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Designers must begin estimating power consumption early in a project. Accurately estimating power throughout the design flow will require significant designer effort, but the tips outlined here should help designers achieve their goals with efficiency and accuracy.

87606-810LF_Datasheet PDF

Designers must begin estimating power consumption early in a project. Accurately estimating power throughout the design flow will require significant designer effort, but the tips outlined here should help designers achieve their goals with efficiency and accuracy.

and thus the forward-link-limited read range will be found to be proportional to the cosine of the misalignment angle.

87606-810LF_Datasheet PDF

Note, finally, that because electromagnetic waves are transverse, there is no electric field along the direction of propagation. A simple linear tag antenna oriented along the direction of propagation (that is, pointing towards the reader antenna) sees no electric field along the wire axis and therefore receives no power.

The polarization of a simple wire antenna is easy to establish by inspection. The polarization of a commercial antenna, particularly when encased in a plastic radome, is not so obvious, and the user must usually refer to the labeling on the antenna or the manufacturer's data sheets, or use a linearly polarized tag to test the polarization of the radiated field. Antennas more complex than simple dipoles may not have the same polarization in all directions; circular polarization often becomes elliptical as the direction of observation moves away from the axis of the main beam.

The next part of this series will cover antenna propagation.

87606-810LF_Datasheet PDF

About the Author Dr. Dobkin has been involved in the development, manufacturing, and marketing of communications devices, components, and systems for 28 years. He holds a BS from the California Institute of Technology, and MS and PhD degrees from Stanford University, all in Applied Physics. He is the author of two books and about 30 technical publications, and holds 7 US patents as inventor or co-inventor. He has given numerous talks and classes on radio-frequency identification in the US and Asia. He specializes in physical-layer issues: radios and signal generation, antennas, and signal propagation. Dr. Dobkin lives in Sunnyvale, CA, with his wife, Nina, children Nicholas and Amelia, and entirely too many toys and video game consoles.

Copyright:Printed with permission from Newnes, a division of Elsevier. Copyright 2008. The RF in RFID: Passive UHF RFID in Practice by Daniel M. Dobkin. For more information about this title and other similar books, please visit www.newnespress.com

87606-810LF_Datasheet PDF

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