Plane-of-Interest Metrics-Guided Flexible Near-Field Sensor for Wrist-Worn Self-Injection-Locked Radar

Wearable self-injection-locked (SIL) radar requires near-field sensors that preserve injection coupling at a millimeter-scale gap under bending and placement variations. This letter introduces plane-of-interest metrics, including uniform-field coverage (UFC), relative standard deviation (RSD), and bending robustness factor ρ_A, to guide robustness-oriented design of ultra-thin flexible near-field sensor for 5.8-GHz SIL wrist sensing, and demonstrates the workflow with a slot-type implementation on polyimide. Full-wave results show that slot-type implementation maintains a strong and spatially uniform field distribution on the plane of interest under wrist-like curvature. System measurements across multiple bending radii and alignment offsets on the same SIL radar platform confirm a robustness trend consistent with the ρ_A ranking. 

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