Simulation of Post-ADC Digital Beam-Forming for Large Area Radar Receiver Arrays

In order to provide instantaneous three-dimensional radar measurements spanning the entire vertical extent of the ionosphere, the planned EIS-CAT_3D incoherent scatter radar system includes multiple receive-only antenna arrays, situated at 90-280 km from the main transmit/receive site. These employs band-pass sampling at 80 MHz, with the input signal spectrum contained in the 6^th Nyquist zone. This paper presents simulations and methods used to investigate use of a post-ADC fractional-sample-delay (FSD) system necessary to perform true time-delay beam-forming. To test the feasibility and limitations of the system an extensive simulation tool has been developed. The simulation system is implemented in Matlab to provide cross-platform compatibility and can be applied to any similar system. Performance degrading aspects such as noise, jitter, bandwidth and resolution can be included in the simulations. The use of FIR-filters in the base-band of a band-pass sampled signal to apply true time-delay beam-forming is shown to be feasible