Dipole antenna aerial tutorial

Dipole Antenna / Aerial Tutorial
Dipole Antenna / Aerial Tutorial the dipole antenna or dipole aerial is a key element in the antenna environment. It can be
used on its own or as part of another antenna system.
DIPOLE TUTORIAL INCLUDES
 Dipole antenna
 Half wave dipole
 Short dipole
 Folded dipole antenna
 Dipole length calculation
 Dipole feeds / impedance
 Dipole radiation patterns
The dipole antenna or dipole aerial is one of the most important and commonly used types of RF antenna.
The dipole aerial or antenna is widely used on its own, but it is also incorporated into many other RF antenna designs where it
forms the radiating or driven element for the overall antenna.
The dipole is a simple antenna to construct and use, and many of the calculations are quite straightforward. However like all
other antennas, the in-depth calculations are considerably more complicated.
Dipole antenna basics
As the name suggests the dipole antenna consists of two terminals or "poles" into which radio frequency current flows. This
current and the associated voltage causes and electromagnetic or radio signal to be radiated.
Basic dipole antenna
As seen the antenna consists of a radiating element that is split, normally in the centre to allow a feeder to apply power to it
from a transmitter, or to take power from it to a receiver.
The length of the radiating element determines many of the properties of the dipole antenna from its impedance, centre operating
frequency, etc. As such this is an important feature of the antenna.
Often the term dipole antenna tends to indicate a half wave dipole. This is by far the most widely used length for a dipole. It
forms a resonant circuit which resonates where the electrical length is half a wavelength long - the electrical length differs from
the wavelength of the signal in free space because of a number of the effects of the radiating element on the signal and it is
very slightly shorter than the signal e/m wavelength in free space...
Half wave dipole antenna
Although the half wavelength dipole antenna is the most popular, a variety of other formats are also available.

Dipole types
The dipole antenna consists of two conductive elements such as metal wires or rods which are fed by a signal source or feed
energy that has been picked up to a receiver. The energy may be transferred to and from the dipole antenna either directly
straight into a from the electronic instrument, or it may be transferred some distance using a feeder. This leaves considerable
room for a variety of different antenna formats.
Although the dipole antenna is often though in its half wave format, there are nevertheless many forms of the antenna that can
be used.
 Half wave dipole antenna: The half wave dipole antenna is the one that is most widely used. Being half a wavelength
long it is a resonant antenna. Read more about the Half wave dipole
 Multiple half wave’s dipole antenna: It is possible to utilise a dipole antenna or aerial that is an odd multiple of half
wavelengths long.
 Folded dipole antenna: As the name implies this form of the dipole aerial or dipole antenna is folded back on itself.
While still retaining the length between the ends of half a wavelength, an additional length of conductor effectively
connects the two ends together. Read more about the Folded-dipole
 Short dipole: A short dipole antenna is one where the length is much shorter than that of half a wavelength. Where
a dipole antenna is shorter than half a wavelength, the feed impedance starts to rise and its response is less dependent
upon frequency changes. Its length also becomes smaller and this has many advantages. It is found that the current
profile of the antenna approximately a triangular distribution. Read more about the Short-dipole
 Non-resonant dipole: A dipole antenna may be operated away from its resonant frequency and fed with a high
impedance feeder. This enables it to operate over a much wider bandwidth.
Dipole antenna current & voltage distribution
The current and voltage on a radiating element vary along the length of the dipole. This occurs because standing waves are set
up along the length of the radiating element and as a result peaks and troughs are found along the length.
The current falls to zero at the end and rises towards the middle. Conversely, the voltage peaks at the end and falls as the
distance from the end increases.
Both the current and voltage on the dipole antenna vary in a sinusoidal manner, meaning that there may be other peaks and
troughs along the length of the radiating sections dependent upon their length.
The most popular form of dipole antenna is the half wave and for this, the current is at a minimum at the ends and rises to a
maximum in the middle where the feed is applied. Conversely the voltage is low at the middle and rises to a maximum at the
ends. It is generally fed at the centre, at the point where the current is at a maximum and the voltage a minimum. This provides
a low impedance feed point which is convenient to handle. High voltage feed points are far less convenient and more difficult to
use.
When multiple half wavelength dipoles are used, they are similarly normally fed in the centre. Here again the voltage is at a
minimum and the current at a maximum. Theoretically any of the current maximum nodes could be used.
Three half wavelength wave dipole antenna
The dipole antenna is a particularly important form of RF antenna which is very widely used for radio transmitting and receiving
applications. The dipole is often used on its own as an RF antenna, but it also forms the essential element in many other types
of RF antenna. As such it is the possibly the most important form of RF antenna.
Half Wave Dipole Antenna / Aerial
- The half wave dipole antenna is a half wavelength version of the popular dipole antenna.
The half wave dipole is the most widely used version of the dipole antenna or aerial.
As the name implies, the half wave dipole is a half wavelength long. The antenna is the shortest resonant length that can be
used for a resonant dipole.
Half wave dipole basics

