The Langmuir probe measurements were carried out in a planar rf discharge of N-2 and Ar gases. The dc characteristic I-U curves are calculated from the measured rf characteristic I-U curves for frequencies 10-60 MHz. The measured parameters such as electron temperature and electron density are compared with the simulated results. At gas pressures 10-40 Pa, the sheath thickness at the powered electrode was proportional to f(-0.5) for simulation and f(-2/3) by using the electrical parameters of the probe measurements and to p(-0.5) for both cases. (C) 2009 Elsevier B.V. All rights reserved.