On the Resonant Electrical Length of Helical Antennas Placed between Metallic Parallel Plates

Helical antennas placed between two infinite metallic parallel plates are investigated. This study is concerned with the resonant electrical length of helical antennas. The first resonance appears as the helical antenna is transiting the frequency gap between its well-known normal and axial modes of operation. A parametric study is conducted to calculate the resonant electrical length as a function of the helical parameters, namely the radius and pitch of the helix. The results are validated by comparing the solutions of two independent problems, one is driven with a source and the other is an eigenvalue problem with periodic boundary conditions. The presented results are useful in the design of gap waveguides where the periodic media are made of helical wires.