I would like to increase the range from 6 meters (20 feet) to 20 meters (66 feet).
The power emitted by passive ultrahigh-frequency (UHF) reader antennas is regulated in most countries. In the United States, a UHF reader is allowed to put out four watts of what is called effective isotropic radiated power (EIRP)—the output of an antenna compared to that of a theoretical antenna radiating equally in all directions.
European regulations allow antennas to emit up to 2 watts of effective radiated power (ERP) between 865.6 and 867.6 MHz. ERP is a different measurement than EIRP. It is equal to the power supplied to an antenna multiplied by that antenna's gain (a measure of intensity), compared to that of a standard antenna.
This means you cannot simply crank up the power output to increase read range. Six to 10 meters (20 to 33 feet) is what you will typically achieve with most passive UHF systems. You can increase that amount, however, by using larger passive tags designed for a longer read range, such as Omni-ID's Ultra tag (see Omni-ID Launches New High-Performance UHF Gen 2 Tags). There are also phased array RFID readers that project RF energy in a narrow beam and use ultra-sensitive antennas to increase the read range.
GS1 maintains a document on its website that lists the power output in many countries around the world (see document), but before you crank up your reader's output, first check with your country's regulators.
—Mark Roberti, Founder and Editor, RFID Journal