Need help identifying a 2.4Ghz antenna

[vamax]

Dear colleagues,
I need help identifying what type is the antenna on the pictures and how it works!
Maybe omni ground plane!?
Thanks in advance!
Dimiter

[S57UUU]

Without those screws, this would be an omnidirectional GP antenna. Not sure what those screws do, or where they connect - for an effective GP they should NOT be there, especially if grounded.

The coaxial stub is probably an attempt at extending the bandwidth (matching).

Marko Cebokli

[vamax]

The M2,5 screws just hold the double side 1mm FR4 PCB attached to the aluminum body!
For my it also looks like Omni GP antenna. What I don`t understand is this "stub" connected to the GND.
The length of the brass tube - 27mm match for an 1/4 GP antenna for 2.7GHz
But the center RF of the device is 2.43GHz

[S57UUU]

The electrical length of the stub also depends on the dielectric within the tube. As I said, it's probably a kind of impedance compensator, to extend the bandwidth of the match.
It could also be there just to ground the center pin, for receiver ESD protection. In that case lambda/4 would be best, because the short on top would transform into open at bottom.

Do the screws have insulating washers below their heads?  But why the strange pattern (not all at the same radius)?

[vamax]

No insulation washers on the bolt heads!
The threads in the aluminum body are also used to attach the RF board from the back side.
I suppose the strange radius is because to match the board design!