Long Term Evolution (LTE) is a new type of illuminators of opportunity for passive radars, with the advantages of broad bandwidth, high coverage, and strong generality. In this paper, the ambiguity function of Frequency Division Duplexing Long Term Evolution (FDD-LTE) signal is analyzed as an illuminator of opportunity. According to the measured signal, it was found that it is necessary to suppress the inter-frame ambiguity strips in the ambiguity function. Furthermore, themechanism of these inter-frame ambiguity strips was analyzed in detail, which revealed that the LTE signal frame structure is the main factor that causes these inter-frame ambiguity strips and is the major energy source of coherent integration. Thus, a method based on Orthogonal Frequency Division Multiplexing (OFDM) symbol subcarrier coefficient normalization is proposed to suppress these inter-frame ambiguity strips. Simulation and experimental results show that the method can suppress inter-frame ambiguity strips effectively, but does not affect coherent integration, which is the foundation of target detection.