A corona igniter for emitting a radio frequency electric field to ionize a fuel-air mixture and provide a corona discharge, comprising: a central electrode formed of an electrically conductive material for receiving a high radio frequency voltage and emitting the radio frequency electric field; an insulator formed of an electrically insulating material surrounding said central electrode and extending longitudinally from an insulator upper end to an insulator nose end; said insulator including an insulator outer surface extending from said insulator upper end to said insulator nose end; said insulator outer surface presenting an insulator outer diameter (D io); said insulator outer surface including an insulator lower shoulder extending outwardly and located between said insulator upper end and said insulator nose end; said insulator lower shoulder presenting an increase in said insulator outer diameter (D io); a shell surrounding at least a portion of said insulator and extending from a shell upper end to a shell firing end; said shell presenting a shell inner surface facing and extending along said insulator outer surface from said shell upper end to said shell firing end; said shell inner surface presenting a shell inner diameter (D si); said shell inner diameter (D si) of at least one location of said shell being less than said insulator outer diameter (D io) along a portion of the length of the insulator from the insulator upper end to the insulator nose end, wherein the the insulator upper end is inserted into the shell bore through the shell firing end, an intermediate part formed of an electrically conductive material, characterised by said intermediate part being disposed between said insulator outer surface and said shell inner surface and between said insulator upper end and said insulator lower shoulder. a central electrode formed of an electrically conductive material for receiving a high radio frequency voltage and emitting the radio frequency electric field; an insulator formed of an electrically insulating material surrounding said central electrode and extending longitudinally from an insulator upper end to an insulator nose end; said insulator including an insulator outer surface extending from said insulator upper end to said insulator nose end; said insulator outer surface presenting an insulator outer diameter (D io); said insulator outer surface including an insulator lower shoulder extending outwardly and located between said insulator upper end and said insulator nose end; said insulator lower shoulder presenting an increase in said insulator outer diameter (D io); a shell surrounding at least a portion of said insulator and extending from a shell upper end to a shell firing end; said shell presenting a shell inner surface facing and extending along said insulator outer surface from said shell upper end to said shell firing end; said shell inner surface presenting a shell inner diameter (D si); said shell inner diameter (D si) of at least one location of said shell being less than said insulator outer diameter (D io) along a portion of the length of the insulator from the insulator upper end to the insulator nose end, wherein the the insulator upper end is inserted into the shell bore through the shell firing end, an intermediate part formed of an electrically conductive material, characterised by said intermediate part being disposed between said insulator outer surface and said shell inner surface and between said insulator upper end and said insulator lower shoulder.