A new analytical model of air-to-ground (A2G) channel between a low altitude unmanned aerial vehicle (UAV) and a mobile station is derived. It is proposed for the dense urban environment at frequencies of (1, 2 and 5.8) GHz. The model terms are determined on the basis of ray-tracing simulation analysis for A2G channel and knife-edge diffraction theory. The model is compared with the other A2G model and shows better results of standard error and confidence interval validation. Furthermore, the effects of changing the frequency and UAV height on path loss and probability of line of sight are discussed. Therefore, the proposed model provides a simple and good estimation compared to the complicity of ray-tracing simulation.