A coplanar waveguide (CPW) resonator built with a completely coplanar technique on a grounded silicon substrate is discussed. The input impedance is investigated experimentally and numerically. The passive planar structure is extensively studied using a space-domain full-wave analysis method. The resonator is fed by a coplanar transmission line through a capacitive gap and shows a marked resonance at the fundamental coplanar waveguide mode. Calculated and measured data agree to better than 5%.