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 in this website are given, or calculated, in meters (see note below).

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:

• azimuth, elevation, 3D and polarization radiation charts
• VSWR charts, incorporating Real- and Imaginary-reactance curves
• an antenna currents diagram
• a Smith chart

Example antenna performance controls section

Calculation of an antenna's performance is achieved using a NEC4.2 (Numerical Electromagnetics Code v4.2) code-base licensed to the site.  Results of the calculations, and the resulting charts and diagrams, are entirely comparable with those presented by programs such as EZNec and 4nec2, for similar antennas.  Nonetheless, NO claims are made concerning 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 this site's Disclaimer for more information.

A Note On Length Units

We use meters as length units exclusively and unapologetically throughout this site, since the metric system has been adopted by almost all major industrialized countries in the world. With just one exception - the United States of America, which still uses the cumbersome and outdated Imperial system of measurements which include feet, inches, yards and miles.

Early attempts to include the Imperial system into the calculations and display of both metric and Imperial values in this site indicated very clearly that the additional effort required was just too much, and greatly hindered the further development of the site. With this in mind, and also noting that the entire US population represents less than 4.5% of the world's population, we decided not to support Imperial measurements, and to go forward with metric, the gold standard used by over 95% of the world's population.

Indeed, many US amateurs themselves have decided not to continue to use the Imperial system when designing and building antennas. See e.g. this Youtube video from Toivo W8TJM, where he explains how he has converted completely to metric, "because it's a lot easier to do antenna calculations metrically, rather than trying to convert inches and feet ... none of that conversion's necessary if you go metric."

We have, however, included a metric/Imperial conversion calculator in the Extras page for those users who may still, in this day and age, be unfamiliar with - or do not yet use - the metric system.

Notes on ground types, and their effects in modelling antennas

The specification of a particular ground type beneath an antenna plays a large rôle in determining the radiation patterns, also gain and impedance, exhibited by the antenna.

Ground types come in three basic flavours:

• "real" ground types, each representative of the surface soil type in the vicinity of the antenna, and each specifying values for the
  conductivity (in S/m) and the dielectric constant (permittivity) of the ground;
• perfect ground - perfectly-conducting ground, with perfect reflection properties;
• free space, indicating the absence of any surface beneath the antenna. The antenna radiates in all directions without reflections
  (other than those that are a function of the modeled antenna structure itself.)

Several basic real ground types have been established over the years, based on measurements made of the conductivity and dielectric constant (permittivity) of the ground in many locations, and representing soil types ranging from rocky and poor, through rich pastoral types, to types encountered in city/industrial areas.  In addition to these real ground types, two water types are given, plus a perfectly conducting ground, and the option to place the antenna in free space.  Here is a listing of the ground types used in this site:

Values for soil and water types in this list are selected from the table in the ARRL Antenna Book, 20th Edition, p.3-13.

These values taken from the ARRL Antenna Book are themselves based on a table of values set out in "STANDARDS OF GOOD ENGINEERING PRACTICE CONCERNING STANDARD BROADCAST STATIONS (550-1600 kc.)" published in 1940 by the US FCC (see Table B, p.34 in that document ). As set out in that document, the values are taken as constants; however, one should note that:

• the values are valid only for the MF frequency range of 550 kHz to 1600 kHz, and not for the HF bands, and
• real ground/earth does not actually display constant values of conductivity or permittivity; instead, these values are frequency-dependent, as has been shown by e.g. G. H. Hagn in the 1987 paper " Ground Constants at High Frequencies (HF) " :

  Analytical models of propagation and antenna performance such as the Numerical Electromagnetics Code (NEC) require accurate input data in order to produce accurate answers. NEC-3 requires information about the macroscopic electrical properties of the soil, the permittivity (relative dielectric constant) and conductivity, in order to model properly wire antennas in proximity to the earth. Most of the values available in the literature are "constants," and many of them were derived from data taken at MF using AM broadcast stations so they do not necessarily pertain to the HF band. The actual values for most soils exhibit dispersion (i.e., they are a function of frequency) which is a primary function of the moisture content of the soil and a secondary function of other variables (e.g., temperature, compaction, mineralization, etc.). This has been known since the mid-1930s...

