ABSTRACT New designs of the circularly polarized micro-strip antennas (CPMSAs) based on tree fractal geometries are proposed, examined experimentally, and compared. The excellent circularly polarized (CP) radiation with minimum axial ratio (AR) of 0.26 dB is achieved by optimization of the key parameters (angle, length, and width) of the fractal trees etched on the ground plane. Parametric study revealed that the fractal tree defected ground structures (FTDGS) are responsible for satisfying the condition of CP operation. The micro-strip antennas with third iterative FTDGS and modified third iterative FTDGS are fabricated on FR4 substrate. The measured 10-dB return loss and 3-dB AR are 99 MHz (2.407–2.506 GHz) and 12 MHz (2.443–2.455 GHz), respectively, with stable gain of 4.52 dBic at 2.45 GHz, for third iterative FTDGS antenna. For modified third iterative FTDGS antenna, measured 10-dB return loss and 3-dB AR are 109 MHz (2.354–2.463 GHz) and 26 MHz (2.386–2.412 GHz), respectively, with gain about 4.62 dBic in the vicinity of center frequency 2.4 GHz. The proposed designs can be good candidates for the unlicensed 2.45 GHz industrial, scientific, and medical (ISM) band applications.

中文翻译：

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分形树加载地平面的圆极化微带天线

摘要 基于树形分形几何结构的圆极化微带天线 (CPMSA) 的新设计被提出、实验检查和比较。通过优化蚀刻在地平面上的分形树的关键参数（角度、长度和宽度），实现了最小轴比 (AR) 为 0.26 dB 的优异圆偏振 (CP) 辐射。参数研究表明，分形树缺陷地面结构（FTDGS）是满足CP操作条件的原因。具有第三次迭代FTDGS和改进的第三次迭代FTDGS的微带天线是在FR4衬底上制作的。对于第三次迭代 FTDGS 天线，测得的 10-dB 回波损耗和 3-dB AR 分别为 99 MHz (2.407–2.506 GHz) 和 12 MHz (2.443–2.455 GHz)，在 2.45 GHz 时稳定增益为 4.52 dBic。对于改进的第三迭代 FTDGS 天线，测得的 10-dB 回波损耗和 3-dB AR 分别为 109 MHz (2.354-2.463 GHz) 和 26 MHz (2.386-2.412 GHz)，在中心频率附近增益约为 4.62 dBic 2.4 GHz。所提议的设计非常适用于未经许可的 2.45 GHz 工业、科学和医疗 (ISM) 频段应用。