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Phase coding and frequency diversity for weather radars




Kumar, Mohit, author
Chandrasekar, V., advisor
Cheney, Margaret, committee member
James, Susan, committee member
Jayasumana, Anura, committee member

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This thesis has developed three main ideas: 1) Polyphase coding to achieve orthogonality between successive pulses leading to second trip suppression abilities, 2) Frequency diversity on a pulse to pulse basis to achieve second trip suppression and retrieval capability in a weather radar, 3) a multiple input, multiple output (MIMO) configuration using the orthogonality features obtained using ideas in 1 and 2. It is shown in this thesis that this configuration for a radar leads to better spatial resolution by the formation of a bigger virtual array. It is also demonstrated that orthogonality is a big requirement to get this improvement from a MIMO configuration. This thesis addresses this issue with a new polyphase code pair and mismatched filter based framework which gives excellent orthogonal features compared to a matched filter processor. The MIMO platform is a long term goal (technologically) and therefore the polyphase codes were used to demonstrate second trip suppression abilities that uses orthogonal features of these codes to reduce range and velocity ambiguity. These are called as Intra-pulse phase coding techniques. The thesis also demonstrates another technique to achieve orthogonality between pulses by coding them on different frequencies. This is termed as Inter-pulse frequency diversity coding. In the beginning, design and implementation of Intra-pulse polyphase codes and algorithms to generate these codes with good correlation properties are discussed. Next, frequency diversity technique is introduced and compared with other inter-pulse techniques. Other Inter-pulse coding schemes like that based on Chu codes are widely used for second trip suppression or cross-polarization isolation. But here, a novel technique is discussed taking advantage of frequency diverse waveforms. The simulations and tests are accomplished on D3R weather radar system. A new method is described to recover velocity and spectral width due to incoherence in samples from change of frequency pulse to pulse. It is shown that this technique can recover the weather radar moments over a much higher dynamic range of the other trip contamination as compared with the popular systematic phase codes, for second trip suppression and retrieval. For these new features to be incorporated in the D3R radar, it went through upgrade of the IF sections and digital receivers. The NASA dual-frequency, dual-polarization, Doppler radar (D3R) is an important ground validation tool for the global precipitation measurement (GPM) mission's dual-frequency precipitation radar (DPR). It has undergone extensive field trials starting in 2011 and continues to provide observations that enhance our scientific knowledge. This upgrade would enable more research frontiers to be explored with enhanced performance. In the thesis, this upgrade work is also discussed.


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frequency diversity
NASA radar
weather radar
multiple input multiple output
phase coding


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