Download Understanding Antennas-A Simplified Perspective

Understanding Antennas
A Simplified Perspective for
Ham Radio Operators
Jim Peisker AF5NP
25 February 2016
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
What to Expect
This presentation provides a working
understanding of amateur radio antennas without
being overly technical or dry.
Some mathematics and basic physics are required
to properly understand antenna operation but this
will be minimized.
The target audience here are newer hams with
limited knowledge of antennas.
It is presented at the Technician license level. You
will see Technician license exam questions and
answers to refresh your knowledge.
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
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What to Expect
While antenna theory works for all frequencies
and types of construction, the emphasis here is
on VHF/UHF antennas used for emergency
communication and repeater use. This is
because most new hams get started with local
(short-range) radio equipment.
Other antennas are discussed, however, and
the information provided is useful for all
antennas types and frequencies.
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
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Disclaimer
The author is not an antenna expert.
Information presented here is from many
different sources and represents that which the
author considers most reliable and useful.
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
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Why Understand Antennas?
The antenna is arguably the most important
component in most radio systems.
Let’s use a sound system analogy to help reinforce
this notion.
With a home audio system, you can have a
$10,000 amplifier with small, cheap loudspeakers
and it will sound awful.
Conversely, with a basic cheap audio amp and
some really good speakers it can sound fabulous.
The speakers make all the difference; they
contribute the most to what we hear.
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
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Why Understand Antennas?
The same goes for an amateur radio station. Here
we can have the nicest transceiver you can buy
paired with a lousy antenna and you won’t hear
much or be heard well.
But take a cheap radio with a good antenna and
you can do wonders. The antenna makes the
most impact on a radio communications system.
Whether transmitting or receiving, a weak signal
isn’t usually due to poor band conditions or lack of
power, it’s more likely caused by a bad antenna.
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
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Why Understand Antennas?
You may hear old-time hams say something like,
“Spend twice as much on your antenna as you
do on your radio.”
That’s not practical advice--considering the
relative costs of the two--but generally good
guidance that we should pay more attention to
the quality of our antenna than we do our fancy
radio equipment.
Because the antenna is so important in radio, it is
essential that we understand the basics of these
devices.
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Definition
An antenna is simply defined as an arrangement of
conductors used to radiate electromagnetic (E-M) energy
into space (the air) or, conversely, for collecting it from
space.
Antenna
Schematic
Symbol
Sounds simple, right? In reality, functional antennas are a
bit more complicated. There are many factors to consider
in practical antenna design. We’ll look at most of them
here.
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Definition
It may also be helpful to think of an antenna as a
transducer which converts alternating current (AC) into
radio waves, and, conversely, radio waves into AC.
You may be unfamiliar with the word transducer but you
already know what they are. A transducer is a device
which changes one form of energy into another.
We are all familiar with the following: speakers,
microphones, temperature and pressure sensors, room
lighting of all sorts, and indicators. We use these every day
and they are all transducers.
We control the electrical side of things in our radios and the
antenna converts that AC into useful radio waves, and viceversa.
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
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Antenna Varieties
There are dozens of different antenna designs
and they all have their place in radio.
Antennas used in emergency communications
(EmComm) are mostly VHF/UHF vertical whips
but you should be familiar with the more
common antenna configurations used at all
frequencies.
These are shown later in the presentation. Until
then we’ll look at some basic features and
details of all antennas.
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Topics
Even a basic understanding of antennas requires
discussion of a number of topics. We will briefly
touch on these:
•
•
•
•
•
•
Reciprocity
Directivity & Gain
Polarization
Impedance
Wavelength
Resonance
•
•
•
•
•
•
E-M Radiation
Physical Length
The Dipole
Efficiency
Bandwidth
Real-World Antennas
Additionally we will cover practical detail such as
antenna types, configurations, safety, and the
peculiarities and limitations of VHF/UHF mobile and
hand-held antennas.
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Common Characteristics
Antennas come in a myriad of sizes, shapes and
configurations. These vary greatly based on the
nature of the application (mainly frequency and
performance).
Regardless of these differences, all antennas
share three common characteristics:
• Reciprocity
• Directivity & Gain
• Polarization
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
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Reciprocity
Reciprocity means it works both ways.
The electro-magnetic characteristics of an antenna
make it work equally well for transmitting and
receiving.
This means that for both transmission and
reception, antennas are equally directive, have
equal gain and bandwidth, and have the same
polarity.
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Reciprocity
Sure, when transmitting it usually involves watts or
tens of watts or hundreds of watts of power.
And when receiving an antenna is dealing with
thousandths of a watt (mW) or millionths of a watt
(μW) or even less.
But the laws of physics don’t distinguish between
big watts and little watts; it’s still power transfer
and energy conversion at issue in an antenna.
Reciprocity works for power as well.
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
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Reciprocity
The practical result of reciprocity is that the same
antenna is almost always used for both
transmitting and receiving. This is where that
transmit-receive (TR) switch comes into play in
your transceiver.
Not that it has to be this way; occasionally a
different receiving antenna is used. In this case it
often involves a separate receiver with a highperformance receiving antenna.
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
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Directivity & Gain
Directivity is an antenna’s ability to focus the
energy to—or from—one or more directions.
All practical antennas have some degree of
directivity, some slightly directive (verticals), some
semi-directional (dipole), and others very
directional (beam).
Only the theoretical isotropic antenna is truly omnidirectional.
T9A01-2014: What is a beam
antenna?
