History of Millimeter Wave Propagation Characteristic
phased arrays on a substrate chip that can steer and focus the energy for greater gain, power, and range.
Millimeter waves also permit high digital data rates. Wireless data rates in
microwave frequencies and below are now limited to about 1 Gbits. In the millimeter-wave range, data rates can reach 10 Gbitss and more.
Millimeter waves open up more spectrums. Today, the spectrum from dc
through microwave 30 GHz is just about used up. Government agencies worldwide have allocated the entire “good” spectrum. There are spectrum shortages and
conflicts. The expansion of cellular services with 4G technologies like LTE depends on the availability of the right sort of spectrum. The problem is that there isn‟t
enough of it to go around.
One of the key limitations of millimeter waves is the limited range. The laws
of physics say that the shorter the wavelength, the shorter the transmission range for a given power. At reasonable power levels, this limitation restrains the range to less
than 10 meters in many cases. In fact, the short range can be a benefit. For example, it cuts down on interference from other nearby radios. The high-gain antennas, which
are highly directional, also mitigate interference. Such narrow beam antennas increase power and range as well. And, they provide security that prevents signals
from being intercepted.
Another challenge is making circuitry that works at millimeter-wave
frequencies. With semiconductor materials like silicon germanium SiGe, gallium arsenide GaAs, indium phosphide InP, and gallium nitride GaN and new
processes, though, transistors built at submicron sizes like 40 nm or less that work at these frequencies are possible. [11]