In this letter, a multiple-input–multiple-output (MIMO) antenna with wideband performance for 5G smartphones is presented. First, a planar inverted-F antenna (PIFA) with an inverted-T-shaped open-slot is introduced. The proposed PIFA operates with a wide bandwidth of 78% due to the multimode technology. Then, two such PIFAs are attempted to be merged as a PIFA-pair, constituting a 2 × 2 sub-MIMO antenna with a similar bandwidth as the PIFA-element. Additionally, the isolation between two PIFA-elements in a PIFA-pair is higher than 10 dB across the broadband. Finally, a 4 × 4 MIMO antenna, which is composed of two PIFA-pairs, is demonstrated to cover the 5G NR frequency bands: n77/n78/n79 and LTE band 46. The simulated and measured results are included for illustrating the performance of the proposed MIMO antenna.

A reconfigurable antenna with radiation pattern and polarization reconfiguration capabilities is investigated in this paper. The antenna consists of a central dielectric resonator antenna (DRA) and two parasitic DRAs made of a liquid solution with low dielectric loss. Utilizing the flowing of liquid, the existing of parasitic DRA can be changed to produce different patterns. An omnidirectional pattern can be realized when only the central DRA radiates, while a unidirectional pattern can be obtained using the parasitic DRAs. Furthermore, the polarization of the antenna with unidirectional radiation can be changed by forming different parasitic DRAs, which can be realized via liquid flowing. Based on this principle, three different radiation states, namely, omnidirectional radiation and unidirectional radiation with x- or y-polarization, can be obtained. To verify the design, a prototype of the antenna operating at 2.4 GHz was simulated, fabricated, and measured. The measurement results indicate that the antenna provides effective impedance matching over the band of interest as well as radiation pattern and polarization reconfiguration capabilities.

In this paper, we presented an ultra-wideband multiple-input multiple-output (MIMO) antenna system with high element-isolation for the application in 5G metal-frame smartphones. We proposed T-shaped and C-shaped slots on the metal frame generating four resonances to enhance the bandwidth. What’s more, we introduce modified H-shaped slots between each antenna-element to improve the element-isolation of MIMO antenna system. As a result, the MIMO antenna system has a wide bandwidth of 58% ranging from 3.3 to 6 GHz and the element-isolation is over 18 dB crossing the effective frequency band. Thanks to the decent element-isolation, the envelope correlation coefficient (ECC) between each antenna-element is below 0.05 providing a reliable anti-interference for the MIMO antenna system. In addition, the measured radiation efficiencies of the MIMO antenna system are higher than 40%. At last, we analyze the effects caused by user’s hands and head to guarantee the robustness of the MIMO antenna system in practical applications.

A mode reconfigurable dielectric resonator antenna (DRA) to realize radiation pattern reconfiguration is presented for the first time. The DRA is composed of two zones: the inner zone is a solid cylinder fabricated by K9 glass ( $\varepsilon _{r} = 6.85$ ) and the outer zone is filled with a dielectric liquid—ethyl acetate ( $\varepsilon _{r} = 7.1$ ). Both of them are put into a cylindrical container fabricated by 3-D printing technology and excited by a single coaxial probe. The inner glass DRA is excited in its broadside HEM $_{\mathrm {11\delta }}$ mode when the ethyl acetate is pumped out, while the conical TM $_{\mathrm {01\delta }}$ mode is excited in the reconstituted cylindrical DRA when the ethyl acetate is pumped in. Consequently, a mechanical reconfiguration of broadside and conical radiation patterns can be achieved over a wide impedance bandwidth of 35.5% from 3.75 to 5.37 GHz. For demonstration, the reconfigurable DRA was fabricated and measured. The measured results of the standing wave ratio, radiation pattern, gain, and efficiency are discussed. Reasonable agreement between the measured and simulated results is observed.

A novel liquid dielectric resonator antenna (LDRA) with circular polarization (CP) reconfigurability is investigated in this communication. The fluidic dielectric for this design is ethyl acetate (εr = 6.6) which is held by a container fabricated by 3D printing technology and excited by a single probe. To realize the CP reconfigurability, the container is designed with two zones: left and right zones. Therefore, the proposed antenna can be switched between two different states: when the liquid solution is injected into the left zone, it can realize left hand circular polarization (LHCP), on the other hand, if the fluidic dielectric is pumped into the right zone, it can obtain right hand circular polarization (RHCP). Consequently, the CP reconfigurability is obtained by flowing liquid control of the ethyl acetate solution. For demonstration, the proposed antenna is design at 2.4 GHz for RFID application with a broad impedance bandwidth (SWR < 2) of 35.6 % which fully cover the wide axial ratio (AR) bandwidth (AR < 3 dB) of 16.3 %. Finally, good agreement is achieved between the measurement and simulation.