This map illustrates the global distribution of telescopes equipped with K-band receivers, either currently operational or under development. Telescopes that have actively contributed to K-CRF observations are shown in blue markers, representing the core of the K-band Celestial Reference Frame (K-CRF) network. The Very Long Baseline Array (VLBA) sessions, consisting of ten 25-m antennas (VLBA-BR, HN, FD, KP, LA, MK, NL, OV, PT, SC), account for the majority of K-CRF observations, contributing approximately 92% of the data through the U.S. Naval Observatory's 50% timeshare allocation. Weekly K-band observations commenced in September 2023, utilizing a diverse network of telescopes, including the Korean VLBI Network (KVN) 22-meter antennas (Ky, Ku, Kt), the 26-meter Hartebeesthoek (HartRAO) antenna (Hh) located in South Africa, the 22-meter Mopra antenna (Mp) in Australia, the 20-meter Sejong geodetic antenna (Kv) in Korea, the 26-meter Hobart antenna (Ho) in Australia, and the 40-meter Yebes antenna (Yb) in Spain. Additionally, the Tianma 64-meter antenna (T6) in China and the Tidbinbilla 70-meter antenna (DSS43/Ti) in Australia have previously participated in selected K-band sessions.

Green markers indicate additional K-band-capable telescopes in the European VLBI Network (EVN), which have demonstrated readiness for K-CRF operations. The EVN has already participated in K-band geodetic and imaging experiments, including work by Gomez et al., 2021 and Charlot et al., 2023). In 2024, global K-band sessions involving more than 20 telescopes across the EVN, VLBA, and Southern Hemisphere were initiated, significantly expanding the geographical and technical coverage of the K-CRF effort. 

Red markers denote Long Baseline Array (LBA) antennas in Australia that are equipped with K-band receivers. A notable early southern campaign was conducted in July 2020 using five Australian stations—ATCA, Ceduna, Hobart26, Mopra, and Parkes—along with Hartebeesthoek (South Africa) and Sejong (South Korea). 

Orange markers represent telescopes with developing or potential K-band capability, indicating future contributors to the expanding global K-CRF network.