In this paper, we firstly construct a wide-band undersampling array, then present a novel frequency and

direction of arrival (DOA) estimation method for a very wide frequency band (2-18GHz). Choosing a set

of appropriate sampling frequencies and antenna spacing, the method can provide unambiguous frequency

and DOA estimation under the sub-Nyquist spatio-temporal sampling. The proposed method can reduce

the computational complexity as it does not need the 2-D spectral peak search and high-dimensional

eigen decomposition. In addition, the proposed method uses the temporal filtering to cascade the

frequency estimation and DOA estimation so that the DOA estimation results are automatically paired

with corresponding frequency. Simulation results demonstrate the effectiveness of the novel method.