In this paper, we extensively report the additive fabrication and characterization of carbon-nanotube and graphene oxide-based 3D printed rectangular patch antennas that can be integrated on curvilinear and deformable surfaces. Our fabricated antennas can be as thin as few microns and demonstrate reflection coefficient (S11) values that confirm their super-high-frequency (in tens of GHz) and ultra-wideband characteristics. For example, the measured result of S11 is below −10 dB in the frequency range of 12 GHz–39 GHz (7 GHz–22 GHz or 5 GHz–25 GHz) for printed patch antennas on flat FR4 substrates (or on curvilinear, bendable PLA substrates). In addition, we quantify other characteristics of these printed antenna structures (e.g., radiation efficiency and gain) and also demonstrate good robustness and reliability (in terms of maintaining the performance) of the antenna structures after being subjected to long-term temperature cycling. Additionally, we measure the radiation efficiency of the printed CNT-GO patch antenna on flat FR4 substrates and also obtain simulation results for quantifying the S11 and the gain of the antenna.
This study presents a simulation-based geometry evolution and performance assessment of a compact four-port 2×2 MIMO antenna for frequencies extending from the mmWave to the sub-THz region. The design evolves from an initial circular patch radiator to a modified petal-like radiator formed by five overlapping and rotated elliptical sections, followed by integration into a four-port MIMO configuration. The radiator, slots, feed and matching sections, partial ground plane, substrate dimensions, and element arrangement were parametrically investigated to improve the simulated impedance-matching and inter-port coupling responses without employing an additional defected ground structure, electromagnetic band-gap structure, metasurface, or dedicated decoupling element. The single-element footprint was reduced from 10×10 mm2 to 10×9 mm2, while the complete four-port footprint was reduced from 24×24 mm2 to 22×22 mm2. Under the investigated CST Studio Suite software, the conventional reflection coefficients remained below −10 dB from 13.6 to 151.91 GHz, corresponding to a simulated impedance bandwidth of 138.31 GHz and a fractional bandwidth of approximately 167.1%. The transmission coefficients remained mostly below −20 dB across this range. The peak realized gain reached 11.87 dBi, while the simulated radiation efficiency remained mostly above 90% up to approximately 120 GHz before decreasing in the upper-frequency region. Surface-current and radiation-pattern analyses showed a transition from comparatively broad lower-frequency current and radiation distributions to increasingly localised, directional, and multi-lobed behaviour at higher frequencies. Active reflection coefficients demonstrated that simultaneous four-port matching depends on the applied excitation amplitudes and relative phases and does not fully coincide with the conventional individual-port bandwidth. The full-band S-parameter-based envelope correlation coefficient (ECC) remained below approximately 0.005, while far-field ECC calculated at 16, 58, 100, and 148 GHz ranged from 0.000042 to 0.010246. The corresponding diversity-gain (DG) values remained close to 10 dB. The total active reflection coefficient (TARC) showed that simultaneous four-port matching is excitation-dependent, while channel capacity loss (CCL) was below 0.4 bit/s/Hz across the operating band. These results support the numerical feasibility of the proposed geometry-evolution approach under the stated simulation assumptions. Future work will focus on prototype fabrication and calibrated four-port mmWave-to-sub-THz measurements to evaluate practical antenna and communication-system performance.
Terahertz wireless systems require adaptive control of polarization as well as beam direction. Chiral metasurfaces offer one route to this control, but structural chirality, spin-dependent wavefront shaping and independent polarization-channel programming describe different physical properties. This mini-review distinguishes these concepts and examines how demonstrated dynamic chiroptical responses could be incorporated into programmable surfaces for 6G-relevant systems. Foundational photoinduced, microelectromechanical and graphene-based devices are compared with phase-change platforms and recent electronically addressable apertures. A quantitative comparison separates measured polarization changes from estimated switching speeds and identifies the distinction between global tuning and spatial programming. Microwave and millimeter-wave polarization-programmable surfaces provide established hardware and communication precedents, while THz array demonstrations expose the constraints imposed by bias routing, insertion loss and control bandwidth. We argue that a chiral reconfigurable intelligent surface should be represented by calibrated, state-dependent polarization scattering matrices and evaluated against a dual-polarized, nonchiral baseline. The principal challenge is to combine a verified chiroptical function with scalable addressing and demonstrate a reproducible link or sensing benefit under feedback control.
Physics-aware active learning can reduce the full-wave electromagnetic (EM) cost of microstrip-patch design, but its sampling priors are commonly tuned to one substrate and band. We present an integrated self-calibrating, matching-first, physics-aware active-learning workflow for probe-fed rectangular patches, together with coarse-mesh screening and full-resolution confirmation. The online calibration estimates sampling bands from each run’s observations instead of prescribing case-specific probe locations. Under an equal budget of 37 openEMS simulations, 4 optimizers were compared on 4 substrate/frequency cases using 10 replicate seeds per case. The integrated workflow produced the lowest mean and median final objective in every case, returned a matched design in all forty runs, and was lower than the three baselines in nine of twelve exact directional Mann–Whitney comparisons after within-case Holm adjustment; six contrasts remained significant in a two-sided unpaired analysis and seven in a paired-by-seed sensitivity analysis. Multi-fidelity screening reduced mean equivalent-high-fidelity cost by 19%–46% across cases (36.9% overall) and returned a matched full-resolution design in 39 of 40 runs, although endpoint objective quality was not uniformly preserved. Nominal near-to-far-field calculations for four selected designs gave broadside directivities of 6.51–7.00 dBi and realized gains of 3.59–5.77 dBi. All 12 finer-mesh, larger-domain, and perfectly matched layer (PML) stability checks remained matched; maximum absolute directivity and realized-gain changes were 0.180 and 0.121 dB. A ten-variable E-shaped-patch case study matched all ten integrated-workflow runs. Its advantage over random search was robust to unpaired and paired-by-seed analyses; inference against unstructured radial-basis-function (RBF) surrogate search depended on the treatment of seed blocks, and the genetic comparison remained unresolved. A five-seed in-loop impedance–gain pilot produced a directionally favorable but non-significant hypervolume trend. The evidence is numerical and openEMS-based; no commercial-solver or fabricated prototype validation is claimed.
The proposed approach introduces an innovative feeding mechanism enabling efficient directive radiation with a planar antenna array. A microstrip T-type power divider is employed for initial power distribution, while two symmetrically placed slots are utilized to achieve direct mode conversion into the higher-order TE50 mode within the SIW structure. A prototype was fabricated to validate the concept experimentally. The measured results demonstrate excellent agreement with simulations, confirming a fractional impedance bandwidth of 3.4% (5.70–5.90 GHz for S11<−10 dB) and a peak realized gain of 10.2 dBi at 5.8 GHz, with a measured radiation efficiency of 87.2%. This design offers significant advantages, including simplified fabrication, reduced production costs, and enhanced tolerance to manufacturing variations, making it well-suited for communication systems at 5.8 GHz requiring directive radiation.
