astrofísica de Andalucía-CSIC, Glorieta de la Astronomía s/n, E-18008 Granada, Spain)
• Keiichi Asada(Institute of Astronomy and Astrophysics, Academia Sinica, Taipei 10617, Taiwan, R. O. C.)
• Bong Won Sohn(Korea Astronomy and Space Science Institute, Daejeon 34055, Republic of Korea, University of Science and Technology (UST), Gajeong-ro 217, Yuseong-gu, Daejeon 34113, Republic of Korea)
• Sang-Sung Lee(Korea Astronomy and Space Science Institute, Daejeon 34055, Republic of Korea, University of Science and Technology (UST), Gajeong-ro 217, Yuseong-gu, Daejeon 34113, Republic of Korea)
• Jongsoo Kim(Korea Astronomy and Space Science Institute, Daejeon 34055, Republic of Korea)
• Sascha Trippe(Department of Physics and Astronomy, Seoul National University, Seoul 08826, Republic of Korea, SNU Astronomy Research Center (SNUARC), Seoul National University, Seoul 08826, Republic of Korea)
• Aeree Chung(Department of Astronomy, Yonsei University, Seoul 03722, Republic of Korea)