Nipont Tangthong

This work presents an S₂₁-based 2.4 GHz microwave sensing system with a 3D-printed dielectric lens for automatic passenger counting in aircraft applications. The proposed system employs a pair of microwave antennas forming a transmission sensing link across the passenger pathway, where the presence of a passenger perturbs the transmitted microwave signal and produces a detectable variation in the transmission coefficient, S₂₁. A hemispherical dielectric lens fabricated from acrylonitrile butadiene styrene (ABS) is integrated with each antenna to improve the directional radiation characteristics of the sensing link. The measurements show that the lens increases the average realized gain from 2.26 to 4.02 dBi while maintaining operation at 2.4 GHz. The sensing system is integrated with a NanoVNA and a MATLAB-based processing platform for sequential S₂₁ acquisition, human-event discrimination, automatic counting, and automatic display updating. Experimental responses obtained from humans and representative non-human materials, including plywood, plastic, and steel, demonstrate distinguishable S₂₁ characteristics under the investigated conditions and provide the basis for an experimentally derived human-response detection window. The complete system was experimentally evaluated in an actual Airbus A320 aircraft using 30 participants over five repeated counting trials. The system achieved a mean counting accuracy of 90.67%. These results demonstrate the feasibility of the proposed microwave sensing approach for aircraft passenger-counting applications.

This study proposes a high-isolation four-port wideband MIMO antenna array designed for sub-6 GHz 5G, IoT, and radar applications. The array is fabricated on a polycarbonate substrate with overall dimensions of 500 × 500 mm² (ε_r = 2.8, h = 1 mm). Four orthogonally arranged modified circular patches with triangular ground planes and optimized inter-element spacing (D₁ = 90 mm) are employed in the antenna’s design to achieve an impedance bandwidth of 0.7–7.0 GHz (Fractional Bandwidth (FBW) > 163.63%) with |S_ii| < −10 dB across all ports. The measurement results indicate that the inter-port isolation is better than 15 dB (worst-case) across the 0.7–7 GHz band, exceeding 25 dB over 63.5% of the bandwidth (with a peak of approximately 50 dB); the envelope correlation coefficient (ECC) is ultra-low (TARC) is less than −10 dB for primary multi-port excitations; the mean effective gain (MEG) is balanced (≈−3 dB); and the group delay is consistent (~0.5 ns). With a maximum realized gain of 10 dBi, the antenna exhibits omnidirectional radiation patterns, showing a significant correlation between the simulation (CST Microwave Studio) and measurement results. The proposed antenna is particularly well-suited for use in high-throughput sub-6 GHz 5G base stations and wideband wireless systems, offering superior port isolation through multi-mode resonance without the need for metamaterials and outperforming existing four-port designs.