Role of Small Permeability in Gigahertz Ferrite Antenna Performance

We demonstrate that even small relative permeability (mu(r) < 2) is effective enough in the improvement of gigahertz (GHz) antenna performance. Based on antenna performance simulation results, a 1.57 GHz small permeability (mu(r) = 1.97) hexaferrite antenna (8 mm x 5 mm x 1.5 mm) was fabricated and characterized for antenna miniaturization factor, fractional bandwidth (FBW), and radiation efficiency (RE). Return loss and FBW were 13 dB at the resonance frequency f(r) of 1.57 GHz and 7% at voltage standing wave ratio of 2.5:1, respectively. On the other hand, antenna simulation results show that an alumina (epsilon(r) = 9.4) antenna with tan delta(epsilon) of 0.01 and 0.05 resonates at f(r) of 1.65 GHz and has FBW of 4.1% and 6.0%. The hexaferrite antenna volume was 30% of the alumina dielectric antenna volume. The experimental RE of the hexaferrite antenna was 66% at 1.57 GHz, which is much higher than the simulated RE of 55.4% for the lossy dielectric antenna (epsilon(r) = 11; tan delta(mu) = 0; tan delta(epsilon) = 0.05), even though ferrite has tan delta(mu) = 0.05 and tan delta(epsilon) = 0.008. The antenna performance simulation results confirmed that the RE of the ferrite antenna can be increased to 80% at tan delta(mu) of 0.01. Both simulation and experimental results demonstrate that even small permeability of GHz hexaferrite greatly contributes to miniaturization, FBW, impedance matching, and RE.