Aerospace and Electronic Systems Magazine October 2016 - 9


one time, and when recalculated at a later time come out the
same [6]. An example is the law of conservation of energy ....
The movement of the planets around the sun can be obtained
solely by following the implications of the laws of conservation of energy and angular momentum [7]. Moreover, the
conservation laws are also deep principles for they relate to
symmetry in physics [8]. For instance, conservation of energy
implies that the laws of Nature are time-invariant, and vice
versa. Also in signal processing and information theory, the
concept of energy is a prominent one. It appears as the energy
required to transfer one bit of information, or one symbol of
the signal alphabet, or sometimes in form of transmit power,
i.e., the rate at which energy must be supplied per unit of time
to keep the communication going. Yet, it is interesting that
the fact that energy is conserved, this very fact that is of such
fundamental importance in physics, apparently plays no role in
standard textbooks on information theory [9], signal processing [10], communication theory [11] or signal theory [12]. The
authors are also not aware of any research work in these areas
where the remarkable fact that energy is conserved is explored
or discussed. The reason for this strange absence of conservation laws in signal processing, information theory and related
disciplines seems to be the fact that inputs and outputs are
described by single variables each, instead of by a pair of conjugated variables, like position and momentum in Hamiltonian
mechanics [8], or voltage and current in circuit theory [13].
Therefore, to address the development of the physical layer adequately and to ensure that systems perform according to design
criteria, it is necessary to merge the principles of electromagnetics, which are primarily related to antennas and maximum power
transfer, to the issues of channel capacity and how it can be quantified using the principles of physics and the radiation efficiency of
antennas rather than use of the maximum power transfer theorem.

PROPERTIES OF ANTENNAS THAT ARE PARAMOUNT IN
SYSTEM DESIGN
Antennas have unique properties that must be understood and correctly applied. First, note that an antenna is a spatial filter. Unfortunately, the EM community only considers this topic when developing
methodologies such as beamforming. An antenna is also a temporal
OCTOBER 2016	

filter, as it can be tuned to a desired bandwidth, which the signal
processing community exploits to develop innovative algorithms
primarily based on the temporal properties of the signals. However,
an antenna is simultaneously both a temporal filter and a spatial filter
that are connected. This space-time relationship and its associated
properties can be characterized in an exact fashion with Maxwell's
equations. This set of equations is one of the few in physics that has
withstood the erosion and corrosion of progress; even the inclusion
of relativity has had no effect on Maxwell's equations, because it is
built into them. Recognition of this important space-time relationship can make it possible to address problems that may not be solved
by using temporal or spatial properties alone or independently.
Second, an antenna does not radiate power; it radiates power density, which is related to the electric (E(w)) and magnetic
(H(w)) fields-the exact relationship is given by the Poynting vector (E(w)H*(w)/2), where * denotes complex conjugation. When
a power density radiated by a transmitting antenna is incident on
a receiving antenna, the receiving antenna integrates the incident
electric field intensity (which has units of volt per meter) to generate a voltage at its terminals. In other words, an antenna is excited
by a voltage source or a current source and not by a power source.
Once the voltage applied to the antenna and the environment into
which it subsequently radiates (which dictates the input impedance
of the antenna) are known, the input power applied to the antenna
can be obtained. When comparing performances of systems containing radiating antennas, it is imperative that the input power to
the radiating antenna be kept fixed; otherwise, the comparison may
not be scientific. Hence, it is relevant to deal with antenna radiation
efficiency rather than use of the maximum power transfer theorem
that has no direct connection with the total amount of applied input
power. Note that in nature, the term power amplifier is a misnomer,
as no such device exists. The only physically realizable amplifier is
either a voltage amplifier or a current amplifier that converts the input direct current (DC) power into alternating current (AC) power;
hence, the terminology power amplifier leads to misunderstandings. Consequently, an antenna excitation needs to be implemented
and analytically modeled using one of these two sources-either
a voltage source or a current source, then focusing on the design
of the antenna, based on the radiation efficiency, which relates the
fraction of the input power that is radiated from it.
The last point addresses an important issue in electrical engineering in which two principles are of paramount importance:

IEEE A&E SYSTEMS MAGAZINE	

9



Table of Contents for the Digital Edition of Aerospace and Electronic Systems Magazine October 2016

