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In this article, an endfire dual-polarized phased antenna array with small ground clearance is proposed for the fifth-generation (5G) millimeter-wave (mmW) applications with a wide bandwidth. In this array, each antenna element consists of a dipole fed by a microstrip line for horizontal polarization and an H-plane horn using substrate-integrated waveguide (SIW) for vertical polarization. To achieve a wide bandwidth for vertical polarization, two metal vias are added at the aperture of the horn antenna. Then, a four-element antenna array is designed by partially overlapping the aperture of each horn element. A prototype has been fabricated using multilayer printed circuit board (PCB) process. The measured results agree well with the simulated ones. The antenna is with an impedance bandwidth of $\vert \text{S}_{11}\vert < -10$ dB from 24.4 to 29.5 GHz for both polarizations. The maximum gains of vertical and horizontal polarizations are 9.16 and 9.27 dBi, with the scanning angle from −34° to 33° for both polarizations with gain deterioration less than 3 dB. The proposed antenna is a promising solution for 5G mmW cellphones or antenna-in-package applications. [ABSTRACT FROM AUTHOR]

In this article, a general decoupling method based on a new perspective of common mode (CM) and differential mode (DM) cancellation is proposed. For two closely spaced antennas, the mutual coupling effect can be analyzed and solved by exciting them simultaneously with in-phase (CM) and out-of-phase (DM) signals. It is theoretically proved that, if CM and DM impedances are the same, the mutual coupling effect between two separated antennas can be totally eliminated. Therefore, we can solve the coupling problem by CM and DM impedance analysis and exploit the unique field properties of characteristic modes to assist in antenna decoupling in a physical intuitive way. To validate the feasibility of this method, two practical design examples, including the decoupling between closely spaced dipole antennas and planar inverted-F antennas, are proposed. Both design examples have demonstrated that the proposed method can provide a systemic design guideline for antenna decoupling and achieve better decoupling performance compared to the conventional decoupling techniques. We forecast the proposed decoupling scheme, with a simplified decoupling procedure, has great potential for the applications of antenna arrays and multi-input multi-output (MIMO) systems. [ABSTRACT FROM AUTHOR]

A novel concept of antenna design, termed differential mode/common mode (DM/CM) design, is proposed to achieve a highly integrated multi-input multi-output (MIMO) antenna unit in mobile terminals. The inspiration comes from a dipole fed by a differential line which can be considered a DM feed. What will happen if the DM feed is transformed into a CM feed? Some interesting features are provided in this article. By symmetrically placing one DM antenna and one CM antenna together, a DM/CM antenna can be achieved. Benefitting from the coupling cancellation of antiphase currents and the different distributions of the radiation currents, a DM/CM antenna can obtain high isolation and complementary patterns, even if the radiators of the DM and CM antennas are overlapped. Therefore, good MIMO performance can be realized in a very compact volume. To validate the concept, a miniaturized DM/CM antenna unit is designed for mobile phones. The 24.2 dB isolation and complementary patterns are achieved in the dimension of $0.330 \lambda _{0} \times 0.058\lambda _{0} \times 0.019 \lambda _{0}$ at 3.5 GHz. One $8 \times 8$ MIMO antenna array is constructed by using four DM/CM antenna units and shows good overall performance. The proposed concept of DM/CM design may also be promising for other applications that need high isolation between closely packed antenna elements and wide-angle pattern coverage. [ABSTRACT FROM AUTHOR]

This paper proposes a polarization-orthogonal co-frequency dual antenna pair suitable for fifth-generation (5G) multiple-input multiple-output (MIMO) smartphone with metallic bezels. The proposed spatial-reuse dual antenna pair consists of a split on the metallic bezel and a slot on the mainboard ground, where the slot is centered on the split. Two orthogonal degenerate characteristic modes operating at half wavelength including in-phase current and slot modes can be excited on the same antenna structure. An end-shorted microstrip line that crosses the split is used to excite the in-phase current mode, producing $y$ -polarized radiation, while a symmetrical slot-centered Y-shaped feeding network with its shorted ends crossing the slot is adopted to excite the slot mode, producing $x$ -polarized radiation. To the best of authors’ knowledge, this is the first time that a co-frequency dual antenna pair suitable for smartphone with metallic bezels is proposed. A sub-6 GHz dual antenna pair operating at 3.5 GHz that occupies a footprint of $25 \times 7 \times 1.5$ mm3 shows a simulated isolation better than −24.1 dB without any external decoupling measures and an envelope correlation coefficient (ECC) lower than 0.008. A four-antenna MIMO array is fabricated and measured to verify the feasibility. Across the operation band, the measured isolation of the antenna pair is better than −20.1 dB and other isolation levels are all better than −12.7 dB, the ECCs of any two antennas are lower than 0.13, and the total efficiency range of the four antennas is 35.2%~64.7%. The proposed dual antenna pair exhibits a great potential to be applied in future 5G MIMO smartphone. [ABSTRACT FROM AUTHOR]

This paper describes the design and testing of a multiple-in multiple-out (MIMO) antenna for metal-frame smartwatch applications. The antenna operates from 2.4 to 2.49 GHz, which can cover Bluetooth/WiFi band. The design procedure is based on the theory of characteristic modes and it is discussed thoroughly. By employing a pair of degenerated modes to design the MIMO antenna, a high port-to-port isolation can be achieved over the operating frequency band. Simulated and measured results are presented to verify the antenna design. Furthermore, the antenna has a low envelope correlation coefficient and a high effective diversity gain even when it is mounted on the human phantom. Hence, the proposed antenna proves to be a good candidate for smartwatch applications. [ABSTRACT FROM AUTHOR]

A new miniature circular high-impedance surface (HIS) is used to design a compact and low-profile multi-in multi-out (MIMO) antenna for wearable applications. The antenna is designed to operate from 2.4 to 2.49 GHz for wireless local area network application. By employing a pair of degenerated characteristic modes of a circular loop antenna, the MIMO antenna can achieve a good port-to-port isolation (>15 dB) without increasing its geometric size. A four-element HIS is chosen to match the antenna profile, and a 2 dBi antenna gain improvement is observed. The design was optimized considering the effect of packaging and then a prototype with the optimal parameters was fabricated and tested. Measurement results are in good agreement with simulation results. Furthermore, the loading effect due to lossy human tissue is also considered and the results show that the antenna has a robust performance against the human phantom and a low specific absorption rate can also be obtained. [ABSTRACT FROM AUTHOR]

The resonant properties of a longitudinal radiating slot in a planar slotted-waveguide array antenna are examined by employing an entire-domain moment method. Attention is focused on the interactions between the slot of interest and its nearest neighbors, and it is shown that if the slot offsets from the guide central line are small, which is usually the case for a large slot array, only one, or at most two, neighboring slot rings formed by the surrounding slots needs to be considered in the evaluations of resonant length and conductance. [ABSTRACT FROM AUTHOR]