Side Lobe Reduction in Equally Spaced Linear Antenna Arrays using Antenna Thinning Technique
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Date
2023-11-22
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Addis Ababa University
Abstract
In antenna array design, the radiation pattern is a fundamental performance metric. It is a mathematical or graphical representation of the spatial distribution of radiated energy of an antenna array as a function of directional space coordinates. Array antennas can vary their directivity patterns through amplitude and phase control. One of the most important aspects of an antenna array is reducing interference and radiation power waste. Reduced side lobe level also avoids false target indication. Thinning is a technique for reducing the total number of active elements in an antenna array while maintaining system performance.
This study aims to improve antenna performance by lowering the side lobe level using antenna thinning applying GA. A genetic algorithm achieves optimal solution by simulating the natural selection process. It starts with randomly selected candidates as the first generation. In the beginning, we studied radiation patterns of equally spaced and non-equally spaced linear antenna arrays; and radiation patterns for uniformly spaced, non-uniformly spaced, and non-uniformly spaced with rotated elements array for N=20. It is demonstrated in the result that non-uniform spacing and rotated elements can significantly improve the directivity and reduce side lobes compared to uniformly spaced arrays.
In addition, it is observed in the beam pattern resulting from one typical first-generation candidate that the sidelobe level is lower in the azimuth direction but higher in the elevation direction compared to the full array. The exact sidelobe level and fill rate of the array is then around 8.7 and 71.75% respectively. This means that 71.75% of the array elements are active and the sidelobe level is approximately 9 dB. It needs to be suppressed further by applying a genetic algorithm with 30 generations. Thus, the result shows the sidelobe level and fill rate of the array after applying GA with 30 generations is around 17.38 and 76.5% respectively. Compared to the first-generation candidate, it uses 5% more active elements while achieving an additional 9 dB sidelobe suppression. Compared to the full array, the resulting thinned array can save the cost of implementing T/R switches behind dummy elements, which in turn leads to a roughly 25% saving on the consumed power. Even though the thinned array uses fewer elements, the beamwidth is close to what could be achieved with a full array.