Enhancing RFID Reader Distance with Power, Frequency, Antennas, and Cables
RFID Reader Distance
When deploying RFID in the real world you must deal with a wide variety of environments. The RF energy carrying the tag information can be reflected, absorbed and even lost in certain materials such as water and metals.
Some types of antennas focus the energy into a narrow beam to increase read range. However, concentrating that power also affects other radio receivers in the vicinity.
Power
RFID tags operate using RF electromagnetic energy, and the power used to send this energy can affect the reader distance. This is a key factor when it comes to choosing an RFID system for your business. It can also be affected by other factors, such as water or metal in the environment and the frequency of operation.
In general, a higher power setting will result in greater read range, but this doesn’t describe all aspects of a reader’s performance. For example, it doesn’t explain receive sensitivity or whether the tags are being used as part of a stack.
In passive RFID, the RF signal used to energize a tag’s microchip can only be absorbed over a limited distance. The return signal is used to transmit the ID of that tag back to the reader, and the reader can then use this information to identify the tag. If the RF signal strength falls by 3 dB, it will only reduce the reading distance by half.
Frequency
There are a few things that can affect the reader distance that a RFID system produces. The most important is the frequency of the tag that is used. The higher the frequency, the farther away the tag can be read.
For passive RFID tags, the maximum read range is usually stated on the tag spec sheet. This is based on a maximum read distance under ideal laboratory test conditions and the maximum strength query signal allowed by regulations.
However, many factors can degrade the performance of RFID in real world applications. For instance, if you place a passive tag on a conductive material or in front of metal, its read range will be significantly reduced. This is due to the fact that passive tags don’t have a battery and instead rely on harvesting RF energy from the reader – absorbing it through its antenna. As the separation between reader and tag increases, the RF intensity decreases by an order of magnitude for every 3 dB increase in transmit power.
Antennas
Most RFID antennas have a linear or circular polarization. Linear polarization only radiates in one direction, whereas circular polarization radiates in a spherical pattern (LHCP or RHCP). Circular polarized antennas are ideal for orientation sensitive tags because they can read them at any angle.
Choosing the right antenna for your application is crucial to achieving maximum reader distance. High gain antennas increase the power received by the RFID tag, resulting in a longer reading distance. If your application doesn’t require a long range scan, a lower gain antenna can work just as well.
The length of the cable connecting the antenna to the reader also impacts read range. Longer cables “leak” energy, reducing the signal strength. If your application requires a long read range, it is recommended to use shorter cables or to compensate for the additional loss by using higher rated insulated wires. RFID systems run on a variety of frequencies, including the 433 MHz frequency, which allows for read distances over 30cm (1 foot). We have even had customers successfully achieve 3 kilometer (1.86 miles) read distances using SkyRFID OEM 433 MHz readers and purpose built antennas.
Cables
A RFID reader sends out electromagnetic energy in the form of a radio wave. The tag absorbs this energy and uses it to transmit a signal that the reader can read to identify the tag.
Choosing the right cables can affect the reader distance. Longer cables lose more energy than shorter ones, and using adapters or multiplexers adds to the losses. For best results, use the shortest cables possible and avoid adding unnecessary adapters and multiplexers.
For example, if you’re tracking files in a stack of folders, the RFID tags on top may be difficult to read because they’re in shadow of those below them. To counter this, try experimenting with different cable lengths and insulation ratings to find the right combination that works for your application. You might also want to consider using a cable-tag holder that has built-in antennas so you don’t need additional RFID antenna cables. These holders are made of high-performance thermoplastic polyester resin and secured with industrial-quality screws to withstand harsh conditions such as impact, pressure, and temperature extremes.