About this site

This site aims to provide radio amateurs with easy-to-use tools to help them design simple, light but effective wire antennas which are especially suitable for portable use while participating in any of the several amateur radio outdoor award schemes.

Antenna types

Currently, the site offers tools to help the user design seven different types of antenna. Click on a link to open a short article describing the chosen antenna type and its' main characteristics:

The site also offers a collection of charts, tables and calculators in the Extras page:

Notes

About the designers

Each of the designers listed here share a common structure and form, while presenting combinations of controls specific to the type of antenna covered.

In each case, the user is presented with a group of controls in the upper left portion of the page: these controls enable the user to completely specify the characteristics of the antenna, namely frequency, wire lengths, angles, and so on. Please note that all length dimensions are given, or calculated, in meters.

Example designer layout

In the upper right portion of the page is a graphics area where the modelled antenna is presented in a 3D context. The graphic can be zoomed, panned and rotated. Antenna feed-points are shown as colored markers; the user may also choose to toggle the appearance of a semi-transparent plane at the height (1.85 meters) of an average person, in order to gain some perspective on how large the antenna would be when erected.

In the lower half of each of the designers, a group of controls enable the calculation of an antenna's performance, and the presentation of charts and diagrams showing the performance in various ways, in any combination of the following:

Example antenna performance controls section

Calculation of an antenna's performance is achieved using a version of the NEC2 (Numerical Electromagnetics Code v.2) code. Results of the calculations, and the resulting charts and diagrams, have been compared with those presented by programs such as EZNec and 4nec2, for similar antennas, and have been found to be closely comparable. Notwithstanding that, we make NO claims as to the accuracy of such information or results; the graphics and data presented in this site are provided "as-is" for the general interest and edification of the user. Refer to the Disclaimer below for more information.

 

Linked dipole designer

The linked dipole antenna designer page enables the user to very quickly design a multi-band linked dipole antenna for portable use in the field, or on a mountain top.

This type of antenna is constructed with one or more sections in series, each for a particular amateur radio band, and which are capable of being linked, or unlinked, as required, to make the antenna resonant on whichever band the radio operator wishes to use. Linking or unlinking sections has, however, the downside of having to lower the antenna to physically reach the very highest links.

4-band linked dipole antenna example

Linked dipole antennas are especially easy to erect, requiring just one support in the center - this could be a pole or a cord suspended from a tree - amd have the added benefit of giving good results even when erected in thick forest. This is due to the fact that, since the antenna radiates predominantly horizontally polarized waves along the main azimuthal lobe, the trees present little obstacle since they are not only physically, but also electrically vertical. Hence, the trees have little influence on the radiated signals - good for heavily-forested hills amd mountain summits.

 

OCFD antenna designer

The OCFD antenna designer page enables the user to quickly design a multi-band OCFD (off-center-fed dipole) antenna for portable use in the field, or on a mountain top. OCFD antennas consist basically of two wires, together comprising one half-wavelength in length, and fed in a similar manner to a center-fed dipole, but fed off-center at a point usually about 1/3 in length from the end; the designer, however, allows the feed-point position to be configured for optimal performance for those bands of interest to the operator.

40-meter OCFD antenna example

The OCFD antenna is often stated to present an impedance of around 200 ohms to 250 ohms at the feed-point, and is often fed through an unun, usually 4:1, to match a 50-ohm system. A current choke is often also needed to suppress common-mode currents on the feed-line. However, the actual impedance values of a particular OCFD antenna configuration will most often be quite different, and will vary with:

Actual values for the impedance at the antenna base frequency can vary between 73 ohms to several hundred ohms, depending on the configuration (refer to the 4th column in the table below).

One big advantage of the OCFD antenna, as compared to a center-fed dipole, is that it can exhibit low VSWR minima on two, three or four higher bands above the principal band for which it has been designed: for example, with a judicious choice of feed-point position, a 40-meter OCFD can resonate also on the 20-meter, 15-meter and 10-meter bands, with the 6-meter band being an added possibility.

