portable-antennas - Vertical antenna designer

The vertical antenna variants

The Vertical antenna designer supports four popular vertical antenna types, including two configurations of the directional two-element parasitic vertical array. Although all share the same basic vertical radiator, they differ in their feed-point impedance, ground requirements and radiation characteristics.

The available configurations are:

1/4-wave vertical, with configurable radials
2-element parasitic vertical array
- with multiple ground radials
- with two elevated radials per element
1/2-wave vertical, with configurable counterpoise
5/8-wave vertical, with configurable radials

Quarter-wave vertical

A simple, efficient and popular antenna requiring a system of radials beneath the antenna. Well suited to both portable and fixed-station operation. The 1/4-wave vertical's radials can be laid out on the ground, with the feed-point at the ground, or with the feed-point raised and the radials sloping down from the feed-point toward, but not touching, the ground.

Ground-mounted radials: 1 to 10 radials spaced equally on the ground, with lengths between 0.1λ and 0.2λ. Resonant frequency highly dependent on ground type and ground conditions.
Sloping radials: the most-often quoted value given for sloping radials is 0.25λ or one-quarter wavelength. Resonant frequency much less dependent on ground type and ground conditions.

NEW Two-element parasitic vertical array

A single-band directional array consisting of a driven quarter-wave vertical and a slightly longer parasitic reflector. Two radial systems are supported. The choice of radial system affects the optimum reflector length and the array's performance.

Array with ground radials

Each vertical uses its own set of the same number of radials laid on the ground. Resonant frequency highly dependent on ground type and ground conditions. For best results, remain within the recommended parameter ranges:

Element spacing: 0.22–0.25 λ (0.24 λ recommended)
Reflector length: 1.06–1.07 × driven element length
Radials per element: 4–6, all the same length, spaced equally and laid horizontally on the ground (very important!). The two sets are arranged so that the radials are interleaved rather than overlapping:
Radial length: 0.16–0.18 λ

Array with elevated radials

Each vertical uses two elevated radials, arranged parallel to one another in azimuth. Modelling indicates that a shorter reflector extension works particularly well with this configuration:

Element spacing: about 0.25 λ
Reflector length: about 1.02 × driven element length
Radials per element: 2
Radial length: about 0.25 λ
Radials arranged parallel to one another, approximately horizontally from the antenna feed-points. Set the height of the radials to about 1.0 or 1.5 meters for the mid- to high-HF bands, or somewhere between 1/50 to 1/20 of the wavelength for the lower HF bands.

Each of these arrays is considerably more sensitive to its design parameters than a single vertical. Element spacing, reflector length, radial system and ground characteristics all strongly influence its performance.

Half-wave vertical

A higher-impedance vertical requiring only a short counterpoise. Less dependent on ground conditions than a quarter-wave vertical.

Five-eighth-wave vertical

A single-band vertical capable of producing a lower radiation angle than a quarter-wave vertical. A matching coil is normally required at the feed-point.

Half-wave vertical dipole

This vertical antenna designer does not offer the possibility to design a half-wave vertical dipole; however, the OCFD antenna designer can be used to achieve this (click here to open the OCFD designer in a new browser tab). In the OCFD designer page, configure the antenna as follows:

Under "First antenna section"
- set length to 50% of total
- set the angle to "not horizontal", and -90° (vertically downwards)
Under "Second antenna section"
- set the angle to "not horizontal", and +90° (vertically upwards)
Set the support point ("Support pole height") to a minimum height of 1/4 wavelength plus two meters: the lower end of the antenna must be clear of the ground by at least two meters for safety reasons.

Click the "Show antenna" button, and you should have a vertical dipole ready to investigate. The coaxial cable feeder should be led away horizontally from the antenna for at least one meter before being led to the radio.

Use the controls on the left-hand side to configure your antenna - set the design frequency, antenna element lengths and angles, wire diameter, wire insulation if required, support height, etc.
When you are happy with your configuration, press the "Show antenna" button to display your antenna in interactive 3D graphics mode in the area on the right-hand side. Each time you change your configuration, you should press the "Show antenna" button to register the changes to the app.
After you have configured your antenna, you can then use the controls further down in the page to generate charts and diagrams to evaluate the antenna's performance - you will need to scroll down in the page to access these controls.
You can choose to view any combination of the available charts and diagrams: these include four radiation pattern types: azimuth, elevation, 3D and polarization patterns; other options include VSWR charts, an antenna currents diagram, and a Smith chart.

