Log-Periodic Patch Array With Coupled T-Probes for Broadband Dual-Polarized Antenna-on-Display

This article proposes a log-periodic patch array with coupled T-probes for broadband dual-polarized antenna-on-display (AoD) applications. The antenna is implemented as thin-metal meshes on a low-profile substrate (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\leq 0.01\lambda _{0}$ </tex-math></inline-formula>), ensuring optical transparency. The array consists of three square patches, each rotated by 45° and fed at two lower edges by T-shaped proximity probes, which excite two orthogonal slant polarizations. The edge lengths of the patches are logarithmically scaled to achieve multiple resonant frequencies, resulting in a broad matching bandwidth. The coupled T-probe structure facilitates efficient feeding of the patches without the need for additional precise tuning, allowing for uniform impedance matching independent of patch length. Since the log-periodic patches radiate primarily at their resonant frequencies, the total radiating fields remain consistent across a wide frequency range, producing flat gains. In addition, the proposed design achieves lower cross-polarization levels due to the cancellation of currents induced in the T-probe on the opposite side. To validate the design approach, a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3\times 1$ </tex-math></inline-formula> array with a feeding network was fabricated and tested. The measured −10-dB impedance bandwidth is 23.7% (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$24.9-31.6$ </tex-math></inline-formula> GHz), and the 3-dB gain bandwidth is 21.1% (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$24.6-30.4$ </tex-math></inline-formula> GHz) with a peak gain of 7.65 dBi at 27.7 GHz. The proposed design is then extended to a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3\times 4$ </tex-math></inline-formula> array, demonstrating a 3-dB gain bandwidth of 20% (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$24.7-30.2$ </tex-math></inline-formula> GHz) with a peak gain of 11.2 dBi at 25.4 GHz.