Ultra wideband (UWB) technology has been widely researched for both radar and communication systems. However, detecting the presence of a signal is essential and challenging for many applications. In this paper, we propose a novel detector for UWB radar signals with UWB communication interference by exploiting the signal cyclic features. A single-cycle detector based on fundamental cyclic frequency of radar signal is proposed to detect UWB radar signal. Simulation results illustrate the possibility to detect the UWB radar signal under the coexistence of a UWB communication signal and the proposed scheme is compared with conventional detectors for UWB radar systems.