Modelling Aftermarket 2.4 and 5.8
GHz Antennas for Miniature UAV Controllers
E-mail: [email protected]
This paper describes 4nec2 model analysis of the expected performance of 2.4 and 5.8 GHz "Parabolic" reflectors, Yagi-Uda antennas, and combination "ParaYagi" antennas for quadcopter radio control links.
Over the past decade, radio-controlled miniature
unmanned aerial vehicles (UAVs) have grown in popularity
among recreational hobbyists and for commercial
surveillance, aerial photography, and military
users. Early civilian radio-controlled model
aircraft used analog modulation on a limited number of
control frequencies in the 27, 49, 50, and 72 MHz
bands. With the coming of
microprocessor-controlled quadcopter drones, smaller
antennas and digital communication protocols on the 900
MHz ISM band and 1.3 GHz video feeds became
popular. Now in the early 21st century,
inexpensive spread spectrum control systems in the
unlicensed 2.4 GHz and 5.8 MHz frequency bands are
In residential and commercial areas, secure UAV flight
control can be compromised by unintentional radio
frequency interference (RFI) from devices and other
users that share 2.4 GHz and 5.8 GHz, including
Bluetooth devices, car alarms, cell phones, computer
peripherals, toys, WiFi networks, wireless speakers,
microwave ovens, and licensed radar, ISM and amateur
radio stations to name a few. Such RFI can unduly
limit the range within which the UAV can safely fly.
UAVs and their controller units typically employ the
maximum permitted transmitter power (typically under 1
watt) and a pair of omnidirectional vertical dipole whip
antennas for diversity reception. The UAV must use
a non-directional antenna due to its variable
orientation; however, a directional antenna on the
controller can enhance the control link by increasing
the signal strength at the UAV and by reducing the
controller's sensitivity to RFI from undesired
The antenna enhancers that have become popular among
UAV pilots are: a passive cylindrical metallic
"parabolic" reflector placed behind each dipole; a
Yagi-Uda configuration of one reflector dipole and
several director dipole elements that slip over the
stock dipole antenna; and, a "ParaYagi" combination of
the parabolic reflector and the Yagi. The model
dimensions reported here are from Ali Vekta's
"ParaYagi P2 Extender" 3D printer files on
Thingiverse.com.2 Several UAV pilots
have field tested similar antennas using their maximum
control range as a measure of the efficiency of each
Figure 1. The 3D Printed 5.8 GHz "ParaYagi" Antennas on a DJI Spark Controller.
The two vertical whips of the DJI Mavic Mini controller (photo below)6 are printed circuit bowtie antennas for 2.4 GHz and 5.8 GHz with a common feed point. The bowtie consists of two identical dipoles for each band connected in parallel to achieve broader bandwidth than a single dipole. Similar to WiFi access points, two whips are used to reduce multipath signal fading through diversity reception. This antenna will exhibit a mostly omnidirectional horizontal donut shaped radiation pattern with nulls directly above and below the antenna (Figures 5 & 6). The proximity of the two whips to each other will skew the omnidirectional pattern to some degree.
Also below are photos7 of the printed
circuit 2.4/5.8 GHz vertical fan dipoles that are glued
inside the sides of the DJI Spark quadcopter. In
the DJI Mavic Mini, the dipoles are located inside the
vertical portion of the two front arms. Two
antennas are again used to achieve diversity
reception. The position of the antennas with
respect to the internal electronics and battery would
also cause some skewing of their otherwise
omnidirectional radiation pattern. The controller
would observe this as a variation in signal strength as
the quadcopter rotates (yaws). Transmitter power and
stock antenna parameters for all DJI drones are
published in FCC
Specifications and Compliance Reports.8
The dimensions are assigned to defined variables to
facilitate the future use of 4nec2's optimization
function on the models.
Figure 5. Dipole Horizontal Pattern
Figure 6. Dipole Vertical Radiation Pattern
The 4nec2 Geometry Builder program is used to construct
the wire frame simulation model of the 90º reflector.
In the 4nec2 model horizontal and vertical plane
radiation patterns and tables:
2.4 GHz "Parabolic" reflector horizontal and vertical radiation patterns compared to the stock dipole antenna.
At 2.4 GHz the "parabolic" reflector model shows equal
gain to the dipole in the forward 90º heading and 5.04
dBi gain towards the rear direction (270º).
5.8 GHz "Parabolic" reflector horizontal and vertical radiation patterns compared to a dipole antenna.
At 5.8 GHz the 4nec2 model of the "parabolic"
reflector shows 5.4 dB gain over the dipole in the
Here are the 3D model diagrams of the 2.4 GHz and 5.8
GHz Yagi antennas.
2.4 GHz Yagi horizontal and vertical radiation patterns compared to the stock dipole antenna.The 2.4 GHz Yagi antenna exhibits 7.8 dB greater gain than the stock dipole antenna in the desired heading. The Yagi antenna offers approximately +/-30° focusing of the beam in both the horizontal and vertical planes.
"DJI Alex" documented greater than 2260m range with the Yagi compared to 1600m range with the stock dipole antenna in his field test video at https://youtu.be/3ALXqGrJxJ4?t=560.3
5.8 GHz Yagi horizontal and vertical radiation patterns compared to the stock dipole antenna.At 5.8 GHz, the Yagi antenna exhibits 2.4 dB additional gain and better directivity compared to the "Parabolic" reflector. The Yagi antenna offers approximately +/-30° focusing of the beam in both the horizontal and vertical planes.
Nick Daly demonstrated similar results in his 5.8 GHz comparison of the Yagi and parabolic reflector in his YouTube video https://www.youtube.com/watch?v=3JlziZsGBdM4
The "ParaYagi" models combine all the elements and
dimensions of the respective "parabolic" reflector and
the Yagi antenna models.
2.4 GHz "ParaYagi" Antenna horizontal and vertical radiation patterns compared to the stock dipole antenna.At 2.4 GHz, adding the "parabolic" reflector slightly enlarges the rear lobe of the Yagi antenna pattern. The reflector adds no significant effect to 2.4 GHz Yagi antenna's forward gain and directivity.
5.8 GHz "ParaYagi" Antenna horizontal and vertical radiation patterns compared to the stock dipole antenna.
At 5.8 GHz the "ParaYagi" combination antenna
suppresses the rear lobes of the Yagi antenna. The
addition of the reflector offers 0.4 dB increase in
forward gain over the Yagi antenna alone.
The observed field test signal strengths agree with the model prediction of greatest signal strength with the Yagi antennas and least signal strength with the stock dipole antennas.
Miniformer published their laboratory gain measurements of various 5.8 GHz antenna extenders.10 Despite some errors introduced by their environmental variables, it is interesting to compare the Miniformer results against the 4nec2 model gain calculations for those antennas. Table 8 lists the Miniformer power measurements in microwatts, their dBu unit equivalents, and these values normalized to the 2.14 dB gain of the stock dipole antenna.
These data agree in that both the Yagi and ParaYagi antennas exhibit greater gain than the Parabolic antenna with no greater than 3.5 dB variance between expected and observed values.
I now rarely observe signal dropouts and video feed lag
in my field tests with the 5.8 GHz Yagi or ParaYagi
antennas. While flying at a distance, I have
observed loss of signal when I divert the antennas more
than 30º vertically or horizontally from the direction
of the quadcopter. The stable and correct aim of
these directional antennas is increasingly important for
flight control over greater distances.