SCOPE: Sidelobe-Controlled Off-grid Profile Estimation for Multiband Multistatic Target Localization in Upper Mid-Band ISAC Systems

Multiband multistatic integrated sensing and communication (ISAC) in fragmented FR3 bands (7-24 GHz) enables high resolution localization via virtual wideband and spatial diversity. However, frequency anisotropy decorrelates target scattering across non-contiguous bands, while large inter-band frequency gaps generate severe grating lobes that create persistent ghost peaks. We propose sidelobe-controlled off-grid profile estimation (SCOPE), a robust localization algorithm that exploits multi-view consistency across distributed receivers and frequency bands to suppress grating-lobe ambiguities. At the transmitter, an iterative minimax precoder suppresses out-of-region sidelobes to reduce false peaks in the coarse likelihood map. At the receiver, SCOPE employs profile likelihood with Top-K inhibition-based peak selection to avoid trapping in ghost basins, followed by derivative-free off-grid refinement. Simulations demonstrate that SCOPE achieves sub-meter localization with 90% probability at -5 dB SNR and 3 mm root mean square error (RMSE) at 25 dB SNR.