We performed an experimental investigation on the electromagnetic effect and the plasma radial uniformity in a larger-area,cylindrical capacitively coupled plasma reactor.By utilizing a floating hairpin probe,dependences of the plasma radial density on the driving frequency and the radio-frequency power over a wide pressure range of 5-40 Pa were presented.At a relatively low frequency(LF,e.g.27 MHz),an evident peak generally appears near the electrode edge for all pressures investigated here due to the edge field effect,while at a very high frequency(VHF,e.g.60 or 100 MHz),the plasma density shows a sharp peak at the discharge center at lower pressures,indicating a strong standing wave effect.As the RF power increases,the center-peak structure of plasma density becomes more evident.With increasing the pressure,the standing wave effect is gradually overwhelmed by the'stop band'effect,resulting in a transition in the plasma density profile from a central peak to an edge peak.To improve the plasma radial uniformity,a LF source is introduced into the VHF plasma by balancing the standing wave effect with the edge effect.A much better plasma uniformity can be obtained if one chooses appropriate LF powers,pressures and other corresponding discharge parameters.