Shaped-conical radiation pattern performance of the backfire quadrifilar helix

It is shown that shaped-conical radiation patterns can be realized by extending the resonant fractional-turn quadrifilar helix to an integral number of turns, i.e., the radiated energy can be concentrated into a cone with the gain decreasing from a maximum at the edge of the cone to a local minimum at the center. This pattern shape is near optimum for many spacecraft communications and navigation applications, providing approximately 3 dB improvement over cardioid shaped patterns.