Radiation from a short helical antenna backed by a cavity

The radiation from a short (1.5 turns) helical antenna backed by a cavity is evaluated on the basis of the numerically determined current distribution. Effects on the radiation field of the angle ψ between the cavity wall and the bottom plane of the cavity are discussed. It is found that the angle coverage of the circularly polarised wave can be widened by increasing ψ. The radiation field for ψ=75° is circularly polarised (an axial ratio within 3 dB) over a hemisphere