An antenna that concentrates
signals in one direction
T9A06-2014: What type
of antennas are the quad,
Yagi, and dish?
Directional antennas
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
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Directivity & Gain
Directivity of an antenna is best understood by
viewing its radiation pattern graphically.
Antennas have radiation patterns viewed from
above (azimuth) and viewed from the side
(elevation). Both may be of interest to the user.
Vertical Monopole
Azimuth
Vertical Monopole
Elevation
Vertical Monopole
3-D
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
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Directivity & Gain
More antenna radiation patterns.
Yagi
Azimuth
Yagi
Elevation
Dipole
Azimuth
Parabolic
(Dish)
Azimuth
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Directivity & Gain
While gain is directly related to directivity, it is more
specifically a measure of the increase in signal in
certain directions relative to a reference antenna.
So directivity is the quality of an antenna to focus
radio waves and gain is the measurement of it.
T9A11-2014: What is meant by the gain of an antenna?
The increase in signal strength in a specified direction
when compared to a reference antenna
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
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Polarization
Recall that radio waves consist of both electric and
magnetic fields oscillating at right angles to each
other.
E=Electric Field
B=Magnetic Field
T3A07-2014: What type of wave
carries radio signals between
transmitting and receiving stations?
Electromagnetic
Animation of E-M wave
T3B03-2014: What are the two
components of a radio wave?
Electric and magnetic fields
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
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Polarization
Antenna polarization is determined by the
orientation of the electric field with respect to the
earth.
T3B02-2014: What property of a radio wave
is used to describe its polarization?
The orientation of the electric field
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
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Polarization
Generally speaking, since the electric field is
oriented parallel to the conductor, the orientation of
the radiating conductor is also its polarization.
A vertical antenna is vertically polarized.
A horizontal antenna is horizontally polarized.
An angled or bent antenna is partially polarized in
both orientations.
T9A02-2014: Which of the following is true
regarding vertical antennas?
The electric field is perpendicular to the Earth
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
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Polarization
For line-of-sight communications in the VHF and
UHF spectrum, antenna polarization is important.
All repeater antennas and mobile antennas are (or
should be) vertically polarized.
Handheld transceivers (HTs) work best when held
with the antenna up and down. You would see
about 3dB signal loss (half power) at a 45º tilt.
For short distances in open space polarization is a
non-issue due to relative signal strength.
T3A04-2014: What can happen if the antennas at opposite ends of a
VHF or UHF line of sight radio link are not using the same polarization?
Signals could be significantly weaker
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
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Polarization
At lower frequencies in the HF spectrum antenna
orientation is less important because ionospheric
propagation randomizes polarization. This blended
E-field orientation is sometimes referred to as
elliptical polarization.
As a result, you can use either vertical or
horizontal antennas on HF bands.
T9A03-2014: Which of the
following describes a simple
dipole mounted so the
conductor is parallel to the
Earth's surface?
A horizontally polarized
antenna
T3A09-2014: Which of the following
results from the fact that skip signals
refracted from the ionosphere are
elliptically polarized?
Either vertically or horizontally
polarized antennas may be used
for transmission or reception
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
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Other Factors
OK, so we’ve reviewed the three properties
common to all antenna types:
Reciprocity, Directivity & Gain, and Polarization.
Hope you’re still with us at this point.
Now let’s explore other factors important to antenna
theory. These start to get a little more complex but
we’ll keep it as simple as practical.
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
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Impedance
As you may recall, impedance is the sum of the
DC resistance plus the inductive and capacitive
reactance at a given frequency [ Z=R+jX ]. In
loose terms, it can be considered “AC resistance”.
Reactance varies with AC frequency. Inductive
reactance increases with frequency [ XL=2πfL ].
Capacitive reactance decreases [ XC=1/(2πfC) ].
All conductors have some measurable inductance
and capacitance in relation to earth and other
conductors.
T5C12-2014: What is meant by the term impedance?
It is a measure of the opposition to AC current
flow in a circuit
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
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Impedance
This means that all antennas have impedance at a
given frequency.
Antenna impedance varies with conductor
arrangement, signal frequency, height above
ground, conductor diameter, nearby objects, and
connecting wires (feedline), among other things.
For maximum power transfer of a source to a load,
the impedance of the source, load and
transmission line must be the same (matched).
Signal
Source
~
Load
Transmission
Line
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
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Impedance
In an antenna system these three impedances are
matched as closely as possible over a specified
range of frequencies.
When there is an impedance mismatch, some of
the signal is reflected back to the source. Of
course, the impedance there doesn’t match so part
of the reflected signal is reflected back again.
And so on: back and forth until the signal is
attenuated into oblivion, losing part of its energy all
the way.
So you see how power is lost with a mismatch.
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
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Impedance
Matching antenna impedance seems obvious
when transmitting, since you want all of your
transmitter power to be radiated from the antenna.
But it also works in reverse (reciprocity). When
receiving, signal strength is also maximized by
properly matched impedances.
Most modern ham radio equipment has a 50Ω
characteristic impedance.
The cable may or may not be 50Ω. The antenna
itself rarely is 50Ω.
T5C13-2014: What are the
units of impedance? Ohms
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
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Impedance
To match the impedance of the radio to the
transmission line and antenna, various means may
be employed. Some are used at the radio, some
at the antenna.
We will not go into detail here; just be aware that
hams use a variety of impedance matching
techniques.
So we see that impedance matching is important
for maximum power transfer when transmitting and
receiving radio signals
T9B01-2014: Why is it important to have a low SWR in an antenna
system that uses coaxial cable feed line?
