Basics of MM Waves

• It lies between the super high-frequency band and the far infrared band, the lower part of which is the terahertz band. Radio waves in this band have wavelengths from ten to one millimeter, so it is also called the millimeter band, and radiation in this band is called millimeter waves.
• Compared to lower bands, radio waves in this band have high atmospheric attenuation: they are absorbed by the gases in the atmosphere.
• The design of millimeter-wave circuits and subsystems (such as antennas, power amplifiers, mixers, and oscillators) also presents severe challenges to engineers due to semiconductor and process limitations, model limitations, and poor Q factors of passive devices.

Propagation:

• Millimeter waves propagate solely by line-of-sight paths.
• They are not reflected by the ionosphere nor do they travel along the Earth as ground waves as lower frequency radio waves do.
• At typical power densities, they are blocked by building walls and suffer significant attenuation passing through foliage.
• Millimeter wavelengths are the same order of size as raindrops, so precipitation causes additional attenuation due to scattering (rain fade) as well as absorption.
• Propagation restrictions dictate the use of small cell sizes for Wi-Fi and cellular networks.
• The short propagation distance can increase the number of access points (APs) to cover a large area but also means fewer client devices will share the bandwidth in each cell.

Uses:

• Millimeter wave has numerous uses, including telecommunications, short-range radar, and airport security scanners. In telecommunications, it is used for high-bandwidth WLANs.
• In general, the overall loss of mm Wave systems is significantly larger than that of microwave systems for a point-to-point link.
• The small wavelengths of mm Wave frequencies enable large numbers of antenna elements to be deployed in the same form factor thereby providing high spatial processing gains that can theoretically compensate for at least the isotropic path loss.
• mm Wave systems are equipped with several antennas, and several computations and implementation challenges arise to maintain the anticipated performance gain of mmWave systems’ short-range personal area networks (PANs).

MM Waves