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| Design and Simulation of a Modified Universal Active-R Bandpass Filter For Ultra High Frequency (UHF) Radio Frequency Identification (RFID) Systems
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Atsuwe,B.A and Mom, J.M
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Abstract:
In this paper, a second order active-R band-pass filter using universal active-R type that was slightly modified was designed and simulated. The filter utilized a single pole mode op-amp and nine resistors which were realized from the calculations using the design equations. Result in table 2 showed that the centre frequencies were all shifted a little from the normal backscattered frequencies, fp of 40 kHz with 39.75 kHz to fp=640kHz with 632 kHz. Although the shifted frequencies were well within the recommended range of deviation from the EPC class 1 Generation 2 protocol for UHF RFID systems. Also the result showed that the mid band gain was low and increased from a value of 0.21dB at fp=40 kHz to 8.37dB at fp=256 KHz and then decreased from fp=320 kHz to 6.12dB at fp=640 kHz. This is a departure from filter theory. Again the bandwidth was at a high at fp=40 kHz with a value of 106.35 kHz and decrease to a value of 37.11 kHz at fp=256 kHz and then increases from a value of 43.28 kHz at fp=320 kHz to 54.59 kHz at fp=465 KHz and then drops to 54.31 kHz at fp=640 kHz. This behaviour is not in line with filter theory. Furthermore, the roll-off rate is observed to approach a single pole roll-off of 20dB/decade with the filter roll-off rate at fp = 40 kHz of -20.94 dB/decade to fp=640 KHz of -24.61db/decade. The filter's irregular behaviour at mid band gain and bandwidth could be attributed to parasitic effect and circuit components which could be chosen carefully if a desired result is required. Therefore from the result, we can conclude that the filter can be used for UHF RFID systems implementation since UHF band of backscattered frequencies are accommodated.
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