The performance of an OCFD antenna is very sensitive to the choice of feed-point position, as the table below demonstrates. This table lists VSWR values at the stated frequencies across several bands for a 40-meter OCFD, principal frequency 7.000 MHz, erected as a flat-top at 10 meters above average ground. VSWR values for the stated frequencies in each band are displayed as a function of the percentage split between the two separate sections of the antenna, here listed as "Left" and "Right":

Split Ratio,
R/L		 Feed-point
impedance
at 7.1 MHz		 Band Bands*
Left
%		 Right
%		 40m
(7.1 MHz)		 30m
(10.1 MHz)		 20m
(14.2 MHz)		 17m
(18.1 MHz)		 15m
(21.2 MHz)		 12m
(24.9 MHz)		 10m
(28.5 MHz)
* where VSWR is <= 3.5,  with alternatives where it's possible to tune out up to 10:1 VSWR

The animation below uses the same antenna configurations as the table, and demonstrates graphically how sensitive an OCFD antenna is to the relative ratios of the two sections, left and right:

40-meter OCFD antenna

From these data, it can be seen that the most often-used 1/3 to 2/3 (or 33% / 67%) ratio section lengths used for a 40-meter OCFD antenna will result in the antenna being resonant on three amateur bands, 40m, 20m and 10m, but NOT on 15m. In order to get a 40-meter OCFD antenna to be resonant also on the 15m band, a different lengths ratio between the antenna sections must be used.

Among the best ratios to be used, as both the graphic and the table show, are close to an 18% / 82% or 20% / 80% ratio which gives good VSWR minima on all four bands 40m, 20m, 15m and 10m. This is also borne out by the comments made in Part 4 of this document on OCFD antennas:
   https://rsars.files.wordpress.com/2013/01/study-of-the-ocf-dipole-antenna-g8ode-iss-1-31.pdf
where the author suggests a 1/6 to 5/6 (or 16.67% / 83.33%) ratio would be the best choice to bring the antenna to resonate on four HF bands 40m, 20m, 15m and 10m, and incidentally also on the 6-meter band.

Changing the angles (within reasonable limits) of the two arms of an OCFD antenna has a much less profound effect on VSWR and bands coverage than the choice of feed-point position. Angling one or both arms downward, however, has the effect of lowering the antenna impedance somewhat.

The OCFD antenna can be a very useful and time-saving field antenna in the field - simply change TRX band to one of the antenna's resonant bands, and start transmitting.

 

EFHW antenna designer

The EFHW antenna designer page enables the user to quickly design a multi-band EFHW (end-fed half-wave) antenna for portable use in the field, or on a mountain top. EFHW antennas consist basically of one single wire, a half-wavelength in length, which can be configured in several ways:

40-meter EFHW antenna example, configured as a sloping inverted-L

Being end-fed, the EFHW is voltage-fed and presents a high impedance (around 2500 ohms to 3500 ohms) at the feed-point, and hence needs an unun, typically 49:1, to match a 50-ohm system.

One big advantage of the EFHW antenna is that it can exhibit low VSWR minima on several bands above the principal band for which it has been designed: for example, a 40-meter EFHW can resonate also on the 20-meter, 15-meter and 10-meter bands, with 6-meters being thrown in for good measure. This can readily be seen in the diagram below:

40-meter EFHW antenna: VSWR curve over several bands, including impedance curves

Careful optimization of the EFHW antenna characteristics is needed to ensure good performance in the field. Ground conductivity plays a part, as well as choice of principal frequency, configuration, and inductive/capacitive loading of the antenna. If done right the EFHW antenna can be a very useful and time-saving field antenna - simply change TRX band to one of the antenna's resonant bands, and start transmitting.

 

Vertical antenna designer

The Vertical antenna designer page enables the user to quickly design a single-band vertical antenna for portable use in the field, or on a mountain top. For portable use, the vertical antenna is most often constructed of wire, supported by a pole of sufficient height to accommodate the complete antenna length.

The designer covers three major variants of the type, for HF and for VHF/UHF:

When configured as a 1/4-wave or 5/8-wave vertical, a set of radials are required to "complete" the antenna. How many radials, of what length, and at what downwards slope angle they should be arranged: these are matters for the builder to decide.

The designer allows the user to set the number of radials, their lengths and slope angle.  A minimum of one radial can be enough to "get a signal out" while operating portable, but at the cost of skewing the radiation patterns; however, 3 or 4 radials equally spaced will give excellent results. Some portable operators use eight or more radials, but it has to be said that the "law of diminishing returns" is at work here - many more radials does not necessarily translate to much better performance.

When configured as a 1/2-wave vertical, however, the antenna does not need radials, and is essentially an end-fed half-wave (EFHW) antenna. As with all such EFHW antennas, a counterpoise is often used, and is recommended, at the feed-point. This counterpoise ideally has a length which optimizes the feed-point impedance: in particular, a length is chosen which brings the reactive component of the impedance as close to zero as possible. Most observers agree that the optimum counterpoise length is 1/20 λ (0.05 λ).

