RFID系统中的读写器天线及关键技术研究

发布时间：2018-11-26 14:39

【摘要】：射频识别RFID)技术是物联网中非常重要的一部分。应用于RFID系统读写器的天线是其最重要的设备之一,目前已经成为了研究热点。一方面,远场应用的RFID天线通常采用高增益的圆极化天线或天线阵列,以增加其读取距离。近场的RFID读写器天线则需要强磁场,宽频带和低增益的特性,同时产生的磁场应该均匀分布以避免产生漏读现象。另一方面,RFID系统中的读写器输入输出信号需要有较好的收发隔离,该隔离度成为影响系统灵敏度的重要因素之一。为了使得系统获得更好的读取标签信号能力,需要尽可能降低接收机中发射机信号的功率。本文的研究工作是在射频识别系统的理论研究和实践设计领域中进行的,根据RFID的实际应用要求,主要对RFID系统中的读写器天线、圆极化天线阵列、圆极化天线罩、近场天线、读写器收发隔离技术等方面进行了研究。所获得的研究结论或成果对于推动射频识别技术的发展和应用具有一定的应用价值。本文的创新点如下 1针对系统对高增益圆极化辐射器的要求,本文重点研究了圆极化天线阵特性,理论分析了多种天线阵类型的耦合效应并提出了一种具有引向器功能的圆极化天线罩。对偶极子、矩形贴片天线、圆形贴片天线三种圆极化天线阵列中各天线单元轴比的耦合效应做了理论推导,得到了任意天线阵元受耦合影响后轴比变化的表达式。对矩形微带天线阵列驻波,轴比,方向图做了详细的仿真分析,结论是最佳轴向轴比的频点会因为耦合改变,|S11|对耦合效应较为敏感,方向图则相对比较稳定。提出的天线罩具有圆极化器和引向器的功能,可以使得线极化天线及天线阵获得圆极化并提高增益,等效天线阵的部分功能。该天线罩使得线极化微带单天线的增益提高达3dB以上 2基于磁场耦合原理的RFID读写器近场天线近些年来发展很快。本文提出了双S形导线环天线与双层终端开路天线,这两种RFID近场天线同时具有宽频带和强磁场的特性,并且结构紧凑,加工简单。两种天线均由两根导线组成,导线均使用弯折的方法,保证了天线上各处电流方向一致。双S形天线通过弯折使得外环上的电流方向一致且强而内部的导线上电流较弱,最大限度的利用了天线产生的磁场能量,并在馈电端使用巴伦将不平衡电流转为平衡电流。双层终端开路天线的馈电位于下层,上层是辐射环。天线环终端有一段导线折向环内部,可以保证外环远离波节点,环上电流更强。相比于双S形天线,该天线尺寸更小,并且馈电部分和辐射部分相隔离,很好的避免了相互之间的干扰,也不用采用巴伦等器件,降低了加工成本。 3针对近场天线本身对磁场的负面影响,本文研究了金属对磁场的影响并提出改进方案,对近场天线进行了环境实验,并提出了一种新型的天线结构以降低天线本身对近区磁场的负面影响。通过详细的金属、液体环境实验和三种RFID系统应用实验,发现天线受到金属、液体影响较大,其他介质也会影响天线的磁场分布,但比金属,液体影响小很多。针对天线结构特点和近场天线导线对磁场分布的负面影响,提出一种改进型的终端结构并将其应用在双层终端开路天线上。用一种电感结构代替普通的直导线,这种新结构有较长的电长度和对磁场影响较小的优点。从仿真和实验的结果可以看出,该结构可以很大程度的减小天线上金属导线对磁场的影响,非常适合开路结构的近场天线。 4RFID系统的读取性能除了和天线有关,还和信号通道中输入输出信号的隔离性能有关,隔离度直接影响了系统对标签信号的读取能力。为了提高收发信号隔离度,除了使得天线自身反射降低以外,本文提出了新型的载波相消技术和提高耦合器隔离度的方法。用一种RFID输入输出信号检测设备监控RFID系统的读写器信号和标签信号,并用定向耦合器分离输入输出信号。在定向耦合器的耦合端增加一段高阻抗线来产生不匹配,使其产生的反射信号与耦合器隔离端的泄露信号等幅反向,提高了耦合器的定向性,使得定向性可以达到30dB以上。载波相消技术则利用对数检测器,单片机,矢量放大器,功分器,定向耦合器等,通过自适应方法产生抵消信号。该抵消信号与接收的标签信号合路,使得标签信号通路中的读写器信号功率水平大大降低。利用载波相消技术处理以后标签信号通路中的读写器信号电压仅为处理前的1/12。该技术对天线本身反射的信号也同样有作用,弥补了耦合器的不足。
[Abstract]:radio frequency identification (rfid) technology is a very important part of the internet of things. The antenna applied to the RFID system reader-writer is one of its most important equipment, and has become a hot topic at present. on the one hand, an rfid antenna for a remote field application typically employs a high gain, circularly polarized antenna or antenna array to increase its read distance. The near-field RFID reader-writer antenna requires a strong magnetic field, a wide band and a low gain characteristic, and the generated magnetic field should be uniformly distributed to avoid the phenomenon of leakage. On the other hand, the reader/ writer input/ output signal in the RFID system needs to be well received and received, and the isolation becomes one of the important factors that affect the sensitivity of the system. in order for the system to obtain a better signal capability to read the tag, it is necessary to reduce the power of the transmitter signal in the receiver as much as possible. The research work in this paper is carried out in the field of the theoretical research and practice design of the radio frequency identification system. According to the actual application requirements of the RFID, the reader/ writer antenna, the circular polarized antenna array, the circular polarization antenna cover and the near field in the RFID system are mainly applied to the RFID system. the antenna, the reader/ writer transmitting and receiving isolation technology and the like are carried out, The results or results of the research have a certain application to the development and application of the radio frequency identification technology. Value. The innovation of this paper In order to meet the requirement of the system to the high gain circular polarization radiator, the characteristics of the circular polarization antenna array are studied in this paper. The coupling effect of multiple antenna array types is analyzed theoretically, and a circle with the director function is proposed. The coupling effect of the axial ratio of the antenna elements in the three circularly polarized antenna arrays of the dipole, the rectangular patch antenna and the circular patch antenna is theoretically derived, and the coupling effect of the arbitrary antenna array elements on the rear axle ratio is obtained. In this paper, a detailed simulation and analysis of the standing wave, the axial ratio and the direction diagram of the rectangular microstrip antenna array are carried out. The conclusion is that the frequency point of the optimal axial-axis