Cloverleaf antenna is a circular polarized antenna for FPV which is way better than the cheap dipole antenna that comes with video transmitters and receivers. Antenna is one of the most important parts of FPV system. In this tutorial I will show you how to DIY one.
Omni circular polarized antenna like Cloverleaf is one of the best FPV video transmitter antennas available to hobbyists. I explained the benefits of a circular polarized antenna over a linear one if you are not sure what are the differences.
What is a Cloverleaf Antenna
The Cloverleaf is a closed loop antenna which the signal and ground wires are connected. The cloverleaf antenna has 3 loops at 120 degree apart, and they are titled at 45 degree to horizontal plane.
Good and bad things about Cloverleaf Antenna
Circular polarized antennas are great for FPV video streams because they’re good at rejecting phase shifted signals (distorted signal) such as multipath interference. The cloverleaf antenna has an excellent radiation pattern and very low gain.
It is not the ideal receiver antenna however, because the reverse polarization rejection pattern is very erratic. You need to choose other types of antennas for the receiver such as the skew planar wheel (4 lobes).
Let’s get started!
Table of Contents
Parts you will need
- 0.8mm copper clad welding wire, it’s stiff and easy to solder (some people used 0.6mm also worked fine)
- RG316 coax cable (or RG405)
- Soldering tool
Measuring and Cutting the antenna wires
The size of the antenna (the length of the wires) does not follow the rule of “bigger, better”. The length of antenna wires affects what signal frequency you can receive. The length you need for your desired frequency can be calculated using mathematical equations. Generally the length of wires would be smaller for higher frequency signals.
To make it easier for our readers, you can use this tool to calculate the required length of the wires:
(Formula: Length in millimeter = 307022 / Frequency in MHz)
Use this tool to calculate where to bend the wires.
(Formula: Length in mm = 76755 / Frequency in MHz)
As an example, for the most common 5.8 GHz FPV system (5800 Mhz), the length of the wires should be 52.93mm, and it should be bend at 13.2mm. This is what the shape and measurements should look like.
Measure and cut 3 pieces of wires at the calculated length, cut them just a little bit longer (marked as optional above, so you have the extra length to solder to the main wire. Trim both ends so they are flat.
I bend the small piece of wire into square U shapes, and I personally don’t really leave the “optional” part in the wire.
The 3D design diagram with angles
Soldering
Cut your coax cable open, so the ground and signal wires are separated, exposed and ready to be soldered.
You don’t have to follow the picture below, you could cut your fingers :)
I put the bent copper wires on some blu-tac, and arrange them according to the 3D diagram above. For example for the VTX antenna, I put them about 120 degree apart, and for the VRX antenna, that should be approximately 90 degree.
And tilt the wires to the right 45 degree. This will make the antenna “right handed” polarized, since this is a more common configuration.
And finally solder all the tips together to the signal wire.
Other Polarized Antenna Design
Skew Planar Wheel Antenna (4 lopes)
Virevent Antenna (4 lopes)
Windmill Antenna (5 lopes)
Conclusion
The key to making a successful FPV antenna is to be precise with measurement. The more accurate you can make the antenna the better it will perform.
26 comments
The calculator doesn’t seem to be working…
Sure these Antennas are right handed? The fist photos look left handed to me.
After copper wire soldered, what type of glue we need use for ensure copper wire joint very stong? Mostly fpv antenna need glue in joint wire area
Result….
rcgroups.com/forums/showthread.php?1388264-Build-IBCrazy-s-Cloverleaf-The-ultimate-circularly-polarized-aerial-antenna%21/page376#post39760978
Oscar
Good article. To tackle antenna design principles in a short article or reply is impossible…entire books are written addressing the subject. Here are my general observations/experiences of 30+ years of building numerous successful antennae while in “ham radio”. First impedance: coaxial length does play an important part, see
66pacific.com/calculators/full-wave-loop-antenna-calculator.aspx
To calculate antenna length of a full wave dipole: (BTW I have used this formula for years, i am pretty sure it’s correct): speed of light/frequency in MHz= length in meters…convert to mm. 300/5800mhz= 0.0517meter convert meter to mm=51.7mm for the purist…using 299.7/5800 = 51.6mm How many hobbyist can measure and cut to within 1/10 of a mm?
Secondly: every antenna will have a ‘center frequency’, some call it the tuned or designed frequency. Let’s use the frequencies that are commonly found on an FPV VTX (not all are legal for every country 5300-5900mhz). For optimum results in planning an FPV antenna, the frequency for calculations should be in the center of the group of frequencies that you plan to use, i.e. 5.6 GHz is what I would use for FPV calculations. All antennae work best at their design frequency and drop off in performance the farther away your VTX frequency gets from the antenna design frequency. So, to use a design frequency of 5.8ghz instead of 5.6ghz will cause the performance of the antenna to drop off much more in the lower frequencies (which causes higher SWR and shorter range). Example: if your VTX uses a frequency at the bottom end of the frequency band say 5.362 GHz, it is twice as far away from the design frequency (5.8 GHz) than the center frequency of 5.6 GHz.
