It is all so simple the antenna receives the signal and the receiver demodulates the signal into usable form.
At the receiver, the signal from the antenna is amplified and downconverted to IF or directly to the original baseband signals. The amplified signal from the antenna is applied to mixers along with the carrier signal. Again, there is a 90° shift between the carrier signals applied to the mixers.
The mixers produce the original baseband analog signals, which are then digitized in a pair of analog-to-digital converters (ADCs) and sent to the DSP circuitry where demodulation algorithms recover the original digital data.
So now you understand the antennas job is to receive the signal am/fm/pm who cares the receiver does all the work.