Set antenna color: Show person-height plane

Principal band

Band:

Frequency:

kHz

Nom. length :

m Corrected length: m

Wvl-fraction :

Vertical antenna configuration

Configure as:

Standard length Shortened length Info

Antenna wire

Wire core:

mm diameter

Material:

Insulation:

thickness

Ins. type:

Corr. factor:

Main vertical section

Length:

Base height:

2-element 1/4-wave array

El. spacing:

λ = m Info

Reflector len.:

= m Info

Radials - for 1/4-wave and 5/8-wave vertical antenna variants

1/4-λ array :

Ground radials
Elevated radials (2 per element) Info

No. of radials:

Radials length:

λ = m Info

Radials angle:

° from horizontal Info

Counterpoise - for 1/2-wave vertical antenna variant

Length:

λ = m Info

Antenna overview

Main vertical section

Radials / Counterpoise

Length

Top
height

Base
height

No.

Length

Angle

End
height

Vertical antenna designer

Use the controls on the left-hand side to configure your antenna.
When you are happy with your configuration, press the "Show antenna" button to display your antenna in interactive 3D graphics mode in this area.
After you have configured your antenna, you can then use the controls further down in the page to generate charts and diagrams to evaluate the antenna's performance ...

portable-antennas.com

Antenna feed-point: ⬥ Load coil: ●

Show display hints:

Antenna performance

Here you can generate plots of radiation patterns, VSWR chart, antenna currents diagram and Smith chart for your antenna over a choice of ground types. By changing the physical dimensions of the antenna, and refreshing these plots, you can learn a lot about how such antennas will perform in the field.
Please note that radiation patterns are here modelled over flat ground - when the antenna is erected on a hill-top or mountain summit, the surrounding sloping ground will generally cause angles in the elevation radiation pattern to be lowered in the direction of the slope: the steeper the slope, the lower the effective elevation take-off angle will be, and the better the chances of making long-distance contacts. Read more...

Note also that, for vertical antennas, the NEC engine used to generate the data for the elevation radiation pattern over-estimates the radiated gain at angles below the pseudo-Brewster angle specific to the antenna, ground type and frequency: this is due to unmodelled ground absorption effects. Below this angle, the gains are less, and often much less, than are presented in the elevation pattern.

Antenna: Configuration: Frequency: GenID:

Antenna
plane
0° - 180°

Azimuth:
Gain:
Beamwidth:	N/A
(At elevation angle: 133°)

Elevation:		PBA: - - - - -	111°
Gain:		PBA Area:
Beamwidth:	N/A
(At azimuth angle: 133°)

General parameters (at 7.000 MHz)

Outer ring:	5.23 dBi
VSWR:	2.06 : 1
Unun ratio:	49 : 1
Feed-point Z:	5125 - j1983 Ω
Transformed Z:	xxx

Show selected azimuth/elevation slices in 3D plot

How to use these diagrams » » »

Export antenna dimensions to file

Export format:
Antenna diagram:	Use original view Use current view
PDF options: Toggle all	Include radiation patterns Include VSWR chart Include currents diagram Include Smith chart If you include any of these options, make sure you refresh the required radiation patterns, charts and diagrams for your antenna before exporting.
Collecting data:	0 %

Vertical antenna designer - correction factors reference

Length-correction factor used in this application - this will be applied automatically

Radials angle impedances - how feed-point impedance varies with radials angle
End-effect multiplication factor - dependent on wire diameter and frequency
Half-wave vertical impedances - 1/2-wave vertical impedances by counterpoise length

Radials angle impedances

Both the 1/4-wave ground-plane (GP), and the 5/8-wave, vertical antennas will need a system of radials attached at the feed-point.

How many radials are to be used is left to the builder to establish - sometimes a single radial will suffice to "get a signal out", although a minimum of 3 or 4 will give excellent results.

Sloping the radials downward from the feed-point will alter the feed-point impedance - how much will depend on the angle, as can be readily determined from the accompanying chart.

In general, the 5/8-wave vertical has a higher feed-point impedance than the 1/4-wave vertical for a given number of radials and radials angle.

Data for the chart derived empirically for 1/4-wave and 5/8-wave vertical antennas using the NEC v4.2 engine. Chart for illustrative purposes only - actual values for a particular antenna will depend on its' configuration.

End effect multiplication factor

Wavelength / wire diameter ratio, λ/d:

End-effect multiplication factor :

Half-wave vertical impedances

The 1/2-wave vertical antenna, unlike its' 1/4-wave and 5/8-wave cousins, presents a high impedance at the feed-point, typically around 1300 Ω to 2000 Ω.

The reactive part of this impedance is often high also: a counterpoise is attached at the feed-point to minimize this reactive component.

Many antenna builders agree that the optimum counterpoise length, to bring the reactive component close to zero, is 1/20λ (0.05λ) - the accompanying chart shows this very clearly.

Calculate loading coil dimensions for shortened vertical

Calculate loading coil dimensions for a shortened vertical

Building a 1/4-wave vertical antenna for the low HF bands can be problematic, since the full length required can be difficult or impossible for many to manage, especially when operating portable. This calculator uses the principle of inductive base loading to electrically lengthen a much-shortened radiator.

