Meaning of negative frequencies in Baseband non sinusoidal, non periodic signal

1. What does it mean when frequency is negative?
2. What is the meaning of negative frequency in Fourier transform?
3. Why do we need negative frequencies?
4. Do negative frequencies exist?

What does it mean when frequency is negative?

Negative frequency is an idea associated with complex exponentials. A single sine wave can be broken down into two complex exponentials ('spinning numbers'), one with a positive exponent and one with a negative exponent. That one with the negative exponent is where you get the concept of a negative frequency.

What is the meaning of negative frequency in Fourier transform?

Negative frequency is the rotation vector in the opposite direction to the positive frequency. For example it is necessary to have a real (non-comlex) signal. Then we have two vectors rotating in opposite directions.

Why do we need negative frequencies?

Negative frequency is a vector that has the same mathematical meaning as the imaginary part of a complex signal. Negative frequencies do not exist in the actual world; hence the spectral content of negative frequencies must be added to the spectral content of positive frequencies in order to save energy.

Do negative frequencies exist?

The experimental results show that negative frequency radiation, in some sense, exists. But it also shows that these frequencies are only observed by their generation (either directly or indirectly) of positive frequency radiation.