Improvement in front-to-back ratio of a bifilar backfire helix by aflared open end

The current distribution of a bifilar helical antenna which radiates a circularly polarized wave in the backward endfire direction is decomposed into forward and reflected currents, and the contribution of each current to the radiation is evaluated numerically. Calculations show that the presence of the reflected current deteriorates the front-to-back (F/B) ratio of radiation. To reduce the reflected current and to improve the F/B ratio, flaring of the open end is proposed and investigated. The flared configuration leads to an improved F/B ratio, with an almost constant input impedance