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1、P1: irp JWBS032-06JWBS032-KarmakarAugust 6, 20106:59Printer Name: Yet to Come PART III PHYSICAL LAYER DEVELOPMENTS OF SMART ANTENNAS FOR RFID SYSTEMS P1: irp JWBS032-06JWBS032-KarmakarAugust 6, 20106:59Printer Name: Yet to Come CHAPTER 6 RFID PLANAR ANTENNASMART DESIGN APPROACH AT UHF BAND SUSHIM MU
2、KUL ROY Department of Electrical and Computer Systems Engineering, Monash University, Clayton, Victoria, Australia NEMAI CHANDRA KARMAKAR Department of Electrical and Computer Systems Engineering, Monash University, Clayton, Victoria, Australia 6.1INTRODUCTION Numerous developments are reported glob
3、ally in conventional RFID technology in the ultra-high-frequency (UHF) band. Following the standardization of ISO 18000- 6C 1 by EPC global 2, RFID operations got a global boost. The band allocated to RFID technology in the UHF band is around 800 MHz in Europe and the Asian nations like Brunei, Hong
4、 Kong, Malaysia, and Singapore 3 and 2. However, for countries like the United States, Australia, or Japan, the frequency range is around 900 MHz. To make a tag and reader work in both the United States and Europe, the solution is to make frequency-agile or dual-band systems that work in both the fr
5、equencies of 800 MHz and 900 MHz. The other option, being taken up by the government organizations, is to come to a general agreement for uniform frequency allocation. With the different frequency allocations, developments are being reported for accessory supporting components also like Power Amplif
6、i ers working in the range of 8001000 MHz 4. New IP backbones are developed to provide intercompatibility between RFID systems or digital radio working at 800 MHz with an analog user 5. The added feature of this work is the convergence of RFID systems working at an 800-MHz UHF system with the digita
7、l public address systems. Organic rectifi ers 6 are reportedly developed at this frequency range to work in the RFID tags. Some advantagesofusingRFIDintheUHFrangenear800MHzcanbefoundinproprietary Handbook of Smart Antennas for RFID Systems, Edited by Nemai Chandra Karmakar CopyrightC?2010 John Wiley
8、 for example, placement of a cross slot on the circular microstrip patch makes it circular-polarized 22. Studies on effects of loading with slots of different shapes are found in 23. The work of Deshmukh and Kumar 23 is particularly helpful for this chapter because it involved the incorporation of s
9、lots in semicircular patches, thereby making the antennas broadband and compact. When a microstrip patch antenna is loaded with a slot, two resonances occur simultaneously. The patch antenna resonates at one particular frequency determined by its geometry. The slot also resonates at a particular fre
10、quency, depending on its geometry. The frequencies of resonances of the aforementioned antenna and slot can be separated by changing the design parameters. Thus the antenna can be made to performindualband,whichisparticularlyimportantforworkingatUHFfrequencies for RFID near 800 MHz and 900 MHz, resp
11、ectively. 6.2.1Bandwidth and Gain Enhancement Techniques Microstrip antennas have an inherent shortcoming of narrow bandwidth. If a mi- crostrip antenna operates at either of the two aforesaid frequencies (800 and 900 MHz), it would perform well but exhibit narrow bandwidth, thereby limiting the ope
12、ration around one of the frequencies. However, if the patch and slot are designed to resonate at the same frequency, then the antenna exhibits a wide bandwidth at the design frequency. This is a technique widely deployed in microstrip technology to produce broadband antennas 13, 15. Different techni
13、ques for increasing the bandwidth of patch antennas are found in 24. One of the common techniques is impedance matching at the source 25. Multilayered structures are proposed in some of the techniques. However, designing broadband microstrip antennas in single layer is shown in 26. Both bandwidth an
14、d gain are reported to be increased simultaneously for compact planar antennas 27. Based on the aforesaid literature review, a semicircular microstrip patch loaded with an L-shaped slot is chosen to make the structure compact and resonate with a wide bandwidth. The aim of this chapter is to design a
15、n antenna for usage in an RFID reader, so high gain is one of the key requirements. In addition to the aforementioned litera- ture, gain enhancement techniques are reported in 2729. Most of the techniques concentrate on the gain enhancement of a single patch by incorporating a layer of thick dielect
16、ric ofhigh dielectric constant such as ceramic, and so on, above the patch P1: irp JWBS032-06JWBS032-KarmakarAugust 6, 20106:59Printer Name: Yet to Come BACKGROUND LITERATURE REVIEW: BASIS OF DESIGN145 layer. Weng et al. 30 reports a novel technique of use of metamaterial structure to increase the gain. The idea behind this technique is the incorporation of microwave lenses. Following the aforementioned literature to keep the antenna compact, experimen- tatio
