A Comparison of Electrically Small Spherical Helix and Spherical Resonator Antennas

Maximizing or increasing the bandwidth of an electrically small antenna is a significant design challenge. The operating bandwidth of a tuned electrically small antenna exhibiting a single impedance resonance within its defined bandwidth can be accurately characterized by the inverse of its quality factor (Q). There is a well known lower bound on achievable Q, implying that there is an upper bound on achievable bandwidth that cannot be overcome with antenna design modifications. Recently, the spherical resonator antenna was introduced and shown to exhibit multiple impedance resonances within its defined bandwidth when tuned or matched. With antenna designs exhibiting this behaviour, the inverse relationship between bandwidth and Q may not hold and the operating bandwidth may be greater than that predicted by the inverse of Q. Designs of this type offer the possibility of achieving wider bandwidths than can be achieved with antenna designs that exhibit single impedance resonances. Here, we compare the radiation properties of antenna designs exhibiting multiple impedance resonances, describe techniques for impedance matching and describe simple techniques for maximizing the operating bandwidth for a specified VSWR.