A transmission line slot antenna is described. Although more generally applicable, the antenna is particularly adapted to conformal applications. The antenna has a ground plate with a conductive top surface having a slot with a feed whose ground reference terminal is connected to one side of the slot and whose signal terminal is connected to the other side of the slot. A conductive cylindrical screen, which can be of an arbitrary cross section and non-uniform in the longitudinal direction, is formed of one or more sections attached along the bottom surface of the ground plate, with each of the sections having a first and second edge conductively connected to the top surface of the ground plate along opposite sides of the slot. The antenna is tuned to support the fundamental mode (H00) of a slotted cylinder transmission line formed by the screen sections and a part of the ground plate with the slot.