Unmanned aerial vehicles (UAVs) can be exploited to provide emergency coverage in disasters, due to its mobility and flexibility. In this paper, we propose multi-antenna precoding design and multi-hop device-to-device (D2D) communication to guarantee the reliable transmission and extend the UAV coverage for downlink in disasters. Firstly, multi-hop D2D links are established to extend the coverage of UAV emergency networks with limited transmit power. In particular, a shortest-path-routing algorithm is proposed to establish the D2D links rapidly with minimum nodes, with closed-form solutions for the number of hops derived. Secondly, the precoding design for the UAV downlink is studied, to optimize the performance of UAV transmission. Due to the non-convexity of the problem, a second-order-cone programming based algorithm is proposed to solve it efficiently. Simulation results show the effectiveness of the proposed schemes for UAV coverage in disasters.