This paper proposes three novel sparse-optimized nested L-shaped array (LA) configurations (ISNA-LA, ANCADiS-LA, AINA-LA) to address the challenges of limited degrees of freedom (DOFs) and mutual coupling in conventional LAs. These configurations optimize element placement in two-level nested arrays (TLNAs) to enhance DOFs and reduce mutual coupling via sparse spatial distribution. A hybrid 2-D DOA estimation framework integrating the least absolute shrinkage and selection operator (LASSO) and the pair-matching method by signal covariance matrices (PSCM) is established, enabling full utilization of difference coarray DOFs and automatic azimuth-elevation pairing. Numerical simulations show that the proposed arrays outperform conventional LAs in DOFs and mutual coupling reduction, while the LASSO-PSCM algorithm achieves superior 2-D estimation accuracy.

This research proposes a wideband printed MIMO antenna, based on two printed inverted-F antennas introduced by authors in past studies. These antennas are connected by isolation and impedance matching section, comprising a crank element, two L-shaped elements and two small rectangular elements. The detachment structure serves as a radiation element, causing resonance to improve isolation and impedance bandwidth. The measured 2-VSWR bandwidth is approximately 97.9% (2.4 GHz -7.0 GHz) with antenna spacing of 0.125 λ_l , where λ_l is the wavelength in free space at the lowest frequency. The transmission coefficient in the frequency band is below -17dB.

This letter addresses the performance degradation of reflectarrays (RAs) in practical operation due to aperiodic arrangement and mutual coupling between units, and proposes a reflection-coefficient extraction method based on the mean scattered electric field obtained from full-wave simulations. The method can accurately quantify the impact of an aperiodic environment on the amplitude and phase of the reflection coefficient at the scale of a single RA unit, while avoiding the modeling bias introduced by the conventional periodic-environment assumption. A 3×3 unit model is established to systematically analyze the influence of various environment-unit states on the reflection coefficient of the central unit. Furthermore, in a 20×20 1-bit RA design example, the proposed approach is integrated with a simulated-annealing algorithm to optimize the unit-size distribution, achieving a gain improvement of approximately 2dB. The results demonstrate that the aperiodic arrangement effect is not only a potential source of performance degradation but can also be transformed into a usable design degree of freedom in optimization, thereby providing a new method and perspective for high-accuracy RA modeling and performance enhancement.

In sixth-generation (6G) mobile communication systems, the development of non-terrestrial networks utilizing low Earth orbit (LEO) satellite communication (SATCOM) is expected to promote connectivity in diverse environments, including mountainous regions and maritime areas. To enhance the capacity of LEO SATCOM, the application of multiuser multiple-input multiple-output has recently garnered significant attention. Conventional studies have mainly evaluated linear precoding (LP) or Tomlinson-Harashima precoding (THP) separately, without exploring adaptive schemes that dynamically switch between them under a wide range of received carrier-to-noise ratio (CNR) conditions peculiar to SATCOM. We propose a method to maximize system capacity by appropriately selecting between THP and LP based on the received CNR, evaluating its effectiveness through computer simulations. The proposed method was validated by comparing its system capacity performance with those of LP-only and THP-only schemes, demonstrating superior performance across varying CNR conditions.

This research presents a design of a printed monopole antenna that is miniaturized with end-fire radiation, and has high gain. The antenna begins with a rectangular monopole antenna that is split into two sides using a narrow rectangular slot. The ground plane is then connected to one side of the split-radiator using a stub. By doing so, the omnidirectional radiation of the antenna changes to an end-fire radiation. Hence, a low gain unidirectional radiation is realized. The gain performance is enhanced by placing a parasitic conductor next to the other split radiator. The peak gain is more than doubled this way. Measurements show that the antenna has an S₁₁ < -10 dB bandwidth of 2.38 - 6.35 GHz (90.9%) and a good front - to - back ratio (F/B) > 10dB across this band. The antenna has a small physical size of 20 × 35 mm², 0.04λ₀² miniature area, 10 dBi peak gain, and stable main beam directions. It doesn’t have reflective structures and ground plane extensions, making it compact and easily implemented.