Automatic target recognition (ATR) in target search phase is very challenging because the target range and mobility are not yet perfectly known, which results in delay-doppler uncertainty. In this paper, we firstly perform some theoretical studies on radar sensor network (RSN) design based linear frequency modulation (LFM) waveform: (1) the conditions for waveform co-existence, (2) interferences among waveforms in RSN, (3) waveform diversity in RSN. Then we apply RSN to ATR with delay-doppler uncertainty and propose maximum-likekihood (ML) ATR algorithms for fluctuating target and nonfluctuating target. Simulation results show that our RSN vastly reduces the ATR error comparing to a single radar system in ATR with delay-doppler uncertainty.