A Space–Time Joint Waveform for Frequency Diverse Array Radar with Spatial Linear Frequency Modulation Weighting

LAN Yu; ZHOU Jianxiong

doi:10.11999/JEIT250561

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LAN Yu, ZHOU Jianxiong. A Space–Time Joint Waveform for Frequency Diverse Array Radar with Spatial Linear Frequency Modulation Weighting[J]. Journal of Electronics & Information Technology. doi: 10.11999/JEIT250561

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LAN Yu, ZHOU Jianxiong. A Space–Time Joint Waveform for Frequency Diverse Array Radar with Spatial Linear Frequency Modulation Weighting[J]. Journal of Electronics & Information Technology. doi: 10.11999/JEIT250561

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A Space–Time Joint Waveform for Frequency Diverse Array Radar with Spatial Linear Frequency Modulation Weighting

doi: 10.11999/JEIT250561 cstr: 32379.14.JEIT250561

LAN Yu,
ZHOU Jianxiong^,

College of Electronic Science and Technology, National University of Defense Technology, Changsha 410073, China

Funds: The National Natural Science Foundation of China(62231026)

Received Date: 2025-06-18
Rev Recd Date: 2025-10-28

Available Online: 2025-10-31

Abstract

Abstract

Objective Frequency Diverse Array (FDA) radar exhibits a fast time-varying beampattern and a space-time coupled steering vector, offering potential advantages for multi-target tracking, wide-area surveillance, and mainlobe interference suppression. However, the beampattern of conventional coherent FDA radar is narrow, resulting in a shorter beam dwell time than that of phased arrays. This limitation prevents the ambiguity function of conventional coherent FDA from achieving both high range resolution and low sidelobe level simultaneously. When the baseband signal is modulated with a Linear Frequency Modulation (LFM) waveform, the ambiguity function presents low range resolution and low sidelobe level. Conversely, when the baseband signal is modulated with a phase-coded waveform, it achieves high range resolution but exhibits high sidelobe levels with strip-like high-gain sidelobes. The degradation in range resolution or sidelobe performance significantly constrains detection capability. To address this problem, this study proposes a novel space-time joint FDA waveform with spatial LFM weighting, which simultaneously achieves high range resolution, low sidelobe level, and reduced Doppler sensitivity. Methods The spatial-domain modulation scheme and the time-domain baseband waveform are two interdependent factors that determine the ambiguity function performance of FDA radar. Selecting a time-domain baseband waveform with a thumbtack-shaped ambiguity function enables the range resolution to remain independent of space-time coupling. By modulating the spatial weighting phase, the beampattern shape of the FDA can be adjusted to extend beam dwell time, suppress strip-like high-gain sidelobes, and smooth sidelobe energy distribution. The proposed space-time joint waveform thus achieves both high range resolution and low sidelobe level. Doppler tolerance is another key metric for evaluating ambiguity function performance. A space-time joint waveform with spatial phase-coded weighting exhibits high Doppler sensitivity, leading to significantly elevated sidelobe levels and sharp reductions in transmit beamforming gain. In contrast, the spatial LFM weighting method proposed in this study enhances Doppler tolerance while maintaining desirable range and sidelobe characteristics. Results and Discussions By combining the spatial LFM weighting method with a time-domain baseband waveform exhibiting a thumbtack-shaped ambiguity function (e.g., a phase-coded waveform), this study addresses the limitation of conventional coherent FDA waveforms, which cannot simultaneously achieve high range resolution and low sidelobe level. The proposed waveform demonstrates robust pulse compression performance, even under target motion. Simulation experiments were conducted to analyze the ambiguity functions under both stationary and motion conditions, and the results are summarized as follows: (1) The average sidelobe levels near the target peak for the space-time joint FDA waveform with spatial LFM weighting and spatial phase-coded weighting are both approximately –30 dB (Fig.3(a)–(b)). In comparison, the average sidelobe level near the target peak for the spatial phase-coded weighting FDA using a time-domain LFM baseband waveform is about –20 dB (Fig.3(c)), while that of the coherent FDA with a time-domain phase-coded waveform is about –12 dB (Fig.3(d)). Thus, the two space-time joint FDA waveforms achieve the lowest average sidelobe levels. (2) The imaging results of both space-time joint FDA waveforms show no strip-like high-gain sidelobes (Fig.4(a)–(b)). By contrast, the spatial phase-coded weighting FDA and the coherent FDA with a time-domain phase-coded waveform both display prominent high-gain sidelobes (Fig.4(c)–(d)). These sidelobes from high Signal-to-Noise Ratio (SNR) targets can obscure nearby low-SNR targets. (3) All four FDA waveforms achieve a range resolution of 0.75 m (Fig. 5), corresponding to a bandwidth of 200 MHz. (4) Under motion conditions, the space-time joint FDA waveform with spatial phase-coded weighting exhibits a notable increase in peak sidelobe level compared with stationary conditions (Fig. 6(a)). In contrast, the space-time joint FDA waveform with spatial LFM weighting maintains the lowest peak sidelobe level among all four FDA configurations (Fig. 6(b)). Conclusions This study proposes a space-time joint FDA waveform with spatial LFM weighting. The proposed waveform effectively resolves the issue of degraded range resolution in conventional coherent FDA systems, ensuring that range resolution depends solely on bandwidth. It also eliminates the strip-like high-gain sidelobes commonly observed in conventional FDA waveforms. Under simulation conditions, the average sidelobe level near the target peak is reduced by approximately 10 dB and 18 dB compared with those of the spatial phase-coded weighting FDA and the coherent FDA with a time-domain phase-coded waveform, respectively. This reduction substantially mitigates the masking of low-SNR targets by sidelobes from high-SNR targets and demonstrates strong Doppler tolerance. However, under relative motion conditions, the proposed waveform exhibits Doppler-angle coupling, which will be addressed in future research through the development of coupling mitigation strategies.
- Frequency Diverse Array (FDA),
- Spatial Linear Frequency Modulation (LFM) weighting,
- Sidelobe level

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References(23)

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