help to explain me how to convert return loss in dB to VSWR

Can any 1 help me to explain how to convert return loss in dB to VSWR.What is the Eco, Ecross, Hteta and Hpi.What is the major different of Eco, Ecross, Hteta and Hpi. Thanks

VSWR=（1+abs（Γ））/（1-abs(Γ)） Γ is reflection coefficient
return loss=20*log(abs(Γ))
I don't know Eco, Ecross, Hteta and Hpin