A compact structure with slot splitting meandered lines defected ground is proposed to reduce the mutual coupling between two microstrip antennas with a center-to-center distance of 0.38λ. The meandered line defected ground structure is symmetrically etched on the ground between the microstrip antennas. The proposed structure is optimized and explained by the common/differential mode theory. For experimental verification, the structure is fabricated and measured. Simulation and measurement results with excellent agreement show that the mutual coupling can be reduced significantly using the proposed structure. In addition, significant improvement is achieved in radiation efficiency, realized gain, and the decoupled array's envelope correlation coefficient.

A surrogate-assisted defected ground structure design is proposed to suppress simultaneously E- and H-plane couplings in a 22 microstrip antenna array at 2.45 GHz. The DGS is designed and analyzed based on the magnetic current and mode theory. Machine learning is employed to sweep the DGS parameters within defined limits and fine-tune them to obtain optimal design, predominantly shortening the DGS design time. A 22 microstrip antennas array is used as a test case to corroborate the efficacy of the proposed scheme. Simulation and measurement results show that the proposed DGS can significantly reduce E- and H-plane couplings.

For cross-polarization (XP) reduction of microstrip antenna, it is proposed to use asymmetric defected ground structure (DGS) under the patch, which perturbs the TM ₀₂ mode. Unlike conventional DGS, the proposed DGS reduces the XP without increasing the back radiation. A method of higher-order modes and surrounding electric fields is used to explain the DGS. The feasibility and superiority of the proposed scheme are further verified by constructing H-plane linear 4-element arrays. The XP reduction and decoupling are achieved simultaneously, as supported by simulation and measurement.

An array with large element spacing is designed for wide scanning. The element is designed to suppress the grating lobe by combining two radiation modes. The two modes are the $\mathrm{T}{\mathrm{E}_{\boldsymbol{1}\delta 1}}$ mode of a square dielectric resonator antenna (DRA) and the TM ₀₁₁ mode of a monopole. The proper phase and magnitude combine the two modes to achieve the required radiation pattern. The element radiation pattern has an asymmetric radiation pattern with the main beam pointing to the anticipated scanning region and a low radiation level in the region of the expected grating lobe. A linear four-element array with an interelement spacing of 0.95 λ ₀ ( λ ₀ is the operation wavelength) is designed, fabricated, and measured for beam scanning in the E-plane to verify the design concept. The array's grating lobe is reduced by more than 11 dB within the scan angle of 15°–60° and bandwidth of 4.51–5.32 GHz. Good agreements between simulated and measured results are observed.

A broadband dual-polarized cup dielectric resonator antenna (CDRA) with stable omnidirectional radiation patterns is presented in this correspondence. Both omnidirectional horizontally polarized (HP) and vertically polarized (VP) radiation patterns can be attained by exciting electric-dipole/TM _01δ mode, TE _011+δ mode using a coil feeding structure and a planar feeding network, respectively. The coil feeding structure motivates the CDRA's mode and another equivalent electric dipole at nearby frequency to the CDRA mode to extend the bandwidth. A broadband TE _011+δ mode is excited by the planar feeding network using a double-tuned method. The CDRA is 0.48 λ ₀ ×0.18 λ ₀ (λ is the free-space wavelength at the center frequency). A prototype is fabricated and measured, achieving an HP bandwidth of 14.5% and a VP bandwidth of 29.8%. The overlapping bandwidth is 14.5% (3.26-3.77 GHz). The proposed antenna can be used in various wireless communications.

Throughput modeling in multiple-input multiple-output (MIMO) systems has attracted widespread attentions. Nevertheless, the current throughput model is confined to the case of fixed data streams (layers) and modulation and coding scheme (MCS). In the proposed study, we expand the conventional throughput model based on the transmit selection diversity and threshold translation mapping techniques to enable its use in systems, where the MCS and layers are adaptively modified depending on channel quality. Excellent agreement between the simulation and measurement results confirms the effectiveness and accuracy of the suggested throughput model.