Elevation plane pattern at high frequency

Hi
The elevation plane pattern of UWB antenna in the elevation plane the main lobes are narrower compared to low frequency.

What is the explanation to the phenomena ?

Regards

Beamwidth is a function of antenna size measured in wavelengths. Keep the antenna physical size constant and increase the frequency (thus shrinking the wavelength) and the beamwidth shrinks. (The antenna is larger in wavelengths.) Most antennas exhibit this characteristic. Look for an increase in gain as well. Your antenna probablly has increasing gain with frequency.

Yes, I know, there are exceptions.