The half wave dipole is formed from a conducting element which is wire or metal tube which is an electrical half wavelength
long. It is typically fed in the centre where the impedance falls to its lowest. In this way, the antenna consists of the feeder
connected to two quarter wavelength elements in line with each other.
The voltage and current levels vary along the length of the radiating section of the antenna. This occurs because standing waves
are set up along the length of the radiating element.
As the ends are open circuit current at these points is zero, but the voltage is at its maximum.
As the point at which these quantities is measured moves away from the ends, it is found that they vary sinusoidally: the voltage
falling, but the current rising. The current then reaches a maximum and the voltage a minimum at a length equal to an electrical
quarter wavelength from the ends. As it is a half wave dipole, this point occurs in the centre.
Half-wave dipole antenna current & voltage waveforms
As the centre point is where the current is a maximum and the voltage is a minimum, this makes a convenient point to feed the
antenna as it present a low impedance. This is much easier to feed as high RF voltages can present many problems for feeders
and matching units.
For a dipole antenna that is an electrical half wavelength long, the inductive and capacitive reactances cancel each other and
the antenna becomes resonant. With the inductive and capacitive reactance levels cancelling each other out, the load becomes
purely resistive and this makes feeding the half wave dipole antenna far easier. Coaxial feeder can easily be used as standing
waves are not present, and it is also much easier to match to a transmitter output that may only want to see a resistive load.
Loads that include reactances lead to higher voltage of current levels that the transmitter may not be able to tolerate.
The impedance for a half wave dipole antenna in free space is dipole 73 Ω which presents a good match to 70Ω coaxial feeder
and this is one of the reasons why coax with this impedance was chosen for many applications.
Half wave dipole length
As the name implies the length of the dipole is a half wavelength. The actual length is slightly shorter than a half wavelength in
free space because of a number of effects.
Calculations for the for the length of the half wave dipole antenna take into account elements such as the ratio of the thickness
or diameter of the conductor to the length, dielectric constant of the medium around the radiating element and so forth.
Read more about dipole length calculations
It is possible to shorten the length of a half wave dipole antenna, or any antenna radiating element for that matter by adding a
loading inductor. This is placed in the radiating element. It works because the dipole antenna can be considered as a resonant
circuit consisting of a capacitor and inductor. Adding additional inductance will lower the resonant frequency, i.e. a given antenna
length will resonate at a lower frequency than that which would be possible had no inductor be present. In this way it is possible
to shorten the length of the antenna.

Half wave dipole field strength
It is possible to plot the field strength for an antenna at a distance from the radiating element to see its radiation pattern. For a
complete 3D view of the radiation pattern both φ and θ angels are required. However to simplify the overall maths behind any
calculations it is possible to express the field strength levels in the planes of interest. These are generally viewed as cross
sections through the overall 3D pattern. The most frequently used one are the horizontal where φ=90° and the vertical planes.
Using the half wave dipole formula given above it is possible to determine the radiation pattern of the half wave dipole antenna
from the far field E vector.
Half wave dipole radiation pattern & directivity
Using the half wave dipole formula, it is possible to calculate the radiation pattern and hence determine the directivity.
As expected the maximum half wave dipole directivity shows the maximum radiation at right angles to the main radiator.
At other angles, the angle θ in the half wave dipole formula above can be used to determine the field strength.
Half-wave dipole radiation pattern
It is also possible to view the radiation pattern in terms of the plane looking around the dipole antenna, i.e. in the plane cutting
the dipole in its field of maximum radiation.
Pattern of radiation with axis of antenna in / out of screen
As can be seen, with the axis of the antenna in / out of the screen, the level of radiation is the same all around the antenna. This
is to be expected as there is nothing to distinguish one direction from another or to affect the radiation in different directions in
this plane.
Practical tips
When developing, designing and installing a half wave dipole antenna, there are a number of general hints and tips that can be
followed to ensure the optimum performance. These are above the normal ones used for antenna installation, for example
ensuring height is optimum, etc.
 Use balanced feeder or balun: The dipole antenna is a balanced antenna. It is therefore necessary to use a balanced
feeder, or if coaxial feeder needs to be used, then some form of balun must be used.
 Half wave dipole is not a half wave: A half wave dipole antenna is not the same length as a half wavelength in free
space. End effects mean that the actual length required is slightly shorter.
 Voltage maxima at the antenna ends: The points of maximum voltage are at the ends of the antenna. If used for
transmitting make sure these cannot be accidentally touched, and also ensure they are adequately insulated. This is
important when using wire antennas where the ends are used as anchor points. These should also be away from
nearby objects that can act to absorb power and detune the antenna.

