Abstract: Slow wave antenna including slow wave structure of a helical coiled conductor having linear capacitance and inductance distribution. Driving point impedance is changed by varying the ratio of the distributive capacitance to the distributed inductance. Tuning is changed by changing the capacitance between the distributive capacitance common and RF ground. Slow wave antenna structure includes a first embodiment having a slotted pipe with a helically wound conductor and a second embodiment includes a helically coiled element with a plane capacitance structure. In the slotted type of helically wound center conductor antenna, the antenna is tuned by changing the distance between the helix and the outside diameter of the pipe. The antenna is also tuned by changing the capacitance between the pipe and the ground of the RF system. In the helical element with a plane capacitance sheet antenna, tuning is accomplished by varying the spacing of the sheet and hence the capacitance between a conductive sheet and the helix.