No label
Aerospace and Electronic Systems Magazine October 2016 - No label
Aerospace and Electronic Systems Magazine October 2016 - Cover2
Aerospace and Electronic Systems Magazine October 2016 - 1
Aerospace and Electronic Systems Magazine October 2016 - 2
Aerospace and Electronic Systems Magazine October 2016 - 3
Aerospace and Electronic Systems Magazine October 2016 - 4
Aerospace and Electronic Systems Magazine October 2016 - 5
Aerospace and Electronic Systems Magazine October 2016 - 6
Aerospace and Electronic Systems Magazine October 2016 - 7
Aerospace and Electronic Systems Magazine October 2016 - 8
Aerospace and Electronic Systems Magazine October 2016 - 9
Aerospace and Electronic Systems Magazine October 2016 - 10
Aerospace and Electronic Systems Magazine October 2016 - 11
Aerospace and Electronic Systems Magazine October 2016 - 12
Aerospace and Electronic Systems Magazine October 2016 - 13
Aerospace and Electronic Systems Magazine October 2016 - 14
Aerospace and Electronic Systems Magazine October 2016 - 15
Aerospace and Electronic Systems Magazine October 2016 - 16
Aerospace and Electronic Systems Magazine October 2016 - 17
Aerospace and Electronic Systems Magazine October 2016 - 18
Aerospace and Electronic Systems Magazine October 2016 - 19
Aerospace and Electronic Systems Magazine October 2016 - 20
Aerospace and Electronic Systems Magazine October 2016 - 21
Aerospace and Electronic Systems Magazine October 2016 - 22
Aerospace and Electronic Systems Magazine October 2016 - 23
Aerospace and Electronic Systems Magazine October 2016 - 24
Aerospace and Electronic Systems Magazine October 2016 - 25
Aerospace and Electronic Systems Magazine October 2016 - 26
Aerospace and Electronic Systems Magazine October 2016 - 27
Aerospace and Electronic Systems Magazine October 2016 - 28
Aerospace and Electronic Systems Magazine October 2016 - 29
Aerospace and Electronic Systems Magazine October 2016 - 30
Aerospace and Electronic Systems Magazine October 2016 - 31
Aerospace and Electronic Systems Magazine October 2016 - 32
Aerospace and Electronic Systems Magazine October 2016 - 33
Aerospace and Electronic Systems Magazine October 2016 - 34
Aerospace and Electronic Systems Magazine October 2016 - 35
Aerospace and Electronic Systems Magazine October 2016 - 36
Aerospace and Electronic Systems Magazine October 2016 - 37
Aerospace and Electronic Systems Magazine October 2016 - 38
Aerospace and Electronic Systems Magazine October 2016 - 39
Aerospace and Electronic Systems Magazine October 2016 - 40
Aerospace and Electronic Systems Magazine October 2016 - 41
Aerospace and Electronic Systems Magazine October 2016 - 42
Aerospace and Electronic Systems Magazine October 2016 - 43
Aerospace and Electronic Systems Magazine October 2016 - 44
Aerospace and Electronic Systems Magazine October 2016 - 45
Aerospace and Electronic Systems Magazine October 2016 - 46
Aerospace and Electronic Systems Magazine October 2016 - 47
Aerospace and Electronic Systems Magazine October 2016 - 48
Aerospace and Electronic Systems Magazine October 2016 - Cover3
Aerospace and Electronic Systems Magazine October 2016 - Cover4
http://www.brightcopy.net/allen/aesm/34-2s
http://www.brightcopy.net/allen/aesm/34-2
http://www.brightcopy.net/allen/aesm/34-1
http://www.brightcopy.net/allen/aesm/33-12
http://www.brightcopy.net/allen/aesm/33-11
http://www.brightcopy.net/allen/aesm/33-10
http://www.brightcopy.net/allen/aesm/33-09
http://www.brightcopy.net/allen/aesm/33-8
http://www.brightcopy.net/allen/aesm/33-7
http://www.brightcopy.net/allen/aesm/33-5
http://www.brightcopy.net/allen/aesm/33-4
http://www.brightcopy.net/allen/aesm/33-3
http://www.brightcopy.net/allen/aesm/33-2
http://www.brightcopy.net/allen/aesm/33-1
http://www.brightcopy.net/allen/aesm/32-10
http://www.brightcopy.net/allen/aesm/32-12
http://www.brightcopy.net/allen/aesm/32-9
http://www.brightcopy.net/allen/aesm/32-11
http://www.brightcopy.net/allen/aesm/32-8
http://www.brightcopy.net/allen/aesm/32-7s
http://www.brightcopy.net/allen/aesm/32-7
http://www.brightcopy.net/allen/aesm/32-6
http://www.brightcopy.net/allen/aesm/32-5
http://www.brightcopy.net/allen/aesm/32-4
http://www.brightcopy.net/allen/aesm/32-3
http://www.brightcopy.net/allen/aesm/32-2
http://www.brightcopy.net/allen/aesm/32-1
http://www.brightcopy.net/allen/aesm/31-12
http://www.brightcopy.net/allen/aesm/31-11s
http://www.brightcopy.net/allen/aesm/31-11
http://www.brightcopy.net/allen/aesm/31-10
http://www.brightcopy.net/allen/aesm/31-9
http://www.brightcopy.net/allen/aesm/31-8
http://www.brightcopy.net/allen/aesm/31-7
https://www.nxtbookmedia.com