A portable antenna is provided for mounting on a motor vehicle's side window and enabling easy and rapid mounting and removal. The portable antenna includes a base member with a current-fed radiator carried by the base member and having a first portion for location on the inside of the side window, a second contiguous portion for overlying the side window and a third portion, contiguous with the second portion, for location outside of the side window with a distal end thereof extending upwardly when in use. A field-canceling conductor is carried by the base portion for location on the inside of the side window. A coaxial cable has its main conductor connected to a proximal end portion of the current-fed radiator and has a ground conductor connected to the field-canceling member. The current-fed radiator is dimensioned so that the second portion thereof is a relatively low impedance area.