Balanced backfire zigzag antennas

Linearly polarized backfire antennas are described which have high front-to-back ratio and very low sidelobes. The backfire radiation is produced from a meandering conductor. The principal directional characteristics can be determined by using linear array theory. When the conductor is periodic this can be related to a series expansion of the fields in space harmonics. A simple first-order theory for the periodic zigzag is based upon known properties of waves on linear conductors. The perturbations from this theory are then related to the introduction of space harmonies in the periodic case. Measured frequency versus phase constant (k-\beta) diagrams are presented to illustrate the correspondence to the first-order theory and to accurate theoretical solutions for propagation on helical conductors. The radiation properties of periodic backfire zigzags are compared to the end-fire type previously reported. Bandwidth limitations on the backfire periodic zigzags are readily extended by tapering the structure to produce a log-periodic antenna. Measured patterns and impedance of several log-periodic zigzag antennas illustrate how the performance is related to that of the periodic structures.