Report on the 2018 Trials of the Multistatic NeXtRAD Dual Band Polarimetric Radar

Abstract

NeXtRAD is a polarimetric, L and X Band, multistatic (three nodes), pulse Doppler radar, developed by UCT and UCL, as a follow on to the NetRAD sensor. This paper reports on the trials carried out in 2018, mostly in Simon's Bay, South Africa. The sensors (one active, two passive) are connected by WiFi communications link, with a maximum separation of 40 km. Practically, results are reported with 8 km maximum baselines. The focus is on targets in sea clutter and micro-Doppler. We report on the final integration and test of the system command and control system that allows for scheduling of measurement and recording of bursts of pulses, as well as video of the radar field of view. Some innovations have been made in terms of digital hardware, firmware, and high performance computing technology. The system is synchronised with the UCT GPS Disciplined Oscillators (one per node), but we also report on bistatic measurements with White Rabbit, fibre timing system, as well as the consequences of GPS failure (GPS Denied Environment).

Multistatic radar synchronisation using COTS GPS disciplined oscillators

“…A radar synchronisation system has been developed to clock and trigger three radar systems, namely, the bladeRAD hybrid radar system [15], the ARESTOR multi-role RF system [16], and the NeXtRAD radar system [4]. The GPSDOs alone, described in the previous section, cannot be used to clock and trigger the radars; instead, a system is needed to derive a common trigger signal, provide network control of GPSDOs, and translate the GPSDO frequency reference to meet the input requirements of each radar system.…”

“…The works by Sandenbergh et al provide key references of experimental results within the recent literature on GPSDO based networked radar synchronisation [1,2,3]. In these papers, three identical quartz-based GPSDOs were designed to provide an alternative to physical synchronisation cables for the NetRAD [1] and NeXtRAD [4] multistatic radar systems. Comparatively, the paper instead investigates the use of two different COTS GPSDOs that use differing LO technologies, namely, double oven-controlled crystal oscillators (OCXO) versus Rubidium oscillators.…”

Multistatic Radar Measurements of UAVs at X-band and L-band

“…NeXtRAD is a coherent multistatic pulsed radar system consisting of three individual nodes, one transceiver and two identical passive receivers. The radar operates at two bands 8.5GHz (X-band) and 1.3GHz (L-band) at a power of 400 W and 1.6 kW respectively [11]. Each node has three ADC channels in total, one L-band and two X-band.…”

“…Dual X-band channels permit simultaneous dual-polarised measurements. Whereas, only single polarised L-band measurements are possible, due to the current system configuration requiring manual polarisation changes [11]. GPS Disciplined Quartz Crystal Oscillators (GPSDOs) are used to provide both phase and temporal synchronisation across the spatially separated nodes.…”

“…As discussed in Section II the NeXtRAD system is capable of capturing dual polarised X-band measurements, or fully polarimetric measurements when HH HV and VV VH are captured on alternating pulses [11]. During the trials the radar was used with a Horizonal transmission polarization to aid detection of the UAV's propeller micro-Doppler.…”