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Codan C multiwire broadband dipole. Two wire broadband HF dipole.

EA4FSI-28T1 – HF Antennas

In this page you will find an analysis of several monopole configurations, the differences between a perfect and an imperfect ground and the effects of using a ground plane made of radials or counterpoises. The analysis are based on simulations performed with the 4NEC2 software and are performed introducing new elements in successive aproximations. The antenna under analysis is an ideal monopolp monopole designed to work in the 20 meters band, adjusted to a central frequency of 14,1 MHz.

In a first approach, an ideal monopole over perfect ground is analyzed. Then, an imperfect ground is introduced and after that the effects of adding radials to achieve an anteba ground plane. In this first analysis we consider a perfect ground and zero radials. The antenna is omnidirectionalthanks to the simulated perfect ground plane, and its gain is 5,15 dBi 3 dBdthat is, twice the gain of a half-wavelength dipole fig.

In the vertical plane, the radiation pattern has its maximum gain just at a null takeoff angle, making the antenna optimal for DX work under these ideal conditions. Using the same design fig. This will help to move the theoretical analysis to the real world. ,onopolo the same length of 5,16 meters, the SWR rises to 1: That is, the antenna is unmatched with an impedance far away of 50 ohms in its feeding point.

It will be necessary to use an impedance transformer or an antenna tuner. Although the antenna is still omnidirectionalthe first observed effect of an imperfect ground is an elevation of the radiation lobe fig. This effect is typical in antennas installed on the side of the roof o a vehicle finite ground plane: The new antenna gain is -7,74 dBi at a takeoff angle of 25 degrees over ground. That is, this is an antenna with losses. This is due to the fact that the currents circulating in the antenna must return through the average soil, which has a very poor electric conductivity.

Those effects would be even worse over a dry soil. Observing the previous analysis, one can conclude that it anfena be of interest to improve the electrical conductivity of the ground plane to avoid distortions in the radiation pattern and a loss of eficiency.


This can be achieved using radials or counterpoises.

Using the name of radial or counterpoise has lead anteha controversy, deeply studied by L. The following analysis takes into account only one radial or counterpoise, monkpolo is the option chosen by several manufacturers of portable vertical HF moonopolo. Furthermore, we will consider that both the monopole and the monoploo are very close to the ground.

There are several theories about the optimal length of the radials. In our experiment we will run an optimization process with 4NEC2 in order to find ,onopolo optimal length for our counterpoise. In the 4NEC2 simulation, in order to avoid the counterpoise to be in direct contact with the ground, we will rise the whole structure 0,1 meters above the ground. In the simulation, the radial or counterpoise is extended all along the X-axis of the ground plane.

We return to the initial value of monopole length calculated in the first analysis 5,16 meters and run an optimization process with 4NEC2 to find antrna optimal length of the counterpoise, with the goal of achieving a minimum SWR. The result is a counterpoise of moopolo meters with an SWR of 1: Please remember that this solution is only valid for this monopole, at this working frequency and over this type of ground. After our counterpoise length optimization process, the SWR is around 1: The radiation pattern is no more omnidirectional: If we analyze the vertical plane of the radiation pattern fig.

If we compare the results with those of example 2, we see that, using the counterpoise, we have improved the antenna gain in 6,5 dB, having also three times more radiation efficiency. With an adequated counterpoise length we can also achieve the impedance matching in the working band. It can be concluded that, for a monopole of given length, the use of a single radial or counterpoise of studied length will benefit the overall antenna efficiency and gain in the direction imposed by the counterpoise.

In fact, the counterpoise is another part of the whole antenna, so its length has to be studied to optimize the SWR. In the previous example we have proven that the gain and radiation efficiency of a monopole are improved angena means of an unique radial or counterpoise.

However, under this condition the monopole is no more an omnidirectional antenna, having more directivity in the direction imposed by the counterpoise. If we want to keep the omnidirectional characteristic, it will be necessary to use at least 4 radials.


In order to ensure that we have an omnidirectional radiation pattern, the four radials are installed at 90 degrees intervals over the ground plane.

In the 4NEC2 simulation, in order to avoid the radials to be in direct contact with the ground, we will rise the whole structure 0,1 meters above ground.

The length of the monopole is the same as in the previous examples 5,16 meters and each radial is 4,79 meters long, as calculated in example 3. The SWR at the design frequency is 1: If we compare the results with those of example 3, we achieve an improvement of 0,8 dB in the antenna gain, with the additional advantage of having an omnidirectional radiation pattern.

The radiation efficiency is almost twice the previous value. The table 1 is a summary of the simulations performed with the ideal monopole over perfect ground, the monopole over real average ground and the effects of using one or monoploo radials or counterpoises.

It also includes the results obtained simulating several radial configurations up to radials. Comparison of several monopole configurations. The real ground makes the currents flowing out of the antenna to return though a medium of low electric conductivity.

The results are even worse over dry soil. The impedance of the antenna at its feeding point changes, making necessary to design again the antenna length, or to use a matching network or antenna coupler.

The radiation efficiency is three times bigger than in the previous case and the antenna gain is 6 dB better. In order to achieve an omnidirectional radiation pattern, an even number of radials must be used, in a completely simmetrical layout.

The higher the number of radials, the bigger the natena efficiency and antenna gain. Using more than radials will not make further difference. Monopole over monoopolo ground.

Monopole over real ground. Monopole with one radial or counterpoise.

antena monopolo de cuarto de onda – Spanish-English Dictionary

Monopole with 4 radials. The resulting SWR is 1: The radiation pattern is again omnidirectional, thanks to the layout of the 4 radials fig. The general conclusions are: