Dual-Band Phased Array for Widely Separated mmWave Frequencies Using Resonant Boundary Control and Passive Spacing Reconfiguration

This article is the first to introduce a new concept of a compact phased array antenna using a single-type antenna element within a single antenna layer structure to simultaneously operate at dual-harmonic frequencies ( ${\mathrm {f}}_{1} =24$ GHz, $2{\mathrm {f}}_{1} =48$ GHz). In order to overcome the structural complexity and performance limitations of conventional multiband array systems, this concept is realized through two newly devised techniques: frequency-reconfigurable boundaries (FRBs) and an adaptive unit-spacing tuning operator (AUTO). These techniques dynamically optimize element spacing and boundary conditions without additional active elements or multilayer configurations. The proposed phased array antenna demonstrates exceptional beam steering capabilities, consistently achieving $\pm 50^{\circ }~3$ dB scan angles at both frequencies with realized gains of 10.0 dBi at 24 GHz and 11.1 dBi at 48 GHz. Comprehensive experimental measurements are conducted to verify bandwidth, realized gain, and scanning range, showing strong agreement with simulation results and demonstrating the real-world applicability of the proposed antenna. The proposed structure offers significant advancements in antenna miniaturization, simplicity, and versatility, demonstrating technical contributions suitable for millimeter-wave (mmWave) wireless applications, including next-generation mobile networks and Integrated Sensing and Communication (ISAC).