Whip antennas must work against a ground plane. If it's a whip antenna built into a handheld radio, the radio body (and you) act as the ground plane. If you're building a vertical whip antenna, it's common to provide a ground plane from ARRL:
The bispectrum, is probably most intuitively understood from its definition derived from the convolution theorem,
where $F(f)$ is the Fourier transform evaluated at frequency $f$. From this, observe that bispectra are simple 2D transforms that allow the observation of relationships between frequency bins of a Fourier ...