An omnidirectional isotropic antenna employing a tubular waveguide 12, a dielectric insert 18 which includes a lens 20 and a depending stem 22. The lens 20 is an elliptoid generated by rotating an elliptoid form about the longitudinal axis 42 of the tubular waveguide 12 with its foci 40 aligned with the longitudinal axis 42 and its major axis 38 lying in a zone of rotation 43 intersecting the horizontal plane 44 that is normal to the axis 42 and containing the foci 40. The stem 22 has integrally formed a polarizing element 36, and an impedance to matching element 21. There is provided a passband filter 50 and a modified tubular waveguide 60 that provides node differences for the RF signals.