RFID System Frequencies
May 20, 2004
Frequencies for passive tags in general
Chip tags are usually made to work at specific frequencies which are licence free. The tolerated power levels and regulations for these vary from country to country. For example, the maximum permitted legal power level (the power level at which the interrogator is set at) for 2.45 GHz in the U.S. is 100 times higher than in the Europe. This creates a huge difference in read range - a 1 meter range in the U.S. may only be a 1 centimeter range in Europe, all else being equal! Therefore, much work still needs to be done to balance these regulatory issues worldwide, though there is some progress.
Frequencies for passive chip RFID
The most popular frequencies used for passive (ie low-cost, modest functionality) RFID devices are 125-134 KHz (Low Frequency - LF), 13.56 MHz (High Frequency - HF), UHF (868 to 928 MHz - Ultra-High Frequency) and 2.45 GHz (Microwave). A popular frequency for lowest-cost RFID tags at present is 13.56 MHz. It is the basis for several international standards, economical electronics is available and it is a good compromise of tag size and range and the extremes of flooding a small volume with radiowaves (LF) or transmitting thin beams (Microwave). Since fewer turns of antenna coil are usually needed, these can be printed (say PCB etched by the method used for printed circuit boards) when 125 KHz tags usually need copper wire. 13.56 MHz is already the agreed frequency for smart cards and one of the frequencies specified for airline baggage tags. It is popular for supply chains in Japan and at least one meter range can legally be achieved in most countries.
However, tags at UHF (around 900 MHz) and 2.45 GHz are being developed for general RFID uses. Many are already in use tracking vehicles, freight etc, particularly in the US (mainly UHF) and Japan (2.45 GHz only). For UHF, that often means 10 meters range and for 2.45 GHz several meters. Thus UHF improves range and gives a smaller tag than HF. Microwaves gives intermediate range but gives the smallest tag of all. The cost of the complete device depends on the size - the price of the chip alone does not change with frequency, but the size of the antenna, and hence cost of the complete tag and its outer protection does.