You can use spectre models in RFDE using the Analog Design Environment (ADE):
Setup>Model Libraries…>Browse to the spectre model files and add to the Model Library Setup. In 2008, U1, U2 (latest version of RFDE) you do not need to do anything else to get the spectre compatibility, the netlister and the simulator are already configure to read in spectre models.
To learn how to setup the ADE in RFDE, you select the Help menu in the ADE top right and choose: RF Design documentation. The CIW window will say: RFDE<MP>: RF Design Environment (*) 332.400 Sep 18 2008. And the RFDE 2008 U2 documentation will appear showing you numerous RFDE documentation references. Select Quick Start > Use Model of RF Design Environment. You can get this same doc from this link:
**broken link removed**