Part #1 - Calculate coil inductance

We first calculate the inductance required to shorten our vertical antenna, given the frequency, antenna wire length, position of the coil and the antenna wire diameter. Show more...

To do this, we use the classic formula, originally published by J. Hall, "Off-center loaded dipole antennas", QST Sept 1974, pp28-34, and re-printed in the ARRL Antenna Handbook, 20th edition, p6-31:

\[ L_{\mu H} = \frac{10^6}{68 \pi^2 f^2} \left\{ \frac{ [\ln(\frac{24(234/f - B)}{D}) - 1] × [(1 - fB/234)^2 - 1] }{(234/f - B)} - \frac{ [\ln(\frac{24(A/2 - B)}{D}) - 1] × [((fA/2 - fB)/234)^2 - 1] }{(A/2 - B)} \right\} \]

where

L_µH = calculated coil inductance in micro-Henrys,
f = frequency in MHz,
A = total vertical length,
B = vertical length from the feedpoint to the center of the loading coil,
D = diameter of the antenna wire.

The formula as it stands originally required lengths to be in feet and inches, but this calculator requires you to enter metric lengths.

Frequency:	MHz (auto)	Coil inductance: µH
New antenna length:	meters
Coil center-height:	meters
Antenna wire diameter:	mm

Part #2 - Calculate coil dimensions

We'll now use the inductance L_µH, which we have derived using the above calculator, to estimate the parameters of a coil which we can use to electrically lengthen a short vertical antenna for use in the lower HF bands. Show more...

Coil former: The relative permeabilities μ_r of most plastics commonly used as coil formers are very close to unity (as for air), with the notable exception of PVC, which should not be used. Hence, in electromagnetic terms they mostly behave identically to air for inductance calculations, and can be safely be ignored in the calculations of coil inductance.

Single-layer helical coil The formula used here is for a single-layer air-cored helical coil:
\[ L_{\mu H} = \frac{N^2 R^2}{9R + 10W} \] where L_µH = coil inductance in micro-Henrys, N = number of turns of wire, R = coil mean radius in inches, W = coil width in inches.	Fig.1 - Single-layer coil
This formula is claimed to be accurate to within 1 percent for coils having W > 0.8R.

Coil inductance:

µH

No. of turns:
Coil width:	mm
Coil wire len.:	m
RF resistance:	Ω

Coil mean radius:

Coil wire diameter:

Windings spacing:

Est. coil Q-factor:

If you intend to use enamelled wire in your coil (acceptable for the higher HF bands or VHF), you can take a coil wire diameter value from this dropdown list of standard enamelled wire sizes:

Enamelled wire sizes:
(Some wire sizes may not be readily available from your suppliers)

For the lower HF bands, you should use as large a wire diameter as is consistent with planned coil size and portability. The greater the coil wire (or tube) diameter, and the greater the coil diameter, the lower the coil losses will be. Be aware that, at these low frequencies, a shortened antenna will also incur greater ground return losses, and greater proximity losses. "There's no such thing as a free lunch" - shortened antennas with loading coils are inherently lossy, and less efficient - sometimes much less so - than antennas of standard length.

Part #3 - A note on radials lengths for shortened verticals

Once you have decided on the length of your shortened radiator section, you need to consider the lengths of the radials you will be using with your antenna. Basically speaking, since radials act more like a loss-reduction system than tuned elements, any length of radials is better than no radials at all, and so shortened radials can be used with your coil-loaded short vertical antenna, but there will be a trade-off:

shorter radials = easier to handle,
but reduced antenna efficiency.

Shortening the vertical with a loading coil mainly fixes reactance (resonance), but it does not reduce the current that must flow in the "ground system". Radials form the return path, or image plane, for current returning to your feed system, so shortening the radials will both:

increase signal loss, and
decrease the bandwidth of your antenna,

Keep this in mind when choosing a length for your radials: 0.25 λ is the optimum choice in terms of efficiency, but if space is at a premium, you may decide to use more radials, each perhaps a little shorter than the 0.25 λ optimum length. There is no special radial-lengths rule to be applied here: ultimately, you make a choice, build your antenna, and test it.

An expanded version of this coil calculator, with more details and references, can be found here

Save antenna configuration

Give your antenna configuration a meaningful title...

