  A generic modular array architecture is proposed, featuring
uniform/non-uniform subarray layouts that allows for flexible deployment. The
bistatic near-field sensing system is considered, where the target is located
in the near-field of the whole modular array and the far-field of each
subarray. Then, the closed-form expressions of Cramer-Rao bounds (CRBs) for
range and angle estimations are derived based on the hybrid spherical and
planar wave model (HSPM). Simulation results validate the accuracy of the
derived closed-form CRBs and demonstrate that: i) The HSPM with varying angles
of arrival (AoAs) between subarrays can reduce the CRB for range estimation
compared to the traditional HSPM with shared AoA; and ii) The proposed generic
modular architecture with subarrays positioned closer to the edges can
significantly reduce the CRBs compared to the traditional modular architecture
with uniform subarray layout, when the array aperture is fixed.
