VOR Polar Diagram RNAV
The VORVOR —VHF Omnidirectional Range uses a rotating limacon polar diagram. Although it is true to say the propagation goes in all directions, the VORVOR —VHF Omnidirectional Range uses not one but two signals (the “reference” and “variphase” signals – together with the principle of phase comparison) to give an aircraft information about what bearing it is on.
These signals are different, so when the polar diagrams for the two signals are “added together”, the shape is a limacon. Do not get this answer confused with the NDBNDB —Non-Directional Beacon (which is omnidirectional) or the ADFADF —Automatic Direction Finder (which has a cardioid polar diagram).