The half wave dipole antenna is possibly the most widely used forms of the dipole - even the most widely used form of antenna.
It is simple, effective and can be incorporated as the driven element in many other forms of antenna from Yagi antennas to
parabolic reflectors and many more.
Short Dipole Antenna / Aerial Tutorial
- The short dipole antenna is a small version of the popular dipole antenna, typically less than a tenth of a wavelength in its
size.
The short dipole antenna is one that is short when compared to a wavelength at the operating frequency.
Typically a short dipole antenna is taken to be one that is less than a tenth of a wavelength long. However this is very much a
'rule of thumb' and slightly different definitions may appear in various quarters.
The short dipole antenna consists of two co-linear conductors that are placed end to end, but with a small gap between them
for the feeder.
Short dipole antenna basics
As already mentioned the short dipole is a form of dipole antenna created by feeding a wire, typically in the centre with a signal.
The electrical length of the overall radiating element typically has to be less than a tenth of a wavelength to make a short dipole
antenna.
In practice, short antennas, and in this case the sort dipole antenna is rarely satisfactory from an efficiency viewpoint because
much of the power entering it is dissipated as heat as the resistive losses are normally very high.
This factor reflects into the reception instance where only low reception efficiency is attained and low signal levels pervade.
Accordingly poor signal to noise ratios will be achieved in the receiver.
The basic concept of a short dipole antenna is shown in the diagram below.
Short dipole antenna
Current distribution for the short dipole follows the same sinusoidal curve as used for all other forms of dipole. However as only
the end section of the sine curve is applicable, this can be equated to a straight line without introducing any major errors.
Short dipole antenna current magnitude

Short dipole antenna radiation resistance
As with any antenna, one of the key parameters of the antenna is its radiation resistance. This is required to be able to determine
the overall feed impedance and hence the required matching. It is possible to calculate the radiation resistance of the short
dipole antenna.
Where:
Rr = radiation resistance in ohms
L = length of antenna element (both sections together)
λ = wavelength
Both length measurements must be in the same units.
The overall input feed impedance for the short dipole antenna is comprised of a number of different elements: the series
inductance, the capacitance, radiation resistance, and the Ohmic resistance. These need to be combined vectorially to obtain
the overall feed impedance.
By definition the antenna is shorter than a half wavelength and therefore it operates below the resonant frequency. This means
that the over-riding reactance will be capacitance. Also as the antenna impedance is complex, i.e. contains capacitive reactance
(in this case) and instead a balanced feeder should be used between the antenna itself and any impedance matching circuit.
Short dipole radiation pattern
As with other antennas there are two planes of interest for the directional pattern or polar diagram of the short dipole antenna.
When the dipole is vertical, the horizontal radiation pattern is just a circle. Then in any vertical plane through the axis, the field
strength varies according to sinθ. In fact the radiation pattern of a short dipole looks like that of a half wave dipole - the familiar
figure of '8' shape..
Short dipole antenna radiation pattern
Folded Dipole Antenna
- Notes and summary about the folded dipole antenna, folded dipole impedance, unequal conductor folded dipoles, and multi-
wire folded dipoles.
The standard dipole is widely used in its basic form. However under a number of circumstances a modification of the basic
dipole, known as a folded dipole antenna provides a number of advantages.
The folded dipole antenna or folded dipole aerial is widely used, not only on its own, but also as the driven element in other
antenna formats such as the Yagi antenna.
Folded dipole antenna basics
In its basic form the folded dipole antenna consists of a basic dipole with an added conductor connecting the two ends together
to make a complete loop of wire or other conductor. As the ends appear to be folded back, the antenna is called a folded dipole.
The basic format for the folded dipole aerial is shown below. As can be seen from this it is a balanced antenna, like the standard
dipole, although it can be fed with unbalanced feeder provided that a balun of some form is used to transform from an unbalanced
to balance feed structure.

