What Are the Shortest and Longest Ranges for RFID Readers?

I am a post-graduate student form India. I am working on a real-time project for a bus-management system, and I have doubts about selecting an RFID reader. I would like to know what the maximum range of a reader is, based on meter, frequency and type, as well as the shortest range—including cost.

—R.S.Ranjini

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Dear R.S.Ranjini,

Your question is a bit like asking what the fastest computer is, and which is the slowest, so it's easy to answer. Are you comparing only desktops to desktops, or are you including Cray Supercomputers and Texas Instruments calculators, all of which compute? There are many kinds of RFID, including passive low-frequency (LF), high-frequency (HF) and ultrahigh-frequency (UHF), as well as active systems that operate at 433 MHz, 915 MHz and 2.45 GHz.

I will assume that you are interested in comparing passive fixed UHF readers, since handhelds and other readers designed as add-ons to smartphones and tablets have a very short read range. I will also assume that you are using a fairly ordinary dipole antenna. Read distance is greatly influenced by the tag used. I have seen passive tags interrogated from a distance of 80 feet, using an ordinary fixed RFID reader.

There are passive UHF systems that have beam-steerable phased-array antennas, some with integrated send antennas for powering up passive tags. If the send and receive functions are integrated, the maximum read distance is about 60 feet. If the send and receive functions are separated (meaning a separate antenna is set up close to the tag to power it up), the tags can be read from as far away as 600 feet. I don't know the cost of these readers, because the companies that make them do not publish pricing, but they cost substantially more than a conventional fixed reader would.

There are low-end USB readers that sell for about $500 apiece. These would offer a read range of only a foot or two, because they are designed for desktop applications. Low-end UHF readers cost around $800 and have a read range of 15 to 20 feet, when reading an ordinary dipole antenna in free space. A higher-end model might be priced at $2,000, with a read range of 30 feet. Note that prices do not include antenna cost.

—Mark Roberti, Founder and Editor, RFID Journal