This paper deals with the effect of structural and doping parameter variations on RF parameters for Si and Si 1-xGe x-based double gate (DG) tunnel FETs (TFETs). For the first time, asymmetric gate oxide is introduced in the gate-drain overlap and compared with that of DG TFETs. The DC parameter subthreshold swing (SS) and RF parameter metrics, unity gain cut-off frequency (ft) and maximum oscillation frequency (fmax) are extracted by varying structural parameters, gate length (Lg), gate oxide thickness (tox), channel thickness (tch), doping parameters, channel doping (Nch), drain doping (Nd) and source doping (Ns) in and around their nominal value. For a channel thickness of 15 nm, a very less SS of 8 mV / dec is achieved in Si 1-xGe x-based DG TFETs with gate-drain overlap. Variations of gate oxide thickness offer better RF performance enhancement for Si-based asymmetric gate oxide devices. This could be achieved because of the higher tunnelling rate of electrons occurring at the source side of asymmetric gate oxide devices. © 2018, Indian Academy of Sciences.