I am studying RF communications and learned that antenna length is proportional to a wavelength of a signal. And many literature say that a high frequency is preferred in wireless communication because a length of antennas can be short, hence, a size of a device can be small.
From here I can deduce a reason that a baseband signal can't be sent through the air. The reason is that, a length of antennas for baseband signals will be infinity, but in a real world, infinity length of antennas is impossible. Hence, sending a baseband signal through the air is impossible.
However, as I am a learner, I can't tell the above statement is valid.