To allow the efficient transfer of power and reduce losses
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
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Impedance
A common way for hams to quantify impedance
matching is with the term Standing Wave Ratio
(SWR).
SWR is a generalized measurement of how well
matched the radio is to the antenna and feedline.
SWR is quite a topic in and of itself, and is more
associated with the transmission line. The
antenna is only one contributor to the subject so
we will leave it at that in this presentation.
T7C03-2014: What, in general terms, is standing wave ratio (SWR)?
A measure of how well a load is matched to a transmission line
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
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Wavelength
Let’s review the concept of wavelength because it
is fundamental to antenna behavior and design.
Amplitude
At any frequency it takes a certain amount of time
for a wave to complete one cycle. A cycle is any
repeating feature of the waveform. Radio waves
have sinusoidal form.
Cycle
Cycle
Frequency = How many
cycles per second (Hz)
# Cycles
1 Second
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
Time
=Hz
32
Wavelength
Because the wave moves over time (very fast!), it
travels a certain distance in any given period.
Wavelength is the distance a wave travels in one
complete cycle. We measure this in meters.
Wavelength is
represented by
the Greek letter
Lambda (λ)
Amplitude
λ
λ
Distance
λ
T3B01-2014: What is the name for the distance a
radio wave travels during one complete cycle?
Wavelength
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
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Wavelength
Viewed in 3D animation, it’s not only cool to look
at, but may help us understand it a little better.
Constant
wavelength (λ)
shown moving
in this area.
The red and blue
sine waves are
the electric and
magnetic fields
oscillating at right
angles to each
other at the radio
frequency.
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
Radio wave is
propagating
this way at ~
the speed of
light.
34
Wavelength
Radio waves are typically oscillating millions of
times per second (MHz).
They are traveling near the speed of light (300
million meters per second).
The time it takes for a radio wave to complete one
cycle equals the speed of light (approximately)
divided by the radio frequency.
300M m/sec
RF Hz
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
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Wavelength
Simplifying the math shows us that to calculate
wavelength, we simply divide 300 by the frequency
in MHz. The millions (Megas) cancel each other
out.
So wavelength at the center of our most common
VHF radio band would be: 300/146=2.05m Hey,
that’s our 2-meter band!
At the center of our popular UHF band the
wavelength would be: 300/435=0.69m
We call
this 0.7m (700mm) wavelength the 70cm band.
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
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Wavelength
So we see that higher frequencies complete one
cycle in less time than lower frequencies.
This means that the wavelength of higher frequencies
is shorter than that of lower frequencies. Frequency
and wavelength are inversely proportional.
Shorter λ
Longer λ
Lower Frequency
Higher Frequency
T3B05-2014: How does the wavelength of a radio wave relate to its frequency?
The wavelength gets shorter as the frequency increases
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
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Resonance
Antenna resonance involves reflecting RF
waveforms which are reinforced by recurring
signals.
Analogous to that sympathetic ringing condition we
hear in a guitar string tuned to a particular note.
This situation occurs when the antenna conductors
are at one half wavelength in dimension.
Graphics on the following slides will help to explain
this concept.
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
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Resonance
This demonstration uses a single wire antenna that
is exactly one half wavelength (λ/2) long at the
resonant frequency.
RF
Source
~
~
A
~
λ/2 Antenna
Wire
B
We apply a RF waveform to end A.
The signal travels down to the wire to point B.
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
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Resonance
RF
Source
~
~
A
~
λ/2 Antenna
Wire
B
At point B the wave sees an open circuit at the end
of the wire and so it reflects back towards the
source at point A.
This reflection is 180º out of phase with the original
signal. That is, its sine wave polarity is flipped.
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
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Resonance
RF
Source
~
~
A
λ/2 Antenna
Wire
B
When the reflected wave arrives back at point A it
is once again reflected back to point B.
This reflection again inverts the polarity of the
wave and so it goes back to 360º (or 0º).
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
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Resonance
RF
Source
~~
~
A
λ/2 Antenna
Wire
B
Due to perfect timing with a half-wave wire length,
a new wave is generated from the signal source
which is exactly in phase.
So now we have the reflected energy from the
previous cycle adding to the new energy of the
next cycle. This additive effect is positive but not
double, due to losses (resistance) in the wire.
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
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Resonance
Synchronized at resonance, the waves reinforce
each other while traveling back and forth on the
antenna wire.
Recurring Wave
Reflected Wave 
Composite Wave
Net Gain
The resulting flow of electrons is maximized and
more energy is converted from RF to E-M (or viceversa). This happens on half-wavelength wires
(and odd multiples).
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
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Resonance
At resonance the antenna elements achieve
maximum in-phase current which improves its
performance in transmission and reception.
The further the waveform deviates from the
resonant frequency, the less supportive the
reflective waves become. In fact, at 180º
reflection (antiresonance), the waves cancel and
most antenna energy is lost.
Recurring Wave
Reflected Wave 
Composite Wave
Net Zero
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
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Resonance
An antenna need not be perfectly resonant to work
well, but it works best at resonance.
This sympathetic reinforcement phenomenon on
half-wavelength wires forms what is called a
standing wave pattern as shown in the animation
below.
Standing waves are a key attribute of resonance.
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
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Resonance
To help visualize resonance, impedance and
standing waves, there is an outstanding video
located at:
https://www.youtube.com/watch?v=DovunOxlY1k
The video presentation is very old (1961) but there
is nothing else quite like it. It is expertly presented
and very interesting and quite applicable to
understanding antenna waves.
