A low-profile vertical polarized antenna is presented for radio frequency identification (RFID)-enabled intelligent parking system applications. In order to reduce the crosstalk between antennas and false detection of vehicles in the parking zone, a bidirectional antenna with low vertical obstacle is required by industry. To that end, a low-profile cavity-excited magnetic dipole-based antenna with vertical polarization is designed. Two vertical sides of the antenna are kept open for the easy access of the reader and powering components. In order to increase the polarization purity along the intended sides, a rectangular truncated ground plane is proved to be beneficial compared to a typical square shaped one. The overall structure of the on-road antenna over the ground plane is around $0.2\times 0.55\times 0.06\,\,\lambda _{0}^{3}$ ( $\lambda _{0}$ is the free space wavelength of the center frequency). The design process and operating principle of the antenna are described in detail along with the effects of different parameters. The antenna is prototyped and measured. The antenna attains high reflection coefficient of −20 dB over 912–930 GHz covering the intended Australian ultrahigh-frequency (UHF) RFID band. The antenna demonstrates bidirectional radiation patterns having a maximum gain of 5 dBi over the required band with −20 dBi cross-polarization level. On-road measurements of the prototype show that the 3 dB beamwidth extends to ±90° elevation angles, which provides high read range while the tags embedded in the vehicle’s license plate are in low elevation. The antenna has a rugged structure to sustain more than 10 years in regular road and traffic conditions. By meeting all the requirements, it has been proved to be an effective part of the on-road RFID-enabled intelligent parking system.

中文翻译：

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用于道路 RFID 智能停车的薄型垂直极化开槽天线

提出了一种用于支持射频识别 (RFID) 的智能停车系统应用的低剖面垂直极化天线。为了减少天线之间的串扰和停车区车辆的误检，业界需要一种垂直障碍低的双向天线。为此，设计了一种具有垂直极化的薄型腔激励磁偶极子天线。天线的两个垂直侧保持打开状态，以便于阅读器和供电组件。为了增加沿预期边的极化纯度，与典型的方形接地平面相比，矩形截断接地平面被证明是有益的。地平面上的公路天线的整体结构约为 $0.2\times 0.55\times 0.06\,\, \lambda _{0}^{3}$ ( $\lambda _{0}$ 是中心频率的自由空间波长)。详细介绍了天线的设计过程和工作原理以及不同参数的影响。天线原型设计和测量。该天线在 912–930 GHz 范围内达到 -20 dB 的高反射系数，覆盖预期的澳大利亚超高频 (UHF) RFID 频段。该天线展示了双向辐射模式，在所需频段上具有 -20 dBi 交叉极化水平的最大增益为 5 dBi。原型的道路测量表明，3 dB 波束宽度扩展到 ±90° 仰角，这提供了高读取范围，而嵌入在车辆牌照中的标签处于低仰角。天线具有坚固的结构，可在常规道路和交通条件下维持 10 年以上。通过满足所有要求，它已被证明是支持道路 RFID 的智能停车系统的有效组成部分。