ratio can be changed because of the coupling change. | S11 | The coupling effect is more sensitive, and the direction map is the same. The proposed radome has the functions of a circular polarizer and a director, so that the linear polarized antenna and the antenna array can be circularly polarized and the gain and the equivalent antenna array can be improved. and the antenna cover is used for improving the gain of the linearly polarized microstrip single antenna, Near-field antenna of RFID reader-writer based on magnetic field coupling principle of over 3dB In recent years, the development of double S-shaped conductor loop antenna and double-layer terminal open-circuit antenna is proposed in this paper. The two antennas are made up of two wires, the wires are all bent, and the antenna is ensured the two-S-shaped antenna is bent so that the current direction on the outer ring is consistent and strong, the current on the inner conductor is weak, the magnetic field energy generated by the antenna is used to the maximum extent, and the balun will not be balanced at the feeding end The current is converted to a balanced current. The feed of the open-circuit antenna of the double-layer terminal is at the bottom The upper layer is a radiation ring. The antenna loop terminal has a length of wire folded into the ring, which can ensure that the outer ring is far away from the node Compared with the double S-shaped antenna, the size of the antenna is smaller, the feeding part and the radiating part are separated, the interference between the feeding part and the radiating part is well avoided, In this paper, the influence of metal on the magnetic field is studied and the improvement scheme is put forward, and a new type of antenna structure is proposed to reduce the cost of the antenna. The negative effect of the body on the magnetic field in the near zone is carried out. Through the detailed metal, liquid environment experiment and the application of the three kinds of RFID system, it is found that the antenna is affected by the metal and the liquid, and the other medium can also influence the magnetic field distribution of the antenna, but Based on the characteristics of the antenna and the negative effect of the near-field antenna lead on the distribution of the magnetic field, an improved terminal structure is proposed and it should be in that open-circuit antenna of a double-layer terminal, an inductance structure is used instead of a common straight conductor, and the novel structure has a long electrical length and the structure can greatly reduce the influence of the metal lead on the magnetic field on the antenna, the read performance of the 4RFID system is related to the isolation performance of the input and output signals in the signal channel, In order to improve the isolation of the transmitting and receiving signals, a new carrier cancellation is proposed in this paper, in addition to the reduction of the reflection of the antenna itself. The invention relates to a method for measuring the isolation of a coupler, which comprises the following steps of: detecting a reader-writer signal and a label signal of an RFID system by using an RFID input and output signal detection device, A high-impedance line is added to the coupling end of the directional coupler to generate a mismatch, so that the reflected signal generated by the directional coupler is inverted with the amplitude of a leakage signal, such as a leakage signal at the isolation end of the coupler, so that the orientation of the coupler is improved, The directional property can reach above 30dB. The carrier cancellation technique uses a log detector, a single chip computer, a vector amplifier, a power divider, a directional coupler, and the like. and generating a cancellation signal by an adaptive method, wherein the cancellation signal and the received tag signal are in the same way, so that the label signal path the signal power level of the reader/ writer is greatly reduced, and the reader-writer in the label signal path after processing by using the carrier destructive technique The signal voltage is only 1/ 12 before processing. The signal is also the same as the signal reflected by the antenna itself
【学位授予单位】：西北工业大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TP391.44;TN820

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