Highly recommended for all hams to spend a half
hour watching this video on the Similarities of
Wave Behavior from the AT&T archives.
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
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Resonance
There is another kind of resonance you may hear
about that involves the interaction of capacitive
and inductive reactance in an antenna.
However, wave resonance is by far the dominant
factor in most antennas so we will only mention
reactive resonance in passing.
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E-M Radiation
We understand that radio waves are made of
oscillating electric and magnetic fields, but what
makes antennas radiate or capture them?
OK, not really magic, but it is complex. This is where
we avoid some highly technical discussion. You just
have to know that accelerating electrons cause an
E-M field to radiate (transmit a radio wave).
Also accept that an E-M field causes electrons to
accelerate in a conductor (receive a radio wave).
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
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E-M Radiation
At radio frequencies, electrons in the antenna’s
conductor are oscillating rapidly in nearlycontinuous acceleration. This acceleration causes
E-M radiation from the antenna at that frequency.
This is what the antenna does as a transducer.
If you really want to dive into the technical details,
study up on Maxwell’s equations, Faraday’s Law
and electrodynamics.
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
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E-M Radiation
All conductors radiate E-M waves to some degree
or another. This varies by many factors, mainly
signal frequency and conductor characteristics.
Antennas are conductors designed specifically to
radiate or capture radio waves at certain
frequencies.
You might say that all other conductors are
unintentional antennas. Their behavior can often
be ignored, but sometimes they contribute to radio
frequency interference (RFI) problems.
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
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E-M Radiation
The term radiation in our context is the emission of
RF waves.
It should not be confused with ionizing radiation
from radioactive sources, which is hazardous to
human health above certain intensity and duration.
RF radiation does have physiological effects at
certain frequencies and power levels, however.
Refresh your understanding of RF exposure
hazards from your Technician license study.
T0C01-2014: What type of radiation
are VHF and UHF radio signals?
Non-ionizing radiation
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
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Theory Meets Reality
So far we’ve reviewed the three properties common
to all antenna types and looked at four important
concepts related to how antennas work:
Impedance, wavelength, resonance, and radiation.
Still with us? Good.
Have a Cookie!
Now we will talk about how all this antenna theory
becomes tangible in the real world. It’s where the
rubber meets the road on the electromagnetic
highway.
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
52
Physical Length
As discussed earlier, resonance is an essential
characteristic in a functional antenna.
Recall that the sweet spot for resonance occurs at
one half wavelength (λ/2) of the resonant
frequency.
Since wavelength is a physical length at a given
frequency, a resonant antenna would simply be a
half-wavelength long at that frequency.
One wavelength (λ) is the speed of light divided by
the radio frequency.
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
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Physical Length
To get a resonant λ/2 antenna length we simply
divide the wavelength by two.
Using the center of the popular 40m band (7.07.3MHz) this would look like:
300/7.15=41.96m
That’s one wavelength so divide this by two to give
us 20.98m as the half-wavelength antenna length
for 7.15MHz. Converting from meters to feet
makes it 68.89ft long.
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
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Physical Length
To avoid dividing by two and converting to meters
here in ‘Merica, the quick formula for half-wave
antenna lengths is simply 492/MHz = feet.
Back to the 40m center frequency of 7.15MHz we
get 492/7.15=68.81ft, nearly the same as before.
Returning to our example of our favored VHF band
(146Mhz) this would look like: 492/146=3.37ft
Converting to inches, that’s 40.4in.
For a quarter-wave antenna length, divide by two.
T9A08-2014: What is the approximate length, in inches,
of a quarter-wavelength vertical antenna for 146 MHz?
19
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
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The Dipole
Let’s spend a little time with the dipole antenna.
The dipole is generally considered the simplest,
most basic antenna form and is usually what is
presented in most antenna discussions.
Many, if not most, antenna configurations are
derivatives of the dipole so it’s important to
understand this foundational design.
No doubt you’re familiar with the dipole antenna
from your Technician license instruction, but we
will give a little more detail on the following slides.
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The Dipole
The form of the dipole is two quarter-wavelength
elements creating a resonant λ/2 center-fed
antenna.
λ/2
λ/4
~
λ/4
Transmitter
or Receiver
The name dipole means “two electrical terminals”
as it involves elements of differential polarity. We
can visualize this on the following slide.
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
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The Dipole
Here we see the alternating voltage waveform in
red switching back and forth on the antenna.
Notice how the voltage peaks at the ends of the
antenna and is minimal at the feed point.
The blue wave is current in the antenna. Current is
minimal at the ends but peaks in the middle.
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
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The Dipole
This voltage and current distribution are true for
λ/2 dipoles and all variants/derivatives. Voltage
will always be highest at the ends and current will
always peak in between the ends.
Note that voltage and current are 180º out of
phase.
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
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The Dipole
Taking the previous animation and adding in the
electric field waveform in an isometric view helps
us visualize the dipole polarity.
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
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The Dipole
With the horizontal dipole we see a horizontal
electric field (horizontal polarization.)
Dipoles are not always oriented horizontally.
When you set the elements perpendicular to earth,
it becomes vertically polarized.
~
Horizontally
Polarized
Dipole
~
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
Vertically
Polarized
Dipole
61
The Dipole
Earlier we gave a formula for 1/2 wave resonant
antenna length: 492/MHz = feet.
When you consider various factors affecting real
world dipole resonance (height, conductor
thickness, frequency, end effects), the formula
468/MHz = feet is more accurate for the HF bands.
