94GHz Radar for civilian structure monitoring
This is an experimental 94 GHz (W-Band) CW-FM Radar that can be configured as a Ground Based SAR for high resolution imaging and interferometry. Several experimental campaigns have been carried out to assess the capability of the system to remotely observe submillimetric deformation and vibration in infrastructures. Several ground based synthetic aperture radars (GBSAR) systems can be found in the literature proposing them for terrain stability control and infrastructure monitoring. Most of these systems operate in the range of 5 to 20 GHz providing accurate interferometric deformation data at short to medium distances up to few kilometers. CW-FM homodyne configurations are particularly suitable for high resolution and low power operation reducing the bandwidth requirements of the echo signal acquisition. The availability of moderate cost components at millimetric Bands have allowed to extend the frequency operation of these CW-FM systems up to W-Band and above.
In this experiment, a Ground Based Synthetic Aperture Radar working at 94 GHz with a 1.5 GHz bandwidth is designed, mainly for short range high resolution imaging and interferometric deformation control. Several outdoor experimental campaigns have been carried out to assess the system potential applications in infrastructure stability control.
The main components of the instrument is a CW-FM coherent radar operating at 94 GHz, an echo signal acquisition subsystem based on a PXI modular digitizer, a linear positioner unit used to control the radar movement along the synthetic aperture, and several support subsystems including power supply, waveform and position synchronisms, etc.
To obtain high resolution images the radar can be configured in a synthetic aperture mode by using a linear positioner.
The characterization of the system stability over time was a priority, taking into account the large wave number at 94 GHz resulting in a strong phase change induced by small thermal drift of active and passive components
The capability to measure infrastructure deformation was also tested in an additional experiment consisting on an interferometric change assessment of a railway bridge during train passages in Monistrol de Montserrat as depicted in the figure. The location of the radar close to the lower bridge structure can be observed. To speed up the measurements the radar was configured in High Resolution Range profiler mode by keeping the position of the radar stable during the measurements.Taking the first acquisition as phase reference, a series of 1D range interferograms were obtained showing the spatial and temporal evolution of the bridge deformation.
The following videos show the train passing on the bridge above the C-55 highway and the displacement along the bridge of different points due to the effect of the train passing on it. The Y-axis span is on the order of mm.