Nonetheless, we adopt here the stance taken by the ARRL, and taken also by the creators of the most popular antenna-modelling software, which also use these values. These sources take the view that, for the purposes of modelling antennas for amateur radio purposes, these values can be taken to be constants.

For modelling of antenna performance, the real ground types used in this site are taken to represent soil in a flat ground surface beneath the antenna, and extending indefinitely to the horizon in all directions.  The program does not take into account terrain variations that may be very important to a given antenna situation (see e.g. the section below this one.)  The soil is assumed to be uniform in type and quality, down to indefinitely large depth - in reality, of course, the ground beneath the antenna is normally stratified and changes quality with depth.

The antenna designers in this site perform calculations using a NEC v4.2 engine to produce radiation patterns, VSWR diagrams, etc. and, for real ground types, employ a fast Sommerfeld/Asymptotic integral calculation method, which gives accurate results in most situations.   The calculations are accurate enough for signals in the upper HF region and above, since these signals penetrate the earth to shallow depths only.  For signals in the lower HF regions or below, the signals can penetrate the earth to considerable depths and can thus be variably affected by the changing soil quality at different depths.  Users should be aware of this when designing antennas for the low HF bands.

In general, the effects of ground on an antenna depends largely on the orientation of the antenna, and its' height above the ground:

• horizontal antennas: at heights lower than 1 wavelength, the ground can have a small, but notable, effect on radiation patterns; at heights above 1 wavelength or so, the differences are minimal.
• vertical antennas: the ground will form part of the return connection for the antenna and the quality of the ground will have an effect, particularly on the feed-point impedance. Vertically polarized radiation is not well reflected by the ground except at grazing incidence, or over very highly conducting surfaces such as sea water. However the grazing angle reflection important for ground wave propagation, using vertical polarization, is in phase with the direct wave, providing a boost of up to 6 dB.

General notes on the effect of ground slope on elevation radiation patterns for portable users

It is a widely-recognized fact that the slope of terrain in the vicinity of an antenna, as well as in the far-field of the antenna, can have a profound effect on the elevation radiation pattern of the antenna.

In general, an antenna set up at the top of a downward-sloping piece of ground - as may occur when activating portable from a summit - will exhibit an elevation radiation pattern (ERP) which will tend to follow the direction of the slope, and will be lowered by an amount less than, and in some cases equal to, that of the slope. The amount by which the ERP is lowered will depend on the ground conditions, and hence on the degree of roughness of the slope, as well as the conductivity and dielectric constant, of the soil or materials constituting the slope.

This lowering is due to the reflected ground wave from the downward slope interfering with the direct wave, effectively lowering the angle at which the antenna radiates its signal. The effect is noticeable with both horizontally and vertically polarized waves from the antenna, although the effect tends to be less in the case of vertically polarized waves.

Steeper slopes can cause the antenna's ERP to split into multiple lobes, rather than a single, well-defined beam. This splitting of the pattern can affect the antenna's gain, sometimes leading to higher gain than expected in some directions, and sometimes lower gain in some directions.

These few notes are of course no substitute for a formal study of this subject, which is very complex and beyond the remit of this site.  Nonetheless, the notes presented here should give the portable operator a good general idea of how slopes near to their antenna may affect their signals.

The ARRL offers a program called HFTA (HF Terrain Assessment for Windows) which is included in the CD included with some editions of the ARRL Antenna Handbook. According to their documentation Operating Instructions for HFTA, Version 1.04 ,

The program uses custom-defined terrain model files, based on USGS map data in DEM (Digital Elevation Model) or NED (National Elevation Database) seamless formats in the USA. In addition, usage of SRTM (Shuttle Radar Topography Mission) 3-arc-second format is described, allowing the user to generate terrain profiles for areas outside the USA.

HFTA has been used by many radio amateurs to model the terrain in different directions around their home QTH. This has allowed them to estimate the effects of the terrain on their signals and to permit them to better plan the arrangement of their antennas to achieve better results in DX and in contests. The amount of work involved is considerable, but can pay dividends for a particular home QTH.  Whether this program can be useful to the occasional activator of SOTA summits or POTA parks remains to be seen.

Glossary of antenna terms

Some terms used in this website, or used in association with building antennas, may be unfamiliar to some users. We present here a short list of such terms, together with descriptions which may prove helpful.