what effect the broadband noise of the power amplifier?

The performance named "broadband noise" of power amplifiers is important for transmitters especially in the full duplex operation.I want to know what can mainly effect the broadband noise performance of the power amplifier,the NF of the prestage, the bias of the gate , the bias of the Drain or the other aspect ? And how to reduced the broadband noise?

Thank you!

All wideband amplifiers generate noise in proportion to their bandwidth.
This noise causes no problem in those amplifiers but it can cause problems when such amplifier is used to amplify a narrow-band signal.
Then, at receiver side, amplifier noise is added to the useful signal; if the receiver has no signal spectrum-matching filter, the signal-to-noise ratio becomes worse.

Also, if such wideband amplifier is e.g. used to amplify a local-oscillator signal power in a receiver mixer, the added noise degrades receiver performance.

Experience: whenever possible, use signal spectrum-matching filters, in transmitters as well as in receivers. Wideband amplifiers and MMICs are now available, so the designers are free to use them without concerns about matching. They should be aware of the above described effects, though.

Does the noise affect the LO phase noise? Such as I use AVA-183+ (6~18G) amplify my LO signal at 9G, would the amplifier degrade the LO phase noise (-132dBc/hz at 1KHz)?

The filtering of the bias (both gate and drain) is important minimizing the broadband noise.
Noise Figure (low signal) is not very important getting low broadband noise in power amplifier design.
The quiescent current of each stage affect the broadband noise of the power amplifier.

The noise in wideband amplifiers is similar to thermal noise- it is in principle the amplified thermal noise.

Phase noise is a different animal- this is the effect of an instability of an oscillator carrier. The phase noise is generated in the first oscillator in a chain, and the following amplifiers contribute to it very small part.. If frequency multipliers follow an oscillator, then the resulting phase noise must be scaled by 20 log N where N is the frequency ratio.

Amplifier phase noise is only important in extreme cases and is usually 20-30 dB below an oscillator phase noise.