What harmonics are present in a square wave?

Sum of 1st, 3rd, 5th, and 7th harmonics approximates square wave. Sum of 1st, 3rd, 5th, 7th and 9th harmonics approximates square wave. The end result of adding the first five odd harmonic waveforms together (all at the proper amplitudes, of course) is a close approximation of a square wave.

1. How many harmonics does a square wave have?
2. Does square wave have even harmonics?
3. Why square waves only have odd harmonics?

How many harmonics does a square wave have?

Note that only the first six harmonics are shown individually, but 10 harmonics are used to generate the square wave.

Does square wave have even harmonics?

A perfect square wave would have no even harmonics. At 1 MHz, the even harmonics are only about 12 dB below the desirable odd harmonics, which means that real information about the DUT may easily be obscured by distortion in the square wave test signal.

Why square waves only have odd harmonics?

All even harmonics shall be zeros. Therefore, what remains to get the inverted output in a form closest to a sine wave is to get red of the dc (so square wave is now alternating positively and negatively) and to get red of the higher order (odd numbered) harmonics.