A single-layer low-profile circularly polarized (CP) filtering patch antenna is investigated for wireless local area network (WLAN) applications. The CP antenna mainly consists of a feeding loop, four L-shaped radiating patches, and a square ground plane. To integrate the filtering function, four thin microstrip stubs and four shorting pins are introduced to the patches, and two U-shaped slots are etched in the feeding loop. These parasitic elements can realize the bandpass filtering function without requiring an external filter. In addition, these elements are skillfully added into the CP antenna, without increasing either the antenna footprint or profile. To verify the design, a prototype operating at 2.4 GHz WLAN band is fabricated and tested. The measured results show that the prototype has a low profile of 0.02 λ ₀ , a passband bandwidth (| S ₁₁ | < –10 dB and axial ratio (AR) < 3 dB) of 4.1%, and a peak gain of 8.3 dBic. Moreover, the prototype also shows a sharp roll-off rate near the passband edge and a good out-of-band suppression level of more than 20 dB in the stopbands.

中文翻译：

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单层薄型圆极化滤波贴片天线

研究了用于无线局域网（WLAN）应用的单层低剖面圆极化（CP）滤波贴片天线。CP天线主要由一个馈电环路，四个L形辐射贴片和一个正方形接地平面组成。为了集成滤波功能，将四个细微带线短截线和四个短路针引入到贴片中，并在馈送环路中蚀刻两个U形槽。这些寄生元件无需外部滤波器即可实现带通滤波功能。此外，这些元素可以熟练地添加到CP天线中，而不会增加天线的占地面积或外形。为了验证设计，制造并测试了在2.4 GHz WLAN频段上运行的原型。测量结果表明该原型的低轮廓为0.02 λ ₀ ，通带带宽（| 小号 ₁₁ | <–10 dB，轴向比率（AR）<3 dB）为4.1％，峰值增益为8.3 dBic。此外，该原型还显示出通带边缘附近的陡峭滚降速率，阻带中的良好带外抑制水平超过20 dB。