Ground‐Aware Target‐Range Selection and Field Synthesis for Wideband Cylindrical‐Wave Near‐Field RCS Measurement

ABSTRACT

Sparse vertical arrays can reduce the measurement distance required for cylindrical‐wave near‐field radar cross‐section (RCS) measurement, but their grating lobes may illuminate the target region directly or through conducting‐ground reflection. Therefore, the target distance should be screened before excitation synthesis when the array geometry and measurement site are already fixed. This paper presents a ground‐aware target‐range selection and field‐synthesis workflow for wideband cylindrical‐wave near‐field RCS measurement. Given the element spacing, array‐centre height, operating band, simulated element pattern and conducting‐ground model, direct and mirror‐ground grating‐lobe intervals are mapped into the target‐range domain. To avoid underestimating ground‐reflected risk, the present design uses the geometric exclusion interval conservatively while retaining element‐pattern and ground‐reflection weighting for more general site models. For the considered 21‐element X‐band geometry, the interval construction gives a recommended target distance of approximately 3.0 m. A multiconstraint wideband alternating projection method (MC‐WAPM) is then applied as the postselection shared‐excitation synthesis stage at the selected distance. Multilevel fast multipole method (MLFMM) simulations showed that MC‐WAPM produced a flatter and more phase‐consistent target‐zone field than Baseline APM and Baseline Taylor. The concrete‐ground response remained close to the no‐ground profile and did not change the PEC‐based range recommendation. In the direct sphere‐calibrated RCS comparison, MC‐WAPM yielded pooled five‐frequency MAEs of 1.60 dB for PEC ground and 1.49 dB for concrete ground.