The most important thing is the Standing Wave Ratio (SWR) which I rarely see stated in antenna ads. The higher the SWR the more power (milliwatts) lost at the antenna in heat (ever feel how warm some of your antennae get?), this usually means lost power (milliwatts) not being radiated out from your antenna. After determining the design frequency and building the antenna the SWR should be checked to find what frequency ended up being the best in terms of low SWR and this would then be the real center frequency of the antenna. If it falls close to the center of your frequencies, great. If not, you would need to adjust the length of the antenna and then recheck the SWR. I would not even think of buying an antenna that does not state the SWR. BTW 1.1 – 1.5 SWR is the acceptable range with the lower number being the best but not always obtainable. Also, a high SWR (2.0 and higher) can damage your VTX equipment. In designing/building your own antenna you need a way to determine SWR (google it). For FPV antennae I would look for an SWR meter or a means to measure SWR of frequencies in the 5.3-5.8GHz range but this equipment can be VERY pricey. Without being able to measure SWR you have no way to determine if the antenna is a good antenna aside from putting it on the quad and hope the SWR doesn’t fry your VTX and that your signal range remains OK for your flying. In the FPV antenna bands EVERY milliwatt counts. Milliwatts that are wasted because of poor workmanship, incorrect center frequency or high SWR shortens the range of your flying and could damage your equipment.
Roger
is that –> ‘307022’ supposed to be the speed of light? where did you get this value?
If you wanna get an almost perfect value, you need to multiply the speed of light in vacuum (299792458 m/s) by the refractive index of air (1.000293)
which is 299880297.19
Calculating wire length (wavelength) using this value gives around 1mm difference in your values
Something confuses me,
the total length should be 1 Wavelength,
the bend should be at 1/4 Wavelength,
you calculate the Wavelength using speed of light 307022000, which equals to 52.93482758620689mm
whereas Speed of light in Air according to Google is
299700000
so far i have found these values
300000000
307022000
299792458
299700000
which one is Accurate?
calculator doesn’t work in chrome or edge browser
fixed now
Well, this went way better than I expected. I used a common a 2.4ghz antenna, like those you have on your internet router. Just removed the cap from it an used the base (connector + 0º/45º/90º tilt angle). Honest, because it’s my first time doing this, it came out ugly, but the result was pretty good. Didn’t try it in the field yet, but inside my house the signal is amazing, even better than my others antennas. Looks like I’ll never buy antennas in my life again :D
Great article, thank you. I would like to add that I use the brass rods available at many model shops easier to use and solder than the mig welding wire you are using. I bought a roll of the welding wire but in comparison to the brass rod found it very difficult to solder to, and the joints were far from reliable.
Sorry I got lost here:
“For example for the VTX antenna, I put them about 120 degree apart, and for the VRX antenna, that should be approximately 90 degree”
How can we create a full circle with 3 leaves 90deg apart?
Appreciate if you can clarify.
Thanks
Hi, because the VRX antenna there are 4 lobes :)
Hello, which antenna do you think is better for a 2.4GHz quadcopter(toy)? Many ppl uses a 5dbi 2.4GHz wifi antenna + a windsurfer
I already made a quadrifilar helicoidal antenna 2.4GHz, testet it with my wifi and works fine, but Im just a noob and don’t know nothing about antennas, would be great if an expert can help me
Hi Oscar,
I couldn’t get the calculator to work, Looking at 2.4 Ghz and 5.4 Ghz. Please send values, or the equation (equation would be better!!! ;) ). Thanks!
Frank
thanks for letting me know, it’s now fixed :)
Hi Oscar
Great post. Do u know what material could be used to make the base rg316 bendable so it can be bent into a specific shape?
Is that wire indispensable? I have 0.8 and 0.6mm stainless steel wire. Can I use this for this purpose? Thanks.
Hi Serkan
I think you are supposed to use wires that have good conductivity, copper is better than steel.
also I prefer thicker wires, because they are tough so you don’t bend them by mistake during usage, or destroy them in a crash.
I want to use the SS wire because I couldn’t find MIG wire in my local shops :) I tried it yesterday but it is really hard to solder it. So I decided to try a brass wire. Electrolizing the SS wire ends with copper sulphate is another choice to me. Also IBCrazy said in one article galvanized wires are best if you we can find it.
Do you mean pure copper while saying “copper”? Thick wires are said to have more interfenece wtih other frequencies. So they say to use as thin as possible. There is a confusion in the internet from this point of view. Some say thicker is better, and some say thicker wires causes interferences and gets the signals which they shouldn’t do. I am really confused and still searching…
when i say thick wire, i mean within reasonable range… 0.8mm – 1mm is my favourite.
What feed line lenght do you use for 5.8 Ghz tx -and rx-antenna? I got some knowledge about antenna theory and if I’m not mistaken feedline impedance is of great importance. How come that all tutorials about building fpv antennas never mention any thing about feedline lenghts? From what I understand it has to be odd multiples of quarter wavelength, including the velocity factor of the cable. I would really epreciate if anyone could clarify on that issue.
Hi Oscar and AuLeeFor
Great question about feedline impedance… I wish i had the answer for you :P
I’ve noticed that the same thing, no guides refer to feedline length at all. And i’m less than impressed with the performance of any of the CL antenna’s i have tried. I guessing that there is a large impedance mismatch going on with the common designs that have been shared around… and i noticed that Ibcrazy’s new bluebeam antenna’s include a balun on the feedline.
Looks like i’m gunna have to brush up on my maths and maybe look into getting myself a LCR meter to figure this one out ;)
I’f you have come up with some answers in your search i’d love to hear it.
nice article, but can u plis tell me where can i read this antenna’s formula for calculate the value of this antenna’s gain? and formula for calculate bend and length of wire without tool for calculated it at above?
you can see all the details in this RCgroups thread,
http://www.rcgroups.com/forums/showthread.php?t=1388264
Very informative article.Excellent description of antenna design.
Thanks.