1/4-wave vertical, with configurable radials

The 1/4-wave vertical is perhaps the best-known of the vertical antenna variants. The main radiating element is shorter than the others covered here, and the total length of the antenna can often easily be laid along a non-conducting support, such as a fiberglass pole.

Like all verticals, the 1/4-wave vertical transmits and receives equally in all directions - the azimuthal radiation pattern is a circle. If erected at about 1/4-wavelength above the ground, the elevation radiation pattern shows a single lobe at a low angle - as seen here to the right.

This makes it a good single-band DX antenna.

If erected higher than about 1/4-wavelength above the ground, the elevation radiation pattern begins to show additional lobes at higher elevation angles, thus increasing the chances of making contacts at shorter distances.

As noted above, the user can choose any number of radials from one single radial, up to a maximum of ten radials - enough for even the most demanding of portable operators. The radials' angle can also be set between 0° for radials laying along the ground, up to a maximum of 50°. Altering the radials' angle will affect the feed-point impedance: an angle of 45° wil result in an impedance close to 50 Ω. A chart of feed-point impedance plotted against radials angle will be found in the Reference dialog in the Vertical Antenna designer page.

1/2-wave vertical, with configurable counterpoise

The 1/2-wave vertical antenna is basically a single element end-fed half-wave (EFHW) antenna vertically arranged. Like all EFHW antennas, the 1/2-wave vertical has a very high feed-point impedance - on the order of 1500 Ω to 2500 Ω - and therefore requires a matching device to transform this high impedance to one close to 50 Ω.

Like all verticals, the 5/8-wave vertical transmits and receives equally in all directions - the azimuthal radiation pattern is a circle. If erected close to the ground, the elevation radiation pattern shows a single lobe at a low angle, similar to that of the 1/4-wave vertical.

The low elevation angle makes it a good antenna for long-distance DX operation.

If erected higher above the ground, the elevation radiation pattern begins to show additional lobes at higher elevation angles, thus increasing the chances of making contacts at shorter distances.

In addition, it is found that the addition of a short counterpoise of a certain length at the feed-point will help to reduce the reactive component of the high feed-point impedance to close to zero. The optimum length of such a counterpoise has been found by many observers to be 1/20 λ (0.05 λ). A chart of feed-point impedance plotted against counterpoise length will be found in the Reference dialog in the Vertical Antenna designer page: the optimum length can be readily ascertained from the chart.

As an example, the optimum counterpoise length for a 10-meter 1/2-wave vertical antenna is found to be close to 0.5 meter - rather short when compared to the 5 meters length of the main vertical element.

The counterpoise itself can be either:

5/8-wave vertical, with configurable radials

In most respects, the 5/8-wave vertical antenna has characteristics closely resembling those of the 1/4-wave vertical, but differs in the shape of the elevation radiation pattern.

Like the 1/4-wave vertical, the 5/8-wave vertical transmits and receives equally in all directions - the azimuthal radiation pattern is a circle. If erected at about 1/4-wavelength above the ground, the elevation radiation pattern shows a single lobe at a somewhat higher angle than the 1/4-wave vertical.

This higher elevation angle makes it a good antenna for middle distances and shorter skip lengths than the 1/4-wave vertical.

If erected higher than about 1/4-wavelength above the ground, the elevation radiation pattern begins to show additional lobes at even higher elevation angles, thus increasing the chances of making contacts at shorter distances.
 

Delta loop antenna designer

The delta loop designer page enables the user to quickly design a single-band triangular delta loop antenna for portable use in the field, or on a mountain top. In its' "apex-up" configuration, the antenna needs just one support, either a pole or a cord suspended from a tree. The "point-down" configuration, on the other hand, requires two such supports.

This type of antenna is constructed as a closed triangular loop, with the apex either at the top of the loop ("apex-up"), or at the bottom of the loop ("apex-down"). The shape of the triangular loop depends strongly on the main configuration, "apex-up" or "apex-down" - in order to keep the feed-point impedance close to 50Ω in each case, the "apex-up" variant needs to be much shallower and broader than the "apex-down" variant, which is narrower and taller, as the graphic makes clear:

20-meter delta loop antenna example: "apex-up" and "apex-down" variants

The user can choose any of the following allowed configurations and feed-point positions in the loop (colored options are not recommended, or give poor results):

Feed-point position Polarization direction
Apex-up configuration Apex-down configuration
At the apex Mixed polarization Horizontal polarization*
At a point 1/4 wavelength down from the apex Vertical polarization* N/A
At one corner of the horizontal section Vertical polarization Mostly horizontal polarization
At the mid-point of the horizontal section Mixed polarization Horizontal polarization
 * = standard feed-point position for the configuration

The table shows that the delta-loop antenna in the "apex-up" configuration exhibits either vertical polarization or mixed horizontal/vertical polarization, depending on the position of the feed-point in the loop. In the "apex-down" configuration, on the other hand, the polarization direction is predominantly horizontal.

