Elimination of Anomalous Resonances in Coaxial-Fed LPDA and its Array With Integrated Φ-Shaped Balun

In this communication, the concept of common-mode (CM) resonance is introduced to analyze radiation anomalies caused by unbalanced coaxial feeding. To address this issue, a novel
$\Phi $
-shaped balun is proposed, and the equivalent circuit is provided for achieving the optimal balanced performance. The proposed log-periodic dipole antenna (LPDA), incorporating the
$\Phi $
-shaped balun, is fabricated and tested, exhibiting stable radiation performance over a broad bandwidth spanning from 0.9 to 2 GHz. Furthermore, a dual-polarized triangular-lattice LPDA array is proposed and tested to validate the effectiveness of the
$\Phi $
-shaped balun in an array environment. Results demonstrate that the proposed array is capable of accurately scanning up to 450 in the E-plane, producing stable and symmetric patterns. The
$\Phi $
-shaped balun is found to be effective and practical in mitigating anomalous radiation in both unit design and array environments. Moreover, the planar configuration of the
$\Phi $
-shaped balun enables direct integration with the antenna, making it valuable in space-limited scenarios.