Cross-Polarization Reduction of a Compact Broadband Printed Log-Periodic Dipole Array Antenna Using Symmetric Coplanar Dipoles

Printed log-periodic dipole array (PLPDA) antennas often exhibit significant cross-polarization, which limits their use in array configurations. This article introduces a simplified technique to address this drawback using a new symmetric coplanar dipole array structure. In the proposed antenna, cross-polarization reduction is achieved by increasing the symmetry of both the dipole array and the feeding network. Theoretical evaluation and characteristic mode analysis are conducted to provide fundamental insight into how enhanced symmetry in a printed dipole reduces cross-polarization compared with an asymmetric design. A conventional PLPDA with a traditional dipole array structure was designed to serve as the baseline for the proposed antenna and is used for a fair comparison. To validate the theoretical analysis and rigorous full-wave simulations, prototypes of both antennas were fabricated and measured. The measured results show that the proposed antenna not only achieves a symmetric radiation pattern, with a cross-polarized radiation level below -34 dB and a front-to-back ratio above 20 dB across the 1.9-6.2 GHz operating band, but also maintains a stable gain of 6.81 dBi without gain anomalies. Furthermore, compared with the conventional PLPDA, the proposed antenna achieves a wider fractional bandwidth of 106.2% (an increase of 11.2%), with an 8 dB reduction in cross-polarized radiation level and a 6 dB improvement in front-to-back ratio.