In the end, we want to achieve resonance and that
happens only at a specific length. Remember,
wavelength is inversely proportional to frequency.
T9A05-2014: How would you change a dipole
antenna to make it resonant on a higher frequency?
Shorten it
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
62
The Dipole
The radiation pattern of a dipole is generally
broadside (perpendicular) to the antenna axis. It is
semi-directional with most of the energy radiating
in a toroidal (donut) shape. Minimal radiation is
exhibited at the ends.
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
63
The Dipole
One caveat to the dipole’s radiation pattern is that
it applies when the antenna is mounted high.
When lower to the ground it becomes more omnidirectional.
T9A10-2014: In which direction is the
radiation strongest from a half-wave dipole
antenna in free space?
Broadside to the antenna
Half-wave antennas such as the dipole are
sometimes referred to as Hertz antennas.
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
64
Efficiency
One of the better definitions of antenna efficiency
comes from the Institute for Electrical and
Electronics Engineers (IEEE): “The ratio of the
total power radiated by an antenna to the net
power accepted by the antenna from the
connected transmitter.”
This ratio would be less than 1 and can be
expressed in decibels (dB) or percentage.
Note that this definition ignores the real power loss
(attenuation) in the transmission line (feedline).
Antenna system efficiency would factor this in as
well.
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
65
Efficiency
In plain language, antenna efficiency is a
measurement of how much transmitted RF power
is converted into useful E-M waves (and vice-versa
in case of reception). You might also view it as
antenna transducer energy conversion loss.
A physically impossible 100% efficient antenna
converts all RF waves to E-M radiation.
An antenna with nearly 0% energy conversion has
extremely poor efficiency.
Real antennas are something in between these
extremes; the more efficient the better.
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
66
Efficiency
Since efficiency is also a measure of energy loss
in the antenna, we should know what causes loss.
The principal factors in antenna loss are
impedance mismatch and non-resonance. Those
are easily controlled by antenna design at a
specified frequency.
Other lossy detriments to antenna radiation are
conductor resistance and dielectric effects.
Lost energy is mostly in the form of resistive
conductor heating. A warm antenna is an
inefficient antenna.
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
67
Bandwidth
Not to be confused with signal bandwidth (that’s
the frequency range occupied by a particular radio
emission type), antenna bandwidth is defined as
the frequency range over which a particular
antenna will perform to a desired level.
The performance measurement depends on how it
is defined. There is no special yardstick for
bandwidth, although there are some widelyaccepted standards.
Most practical antennas will perform acceptably
well over an entire ham radio band.
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
68
Bandwidth
Generally speaking, with increased bandwidth
come reduced directivity, gain and efficiency.
The higher the performance of an antenna (gain &
efficiency), the less the bandwidth. Remember, an
antenna is resonant at only one frequency.
Antenna conductor diameter also plays a role in
bandwidth. The larger the diameter, the greater
the bandwidth.
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
69
Questions?
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
Real-World Antennas
All this theoretical study of antennas is fine and
necessary but in the real world a practical antenna
is imperfect.
A real antenna system is always a compromise or
tradeoff between two or more competing interests:
•
•
•
•
Bands/Frequencies
Directivity & Gain
Bandwidth
Space Available
•
•
•
•
Practical Height
Cost
Stealthiness/Visibility
Spousal Approval
The ham needs to decide which of these is most
important and prioritize accordingly.
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
71
Real-World Antennas
Ultimate antenna performance is achieved only at
the resonant frequency. That’s fine if we only
operate at one frequency, but most hams operate on
multiple bands and move around within them.
One of the bigger compromises a ham will make is
choosing wide bandwidth or high performance.
Most hams will be happy to have OK performance
over a wider range of frequencies.
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
72
Real-World Antennas
A few hams are blessed to have acreage and money to
install tall towers and have a large “antenna farm”. They
will have outstanding performance with fewer
compromises, assuming quality design and installation.
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
73
Real-World Antennas
On the other extreme, many hams live in urban or suburban
areas with little or no space to install antennas, or have
restrictions on what is allowed. These hams will have to
limit their bands of operation, use lower power, and use
stealth antennas. They will have to compromise quite a bit
and experience more modest performance.
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
74
Types & Configurations
Now we will look at some common antenna types
and configurations.
The basic description and essential characteristics
will be presented. Advantages, disadvantages and
other details of these types is beyond the scope of
this discussion. The reader is encouraged to
research this on their own.
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
75
Types & Configurations
Standard Dipole
Typically half-wave center-fed antenna with two
quarter-wave symmetrical elements.
Resonant at one frequency (single-band).
Three common orientations: horizontal, vertical,
and sloping.
Sloper
~
Horizontal
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
~
Vertical
76
Types & Configurations
Inverted Vee
Common variant to the standard 1/2-wave dipole.
The name derives from the orientation of the
dipole elements that are supported in the middle
and angled down.
This dipole occupies less horizontal space and
requires only a single center support, which makes
it popular for EmComm or field use on HF bands.
Inverted Vee
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
~
77
Types & Configurations
OCF Dipole
Half-wave antenna with asymmetrical elements.
Feed point is off-center (OCF=off-center fed). Also
known as a Windom antenna.
Proper design permits multi-band operation.
Horizontal, sloping, or inverted vee orientation.
~
OCF
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
78
Types & Configurations
Vertical Monopole
Derived from the half-wave center-fed dipole, this
is commonly known as a quarter-wave (λ/4)
ground-plane antenna.
