A compact 5‐cm‐diam multipolar electron cyclotron resonance (ECR) ion source is characterized. The source is experimentally studied with no grids using argon gas with 50–250 W of 2.45‐GHz microwave input power. Using a microcoaxial probe it was confirmed that the exciting electromagnetic fields within the resonant cavity were indeed TE111, as expected from the critical cavity dimensions. Double Langmuir probe measurements indicate high densities of about (4–5)×1011/cm3near the source, and 5 cm downstream from the source output the densities become very uniform with a value of about 5×1010/cm3over a 10‐cm diameter. Electron energy distribution functions (EEDF) were measured using a single Langmuir probe. Average electron energies were seen to be about 8–10 eV with an energy distribution function falling between a Maxwellian and a Druyvesteyn distribution. Ion energy distribution functions (IEDF) were measured with a multigrid energy analyzer. It was seen that the distribution functions were narrow and peaked [with a full width half maximum (FWHM) of about 5 eV] except under certain conditions. Above 200‐W input power, and also below about 0.5 mTorr there is significant broadening of the ion distribution function. It is speculated that the former may be caused by gas heating, and the latter may be caused by the presence of Ar+2ions. With its high current densities (≳10 mA/cm2) and low average ion energies (<40 eV), it is expected that this ion/plasma source will be very useful in many etching and deposition applications.