Can you recognize this antenna?

[vmarangoni]

Hi guys,

This kind of antenna is commonly used by brazilian truck drivers to communicate with UHF Milsat. In Brazil this satellite is known as "bolinha" and you probably already heard about it. I'm wondering if this antenna design really makes sense for satellite communication or if it was misdesigned from other well-known antennas.




It looks like an X Wing antenna as this one, but the "brazilian version" has the tip curved: MT magazine UHF Satcom antenna project

The curved tip makes it look like AS-2815/SSR-1: https://upload.wikimedia.org/wikipe...onics_Technician_-_Volume_7_-_Figure_2-30.jpg


I don't understand much about antennas, and I hope you can help me to understand both if this is a well-known antenna and if this design (specially the curved tip) makes sense for UHF Milsat communication.

Thanks.

 

[prcguy]

We don't know how the elements are connected but lets assume they are a pair of dipoles at a right angle and one is feed 90deg out of phase for RHCP. The dipoles would have maximum gain around .2 to .25 wavelengths above a ground plane with a main lobe 3dB beam width around 45 degrees if the elements were perfectly straight. Bending the ends of the antenna down and back probably changes the radiation pattern making it broader and giving up a little gain. It will also change the matching pulling the impedance down some.

The SSR-1 is a different type antenna with a broader pattern and low gain. I had one and it didn't work very well.

 

[RFI-EMI-GUY]

I am fascinated by the converter box. I read that they had a simple diode frequency doubler for the uplink TX. The second picture looks like a more refined product. You would need some pair of bolinhas to operate that in CONUS but I am intrigued. Hmm; I do have that Andrew BiFilar helical in my back yard.

 

[vmarangoni]

A friend of mine found this pretty similar antenna [1], also used specifically for UHF Satcom On-The-Move communication. Someone may have been inspired in the past by this antenna and found a way to build it at home.




Other similar UHF Satcom On-The-Move antennas have this same "umbrella" shape:



The only part different from the truck drivers antenna is what seems to be a plastic connecting the four ends of the antenna. I don't think it's a good guess, but maybe the only purpose of this connecting part is to make it more rigid. What do you think?

[1] - UHF Satcom On-The-Move Antenna Magnetic - Cooper Antennas