The vertical monopole differs from a verticallyoriented dipole in that it does not have a symmetric
λ/4-wave lower element as shown below.
~
Vertical
Dipole
Lower λ/4
Element
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
79
Types & Configurations
Vertical Monopole
Instead the vertical monopole replaces the lower
element by the earth (ground) or a substitute
called a counterpoise or ground plane.
Vertical
Monopole
~
Ground Plane or
Counterpoise
This is the antenna type used on all mobile
(vehicle) and marine (boat) installations as well as
with hand-held radios (HTs).
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
80
Types & Configurations
Vertical Monopole
The counterpoise may be radial wires in the earth
(ground-mount). Or they could be sticking out
below a vertical radiator (mast-mount).
The counterpoise may also be a vehicle chassis,
water, or even a human body.
Antenna performance is highly dependent on the
quality of the ground plane and is often inferior to a
λ/4 antenna element.
Quarter-wave vertical monopoles are sometimes
referred to as Marconi antennas.
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
81
Types & Configurations
Vertical Monopole
As with the λ/2 dipole, voltage (E) peaks at the
open end of the antenna. In this case we have
only one open end.
Current (I) peaks close to the feed point so in this
case it would be at the base of the antenna.
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
82
Types & Configurations
J-Pole
Half-wave (λ/2) end-fed antenna also known as
the Zepp (originally developed for use on airships
with the antenna trailing behind).
Features a λ/4 parallel tuning stub (for impedance
matching) that forms a J-shape.
Slim-Jim version folds over longer element for
greater gain.
J-pole
~
VHF Jpole
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
Slim-Jim
Variant
83
Types & Configurations
J-Pole
Vertically-oriented J-poles are popular for
VHF/UHF operation due to improved gain
over a λ/4 ground-plane antenna (vertical
monopole).
Roll-up J-poles made of ladder line or
twin-lead cable are lightweight and
compact, making them great for
EmComm field deployment.
Long-wire variants of the J-pole are also
popular for multi-band HF use.
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
Twin-Lead and
Ladder Line
VHF J-poles
84
Types & Configurations
Yagi
Directional (beam) half-wave center-fed antenna
with two quarter-wave symmetrical elements.
Essentially a dipole with extra elements to provide
directivity. Officially termed Yagi-Uda (inventors).
More commonly oriented horizontally but may be
vertical for local VHF/UHF use.
6-Element
Vertical
Yagi
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
~
Typical 3Element
Yagi
85
Types & Configurations
Yagi
Directivity achieved through the use of parasitic
reflector and director elements.
Reflector is slightly longer than λ/2 and there may
be more than one.
Director is slightly shorter than λ/2 and there may
be any number of them.
Director
Driven Element
~
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
Reflector
86
Types & Configurations
Loop
Loops are generally grouped into two classes.
These will be shown on the following three slides.
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
87
Types & Configurations
Small Loop
The small (AKA magnetic) loop is a fractional
wavelength antenna with poor efficiency.
This magnetic loop has superior directional qualities
and is often used in radio direction finding. Small
loops also have excellent electrical noise immunity.
Matching requires fine tuning with a large variable
capacitor. For this reason it is not often a ham’s
primary HF antenna. However, it is well-suited for
low-power (QRP) portable use.
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
88
Types & Configurations
Large Loop
The large (AKA resonant) loop is simply a single
full wavelength element, λ in circumference.
The loop shape is generally round but it does not
have to be circular. It can be oval, hexagonal,
square or even triangular. Acute angles should be
avoided.
Round
Loop
Ovoid
Loop
Hex
Loop
Square
Loop
~
~
~
~
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
89
Types & Configurations
Large Loop
Due to the long lengths required for full-wave
antennas, resonant loops need a lot of space.
For the 80m band, the loop would be around 270ft
long. On 40m the circumference would be 140ft.
On 20m you need a 70ft loop.
Although multiple turns may be used to reduce the
diameter, performance improves with greater loop
area. Lower-frequency HF band loops are often
relatively low to the ground and horizontally
oriented.
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
90
Types & Configurations
Quads & Deltas
Directional (beam) antennas derived from the loop.
Usually two-element antennas with parasitic
reflector slightly longer than λ.
Gain comparable to a 3-element Yagi.
Polarization depends on orientation of feedpoint.
Quad
~
~
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
Delta
91
Types & Configurations
VHF/UHF Mobile
Vertical monopole with the vehicle body/chassis
acting as the ground plane (counterpoise).
Nominally λ/4 whip for general omni-directional
radiation pattern.
5/8-wave mobile antennas are more popular
because they have radiation lobes closer to
horizontal with relative gain over 1/4-wave.
T9A12-2014: What is a reason to use a properly mounted
5/8 wavelength antenna for VHF or UHF mobile service?
It offers a lower angle of radiation and more gain
than a 1/4 wavelength antenna and usually
provides improved coverage
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
~
Vertical
Monopole
92
Types & Configurations
VHF/UHF Mobile
With the 5/8-wave whip an inductor (loading coil) is
added for impedance matching and is usually
located in the middle but sometimes at the base.
T9A14-2014: Which of the following
terms describes a type of loading when
referring to an antenna?
Inserting an inductor in the
radiating portion of the antenna to
make it electrically longer
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
93
Types & Configurations
VHF/UHF Mobile
Most VHF mobile antennas work well on UHF so
are often called dual-band antennas.
This is unique to the 2m and 70cm amateur bands
where the UHF band is 3x the frequency of the
VHF band.
