Ardeshir Tanha, M; (2016) Phased Array Antenna for Geophysical FMCW Radar. Doctoral thesis , UCL (University College London).

Abstract

Snow avalanche is a significant threat to human and infrastructures. Therefore, by risk assessment of the areas which are prone to avalanche based on the statistical analysis, the avalanche risk zones can be calculated. Radar, as a remote sensing tool, has been used extensively to characterise and monitor the dynamics of snow avalanches. Having such data, it is possible to mathematically model snow avalanches. There are other different types of techniques such as video imaging and using seismic sensors to extract snow avalanche dynamics. However, the former cannot be used during the night and latter cannot be used to detect the avalanche outer layers as these types of sensors are usually buried under the track of the avalanche in the ground. Therefore, the radar is one of the best techniques which can be utilised for avalanche imaging applications. The avalanche models can be used to evaluate and identify avalanche risk zones and gather statistical data. However, previously developed radar systems cannot provide accurate representations of the flow of snow avalanches due to their inadequate range and cross-range resolution and high antenna sidelobe levels. For this application an antenna with beam steering capability was required to be able to illuminate the entire flow of the avalanche such as phased array antenna. This thesis presents the design and development of an advanced phased array FMCW radar receiver front-end, allowing the provision of high resolution two dimensional images of snow avalanches. The phased array antenna is a fully populated uniformly spaced spatial anti-alias filter with ± 14.5◦ azimuth beamwidth, 14.4dBi gain and -20.3 dB sidelobe level. The sub arraying overlapping technique is used to eliminate the grating lobes. The design of the radiating elements of this phased array antenna is also presented in detail based on an extensive review of the existing literature. Moreover, the design of the power distribution network of the phased array, constituted of a unique and novel set of power dividers used to reduce the phased array sidelobe level, is discussed. Also, the phased array antenna prototype fabrication steps and the ensuing measurements in anechoic chamber are thoroughly explained. The phased array FMCW radar operating frequency is 5.3 GHz with 200 MHz bandwidth. The FMCW radar maximum range is 2500m with 0.75m range resolution. The receiver chain of the phased array FMCW radar consists of several stages of amplification, filtering, mixing and deramping with approximately 30dB gain, placed at the same antenna PCB board for an improved sensitivity compared to the previous existing radar systems. The phased array FMCW radar signal processing algorithms to produce an image of the snow avalanche, both off-line and in real-time are presented. The off-line signal processing was performed on the stored data recorded by the radar in Matlab and the the real-time signal processing was implemented on an FPGA. The real-time signal processing of the snow avalanche performed on synthetic data is presented and the results are compared to Matlab results to validate the techniques and algorithms. The real-time signal processing of the snow avalanche enables geo-physicists to develop a technique to predict the behaviour of snow avalanches by monitoring different features of their flow in real-time. The developed phased array FMCW radar is now installed at the avalanche test site in Switzerland. The preliminary measurements of the radar system on a moving car validate that the system can potentially produce high resolution images of snow avalanches.

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