The folded dipole antenna uses an extra wire connecting both ends of the previous dipole as shown. Often this is achieved by
using a wire or rod of the same diameter for all sections of the antenna, but this is not always the case.
Also the wires or rods are typically equi-spaced along the length of the parallel elements. This can be achieved in a number of
ways. Often for VHF or UHF antennas the rigidity of the elements is sufficient, but at lower frequencies spacers may need to be
employed. To keep the wires apart. Obviously if they are not insulated it is imperative to keep them from shorting. In some
instances flat feeder can be used.
Half-wave folded dipole antenna
One of the main reasons for using the folded dipole aerial is the increase in feed impedance that it provides. If the conductors
in the main dipole and the second or "fold" conductor are the same diameter, then it is found that there is a fourfold increase
(i.e. two squared) in the feed impedance. In free space, this gives an increase in feed impedance from 73Ω to around 300Ω
ohms. Additionally the RF antenna has a wider bandwidth.
Folded dipole impedance rationale
In a standard dipole the currents flowing along the conductors are in phase and as a result there is no cancellation of the fields
and radiation occurs. When the second conductor is added to make the folded dipole antenna this can be considered as an
extension to the standard dipole with the ends folded back to meet each other. As a result the currents in the new section flow
in the same direction as those in the original dipole. The currents along both the half-waves are therefore in phase and the
antenna will radiate with the same radiation patterns etc. as a simple half-wave dipole.
The impedance increase can be deduced from the fact that the power supplied to a folded dipole antenna is evenly shared
between the two sections which make up the antenna. This means that when compared to a standard dipole the current in each
conductor is reduced to a half. As the same power is applied, the impedance has to be raised by a factor of four to retain balance
in the equation Watts = I^2 x R.
Folded dipole transmission line effect
The folded element of the folded dipole antenna has a transmission line effect attached with it. It can be viewed that the
impedance of the dipole appears in parallel with the impedance of the shorted transmission line sections, although the arguments
for the impedance given above still hold true - it is just another way of looking at the same issue.
This can help to explain some of the other properties of the antenna.
The length is affected by this effect. Normally the wavelength of a standing wave in a feeder is affected by the velocity factor. If
air is used, this will by around 95% of the free space value. However if a flat feeder with a lower velocity factor is used, then this
will have the effect of shortening the required length.
The feeder effect also results in the folded dipole antenna having a flatter response, i.e. a wider bandwidth than a non-folded
dipole.
It occurs because at a frequency away from resonance, the reactance of the dipole is of the opposite form from that of the sorted
transmission line and as a result there is some reactance cancellation at the feed point of the antenna.

Folded dipole advantages
There are a number of advantages or reasons for using a folded dipole antenna:
 Increase in impedance: When higher impedance feeders need to be used, or when the impedance of the dipole is
reduced by factors such as parasitic elements, a folded dipole provides a significant increase in impedance level that
enables the antenna to be matched more easily to the feeder available.
 Wide bandwidth: The folded dipole antenna has a flatter frequency response - this enables it to be used over a wider
bandwidth.
Unequal conductor folded dipoles
It is possible to implement different impedance ratios to the standard 4:1 that are normally implement using a folded dipole
antenna. Simply by varying the effective diameter of the two conductors: top and bottom, different ratios can be obtained.
Folded dipole with unequal conductor diameters
In order to determine the impedance step up ratio provided by the folded dipole, the following formula can be used:
Where:
d1 is the conductor diameter for the feed arm of the dipole
d2 is the conductor diameter for the non-fed arm of the dipole
S is the distance between the conductors
r is the step up ratio
When determining the length of a folded dipole using thick conductors, it should be remembered that there is a shortening effect
associated with their use as opposed to normal wire or thin conductors.
Multiconductor folded dipoles
Although the concept of a folded dipole antenna often implies the use of one extra conductor, the concept can be extended
further by adding additional 'folds' or conductors. This has the effect of increasing the overall impedance even more and further
widening the bandwidth.
Three conductor folded dipole
Assuming the special case where all the conductors have the same diameter, then the impedance is increased by a factor of
three squared, i.e. 9. This means that the nominal value for a folded dipole with three 'elements' is 600Ω
Again this can be useful in antennas such as Yagi’s, where the close spacing of the reflector and directors can significantly
reduce the impedance of the driven dipole element. Using a folded dipole with three 'elements' may bring back the drive
impedance to the required level.

