Generating a square wave that will modulate an RF signal sitting at 2.8GHz,

I need to generate a square wave that will modulate an RF signal sitting at 2.8GHz, looking at the app note AN-0996 the direct conversion architecture would work, however I'm looking for a simple solution for the waveform generation essentially control of the magnitude, phase and timing for the I/Q channels. Can you please suggest an appropriate hardware solution.. a modulation bandwidth of 100MHz should suffice.