RFID Journal Staff asked 8 years ago I am using Impinj Speedway Revolution readers for an installation, and I am having some trouble with collision between reader antennas. I am trying to figure out a formula for the "transmit" and "receive" functions. I have two antennas connected to the Impinj reader with a cable length of X meters. I placed them in a gate about Y meters in height. The distance (separation) between the antennas is Z meters.
I am searching for a solution by which if I changed the length of cable, the height of the gate fixed antenna and the separation between antennas, I could change the reader's values for transmit power and receive sensitivity accordingly. I need a formula that would allow me to determine the right settings, rather than going through a trial-and-error process with each reader portal. Any help your team might be able to provide would be greatly appreciated.
—RV (India)
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Dear RV,
To answer your question, I reached out to Impinj. Here is the response from the company's engineering team:
"There are several formulas that are useful when designing a RAIN RFID system:
• Power incident on tag = reader transmit power + path loss
• Power received by reader = power incident on tag + modulation loss + path loss
• Receive sensitivity of the reader = transmit power from the reader + antenna gain + tag antenna gain + 20log10(λ/4πR), where λ = 30cm and R = the distance in meters between the reader and the tag
For more information, visit the Impinj Support Portal and download the RFID Link Budget white paper."
Other helpful resources include:
• Wikipedia's description of the Friis equation
• This cable loss reference chart—see the 900 MHz row
• This handy decibel-gain calculator, provided by Daycounter
If any of our readers have any other relevant resources to recommend, I encourage them to post information below.
—Mark Roberti, Founder and Editor, RFID Journal
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