Folded dipole applications
Folded dipole antennas are sometimes used on their own, but they must be fed with a high impedance feeder, typically 300
ohms. This on its own can be very useful in certain applications where balanced feeders may be used.
However folded dipoles find more uses when a dipole is incorporated in another RF antenna design with other elements nearby.
The issue is that incorporating a dipole into an antenna such as a Yagi where elements are closely coupled reduces the feed
impedance. If a simple dipole was used, then the feed impedance levels of less than 20 Ω or less can easily be experienced.
Using a folded dipole enables the impedance to be increased by a factor of four or whatever is required by having multiple wires
in the folded dipole.
The widespread use of folded dipole antennas can be seen when looking at their use in domestic television and VHF FM
broadcast antennas that are used. In addition to this, folded dipoles are used in very many commercial applications as well.
Dipole antenna length calculation & formula
- Notes and details about the dipole antenna length calculation & formula for a half wave dipole.
The length of a dipole is the main determining factor for the operating frequency of the dipole antenna. Typically a dipole is a
half wavelength long, or a multiple of half wavelengths.
However the dipole length is not exactly the same as the wavelength in free space - it is slightly shorter.
Dipole length variation from free space length
Although the antenna may be an electrical half wavelength, or multiple of half wavelengths, it is not exactly the same length as
the wavelength for a signal travelling in free space. There are a number of reasons for this and it means that an antenna will be
slightly shorter than the length calculated for a wave travelling in free space.
For a half wave dipole the length for a wave travelling in free space is calculated and this is multiplied by a factor "A". Typically
it is between 0.96 and 0.98 and is mainly dependent upon the ratio of the length of the antenna to the thickness of the wire or
tube used as the element. Its value can be approximated from the graph:
Multiplication factor "A" used for calculating the length of a dipole
Dipole length formula
It is quite easy to use
In order to calculate the length of a half wave dipole the simple formulae given below can be used:
Length (metres) = 150 x A / frequency in MHz
Length (inches) = 5905 x A / frequency in MHz
Using these formulae it is possible to calculate the length of a half wave dipole. Even though calculated lengths are normally
quite repeatable it is always best to make any prototype antenna slightly longer than the calculations might indicate. This needs
to be done because changes in the thickness of wire being used etc. may alter the length slightly and it is better to make it
slightly too long than too short so that it can be trimmed so that it resonates on the right frequency. It is best to trim the antenna
length in small steps because the wire or tube cannot be replaced very easily once it has been removed.
Computer simulation programmes are normally able to calculate the length of a dipole very accurately, provided that all the
variables and elements that affect the operation of the dipole can be entered accurately so that the simulation is realistic and

therefore accurate. The major problem is normally being able to enter the real-life environmental data accurately to enable a
realistic simulation to be undertaken.
Dipole Antenna Feeders & Feed Impedance
- knowing how to properly feed a dipole antenna can improve its performance as well as reducing unwanted effects.
Calculating the feed impedance is also a key part of this process.
The feed impedance is of particular importance along with knowing the best way of feeding a dipole antenna.
To ensure the optimum transfer of energy from the feeder, or source / load, the dipole antenna feed impedance should be the
same as that of the source or load.
By matching the feed impedance of the dipole to the source or load, the antenna is able to operate to its maximum efficiency.
Dipole feed impedance basics
The feed impedance of a dipole is determined by the ratio of the voltage and the current at the feed point. A simple Ohms Law
calculation will enable the impedance to be determined.
Although a dipole can be fed at any point, it is typically fed at the current maximum and voltage minimum point. This gives a low
impedance which is normally more manageable.
Most dipoles tend to be multiples of half wavelengths long. It is therefore possible to feed the dipole at any one of these voltage
minimum or current maximum points which occur at a point that is a quarter wavelength from the end, and then at half wavelength
intervals.
Three half wavelength wave dipole antenna showing feed point
points λ/4 from either end could also be used
The vast majority of dipole antennas are half wavelengths long. Therefore they are centre fed - the point of the voltage minimum
and current maximum.
The basic half wave dipole antenna with centre feed point
The dipole feed impedance is made up from two constituents:
 Loss resistance: The loss resistance results from the resistive or Ohmic losses within the radiating element, i.e. the
dipole. In many cases the dipole loss resistance is ignored as it may be low. To ensure that it is low, sufficiently thick
cable or piping should be used, and the metal should have a low resistance. Skin effects may also need to be
considered.
 Radiation resistance: The radiation resistance is the element of the dipole antenna impedance that results from the
power being "dissipated" as an electromagnetic wave. The aim of any antenna is to "dissipate" as much power in this
way as possible.
As with any RF antenna, the feed impedance of a dipole antenna is dependent upon a variety of factors including the length,
the feed position, the environment and the like. A half wave centre fed dipole antenna in free space has an impedance 73.13
ohms making it ideal to feed with 75 ohm feeder.
Factors that alter the dipole feed impedance
The feed impedance of a dipole can be changed by a variety of factors, the proximity of other objects having a marked effect.
The ground has a major effect. If the dipole antenna forms the radiating element for a more complicated form of RF antenna,
then elements of the RF antenna will have an effect. Often the effect is to lower the impedance, and when used in some antennas

