Thursday, May 22, 2014

Make a DIY Cloverleaf Antenna

http://blog.oscarliang.net/make-diy-cloverleaf-antenna/

Make a DIY Cloverleaf Antenna

cloverleaf-antenna-wire-soldering7

What is a Cloverleaf Antenna

The cloverleaf antenna is a circular polarized antenna which is way better than the cheap whip antenna that comes with most transmitters. In fact it is one of the best FPV video transmitter antennas available to hobbyists at the moment. I explained the benefits of a circular polarized antenna over a linear one if you are not sure what are the differences. 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.

cloverleaf-antenna-angle-diagram

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). The cloverleaf antenna has an excellent radiation pattern and very low gain. It’s possible to achieve a 1.0 SWR which is the perfect efficiency in signal transmission.
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.
Also it’s not easy to make, pretty fragile, takes up space, affected by wind, and not possible to tune to the desired frequency after it’s made.

Let’s get started!

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
cl1
build-cloverleaf-antenna

Measuring and Cutting the antenna wires

The size of the antenna (the length of the wires) does not follow the rule of “the bigger the better”. The length of the 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.
Enter the frequency (for example 5.8 GHz = 5800 Mhz)
MHz
Cut wires to:
mm
Use this tool to calculate where to bend the wires.
Enter the frequency  (for example 5.8 GHz = 5800 Mhz)
MHz
Bend wires at:
mm
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.
cloverleaf-antenna-wire-measurement
Measure and cut 3 pieces of the calculated length, cut them a 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. Pretty straightforward, I followed this youtube video.
cutting-antenna-wire
cloverleaf-antenna-wire-cutting

The 3D design diagram with angles

cloverleaf-antenna-angle-diagram3
cloverleaf-antenna-angle-diagram2

Soldering

Cut your coax cable open like this, so the ground and signal wires are exposed and ready to be soldered.
build-cloverleaf-antenna2
build-cloverleaf-antenna3
Solder the wires to the coax cable one by one about 120 degree apart.
cloverleaf-antenna-wire-soldering
cloverleaf-antenna-wire-soldering2
And tilt the wires to the right 45 degree. This will make the antenna “right handed” polarized, since this is a more common configuration.
cloverleaf-antenna-wire-soldering4
cloverleaf-antenna-wire-soldering3
Now bend the wires, so the tip of the wires can reach the signal wire of the coax cable.
cloverleaf-antenna-wire-soldering5
cloverleaf-antenna-wire-soldering6
And finally solder all the tips together to the signal wire.
cloverleaf-antenna-wire-soldering7

Other Polarized Antenna Design

Skew Planar Wheel Antenna (4 lopes)
medium
Virevent Antenna (4 lopes)
Virevent-antenna
Windmill Antenna (5 lopes)
windmill-antenna

Conclusion

It’s been suggested that the circular polarized antenna at the transmitter side works better with a helical antenna at the receiver. But of course it’s your choice and the results vary from case to case.
circular-fpv-antenna
The key factor of making a successful FPV antenna is to be precise with measurement. The more accurate you can make the antenna the better it will perform.