We use antennas which are incredibly directional for Mars rovers. Compare a regular lightbulb vs a flashlight with a lens. Total light emitted might not be that different, but the intensity at the same distance (or how far the light reaches) is because the beam is focused. That works the same with receiving signal: a giant dish will focus the signal to a central point, and a Yagi-Uda antenna will use a similar phenomenom to focus the signal on a dipole.
Ofcourse car bluetooth presumably has an antenna that radiates roughly sphere-like, it wouldn’t make sense to pick up signals on the right of the car with a dish or something.
To that end, bigger antenna doesn’t do a whole lot to boost signal. There might be other factors at play increasing the reception though, such as signal polarity and whether the length of the antenna matches the frequency in a correct way (or is some multiplier of it). For Bluetooth that’d be roughly 13cm or 6.5 or so.
Because it wouldn't be as directional as a big dish. The relative size of the dish vs wavelength plays a factor here. If you make a dish thats the size of the wavelength it wouldn't even work as a dish, it would receive the signal from all angles. This is also why high gain antennas for higher frequencies can be much smaller than for e.g long waves.
It works two ways: one is that you can go lower in frequency (e.g. bigger wavelength) if your dish is bigger, the other is that you just capture more of the signal. If you take light as a metaphor, a bigger lens will just provide more 'signal' at the focal point.
Ofcourse car bluetooth presumably has an antenna that radiates roughly sphere-like, it wouldn’t make sense to pick up signals on the right of the car with a dish or something.
To that end, bigger antenna doesn’t do a whole lot to boost signal. There might be other factors at play increasing the reception though, such as signal polarity and whether the length of the antenna matches the frequency in a correct way (or is some multiplier of it). For Bluetooth that’d be roughly 13cm or 6.5 or so.