An antenna that includes a radial waveguide defining a waveguide region between opposed first and second surfaces. A radio frequency (RF) probe is disposed in the waveguide region for generating RF signals, and a plurality of radiating slot antenna elements are disposed on the first surface for emitting the RF signals from the waveguide region. A plurality of spaced apart conductive elements are disposed within the waveguide region. The antenna includes tunable elements that each include a quarter wavelength RF choke coupled through a variable capacitance and an inductive line to a respective one of the conductive elements. A plurality of DC control lines are provided, with each DC control line being connected to at least one of the tunable elements to adjust the variable capacitance thereof. A control circuit is coupled to the DC control lines and configured to selectively apply DC current values to adjust the variable capacitances of the tunable elements to control a propagation direction of the RF signals from the RF probe.