Hi @JLC,
An antenna boosts the 4G reception of the router (although it can often reduce the overall speeds obtained), but it doesn't increase the range of the Wi-Fi from the router.
If I've understood correctly you're getting Wi-Fi in other parts of your property, but the router is too far from the conservatory? If that's the case, I think you're looking for a solution like a Wi-Fi extender, mesh system, or possibly a powerline adapter. These are all viable options, you could look into, but I can't recommend a particular product. I hope this helps you research a solution though.
Thanks,
Jonathan
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