NOTE: When the feed-point is positioned at 1/4 wavelength down from the upper apex point, it is important to note that the coaxial cable inner conductor is attached to the 1/4-wave section, and the coax shield is attached to the other short section on that side.

The delta-loop antenna generally features a low vertical take-off angle, even though such antennas are erected with either their lower side (in "apex-up" configuration) or their apex point (in "apex-down" configuration) only a couple of meters above the ground. The low take-off angle makes this kind of antenna a worthwhile prospect for DX-ing, especially while operating portable. If erected on a summit where the ground drops away appreciably from the summit, the take-off angle will be even lower; placing the delta-loop antenna higher up on its' center support will also lower the take-off angle.

Another feature of the delta-loop azimuthal radiation is the deep, or even very deep, low at high elevation angles (see the diagram below), meaning much less power is dissipated at high angles. This means, however, that this antenna is not a good choice for NVIS communications.

Delta loop antenna designer - interactive radiation pattern display

The delta-loop antenna is also fairly broadband on its' designated band - the 2.0:1 VSWR range on the 20-meter band for example, at ~350kHz wide, covers the entire band.

Two slight disadvantages can be encountered when erecting the delta-loop antenna:

One should also note that the antenna will exhibit high voltage points, the placement of which are dependent on the configuration and feed-point position: the user should check the currents diagram for points at which the current is low, and the voltage therefore high. The antenna should be erected high enough (2 meters minimum) that neither the operator nor a casual passer-by can easily come into contact with any such high voltage point(s).

 

Half-square antenna designer

The half-square antenna designer page enables the user to quickly design a half-square antenna for portable use in the field, or on a mountain top. This type of antenna needs two supports: a combination of pole(s) and/or cord(s) suspended from a tree. Half-square antennas can be configured in one of two ways:

40-meter half-square antenna example, configured as a multi-band EFHW
Half-square antenna configured as a full-wave single-bander

When configured as a full-wave single-bander, the impedance at the upper corner feed-point is approximately 50 ohms, and hence does not necessarily need an unun at the feed-point, although a 1:1 unun is often used. It's important to run the coax feed-line at 90° to the antenna for a couple of meters in order to minimize common-mode currents on the coax sheath.

This configuration results in a fairly low angle (~ 20° to 25°) elevation radiation pattern, with good broadside lobes, deep (typically better than 12dB) rejection in the plane of the antenna, and a deep (~15dB) minimum at high elevation angles. This makes this configuration a good choice for single-band DX work.

Half-square antenna configured as an EFHW half-wave multi-bander

When configured as a half-wave multi-bander, the impedance at the end of the wire is around 2500 ohms to 3500 ohms, and hence an unun, typically 49:1, is needed at the feed-point. In addition, the antenna will also most often need a short (~1/8 wavelength) counterpoise.

Like other EFHW antennas, this configuration can exhibit low VSWR minima on several bands above the principal band for which it has been designed: for example, a 40-meter half-square configured in this way can resonate also on the 20-meter, 15-meter and 10-meter bands, with 6-meters being thrown in for good measure.

 

Moxon antenna designer

The Moxon antenna designer page enables the user to quickly design a Moxon 2-element beam antenna for portable use in the field, or on a mountain top. This type of antenna needs a single support only.

First designed in the early 1950's, and later further developed by L.B.Cebik in the 1980's, the Moxon antenna has become a firm favourite for those interested in building a lightweight beam antenna for home or portable use.

10-meter horizontal Moxon antenna example

Since the Moxon is a beam antenna consisting of a driver element and a single parasitic reflector element, both folded toward each other, it makes for a usefully compact array. It can be made of wire supported by spreaders, or from lightweight tube which is mostly self-supporting. In both cases, however, a single support only is needed, which is very handy when erecting the antenna for portable operations.

