The ADF4159 is capable of produce a 2 GHz ramp. I have attached an ADIsimPLL file for your system.
- ADIsimPLL free download and introduction video here: www.analog.com/adisimpll
- ADIsimPLL ramping video (very relevant) here: http://ez.analog.com/docs/DOC-2419
You main challenge will be finding a VCO that covers your frequency range. The evaluation board offers a VCO tuning range of 0 V to 15 V, so you need to find a VCO with a 2 GHz - 4 GHz output range within a 0 V to 15 V tuning range. You can see the VCO pinout in the ADF4159 evaluation board user guide: http://www.analog.com/static/imported-files/user_guides/UG-383.pdf
On the evaluation board, you will need to use the reference divide-by-2 feature to generate a 50 MHz PFD frequency. You need to use 50 MHz PFD frequency to achieve your 2 GHz output because the minimum N value is 23.