Haiyan Piao

This communication presents a novel dual-mode decoupler (DMD) that integrates orthogonal J-mode and M-mode within a single planar structure, enabling simultaneous suppression of E-plane and H-plane coupling in compact patch antenna arrays. Analytical modeling, based on a four-port impedance network, clarifies the operation mechanism, showing how mode-specific impedance loading achieves robust decoupling. Experimental results demonstrate the DMD’s versatility: J-mode or M-mode can be selectively employed for independent E-plane or H-plane decoupling, while synergistic operation supports dual-polarized MIMO, 2D 4 × 4 MIMO, and same-sense circularly-polarized (CP) MIMO designs. Simulations and measurements confirm the CP MIMO implementation achieves a 5.1 dBi peak gain and a 180 MHz axial ratio bandwidth (3.6% at 5 GHz). The DMD mitigates E-plane and/or H-plane coupling in dense arrangements, improving scalability and multi-polarization performance for wireless systems.

In this study, a simple and efficient dual‐port single‐loop antenna unit, intended for full metal‐frame terminals, is presented as the first of its kind. The proposed multiple‐input and multiple‐output (MIMO) antenna unit is constructed within a loop resonator, inserted between the metal frame and the ground plane without any slits or cuttings. Two voltage ports are utilized to simultaneously excite the shared loop resonator as radiators; however, the strong mutual coupling is induced from one port to another because of the shared loop resonator. Herein, a simple and efficient decoupling capacitor is loaded at the center of the loop resonator, decoupling and decorrelating the two‐port loop resonator. In this way, a dual‐port single‐loop antenna unit is accomplished for 5G MIMO applications. Two units are constructed, forming 4 × 4 MIMO antennas, which are validated in both simulation and measurement.

This study presents a dual-port single-dipole MIMO antenna pair, which is accomplished by selectively exciting the dominant dipole-type current mode and the second higher current mode of a single suspended metal strip. A magnetic coupling method based on a feeding loop is implemented at the current maximum portion of the dominant mode of the suspended metal strip, such that the suspended metal strip operates as a half-wavelength dipole radiator. An electrical coupling method based on a feeding capacitor, otherwise, excites the wavelength dipole mode of the suspended metal strip, and this higher mode resonance is further controlled by a tuning capacitor. In this way, the suspended metal strip involves a dual-port MIMO antenna pair, and both antennas operate as dipole-type radiators while having high port-to-port isolation because of the modal orthogonality. Therefore, the operation mechanism of the proposed technique is straightforward, and the implementation is simple, free of any additional decoupling components or a complex excitation network. This feature makes the proposed technique an attractive solution in metal-rimmed terminals for 5G applications, so 4 × 4 MIMO antennas operating at the N78 band were constructed and verified in both simulation and measurement.

This paper investigates the design of a compact multiple-input multiple-output (MIMO) ground-radiation antenna system for 5G terminal devices. Ground-radiation antennas are small loop-type resonators that can excite the ground plane as radiators while having advantages of small size and convenient tunability, but their compact MIMO systems remain as unsolved issues. In this study, a novel and straightforward decoupling technique based on a closed-decoupling-loop is presented for MIMO applications in the first of its kind. The proposed closed-decoupling loop can be viewed as a coupling transformer between two antenna elements by acting as a half-wavelength loop-type resonator and by introducing a current null at its center; in this way, a tremendous isolation improvement is accomplished even though the distance between two antennas is only 1 mm. Therefore, a compact 2 × 2 MIMO ground-radiation antenna system and its 8 × 8 MIMO system are demonstrated for 5G applications. Both simulation and measurement are taken to validate the proposed decoupling technique and the compact MIMO ground-radiation antenna system.

This paper studies an isolated ground-radiation antenna (iGradiANT) that has inherent isolation with another closely-located antenna element and demonstrates its applications in 5G multiple-input multiple-output (MIMO) antenna array. The proposed iGradiANT is accomplished by merely employing a small out-of-ground loop into a traditional ground-radiation antenna (GradiANT). Hence, in contrast to the traditional GradiANT, the proposed iGradiANT can simultaneously support an in-ground loop-type current mode and an out-of-ground loop-type current mode, responsible for far-field radiation and near-field energy cancellation, respectively. In this way, the proposed iGradiANT can exhibit an intrinsic decoupling effect with the adjacent antenna element. Hereby, a typically used inverted-F antenna (IFA) and a normal loop antenna are adopted to separately validate the functionality and versatility of the proposed iGradiANT in establishing 2 × 2 MIMO antenna sets without any separation. Furthermore, an 8 × 8 MIMO antenna array is demonstrated for the usage of 5G terminal devices; both simulation and measurement are conducted to verify its radiation performance and diversity performance.

This study investigates a compact and straightforward self-decoupled $2\times 2$ multiple-input multiple-output (MIMO) antenna set and its applications for current and future 5G terminal devices. The proposed self-decoupled MIMO antennas include a popularly used loop antenna and a compact loop-type ground-radiation antenna without utilizing any supplementary decoupling structures or undergoing complex tuning process. It is revealed that the loop antenna and the ground-radiation antenna can be modeled as an electric-current element and a magnetic-current element, respectively. This orthogonality allows the self-decoupled characteristic of the proposed MIMO antennas even though the antenna elements are tightly arranged and collocated together. An $8\times 8$ MIMO antenna system is further demonstrated for 5G MIMO applications, where both simulation and measurement are conducted to validate the feasibility of the proposed technique. It is concluded that the proposed MIMO antenna system is a smart way to generate high isolation and low correlation characteristics while having advantages of low profile and easy fabrication so that it can be recognized as a promising candidate for 5G applications.

This paper proposes a simple and efficient technique to improve the antenna radiation performance in stacked printed circuit boards (PCBs) for Internet-of-Things (IoT) applications. In the proposed design, a planner loop-type ground radiation antenna with compact size is implemented at the upper PCB for 2.4 GHz applications, while the lower PCB overlaps with the upper PCB, inducing out-of-phase current distributions over the lower PCB, thereby resulting in a narrow bandwidth and low efficiency. Therefore, a small parasitic resonator is utilized on the lower PCB to diminish the undesired out-of-phase current. Higher efficiency and wider bandwidth are thus achieved by tuning the impedance characteristic of the parasitic slot, indicating the proposed technique is effective in improving antenna performance for devices with stacked PCBs.