Simplified Vector Potential and Circuit Equivalent Model for a Normal-Mode Helical Antenna

A normal-mode helical antenna with open-ended and center-fed configurations is investigated. The investigation is twofold. First, explicit formulas are derived by employing the vector potential with the triangular current distribution for a normal-mode helical antenna. These give straightforward results when compared to previous numerical analysis. Second, the equivalent circuit model is proposed to obtain the input impedance. The proposed equivalent circuit model consists of a parasitic capacitance, an effective self-capacitance, an effective inductance, and a radiation resistance in a series combination. The radiation characteristics are compared to the commercial simulation to verify whether the obtained formulas and the equivalent circuit model achieve a good agreement.