  We present the results of Very Long Baseline Interferometry (VLBI)
observations using the phase reference technique to detect weak Active Galactic
Nuclei (AGN) cores in the Virgo cluster. Our observations were carried out
using the Korean VLBI Network (KVN). We have selected eight representative
radio galaxies, seven Virgo cluster members and one galaxy (NGC 4261) that is
likely to be in the background. The selected galaxies are located in a range of
density regions showing various morphology in 1.4 GHz continuum. Since half of
our targets are too weak to be detected at K-band we applied a phase
referencing technique to extend the source integration time by calibrating
atmospheric phase fluctuations. We discuss the results of the phase referencing
method at high frequency observations and we compare them with self-calibration
on the relatively bright AGNs, such as M87, M84 and NGC 4261. In this
manuscript we present the radio intensity maps at 22 GHz of the Virgo cluster
sample while we demonstrate for first time the capability of KVN phase
referencing technique.