Antennas are resonant on odd multiples of the
wavelength. 70cm (435MHz) is conveniently close
to the third harmonic of 2m (146MHz).
Radiation patterns are a little different but a 2m
antenna generally works for 70cm.
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
94
Types & Configurations
VHF/UHF Hand-Held
Vertical monopole with the human body acting as
a capacitively-coupled counterpoise (ground
plane).
~
Manufacturer provides fractional-wavelength
electrically-short helical antenna with the radio.
This “rubber duck” is a poor antenna by most
Vertical
standards.
Monopole
Performance significantly improved by replacing
factory antenna with λ/4 or 5/8-wave whip.
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
95
Types & Configurations
There are many other antennas out there with
some really interesting names: Bazooka, Discone,
Parabolic, Log-Periodic, Beverage, Nord, Helical,
Cloverleaf, Bowtie, and others.
We could spend hours discussing antenna types
but have presented the most common ones that an
ordinary ham is likely to see or use.
It would be good to investigate the merits and uses
of other antenna types on your own.
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
96
Transmission Lines
An antenna’s transmission line is the feedline
(coaxial cable, ladder line, or hard line) that
connects the radio to the antenna.
Transmission line is in and of itself a significant
topic that we will not delve into here.
Simply be aware that the feedline is a major part of
a complete antenna system along with the antenna
and impedance match and plays a crucial role in
antenna performance.
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
97
Mobile VHF/UHF Considerations
Mobile radio generally refers to use in a vehicle,
typically a personal car or truck for most hams.
Quite useful for EmComm or public service events.
A HT can be used in a car with an external
antenna but mobile transceivers are greatly
preferred for this (more power, better microphone
and controls).
Ah, the good
old days of
mobile radio.
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
98
Mobile VHF/UHF Considerations
Quality of the ground plane (contact resistance,
area, uniformity) affects antenna gain and
radiation pattern.
Antennas are almost always removable by
unthreading from the base/mount. Use rain/dust
cover when an antenna is not installed.
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
99
Mobile VHF/UHF Considerations
Mobile mounts come with different connections or
threads to match the antenna. This is the buyer’s
preference. Consider interchangeability (different
antennas on one vehicle or between vehicles).
Mobile antenna mounts include a length of coaxial
cable. Specify connector type to match radio or
use an adapter.
The three most common types of mobile VHF/UHF
antenna mounts are: Permanent, Magnetic (mag
mount), and Lip or Bracket.
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
100
Mobile VHF/UHF Considerations
Permanent mount is superior when centered and
properly installed.
Permanent mount involves drilling at least one
hole in the roof or trunk of the vehicle. Not all
hams are willing to do this.
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
101
Mobile VHF/UHF Considerations
Magnetic mount does not provide direct contact
with counterpoise (roof or trunk); it is capacitively
coupled so not as efficient.
Small magnets may not stay in place at high
vehicle speeds. Recommend 3½” size minimum.
Mag mounts also can damage the paint if not used
carefully. They also become projectiles in case of
a vehicle crash (insurance and liability factor).
Recommended for temporary use only, although
some hams are happy with their permanently
installed mag mounts.
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
102
Mobile VHF/UHF Considerations
Lip or bracket mounts give better contact to the
ground plane than mag mounts. However, they
usually locate the antenna away from the center of
the vehicle due to their edge- or side- attachment
method.
For true omni-directional radiation, the antenna
should be centered over a large metal surface.
Avoid mounting near edges.
T9A13-2014: Why are VHF or UHF mobile
antennas often mounted in the center of the
vehicle roof?
A roof mounted antenna normally provides
the most uniform radiation pattern
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
103
Mobile VHF/UHF Considerations
As mentioned previously, 5/8-wave antennas give
superior performance than the shorter ones.
Unless you have a practical reason to have the
shorter antenna, choose 5/8-wave over λ/4.
λ/4 mobile whip on
right not much
longer than HT
whip.
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
λ/4 whip on left
compared to 5/8wave.
104
Hand-Held VHF/UHF Considerations
Hand-held portable radio is
quite useful for EmComm
and public service events.
We have come a long way
with radio technology since
the 1920s!
Next time you want to whine
and fuss over carrying your
HT around, think of these
guys.
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
105
Hand-Held VHF/UHF Considerations
The factory-supplied “rubber duck” antenna for
HTs is a poor performer except over short
distances and clear space.
It is essentially a coil of wire surrounded by a
flexible protective jacket.
The rubber duck has 5db negative gain compared
to a λ/4 whip antenna. The resulting effective
radiated power (ERP) is only 1W with a 5W radio.
T9A04-2014: What is a disadvantage of the
“rubber duck” antenna supplied with most
handheld radio transceivers?
It does not transmit or receive as
effectively as a full-sized antenna
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
106
Hand-Held VHF/UHF Considerations
Sometimes disparagingly referred to as a “rubber
resistor,” this vertical monopole’s advantages are
short length, a blunt tip, and robustness. The
manufacturers have apparently decided that these
qualities outweigh performance.
Rubber duck performance inside a vehicle is even
worse, although a longer antenna may be
awkward in a small car.
T9A07-2014: What is a good reason not to use a
“rubber duck” antenna inside your car?
Signals can be significantly weaker than
when it is outside of the vehicle
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
107
Hand-Held VHF/UHF Considerations
Hams who want better performance will get an
after-market λ/4 whip or telescoping antenna .
λ/4 HT whip on right
compared to rubber
duck.
