The term microwaves is used to describe electromagnetic waves with frequencies from 300 MHz to 300 GHz, corresponding to wavelengths in free space from 1 m to 1 mm. Within the microwave range, from 30 GHz to 300 GHz the wavelengths are between 1 mm and 10 mm, and hence these waves are known as millimeter waves. Below 300 MHz the spectrum of electromagnetic waves is known as the radio frequency (RF) spectrum, while above the microwave spectrum are the infrared, visible optical, ultraviolet, and x-ray spectrums. Wireless communications uses only the electromagnetic waves in the range of the microwave and RF spectrums. In the wireless communications literature, the term RF is often used to represent the entire RF and microwave spectrums.
Receiver performance requirements
The requirements on RF receivers are typically more demanding than those on transmitters. In addition to the requirements on gain and noise figure, the receiver must have:
A good sensitivity to the minimum power at the antenna for a given BER requirement. For example, the GSM standard requires a reception dynamic range from −102 dBm to −15 dBm, IEEE 802.11g requires a reception range of −92 dBm to −20 dBm, for WCDMA it is −117 to −25 dBm (before spreading), for CDMA2000 it is −117 dBm to −30 dBm, and for WideMedia it is −80.8 dBm/MHz (or −72.4 dBm/MHz at highest speed) to -41.25 dBm/MHz. For multiple data rates, a higher data rate requires a higher sensitivity, since it requires a larger SNR.