the feed impedance of the dipole element may fall to ten ohms or less, and methods need to be used to ensure a good match
is maintained with the feeder.
Dipole height above ground
For larger dipole antennas like those used for frequencies below about 30 to 50 MHz, the height above ground can be a major
influence on the feed impedance. At these frequencies the distance between the antenna and the ground may be only a
wavelength or two in many instances. At these sorts of heights, the ground can have a major influence on the impedance,
especially when the antenna is mounted horizontally as is often the case.
Variation of a half wave dipole at different heights above ground
As can be seen from the impedance variation plot, the largest swings of impedance are seen when the dipole antenna is closest
to the ground. It then closes in on the free space value.
Dipole Radiation Pattern: Polar Diagram
- Polar diagrams are used to indicate the response of dipole antennas and other antennas in different directions.
The radiation pattern of a dipole antenna is of particular importance.
The radiation pattern reflects the 'sensitivity' of the antenna in different directions and a knowledge of this allows the antenna to
be orientated in the optimum direction to ensure the required performance.
Radiation pattern and polar diagram
The radiation pattern of any antenna can be plotted. This is plotted onto a polar diagram.
A polar diagram is a plot that indicates the magnitude of the response in any direction.
At the centre of the diagram is a point of referred to as the origin. This is surrounded by a curve whose radius at any given point
is proportional to the magnitude of the property measured in the direction of that point.
Antenna polar diagram concept
Polar diagrams are used for plotting the radiation patterns of antennas as well as other applications like measuring the sensitivity
of microphones in different directions, etc.
The radiation pattern shown on a polar diagram is taken to be that of the plane in which the diagram plot itself. For a dipole it is
possible to look at both the along the axis of the antenna and also at right angles to it. Normally these would be either vertical
or horizontal planes.
One fundamental fact about antenna radiation patterns and polar diagrams is that the receiving pattern, i.e. the receiving
sensitivity as a function of direction is identical to the far-field radiation pattern of the antenna when used for transmitting. This

results from the reciprocity theorem of electromagnetics. Accordingly the radiation patterns the antenna can be viewed as either
transmitting or receiving, whichever is more convenient.
Half wave dipole radiation pattern
The radiation pattern of a half wave dipole antenna that the direction of maximum sensitivity or radiation is at right angles to the
axis of the RF antenna. The radiation falls to zero along the axis of the RF antenna as might be expected.
Radiation pattern of a half wave dipole antenna in free space
In a three dimensional plot, the radiation pattern envelope for points of equal radiation intensity for a doughnut type shape, with
the axis of the antenna passing through the hole in the centre of the doughnut.
Radiation patterns for multiple half wavelength dipoles
If the length of the dipole antenna is changed from a half wavelength then the radiation pattern is altered. As the length of the
antenna is extended it can be seen that the familiar figure of eight pattern changes to give main lobes and a few side lobes. The
main lobes move progressively towards the axis of the antenna as the length increases.
Antennas, Aerials, & Propagation
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radio propagation, and radio spectrum issues.
Key aspects and essentials about antenna or aerial technology as well as many antenna types, radio propagation modes and
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Dipole antenna aerial tutorial

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