This paper deals with the effect of structural and doping parameter variations on RF parameters for Si and $\rm{Si_{1−x}Ge_{x}}$ -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 ($f_{t}$) and maximum oscillation frequency ($f_{max}$) are extracted by varying structural parameters, gate length ($L_{g}$), gate oxide thickness ($t_{ox}$), channel thickness ($t_{ch}$), doping parameters, channel doping ($N_{ch}$), drain doping ($N_{d}$) and source doping ($N_{s}$) in and around their nominal value. For a channel thickness of 15 nm, a very less SS of 8 mV/dec is achieved in $\rm{Si_{1−x}Ge_{x}}$ -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.