Title:

Manage saved antenna configurations

Your saved antenna configurations:

Click on
an antenna
configuration
to select it

Double-click
to load a
configuration

Coordinates of each section can be used to model this antenna in a separate program

Main antenna characteristics
Band	Frequency (kHz)	Units	Wire diam.	Antenna length	Base height	No. of radials	Radials angle
a	b	c	e	d	f	g	h

Antenna sections
Section		Segment start			Segment end
Segment	Length	x	y	z	x	y	z
Vertical	1	1	1	1	1	1	1

Copy this CSV text and paste into your favorite spreadsheet program

Vertical antenna designer

Combined azimuth + elevation patterns

Using combined azimuth + elevation patterns

The new combined azimuth and elevation patterns diagrams are fully interactive, allowing dynamic re-plotting of the patterns. You can choose any one of the following levels of interactivity:

No interaction
- the diagrams remain fixed at their default azimuth and elevation cuts.
Hover the mouse over the circular region in one diagram
- a green radial line and marker pair will appear in the diagram;
- the line and marker will follow the mouse around the diagram;
- angle and gain values at the mouse position are updated in the texts directly below the diagram.
Click within the circular region in one diagram
- the radial axis (the black line with numbers) is re-positioned to the selected angle;
- this new radial-axis position defines a new "slice" through the 3D radiation-patterns data;
- the other diagram is then re-plotted to reflect the new slice through the data;
- if the 3D radiation-pattern diagram is visible, then it too will be re-plotted to reflect the new slice through the data.
Click and drag within the circular region in one diagram
- the radial axis follows the mouse position in that diagram continuously;
- releasing the mouse fixes the radial axis at the selected angle;
- a new slice through the 3D radiation-patterns data is generated;
- the other diagram is then re-plotted to reflect the new slice through the data.
- if the 3D radiation-pattern diagram is visible, then it too will be re-plotted to reflect the new slice through the data.

All these different levels of interactivity are not just for show - they are designed to engage your curiosity about azimuth, elevation and 3D patterns and curves, and to help you learn about them.

By using the different levels of interactivity, you should gain a deeper insight into how each of the patterns and curves are intimately connected. Change one, and the other two are affected.

How deeply you venture into this, is entirely up to you: the tools are provided for you to use.

Choose ground type of land in the vicinity of the antenna:	Conductivity: S/m Relative permittivity:
View radiation patterns:	Azimuth + Elevation Polarization patterns
	3D pattern Choose type: Classic 3D plot
Set ref. elevation angle:	Auto Choose:
Set ref. azimuth angle:	Auto 0° (inline) 90° (broadside)
Impedance transformer:	unun
View VSWR chart:	VSWR
Effect of coax on VSWR: Coax losses info » » »	Include coax losses Coax length: Type: Effect of coax- and system-losses on VSWR When a coaxial cable is used to connect the antenna to a transmitter, the cable introduces signal loss, the magnitude of which can vary strongly with both frequency and antenna feed-point impedance. The main blue VSWR curve for this antenna is calculated at the antenna feed-point. The optional green curve represents the VSWR "seen" at the transmitter after losses in the coaxial cable are taken into account. At frequencies of antenna resonance, the blue and green curves usually coincide closely, since the coax contributes little additional attenuation at those frequencies. At frequencies away from resonance, however — often those corresponding to WARC bands — the feed-point impedance may become highly mismatched, producing very high VSWR values in the blue curve while the green curve shows substantially lower values. This reduction in VSWR at the transmitter occurs because signal losses in the coaxial cable attenuate both the forward and reflected waves. As a result, the reflected signal returning to the transmitter is weaker, causing the transmitter-end VSWR to appear lower than the actual feed-point VSWR. This effect can make some bands appear more "usable" from the transmitter's perspective, even though the antenna system may still be operating inefficiently at those frequencies. The green curve represents the "flattening" of the VSWR caused by the coax. Additional losses elsewhere in the system can further reduce the transmitter-end VSWR - these may include: ferrite heating and winding losses in baluns/ununs common-mode currents suppression coupling of RF energy into nearby ground and objects matching network / antenna tuner losses The magnitude of such losses, and their effect on actual radiated RF power, can only be estimated reliably through careful analysis of a particular antenna setup. In every-day portable operations, such losses can only be roughly estimated; however, comparisons can be made between commercially-produced EFHW and OCFD antennas for amateur radio use, and carefully-configured NEC models of those same antennas. Useful estimates can then be made of the efficiency of the commercial products by comparing their published VSWR curves, and the VSWR curves produced from the models. Improved transmitter-end VSWR therefore does not necessarily imply improved radiation efficiency: in some cases, a significant proportion of the transmitted power may simply be lost: dissipated as heat within the antenna system. Read more...
View currents diagram:	Antenna currents diagram
View Smith chart:	Smith chart
Antenna gains at 0° elevation:
Feed-point impedance:
Estimated bandwidth:

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Vertical antenna designer

Antenna performance

Effect of coax- and system-losses on VSWR

Radials angle impedances

End effect multiplication factor

Half-wave vertical impedances

Calculate loading coil dimensions for a shortened vertical

Part #1 - Calculate coil inductance

Part #2 - Calculate coil dimensions

Part #3 - A note on radials lengths for shortened verticals

Using combined azimuth + elevation patterns