FarWave 11dBi Antenna Booster

What is it good for?

"FarWave 11dBi" is a Yagi-Uda like antenna for the 2.4GHz range. It is calculated and constructed for the Mavic Mini CE and amplifies the original antenna (2.2dBi) signal by focusing the wave pattern in the forward direction.
Signal strength is amplified by a factor of 8 or +9dB. This significant power boost can be helpful for better signal stability in difficult areas or it can be used to increase the achievable range by a factor of almost 3. There is no need for electric connections or any assembling.
This antenna booster is "plug and play". It is slipped over the left remote antenna only. The second antenna is not used at all in the Mavic Mini CE version.

How does it work?

The Yagi-Uda antenna (mostly known as "Yagi antenna") was invented in 1926 by Shintaro Uda and Hidetsugu Yagi. It is a high gain directional antenna consisting of multiple parallel wires or metal rods in a line. Yagi-Uda antennas were widely used for television receivers, long range communication and are used by radio amateures. All metal rods are symmetrically aligned in one plane and their correct distances and lengths are very important to make this antenna work as desired. The interesting thing with the Yagi-Uda antenna is the fact, that only 1 element is driven (connected to electronic components), whereas all other metal rods are isolated (but they can even be connected center wise via a conductive beam too). So if we have an omni directional dipol antenna, and we do the math right, we can simply make an "addon" antenna to amplify this antenna (receiving and transmitting) in one direction. There are many papers, instructions and online calculation tools available to construct such an antenna. But it turned out that they are mostly designed for much longer wave lengths and linearly scaled down for the short 2.4GHz range, and they do not work well. It seems that the correct wire diameter is more critical for this short wavelength. So the FarWave antenna was designed and calculated from scratch for the 2.4GHz range by using a numerical electromagnetic FE software.

3D radiation pattern of FarWave 11dBi antenna

Calculated 3D radiation pattern of the FarWave 11dBi antenna at 2440MHz. The units are "dBi" which means amplification in decibel compared to an isotropic radiator. The original Mavic Mini antenna is a λ/2-dipol like antenna with about 2.2dBi. So the additional gain of the FarWave antenna is the difference of 11.4dBi-2.2dBi which results to +9dB gain or +700% signal power compared to Mavic Mini stock antenna.

The electromagnetic wave of the driven element excites the freely movable electrons within the metal rods to perform a similar oscillation. There is some phase shift (or even phase jump), mainly depending on the length and diameter of the rod. The rod behind the driven element (Mavic Mini remote antenna) is called reflector. Its excited radiation interferes in that way, that the forward direction is in phase and amplified, while the backwards direction is more or less annihilated. The rods in front of the Mavic Mini antenna (called directors) are excited too and interfere constructive in forward direction and destructive in all other directions. Of course the complete resulting wave sum has always to be considered and therefore calculation by hand is not trivial.

2D radiation pattern of FarWave 11dBi antenna

Calculated 2D radiation patterns of the FarWave 11dBi antenna at 2440MHz. The blue line shows the vertical plane (pattern seen from the side) and the red line shows the horizontal plane (pattern seen from above). In these plots it is easy to see how narrow the angles of high amplifications are. Reaching an aiming error of 45° reduces the resulting antenna gain from over 11dBi to below 1dBi which underlines the strong forward characteristic of this antenna. So for getting the best results with this antenna, aiming accuracy should be 15° or better.

The astonishing high gain forward amplification of Yagi-Uda antennas is based on wave interference and therefore very frequency depending. This can be a big disadvantage if broadband amplification is desired and in that case parabolic antennas would be a much better choice. Or this can be an advantage if only a single frequency is of interest (2.4GHz for example) and other disturbing frequencies should be filtered out. But even for the small used 2.4 GHz range, channel 1 (2412 MHz) to channel 13 (2472 MHz), the design has to be optimized to achieve channel independent high gain performance.

frequency pattern of FarWave 11dBi antenna

Calculated maximum gain values depending on selected frequency (channel). If no care is taken during design, gain drops within the used channel range of more than 2dBi are possible.

Many antenna models during development have been measured via a simple spectrum analyzer to validate the calculated data and, although farfield measurements are not that easy, calculations and measurements fit nearly perfectly.

spectrum analyzer measurement

Image of the spectrum analyzer for farfield measurements. Software was used to average and accumulate the received short transmission spikes to get accurate data during a simulated Mavic Mini flight session.

Real range tests in known areas have surpassed all expectations and Mavic Minis battery capacity (>4km).

Additional design information

The lateral radiation patterns shown above are calculated for 2440MHz and differ slightly for 2400MHz or 2480MHz. During the research and developing phase many designs have been tested, partly with much better back lobe suppression and even little more gain. But as it turned out, there are many possible designs with "unstable" solutions. That means, that small changes in rod distances or lengths (+-0.1mm) can have a big impact on the amplifying properties. The design of FarWave was optimized to get the most robust solution, so that small mechanical variations of the antenna rods do not have appreciable negative consequences for the antenna gain. Another question is, which metal should be choosen for the rods? Copper, brass, aluminium and steel have been checked. Copper is too soft. Steel is already a too bad electrical conductor and will loose 0.3dBi. Brass would be the best choice if high mechanical stability is necessary. We have choosen aluminium for its (by far) lowest weight, without compromising performance. The boom is 3D printed with PETG to achieve optimal mechanical outdoor properties.

How does FarWave compare against other antenna products?

As far as we know there is only one other plug&play (no remote disassembling/soldering necessary) antenna type for the Mavic Mini available. It is a parabolic reflector like construction. There are several vendors of such products with only small design differences. The internet community is not sure if they even work, so we tried some of them. And yes, some of them work, but not as they are intended. To work as parabolic reflector at this wavelength the distance from the dipol antenna to the reflector has to be much larger (farfield). So the reason why some of them work is, that if constructed correctly as a nearfield (yagi like) reflector, with an exact distance betweeen reflector and dipol antenna (about λ/4), they could reach up to +6dB (8dBi) gain. So even then no match for the FarWave 11dBi in our opinion.