I have an ESP32-S3 WROOM 1U, which has an U. FL (IPEX) connector. If I search on Google for an IPEX antenna, they are all very big and bulky. I know that wires can act as antennas but I'm not that familiar with the best approach to designing an antenna. Can I just use any wire to act as an antenna or what do I need to take into consideration? I need the antenna to reach my router from the basement.
If you imagine a camera for long range uses a large series of high quality lenses, you will understand better the tradeoff between beamwidth and gain or direction and range.
So a single loop , somewhat like dipole has an omnidirectional view like a wide angle lens with a very short range for the same quality. A poor example is stacking a bunch of magnifying lenses compared to a telescope but essentially they do the same tradeoff but with lower losses my optical impedance matching with low reflectance coatings and very low loss clear lenses shaped precisely for spacing and focus.
Adding more range means to focus the direction with more similar element sizes like a Yagi TV antenna. Except those often range in sizes to match a range if 1/2 wavelengths.
If the loop merely adds impedance without spacing each loop to capture more signal, then the gain is less than optimal. A spiral helix is the best example of this, which can achieve gains well beyond 20 dB which can extend the range considerably from Friis Loss but at great expense to achieve ~ 0.1% tolerances on the geometry.
I don't know what an "IPEX C" Connector is.
Have you thought about bringing better WiFi coverage nearer you basement? Do you have the ability to add a WiFi access point?
You can purchase ESP32 boards with an external antenna connector:
You can then purchase an external antenna to connect to the ESP32 board: