Tilted Beam from a Spiral Antenna

The two arms of a spiral antenna are made of metalines. This spiral antenna is designed for steering its circularly polarized (CP) beam in the vertical plane. For this, two factors are introduced for the antenna excitation: phase factor ξ and voltage factor Ω The excitation is decomposed into balanced and unbalanced excitation terms. The balanced term generates a broadside beam, called the B-beam, which is transformed into a tilted beam by the unbalanced term generating a beam off the broadside axis, called the U-beam. It is found that, when the phase factor is fixed to be ξ = 0, the tilted beam seamlessly scans in the vertical plane with change in voltage factor Ω.