  Electronic Whispering Gallery Modes (EWGMs) have been recently observed in
several circular graphene junctions, pn and pp0, created in scanning tunnelling
microscope experiments. By computing the local density of states within the
Dirac-Weyl formalism for massless fermions we demonstrate that the EWGMs may
really be emerged in any type of the electrostatic potential induced circular
graphene junctions, including uni-junctions (e.g. np- or pp0-junctions) as well
as bipolar-junctions (e.g. pnp-heterojunctions). Surprisingly, quantitative
analyses show that for all the EWGMs identified (regardless of junction types)
the quality (Q) factors seem to be smaller than 100, very small compared to
those in ordinary optical whispering gallery modes microresonators, while the
corresponding mode radii may tunably be in nanometer-scale. Our theoretical
results are in good agreement with existent experimental data, putting a
question to the application potential of the EWGMs identified.
