Analysis of dipole antennas which are integrated on a Si substrate is carried out. Equivalent circuit models of Si integrated dipole antennas are proposed for ultrawideband (UWB) signal transmission in Si substrates. The equivalent circuit parameters are extracted by comparing measurement data and circuit simulation. The equivalent circuit simulation reproduces the transmission characteristics both in frequency and time domains. Attenuation rates of Gaussian monocycle pulses were –1.83 dB/mm for S 21 and –1.37 mV/mm for the Gaussian monocycle pulse.