What are microwaves?
A: Microwave is a form of electromagnetic radiation with wavelengths ranging
from about one meter to one millimeter corresponding to frequencies between
300 MHz and 300 GHz respectively.
A more common definition in radio-frequency engineering
is what?
A: The range between 1 and 100 GHz (wavelengths between 0.3 m and 3 mm).
In all cases, microwaves include what?
A: The entire SHF band (3 to 30 GHz, or 10 to 1 cm) at minimum.
The prefix micro- in microwave is not meant to suggest
what?
A: A wavelength in the micrometer range.
The prefix micro- in microwave indicates what?
A: That microwaves are "small" (having shorter wavelengths), compared to the
radio waves used prior to microwave technology.
The boundaries between far infrared, terahertz
radiation, microwaves, and ultra-high-frequency radio waves are what?
A: Fairly arbitrary and are used variously between different fields of
study.
Microwaves travel by line-of-sight; unlike lower
frequency radio waves they do not what?
A: Diffract around hills, follow the earth's surface as ground waves, or
reflect from the ionosphere.
Terrestrial microwave communication links are limited
by what?
A: The visual horizon to about 40 miles (64 km).
At the high end of the band, they are absorbed by what?
A: Gases in the atmosphere, limiting practical communication distances to
around a kilometer.
Microwaves occupy a place in the electromagnetic
spectrum with frequency above ordinary radio waves, and below what?
A: Infrared light.
Microwaves travel solely by what type of paths?
A: Line-of-sight.
Unlike lower frequency radio waves, they do not travel
as ground waves which follow what?
A: The contour of the Earth, or reflect off the ionosphere (skywaves)
Although at the low end of the band they can pass
through what?
A: Building walls.
Microwaves are absorbed by moisture in the atmosphere,
and the attenuation increases with what?
A: Frequency, becoming a significant factor (rain fade) at the high end of
the band.
Beginning at about 40 GHz, atmospheric gases also begin
to absorb microwaves, so above this frequency microwave transmission is
limited to what?
A: A few kilometers.
Above 100 GHz, the absorption of electromagnetic
radiation by Earth's atmosphere is so great that it is in effect what?
A: Opaque.
In a microwave beam directed at an angle into the sky,
a small amount of the power will be randomly scattered as the beam passes
through what?
A: The troposphere.
What can pick up the signal?
A: A sensitive receiver beyond the horizon with a high gain antenna focused
on that area of the troposphere.
This technique has been used at frequencies between
0.45 and 5 GHz in tropospheric scatter (troposcatter) communication systems
to communicate beyond the horizon, at distances up to what?
A: 300 km.
The short wavelengths of microwaves allow
omni directional antennas for portable devices to be made what?
A: Very small, from 1 to 20 centimeters long.
Microwave frequencies are widely used for wireless
devices such as what?
A: Cell phones, cordless phones, and wireless LANs (Wi-Fi) access for
laptops, and Bluetooth earphones.
Antennas used include short whip antennas, rubber ducky
antennas, sleeve dipoles, patch antennas, and increasingly what?
A: The printed circuit inverted F antenna (PIFA) used in cell phones.
