Interferometric array planning using division algorithm for radio astronomy applications

• Main Author: Kiehbadroudinezhad, Shahideh
• Format: Thesis
• Language: English
• Published: 2017
• Online Access: http://psasir.upm.edu.my/id/eprint/70200/1/FK%202017%20114%20-%20IR.pdf; http://psasir.upm.edu.my/id/eprint/70200/
• Institution: Universiti Putra Malaysia

In order to measure the fine angular detail in the radio frequency range from the sky, two-element interferometers which form radio interferometers and synthesis array are utilized. The angular resolution of a single telescope does not provide sufficient information for astronomy applications, therefore a synthesis array or radio interferometers is used to fulfil the aim of the end users. The light waves from very distant stars or galaxies take a long time to travel through space to our telescopes; therefore it makes limitation to astronomers to visually observe light waves in time. They are seen as they were a very long time ago. This issue leads astronomers to build more powerful telescopes to visually recognize the first stars and galaxies formed. In terms of existing correlator array antenna like the Giant Metrewave Radio Telescope (GMRT), expansion of the array is required to obtain higher resolution. A project of the Square Kilometre Array (SKA), which involves more than ten countries worldwide, is the most powerful radio telescopes array to date. It will observe the blue sky and produce images from radio waves with very high resolution. However, the position of the telescope limits the image quality and has a direct effect on the sidelobe levels (SLLs). In this thesis, we focus on the design procedure of algorithms and new methods of a correlator antenna array in radio frequency. It includes the process of designing the proposed algorithm and methods assisted interferometric, and how it can be implemented in a correlator antenna array and SKA scenario. The ability of the proposed receiver to suppress the severe effect of the SLL, increasing the u-v plane coverage, and smoothening out the linear ridges in u-v plane coverage at snapshot or low duration of observation is demonstrated through simulation. The algorithms and methods were developed using Matrix Laboratory (Matlab) software, and the proposed position of the array was evaluated using Astronomical Image Processing System (AIPS) software. This proposed method can be used as an application for astronomy projects such as SKA. This application lets the scientists to observe the sky according to the suggested configurations with the optimum enhanced image. New Zealand, Australia and 8 other African countries are involved with this project. It would be useful for Malaysia to be involved in this project in the context of astronomical observation. In this thesis we also propose a new theory of localization an array of antennas for astronomy applications to suppress the side lobe levels and/or increase the samples in uv plane coverage. The proposed methods optimize the data samples and minimize the side lobe levels in the angular domain to enhance the image quality as much as possible in addition to smoothen the linear ridges. The first method uses the optimization of the array configuration problem with various changes of coordinates in a specific area with GMRT's arms as an illustrative example. The results show that spiral configurations give very good results in both aspects of u-v plane and side lobes. It is found that a spiral configuration result in less overlapped samples in both snapshot and hour-tracking observations than the antennas placed along three arms of the GMRT with 21.98% and 34.84% of overlapped samples at the snapshot and the hour-tracking observations, respectively. Using the arms of current GMRT configuration the spiral configuration reduces the first side lobe from -13.01 dB to -15.64 dB and the 5-arm spiral configuration has the minimum value of the first three side lobes and the peak side lobe of -17.68 dB and -11.64 dB, respectively. In the second scheme, a genetic algorithm is developed, in order to optimize a correlator array of antennas by using Genetic Algorithm (GA). The algorithm is able to distribute the u-v plane more efficiently than GMRT with 49.77% overlapped samples. The calculated parameter of the overlapped samples for hour-tracking varies from 74.12% for GMRT, to 58.46 % for 25th generation configuration, and 53.36% 150th generation configurations. Finally, the algorithm is able to reduce SLL to -25.23 dB. The third method develops a new algorithm named Division Algorithm (DA) to solve the optimization problems. The parameter of overlapped samples is valued at 50.11% compared to the GA (53.36%) for 6-hour tracking observation. The values of the first SLL, mean values of the first three SLLs, and peak SLL are -25.23 dB, -23.07 dB, and -21.74 in 150th generation using GA and -31.55 dB, -25.42 dB, and -22.14 dB in DA array, respectively. It shows that the DA outperforms SLL in decreasing the SLL. The above methods are expanded to extend the interferometric array to investigate the feasibility of extending the interferometric array and 10 numbers of antennas that would be deployed in Malaysia.