“Pentek's Cobalt® Model 71621 was selected as the SDR interface because it is well suited to the radar's requirements, providing three A/D converters and a dual-channel 800 MHz D/A converter,” said Mr. Dane du Plessis, member of the system integration team for NeXtRAD.
NeXtRAD is a multi-sensor network comprised of three stations (or nodes) separated by several hundred meters, all focusing on a common target area. The system requires a usable bandwidth of 50 MHz to achieve a range resolution of three meters. Each node has dual-polarized L- and X-band antennas (IEEE definition) with a 10-degree beamwidth.
This arrangement effectively forms a pair of bistatic radars in combination with a monostatic radar, which means that target data can be simultaneously acquired from three perspectives. This topology has advantages over single-sensor radars. NeXtRAD is a more capable version of NetRAD, a single-frequency multistatic radar developed by UCT and UCL.
NeXtRAD requires that waveform generation and digitization be fully coherent at each node. To achieve coherency, each node is supplied a very stable 10 MHz reference signal from a local GPS-disciplined oscillator (GPSDO), which is distributed via a frequency distribution unit (FDU) to the Cobalt module and to the receiver exciter (REX). This ensures that there is no phase drift between oscillators in a given node and that the relative phase of oscillators between any two nodes is constant.