Analysis of umbrella antenna at the Omega navigation station

The characteristics of the electrically very small umbrella antenna used for the Omega navigation system are examined by numerical analysis. The transmitting antenna of height about 0.02 wavelength, with 16 inclined elements, at the Tsushima station is analyzed as an example of electrically very small umbrella antenna. In the analysis the ground is assumed to be a perfectly conducting plane and the Hallen-type integral equation is used. The difference between the calculated input resistance and the measured one is estimated as the earthing resistance. The approximate equation of radiation resistance is derived, and the relation between the inclined elements and the antenna characteristics is discussed.