Provided is a radiator transition assembly for exciting a long slot radiator of an antenna, the transition assembly including a folded flexible circuit substrate including at least two folds forming a long slot radiator, an excitation circuitry configured to generate signals for exciting the long slot radiator, and a microstrip transmission line coupled to the excitation circuitry and positioned along the folded flexible circuit substrate, where the microstrip transmission line extends across an opening of the long slot radiator.