Telescoping HT whip
on left compared to
5/8-wave mobile
antenna.
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
Telescoping HT whip
collapsed, not much
longer than rubber
duck.
108
Hand-Held VHF/UHF Considerations
While the antenna can be improved with a longer
whip, vertical monopole performance is limited by
the HT’s indirect ground plane.
The counterpoise that makes the vertical
monopole behave like a λ/2 dipole on a HT is the
operator’s body. It is capacitively coupled to the
ham’s body through the plastic case and metal
shell around the RF circuitry.
This indirect counterpoise coupling is not only
weak but also highly variable and unpredictable.
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
109
Hand-Held VHF/UHF Considerations
The good news is that we can improve the
counterpoise simply by adding a wire to the HT
antenna connection.
By connecting a λ/4 wire (~19” for 146MHz) to the
antenna connector outer terminal, we create a
physical counterpoise in place of the indirect
ground plane through the operator’s body.
This gives superior performance under difficult
conditions and is easy to do.
These physical counterpoise wires are known as
rat tails or tiger tails due to their appearance.
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
110
Hand-Held VHF/UHF Considerations
Simply unscrew the antenna, slip the rat tail over
the connector and re-attach the antenna.
Rat tail counterpoise
installation is quick
and easy.
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
111
Hand-Held VHF/UHF Considerations
The rat tail can simply hang down in a gentle arc
where it won’t be much in the way of anything.
Bonus feature is that you can hold the wire out and
point it in the direction of communication.
Gain/directivity is achieved by pointing the rat tail.
The rat/tiger tail combined with a quality λ/4 whip
antenna achieves the best possible antenna
performance with a HT while walking around.
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
112
Antenna Safety
Basic antenna safety involves two primary
concerns:
First is avoiding overhead power lines or other
hazardous energy sources when installing or
working on an antenna.
RF exposure by contact or radiation is the second
issue.
T0B06-2014: What is the minimum safe
distance from a power line to allow when
installing an antenna?
So that if the antenna falls
unexpectedly, no part of it can come
closer than 10 feet to the power wires
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
113
Antenna Safety
RF exposure by contact means: Do not touch the
antenna elements when transmitting. It also
means never install an antenna where people or
animals might contact it.
RF exposure by radiation must also be considered.
Be aware of power levels and frequencies where
this becomes a safety concern. Understand
Maximum Permissible Exposure (MPE) and the
FCC regulations associated with it.
T0C07-2014: What could happen if a person accidentally
touched your antenna while you were transmitting?
They might receive a painful RF burn
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
114
Antenna Safety
Many of the Technician license exam questions
involve antenna tower safety.
Of course, those are important but most hams
don’t have climbable towers so we won’t spend
time on that topic here.
If you have the luxury of an antenna tower, study
up on all the rules and procedures for tower safety
and proper grounding.
T0B03-2014: Under what circumstances is it safe
to climb a tower without a helper or observer?
Never
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
115
Related Topics
There are other topics closely associated with
antennas that were not discussed here and would
be worth exploring on your own.
A more complete and practical understanding of
antennas would involve these as well:
•
•
•
•
Propagation
Transmission Lines
Impedance Matching
Standing Wave Ratio
(SWR)
• Antenna/Feedline
Connectors
• Ground Planes
• Common-Mode
Noise & Filtering
• Antenna “Tuners”
• Antenna Analyzers
• RFI/Noise
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
116
Questions?
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
Acknowledgements
Concepts, information and detail taken from the following sources.
Nothing was copied directly; it is reference information only:
The ARRL Handbook for Radio Communications, 2013 edition.
Electronics Technician: Volume 7—Antennas and Wave Propagation, US Navy training publication
NAVEDTRA 14092
Why an Antenna Radiates, Kenneth Macleish W7TX, QST November 1992
Understanding electromagnetic fields and antenna radiation takes (almost) no math, EDN Magazine,
March 2, 2000
Electromagnetic Radiation Explained (How Radio Waves Are Born), Jim Hawkins K2JHV,
hawkins.pair.com/eRadiation.html
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
118
Acknowledgements
Select graphics attributed to the following sources:
Electromagnetic wave model animated GIF from http://weelookang.blogspot.com/2011/10/ejs-opensource-propagation-of.html.
Animation of E-M wave copied from http://hawkins.pair.com/eRadiation.html (note: graphic shown
described as misleading).
Electromagnetic wave graphic copied from https://en.wikipedia.org/wiki/Electromagnetic_radiation.
Standing wave enhancement/cancellation graphics copied from http://www.planetoftunes.com/soundaudio-theory/so_media/standing_waves.gif.
Dipole antenna electromagnetic wave interaction and dipole antenna voltage/current distribution
animations from Wikipedia: https://en.wikipedia.org/wiki/Dipole_antenna.
Antenna polarization copied from Radio Fundamentals found at robrobinette.com.
Dipole voltage/current distribution graphic copied from The ARRL Handbook for Radio
Communications, 2013 edition
Antenna radiation patterns and dipole voltage/current distribution copied from the ARRL Handbook for
Radio Communications, 2013 edition.
Quarter-wave vertical monopole voltage/current distribution copied from Antenna Voltage, Phase,
Power and Impedance Distribution found at Chemandy.com.
Unicorn Magic animated GIF copied from http://i.imgur.com/YsbKHg1.gif.
Certain photos were copied from the internet with no attributable source.
All other graphics and photos are original to this presentation.
Understanding Antennas / A Simplified Perspective : Jim Peisker, AF5NP
119