Coherent frequency diverse array (FDA) radar is able to cover all directions with a stable gain by transmitting a single frequency-shifted waveform. However, it is revealed in this work that the range resolution scales linearly with the number of elements, which is limited by the fixed element number. By leveraging the relationship between the beam direction and the signal frequency, we link the sub-bands of the emitted signal to angular sectors. Based on the fact, a novel transmit diversity technique, referred to as two-dimensional (2-D) space-time coding (STC), is proposed to improve the range resolution. For a specific observation direction, the frequency band of each pulse is shifted by STC to synthesize a full bandwidth after the pulse accumulation. Furthermore, the piecewise LFM (linear frequency modulation) waveform design can be combined with the STC technique to synthesize the transmit beampattern flexibly without range resolution degradation for each pulse. Compared with the state-of-the-art technologies, the proposed STC technique has superiorities in range resolution improvement, ultra-low range sidelobe level, interference suppression, and beampattern design capability. In addition, multi-dimensional ambiguity functions are derived to assess the performance in range-angle-Doppler domain, including the range and angle resolutions, the sidelobe level (SLL) and the angular coverage. To satisfy practical demands, the general receive processing procedures are also designed. The proposed method and corresponding theoretical analysis are verified by extensive numerical results.

中文翻译：

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相干频率分集阵列空时编码技术


相干频率多样化阵列（FDA）雷达能够通过发射单个频移波形以稳定的增益覆盖所有方向。然而，这项工作表明，距离分辨率与元素数量成线性比例，而元素数量受到固定元素数量的限制。通过利用波束方向和信号频率之间的关系，我们将发射信号的子带链接到角扇区。基于此，提出了一种称为二维（2-D）空时编码（STC）的新型发射分集技术来提高距离分辨率。对于特定的观察方向，每个脉冲的频带经过STC偏移，在脉冲累积后合成全带宽。此外，分段LFM（线性频率调制）波形设计可以与STC技术相结合，灵活地合成发射波束图，而不会降低每个脉冲的距离分辨率。与现有技术相比，所提出的STC技术在距离分辨率提高、超低距离旁瓣电平、干扰抑制和波束方向图设计能力方面具有优势。此外，还导出了多维模糊度函数来评估距离-角度-多普勒域的性能，包括距离和角度分辨率、旁瓣电平（SLL）和角度覆盖。为了满足实际需要，还设计了通用的接收处理流程。所提出的方法和相应的理论分析通过大量的数值结果得到了验证。