Applications of Microwave Engineering: by Hamood Ur Rehman, Graduate Assistant Fee
Applications of Microwave Engineering: by Hamood Ur Rehman, Graduate Assistant Fee
Applications of Microwave Engineering: by Hamood Ur Rehman, Graduate Assistant Fee
Applications of
MicroWave
Engineering
By HAMOOD UR REHMAN, Graduate Assistant FEE.
1/31/2018
Applications of Microwave Engineering
Just as the high frequencies and short wavelengths of microwave energy make for difficulties in
the analysis and design of microwave devices and systems, these same aspects provide unique
opportunities for the application of microwave systems. The following considerations can be
useful in practice: Antenna gain is proportional to the electrical size of the antenna. At higher
frequencies, more antenna gain can be obtained for a given physical antenna size, and this has
related to data rate) can be realized at higher frequencies. A 1% bandwidth at 600 MHz is 6
MHz, which (with binary phase shift keying modulation) can provide a data rate of about 6 Mbps
(megabits per second), while at 60 GHz a 1% bandwidth is 600 MHz, allowing a 600 Mbps data
rate. Microwave signals travel by line of sight and are not bent by the ionosphere as are lower
frequency signals. Satellite and terrestrial communication links with very high capacities are
therefore possible, with frequency reuse at minimally distant locations. The effective reflection
area (radar cross section) of a radar target is usually proportional to the target’s electrical size.
This fact, coupled with the frequency characteristics of antenna gain, generally makes
microwave frequencies preferred for radar systems. Various molecular, atomic, and nuclear
resonances occur at microwave frequencies, creating a variety of unique applications in the areas
of basic science, remote sensing, medical diagnostics and treatment, and heating methods. The
majority of today’s applications of RF and microwave technology are to wireless networking and
communications systems, wireless security systems, radar systems, environmental remote
sensing, and medical systems. As the frequency allocations listed in Figure 1.1 show, RF and
microwave communications systems are pervasive, especially today when wireless connectivity
promises to provide voice and data access to “anyone, anywhere, at any time.” Modern wireless
telephony is based on the concept of cellular frequency reuse, a technique first proposed by Bell
Labs in 1947 but not practically implemented until the 1970s. By this time advances in
introduction of several early cellular telephone systems in Europe, the United States, and Japan.
The Nordic Mobile Telephone (NMT) system was deployed in 1981 in the Nordic countries, the
Advanced Mobile Phone System (AMPS) was introduced in the United States in 1983 by AT&T,
and NTT in Japan introduced its first mobile phone service in 1988. All of these early systems
used analog FM modulation, with their allocated frequency bands divided into several hundred
narrow band voice channels. These early systems are usually referred to now as first-generation
performance by using various digital modulation schemes, with systems such as GSM, CDMA,
DAMPS, PCS, and PHS being some of the major standards introduced in the 1990s in the United
States, Europe, and Japan. These systems can handle digitized voice, as well as some limited
data, with data rates typically in the 8 to 14 kbps range. In recent years there has been a wide
variety of new and modified standards to transition to handheld services that include voice,
texting, data networking, positioning, and Internet access. These standards are variously known
as 2.5G, 3G, 3.5G, 3.75G, and 4G, with current plans to provide data rates up to at least 100
Mbps. The number of subscribers to wireless services seems to be keeping pace with the growing
power and access provided by modern handheld wireless devices; as of 2010 there were more
than five billion cell phone users worldwide. Satellite systems also depend on RF and microwave
technology, and satellites have been developed to provide cellular (voice), video, and data
connections worldwide. Two large satellite constellations, Iridium and Globalstar, were deployed
in the late 1990s to provide worldwide telephony service. Unfortunately, these systems suffered
from both technical c01ElectromagneticTheory Pozar July 28, 2011 8:7 4 Chapter 1:
Electromagnetic Theory drawbacks and weak business models and have led to multibillion dollar
financial failures. However, smaller satellite systems, such as the Global Positioning Satellite
(GPS) system and the Direct Broadcast Satellite (DBS) system, have been extremely successful.
Wireless local area networks (WLANs) provide high-speed networking between computers over
short distances, and the demand for this capability is expected to remain strong. One of the newer
examples of wireless communications technology is ultra wide band (UWB) radio, where the
broadcast signal occupies a very wide frequency band but with a very low power level (typically
below the ambient radio noise level) to avoid interference with other systems. Radar systems
find application in military, commercial, and scientific fields. Radar is used for detecting and
locating air, ground, and seagoing targets, as well as for missile guidance and fire control. In the
commercial sector, radar technology is used for air traffic control, motion detectors (door
openers and security alarms), vehicle collision avoidance, and distance measurement. Scientific
applications of radar include weather prediction, remote sensing of the atmosphere, the oceans,
and the ground, as well as medical diagnostics and therapy. Microwave radiometry, which is the
passive sensing of microwave energy emitted by an object, is used for remote sensing of the
atmosphere and the earth, as well as in medical diagnostics and imaging for security applications.