There are several steps you can take to try to diagnose and fix WiFi antenna issues:

1. Check the antenna connection: Make sure the antenna cable is securely connected to your router.
2. Check the Wi-Fi signal strength:If the signal strength is weak, try relocating the antenna and router.
3. Restart the router and modem: Disconnect both, then plug them back in and try to connect your device to the WiFi.
4. Check any antenna extension cables: Ensure that the cables are still in working condition and connected properly.
5. Disable any other active antennas: If you’re using multiple antennas, disable the others to test connectivity with just the antenna that has the issue.
6. Check for any signal-blocking physical barriers: Look for any physical objects like walls, plants, or furniture that could be reducing signal strength.