Helical antenna 5.8 GHz

3D printable 5-loop and 6-loop helical directional antenna to be used on 5.8GHz FPV video receivers (e.g. FPV goggles). 

Unique features:

• The coil support in this version has three legs instead of the four that you will find in already existing models. 

• The coil support is printed in one piece, without need for support material.

• It also allows you to use any kind of thin sheet metal as a reflector (no need to source fiberglass copper PCB board, just use whatever you find in the trash)

• The coil former has a flat section, which allows you to form the wire in the shape necessary to fit in this antenna.

• The antenna is right-hand polarized (RHCP). If you need LHCP, you must mirror the STLs in your slicer before printing (see below). 

Additional materials needed:

• ⌀  ~1mm copper wire

• a thin (~0,2mm) and flat metal reflector baseplate (I used a coffee can) that can be soldered onto

• cable & connector:

  • Either some co-axial cable (e.g. RG405) + a connector of your choice (e.g. SMA connector) 

  • Or the connector and coax cable of a broken antenna.

• (optional) Heat shrink

• (optional) Hot glue or Epoxy

Tools needed:

• 3D printer

• Soldering iron & solder

• Pliers / wire cutters

• Drill bit with ⌀ of your co-axial cable 

• A tool to cut the metal reflector (e.g. dremel with cutting disk or metal scissors)

Instructions:

What and how to print: 

None of the prints require any support. 

Choose whether you want 5 or 6 loops. The version with 6 loops has more gain (i.e. a stronger signal) but a narrower beam width.  Print the corresponding coil support. 
Important: print the coil support with 0.2mm layer thickness, at least for the first two layers. 

Also print a Reflector Support and a Coil Former.

I have used Prusament PETG for my prints; PLA or ABS will most certainly also be fine. Be aware that PLA is not ideal if you plan to use the item in high-heat or high-UV conditions.

Antenna polarization (LHCP and RHCP):

All downloadable files are correctly set up for an RHCP (right hand circular polarization) polarized antenna. If you want to change the polarization from RHCP to LHCP (left hand), mirror the coil support you chose and the coil former along the X OR Y axis (not both!) in the slicer (in prusaslicer: right click on the object and then mirror -> X).

The reflector: 

Find a thin, flat piece of metal. Test if you can solder onto it first. It may be necessary to sand off the surface coating.
Cut a round shape, using the exterior of the coil support as a template. It is important that the reflector is still flat at the end of the cutting. 

Assembly:

Use an appropriate length of ⌀ 1mm (I have also used 1.2mm but 1mm is ideal) copper wire.

Pull the wire straight by snapping it straight while holding it with two pliers.

Form the coil on the printed coil former. Start at the side with the hole, and also follow the flat section. When done, cut the ends of the wire and gently unwind it from the coil former.

Cut a piece of coax. The inner vein of the co-axial cable should protrude a few millimeters on both ends. The length of the cable itself does not matter.  

The coax cable should penetrate the reflector at the position where the 4mm hole is visible in the printed coil support. Again using the coil support as a template, mark the 4mm hole on the reflector and precisely drill a hole on that position. The hole should match the diameter of the coax cable. 

Now, the antenna coil can be wound onto the coil support from the top (narrow part) down. Near the base of the coil support, the coil has to run parallel to the reflector for a bit. This is intentional. The coil should end right in the middle of the 4mm hole on the coil support. Make sure the coil sits parallel with the bottom of the coil support for at least the last ⅓ loop.

Soldering:

Next step is attaching the coax cable to the reflector and to the antenna coil. The coax sheeting (the outer metallic braiding) must be soldered to the reflector (preferably on the rear of the reflector), while the center wire of the coax cable must be soldered to the copper coil.

On the other end of the coax cable, attach the connector of your choice (e.g. SMA connector).

Final Assembly:

Click the reflector support onto the coil support.

Add some hot glue or epoxy to stabilize the connection between the reflector and the coax cable. 

Drop a like/comment on printables.com ;-)  
And if you have the time, show off your make in the “makes” section. 

Done! Now go out and fly! 

Please leave a like and don't forget to tell your friends :-)

Shoutouts & references:

• RCModelReviews video on youtube: 

• sgderek's helical antenna calculator: https://sgcderek.github.io/tools/helix-calc.html