[求助]rfid标签天线带宽到底以-3db以下还是-10db以下为标准？

采用蜿蜒曲折的方法增大电长度，实现小型化

一般的被动式Tag因该s11要在-10db以下或是更低才是，因为被动式tag的缺点就是会消耗很多能量，距离会变的非常有限，我认为tag的天线因该还要比一般天线更严格才是 HhvG
#Sam!  

呵呵，用公式S11=(Zant-conj(Zic))/(Zant+conj(Zic))算出来的都是所谓的return loss没有任何价值，不过看到很多人发到IEEE得文章都是用这个算的，悲哀，正确的算法是用S11==(Zic-conj(Zant)/(Zic+Zant)。这样算出来s11小于0.5（-3db）就是传输的功率大于0.5.当然匹配的好的也可以小于-10db，不过很难。当然你用错误的公式来算的话很容易实现一个很宽的频带内实现s11小于-10db。

楼上可不可以解释一下，你所说的公式S11==(Zic-conj(Zant)/(Zic+Zant)，是怎么来的？如何得到这个公式的？ M
~Qj'VVL  

10的话要求还是挺高的呢.

可以参考这篇文献 jj!N39f   
P.V.Nikitin,K.V.S.Rao,and S.F.Lam, “Power reflection coefficient analysis for complex impedances in RFID tag design,” IEEE Transactions on Microwave Theory and Techniques, Vol.53,No.9, September 2005,pp.2721-2725.

参考资料，电子版自己去google一下吧：Daniel M. Dobkin, "The RF in RFID: Passive UHF RFID in Practice" GS ;HtUQ  
Newnes; Pap/Cdr edition (September 3, 2007) | ISBN: 0750682094 | 504 pages | PDF | 10,1 Mb 'y4zBLY  
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This book includes a survey of all RFID fundamentals and practices in the first part of the book while the second part focuses on UHF passive technology. This coverage of UHF technology and its components including tags, readers, and antennas is essential to commercial implementation in supply chain logistics and security. ]By0Xifew  
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Reaaders of this book should have an electrical engineering background but have not yet dealt with RFID. To this end, Dr. Dobkin will be very careful to illustrate all concepts and detail his explanations meticulously. In this way he will bring the reader along organically showing him/her what to expect, develop, and use while implementing an RFID system. 1l/AKI(!  
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Chapter 1:Introduction /"""z=q  
Chapter 2: History and Practice of RFID 5/B#)gm  
Chapter 3: Radio Basics For UHF RFID /Jxq 3D)v  
Chapter 4: UHF RFID Readers 5LQk8NPh  
Chapter 5: UHF RFID Tags t_dcV%
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Chapter 6: Reader Antennas , Aq9fyC%  
Chapter 7: Tag Antennas >vWEUE[  
Chapter 8: UHF RFID Protocols *.,"N}  
Afterword VK2@2`$  
Appendix 1: Radio Regulations C-llq
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Appendix 2: Harmonic Functions s0cs'Rg  
Appendix 3: Resistance, Impedance and Switching J| SwQE~  
Appendix 4: Reflection and Matching j)jCu ;`  

我觉得s11还是要-10dB以下会比较好，毕竟有-10dB时，等于是射频功率有90%被辐射出去，效率较好。 Uo~T'
mA"  

-3DB 指的是半功率带宽，而S11是阻抗带宽。我个人觉得应该在HFSS里导出阻抗数据，根据功率反射系数的公式，然后用画图软件将曲线画出来 -}P7$|O&  

没有想到-3dB和-10dB这个问题，看看资料