Radiation Characteristics by Balanced and Unbalanced Feedings of Log-Periodic Loop Antennas for Mobile Handset Applications

Small conducting wire antennas for mobile handset applications are considered to make log-periodic array structures. A log-periodic loop antenna (LPLA) and a monopole-type LPLA (MLPLA) with a ground reflector (GR) are designed, taking into account the antenna feeding configuration with or without a balun attached in order to investigate the effects of unbalanced direct feeding on radiation performance, and electromagnetic characteristics of these antennas are examined experimentally and computationally in the operating frequency range of about 2.0–3.0 GHz. For an LPLA-GR, antenna gains above 10 dB from 2.0 to 3.25 GHz with less than 3-dB variation, providing the gain bandwidth of 47.62%, are obtained based on the electromagnetic surface patch (ESP) calculation. Meanwhile, an MLPLA-GR without a balun provides the 10-dB beamwidths of 240° and 212° at 2.8 GHz in the xz-plane and yz-plane, respectively.