The standing wave forms with this desired pattern at the design frequency, f0, and antennas are normally designed to be this size. However, feeding that element with <answer>3f0</answer> (whose wavelength is 1⁄3 that of f0) will also lead to a standing wave pattern. Thus, an antenna element is also resonant when its length is 3⁄4 of a wavelength. This is true for all odd multiples of 1⁄4 wavelength. This allows some flexibility of design in terms of antenna lengths and feed points. Antennas used in such a fashion are known to be harmonically operated.
What can be added to f0 to create a standing wave pattern?
3f0