Concentric circles and spiral configurations for large correlator arrays in radio astronomy

Aperture synthesis arrays are commonly used in radio astronomy to take images of radio point sources, with the planned Square Kilometre Array (SKA) being the most common example. One approach to enhancing the quality of the images is to optimize an antenna array configuration in a possible SKA implementation. An ideal arrangement must ensure optimal configurations to capture a clear image by either decreasing the sidelobe level (SLL) in the l-m domain or increasing the sampled data in the spatial-frequency domain. In this paper a novel configuration is considered to optimize the array by considering all possible observation situations through the positions of the antenna array elements via a mathematical model that we call geometrical method (GM). To demonstrate its efficiency, the technique is applied to developing an optimal configuration for the elements of the Giant Metrewave Radio Telescope (GMRT). The effect of these changes, particularly in the forms of circular and spiral arrangements, is discussed. It is found that a spiral configuration results in fewer overlapping samples than the number of antennas placed along three arms of the GMRT with fewer than 11% and 27% overlapping samples in the snapshot and 6 hr tracking observations, respectively. Finally, the spiral configuration reduces the first SLL from -13.01 dB, using the arms of the current GMRT configuration, to - 15.64 dB.Web of Science1564art. no. 17

Expansion of a Y-shaped array antennas for radio astronomy

Observing celestial objects is common in radio astronomy. The Giant Meterwave Radio Telescope (GMRT) is one of the world's latest telescopes of its kind. The aim of this paper is to extend the number of array antennas and optimize configurations by changing the position of antennas for getting low sidelobes and high u-v plane coverage. Initially, the expansion along three arms configuration was studied and then expanding it to spiral shape. The results show about 98.5 percents less coverage of GMRT without expansion compare to the extended GMRT. The spiral expanded shows ability to cover the u-v plane more than expansion in three arms by sixteen percents

Interferometric array planning using division algorithm for radio astronomy applications

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

The Spatial Correlation of a Multiple-Input Multiple-Output and Channel Model using Huygens-Fresnel Principle for Underwater Acoustic

In this work, the spatial correlation of a multiple-input multiple-output (MIMO) for underwater acoustic (UWA) channel is modelled. To obtain the spatial correlation for such a channel, a mathematical method to model the effect of the surface on the acoustic propagation is studied. The sea surface has a significant impact on the underwater acoustic propagation (UWA) channel since the sound field is scattered, particularly in rough sea conditions. In a situation where the sea surface is calm, the reflection is specular. In contrast, a sea surface subject to high sea states generates scattered waves. In these conditions, more complex mathematical equations are required to model the propagation. Current analytical models have limitations in terms of complexity and are not practical. Therefore, this study aims to consider a specular reflection to model the time-varying sea surface on the UWA channel. It is a simple model with low computationally complexity and can be used to assess the performance of UWA communications. Specifically, the specular reflection and transmission of an acoustic wave at a calm sea surface is studied, using the Huygens-Fresnel principle and the superposition theorem. The analytical model is developed using physical oceanic parameters representing the sea conditions. The results show a good agreement with the experimental analysis

Optimization of an antenna array using genetic algorithms

An array of antennas is usually used in long distance communication. The observation of celestial objects necessitates a large array of antennas, such as the Giant Metrewave Radio Telescope (GMRT). Optimizing this kind of array is very important when observing a high performance system. The genetic algorithm (GA) is an optimization solution for these kinds of problems that reconfigures the position of antennas to increase the u-v coverage plane or decrease the sidelobe levels (SLLs). This paper presents how to optimize a correlator antenna array using the GA. A brief explanation about the GA and operators used in this paper (mutation and crossover) is provided. Then, the results of optimization are discussed. The results show that the GA provides efficient and optimum solutions among a pool of candidate solutions in order to achieve the desired array performance for the purposes of radio astronomy. The proposed algorithm is able to distribute the u-v plane more efficiently than GMRT with a more than 95% distribution ratio at snapshot, and to fill the u-v plane from a 20% to more than 68% filling ratio as the number of generations increases in the hour tracking observations. Finally, the algorithm is able to reduce the SLL to –21.75 dB