In this article, a dual band patch antenna is achieved by introducing T-slot in circular disk with small frequency ratio. It is theoretically investigated using equivalent circuit theory concept. The resonance frequency is found to be 1.84 and 2.02 GHz suitable for DCS-1800, PCS-1900 and IMT-2000 The measured bandwidths at lower and upper resonances are found to be 6.59% and 6.89% respectively for proposed antenna specifications. The effect of slots dimension in the patch is studied. The frequency ratio is found to be 1.09. The maximum gain of the proposed antenna is found to be 6.52 dBi whereas efficiency is found to be 62.17% and 76.42% at lower and upper resonance frequencies respectively. The theoretical results are compared with simulated and measured results and they are in good agreement.