Moxon antenna gain

Like other beam-type antennas, the Moxon can be configured either as a horizontal beam, or as a vertical beam, with the radiation polarized as the configuration. The gain to be expected from the horizontal Moxon is quite high, at 10dBi or greater; the vertical Moxon, on the other hand, exhibits rather lower gain, at about 5 dBi or 6 dBi, depending on height AGL.

In either configuration, as with all 2-element driver-reflector beams, the gain is highest at the low end of the band and tapers off as the frequency is increased. See the following sections for more information...

Moxon antenna configured as a horizontal beam

The horizontal Moxon beam offers a broad forward azimuthal radiation lobe giving modest directivity of about 2dB, with a deep null toward the back end, giving a high front-to-back ratio: gains of up to 9.7dBi are possible. The azimuthal radiation pattern is only moderately sensitive to the height of the antenna above ground, whereas the shape of the elevation pattern depends very strongly on the height of the antenna above ground. The following animation shows both azimuth and elevation patterns for a horizontal 10-meter Moxon beam at heights between 4m and 10m above ground level (height measured at the antenna center):

Horizontal Moxon

As can be seen from the graphic, at lower heights of 4m or 5m AGL, the elevation pattern consist of a single lobe with elevation angle of around 25° to 35°. At greater heights AGL, the elevation pattern splits into two very distinct lobes, one low and one high, such that the signal is "shared" between them - this can be useful for both long-distance DX contacts, as well as for more close-in contacts.

Moxon antenna configured as a vertical beam

The vertical Moxon beam offers a very broad forward cardioid azimuthal radiation lobe giving modest directivity, with a deep null toward the back end, giving a high front-to-back ratio. Both the front-to-back ratio and the SWR depart from optimal values more rapidly below the design frequency than above it. Hence, the design frequency will normally be about 1/3 the way up the overall operating passband.

The azimuthal radiation pattern exhibited by the vertical Moxon beam is only moderately sensitive to the height of the antenna above ground, whereas the shape of the elevation pattern again depends very strongly on the height of the antenna above ground.

The following animation shows both azimuth and elevation patterns for a vertical 10-meter Moxon beam at heights between 1m and 8m above ground level (height measured at the lowest part of the antenna):

Vertical Moxon

As with the horizontally-oriented Moxon, the elevation pattern at different heights AGL also shows a second elevation lobe above the main lobe, but at shallower angles than with the horizontally-oriented Moxon. At lower heights of 1m or 2m AGL (measured at the lowest part of the vertically-oriented antenna), the elevation pattern mainly consists of a single lobe with elevation angle of around 15°.

At greater heights AGL, the elevation pattern splits into two lobes, one at low elevation and one at a somewhat higher elevation, such that the signal is "shared" between them, but in this case, the two elevation pattern lobes are much closer together than is the case with the horizontally-oriented Moxon, and present more of a low- to mid-angle "broad front", serving both DX and middle-distance contacts.

Moxon antenna VSWR curve

The Moxon antenna has a very distinctive VSWR curve, the shape of which is only weakly dependent on orientation and/or height AGL:

Horizontal 10-meter Moxon antenna at 5m AGL: VSWR, impedance and bandwidth curves

The curve displays a steep rise at frequencies below the VSWR minimum, and a more shallow rise at frequencies above the VSWR minimum.
In all cases, and using the calculated dimensions, the feed-point impedance stays close to 50 Ω, the VSWR is low (2.5 or less) and bandwidth is high - even across such wide bands as 10 meters, 6 meters and 2 meters.

 

Extras page

The extras page offers the following in separate tab-pages:

More tools are planned for this page.

 

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Acknowledgments

We've recently updated the software used in this site to generate antenna radiation plots data, and also the plot routines themselves. By developing our own software to analyze the NEC-generated data, and our own chart-plotting routines, we have eliminated several third-party software "plugins". This has resulted in tighter, faster data flow to you, the user.

We are grateful for the opportunity to use these resources, and acknowledge our debt of gratitude to their respective developers.

Please note:  due to the reliance on sizeable graphics and groups of controls in this site, it is not suited to display on small screens. We apologize for any inconvenience this may cause.

 

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Disclaimer

All information on this web site is provided "as is", for general information purposes only, to the amateur radio community and those with an interest in radio technical matters.

The operator of this web site makes no representations or warranties of any kind, express or implied, about the content, completeness, accuracy, reliability, legality, suitability or availability, with respect to the website or the information, products, services, or related graphics contained on the website, for any purpose. Any reliance you place on such information is therefore strictly at your own risk.