The phenomenology of sub-THz radar sea clutter

Abstract

This thesis presents the design and development of a new 201 GHz / 207 GHz frequency modulated continuous wave (FMCW) Doppler radar, 'Theseus', for environmental sensing and the measurement of targets, and shows the results of measurements made by this radar of low grazing angle sea clutter. The development of the radar and the measurement of sub-THz sea clutter was motivated by the future sensing needs of marine autonomy.

The design process for the Theseus radar is described, where each radar subsystem is characterised separately, along with the characterisation of the instrument as a whole. The range calibration matches modelled results well, the average difference being -1.66 dB at 201 GHz and -1.61 dB at 207 GHz. The noise floor is measured to be ~-74 dBm between 30 to 120 m. An improvement to the instrument noise floor due to a reduction in transmitter phase noise is demonstrated.

Sea clutter measurements made at a wave tank are then analysed: first qualitatively alongside coincident video; and then quantitatively with both the distribution of amplitude values and the mean σ0 being examined. The key results are: vertical-vertical polarisation (VV) returns initially increase and then plateau with wave height; between grazing angles γ = 5° and γ = 8°, backscatter intensity increases by >15 dB in both polarisations; horizontal-horizontal polarisation (HH) returns are greater than VV returns by ~10 dB; and where in general, the mean σ⁰ between γ = 5° and γ = 8° is -20 to 0 dB, and similar to published results at W-band. The amplitude distributions tend to become longer-tailed with the same trends as increasing backscatter, and in general are much longer-tailed than results at lower frequencies.