could antenna pattern keep constant with varying input signal?

Hello

guys.

Recently, I am doing a project about direct antenna modulation. I have got questions about antenna.

1, the feed is the modulated signal, right?
2, if it is, why the radiation pattern keep constant since the frequecy and amplitude of input are changing.

( As my reference says, the pattern keep constant, in conventional modulation scheme, i.e the signal is modulated then up-converted to antenna.)

THX

If antenna is non-linear due to direct modulation material or geometry close to wavelength properties, you cannot assume the radiation pattern is constant. This assumption may be valid if wavelength is >10x antenna geometry.

THX so much

The radiation pattern of an antenna will change with frequency. But unless you are using a wide bandwidth of modulation (wide compared to the centre frequency), this is likely to be negligable, so you might not be able to measure it.