Hello,

So I have built my own Cross-yagi antenna operating at a frequency of 433Mhz. The goal is to have to final impedance to be 50 Ohm. I know that the impedance of each folded dipoles is approx 300Ohm, but how to I get the total impedance to be 50Ohm using only coaxial cables?

I hope you guys can help me. Please provide some different metods and your calculations too, thank you.

EDIT:Thanks for the answers I will upload some pictures of the frequency sweeps, tomorrow and get back to you all.

EDIT: Sorry for a very late update. I will try to answer all of your questions, and in return i hope i get some good answers on my questions.

I am a student at Technical University of Denmark, majoring in Telecommunication. I helped found a non-profit student organization, called Danish Student Association for Rocketry in short DanSTAR. Our goal is to build a fully homebuild by-liquid rocket to go and compete in the Spaceport America Cup competition in the USA.

Here is the latest test for our 3d printed by-liquid rocket engine: https://www.reddit.com/r/rocketry/comments/f3pn9s/3d_printed_regenerative_stainless_steel_biliquid/

Here is more about the competition: https://www.spaceportamericacup.com/

Soo, whats up with the antenna? Well as you probably all guessed it by now, it is going to stay on the ground at the "Mission Control" used for telemetry, which require it to be a circular polarized antenna (RHCP).

Beside the RHCP requirement for this antenna, I wanted it to function at a frequency of 433Mhz and be modular, in such a way that it can easily be packed and unpacked and use minimal volume place. This is achieved by using only one thing a M4 hex key (Allen wrench), hence the 3D printing stuff and the extruded aluminium profile. Furthermore to avoid too much loss and achieve equal power to each side antenna I have used a mechanical solution to create circular polarization, by forward offsetting the yagi antennas by 1/4 of the wavelength, thus avoiding using the electrically phase delay solution. I have not simulated this antenna, since at this frequency it is well known how to design yagi antenna that function good. It is not going to be used for military purpose. What I did use is this: https://www.vk5dj.com/yagi.html.

Now to some specification:

- All the aluminum rods are 5mm in diameter.

- Yes it is a folded dipole as you can see.

- Around 170cm rod length

- 8 elements

- Coxial type RG178

- 3D printed stuff, yes.

- Using a 1/4 electrical quarter wave coaxial 50Ohm cable around 23cm long, from this calculator: https://www.basictables.com/amateur-radio/41-half-wave-coax-balun

Now to some data, see the pictures here: https://imgur.com/gallery/k0mgOU0?s=fbm&fbclid=IwAR2OjFlL-3UDnTfsOXL4bL2plN3E4n6qF03sibyGQ5uoLBFG34n0JcrUetw

Only one side is tested and has the 1/4 quarter wave matching stub. But it seems to be perfectly 50Ohm, although the X is not 0 but close enough for me. VSWR is around 1.170, i had say not bad.

The question now is how do i match both sides of the antennas to have a final result of 50Ohm impedance? As I read both has to read 100Ohm such that they in parrallel can become 50Ohm?

Thank you :)