A hybrid antenna is proposed for future 4G/5G multiple input multiple output (MIMO) applications. The proposed antenna is composed of two antenna modules, namely, 4G antenna module and 5G antenna module. The 4G antenna module is a two-antenna array capable of covering the GSM850/900/1800/1900, UMTS2100, and LTE2300/2500 operating bands, while the 5G antenna module is an eight-antenna array operating in the 3.5-GHz band capable of covering the $C$ -band (3400–3600 MHz), which could meet the demand of future 5G application. Compared with ideal uncorrelated antennas in an $8 \times 8$ MIMO system, the 5G antenna module has shown good ergodic channel capacity of $\sim 40$ b/s/Hz, which is only 6 b/s/Hz lower than ideal case. This multi-mode hybrid antenna is fabricated, and typically, experimental results such as S-parameter, antenna efficiency, radiation pattern, and envelope correlation coefficient are presented.

4G/5G Multiple Antennas for Future Multi-Mode Smartphone Applications

A dual-polarized hybrid eight-antenna array operating in the 2.6-GHz band (2550–2650 MHz) for 5G communication multi-input multi-output (MIMO) operation in the smartphone is presented. The proposed hybrid antenna array elements are symmetrically placed along the long edges of the smartphone, and they are composed of two different four-antenna array types (C-shaped coupled-fed and L-shaped monopole slot) that exhibit orthogonal polarization. Therefore, coupling between the two antenna array types can be reduced, and the MIMO system performances are enhanced. A prototype of the proposed eight-antenna array is manufactured and measured. A good impedance matching (10 dB return loss or better), desirable cross-polarization discrimination (better than 15 dB), and an acceptable isolation (better than 12.5 dB) are obtained. Envelope correlation coefficient and channel capacity are also calculated to evaluate the MIMO performances of the proposed antenna array.

Eight-Port Orthogonally Dual-Polarized Antenna Array for 5G Smartphone Applications

A compact two-antenna building block for forming the multiple-input multiple-output (MIMO) array in the mobile device such as the smartphone is presented. The building block has a planar structure of small size $7 \times 10$ mm2 (about $0.08\lambda \times 0.12\lambda$ ) for operating at 3.5-GHz band (3.4–3.6 GHz), which is the recently identified frequency spectrum in World Radiocommunication Conference 2015 for future broadband mobile services. The building block is formed by two gap-coupled loop antennas having asymmetrically mirrored (AM) structures with respect to the system ground plane of the smartphone. The two AM antennas show good isolation thereof and their envelope correlation coefficient is much less than 0.1 in the operating band, showing very good independence of the two antennas in their far-field radiation characteristics. By using four such building blocks, an eight-antenna MIMO array at 3.5-GHz band in the smartphone is easily implemented. The channel capacity of the eight-antenna MIMO array in an $8 \times 8$ MIMO system is calculated to be about 36 b/s/Hz with 20-dB signal-to-noise ratio. The measured channel capacity obtained using an $8 \times 8$ MIMO measurement setup is also presented, which generally agrees with the calculated results. The obtained eight-antenna MIMO array is promising for future or fifth-generation smartphone applications.

Two Asymmetrically Mirrored Gap-Coupled Loop Antennas as a Compact Building Block for Eight-Antenna MIMO Array in the Future Smartphone

An antenna element that has not only the self-isolated property but also a compact size is proposed for the fifth-generation multiple-input and multiple-output (MIMO) system in mobile phone applications. In particular, the size reduction is done by introducing two vertical stubs into the original self-isolated antenna element. It is demonstrated that very good isolation and antenna efficiency for an 8-antenna MIMO system can be obtained without using any additional isolation elements or decoupling techniques. An antenna prototype is fabricated and measured; and a quite good agreement between simulation and measurement is obtained.

Size Reduction of Self-Isolated MIMO Antenna System for 5G Mobile Phone Applications

A high-isolation eight-antenna multi-input multi-output (MIMO) array operating in the 3.5 GHz band (3.4–3.6 GHz) for future smartphones is proposed. Here, a novel balanced open-slot antenna is designed as an array antenna element, in which this antenna design can yield a balanced slot mode (with reduced ground effects) that can enhance the isolation between two adjacent input ports. Furthermore, by meticulously arranging the positions of the eight antenna elements, desirable polarization diversity can also be successfully achieved, which further mitigates the coupling between antenna elements. A prototype was manufactured to validate the simulation. A good impedance matching (return loss > 10 dB), high isolation (>17.5 dB), high total efficiency (>62%), and low envelope correlation coefficient (ECC, <0.05) were measured across the desired operation bandwidth. To verify the MIMO performance, ergodic channel capacity using the Kronecker channel model was calculated. The effects of hand phantom were also studied.

High-Isolation 3.5 GHz Eight-Antenna MIMO Array Using Balanced Open-Slot Antenna Element for 5G Smartphones

Using the quad-antenna linear (QAL) array as a building block, the 8-antenna and 16-antenna arrays for the 3.5-GHz long term evolution multiple-input multiple-output (MIMO) operation in the smartphone are demonstrated. The QAL array has a planar structure of narrow width 3 mm (0.035λ) and short length 50 mm (0.58λ), with λ being the wavelength at 3.5 GHz. For the 8-antenna array, two QAL arrays are disposed along two opposite side edges (denoted as Array A) or the same side edge (denoted as Array B) of the system circuit board of the smartphone. The obtained envelope correlation coefficient values of the antennas in Array A and B are shown. The calculated channel capacities for Array A and B applied in an 8 × 8 MIMO system are also analyzed. The 16-antenna array formed by four QAL arrays disposed along two opposite side edges (denoted as Array C) is then studied. For operating in a 16 × 16 MIMO system, the calculated channel capacity of Array C can reach about 66–70 bps/Hz with a 20-dB signal-to-noise ratio. The obtained channel capacity is about 5.7–6.1 times that (11.5 bps/Hz) of the upper limit of an ideal 2 × 2 MIMO system with 100% antenna efficiency for the antennas therein. Details of the proposed Array A, B, and C are described, and the obtained results are presented. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:174–181, 2016

8-antenna and 16-antenna arrays using the quad-antenna linear array as a building block for the 3.5-GHz LTE MIMO operation in the smartphone

A small-size tablet device antenna formed by a simple folded metal plate excited by a low-band feed (direct feed with matching network) and a high-band feed (gap-coupled feed with matching network) for the LTE/WWAN operation in the 698–960 and 1710–2690 MHz bands is presented. The folded metal plate has a size of 3 $\, \times \,$ 5 $\, \times \,$ 30 mm $^{3}$ and is disposed in a clearance area of 10 $\, \times \,$ 30 mm $^{2}$ (300 mm $^{2}$ ) above the top edge of the device ground plane. The matching network in the low-band feed compensates for additional capacitance for the folded metal plate with a resonant length much less than 0.25 wavelength in the lower band (698–960 MHz) and enhances the antenna's impedance matching to achieve a wide lower band. The matching network in the high-band feed also enhances the antenna's impedance matching to achieve a wide higher band (1710–2690 MHz). In addition, the coupling gap in the high-band feed can reject the low-band frequency. Also, the matching network in the low-band (high-band) feed includes a bandpass circuit which can help reject the high-band (low-band) frequency. Good isolation between the two hybrid feeds can, hence, be obtained, which makes the antenna with simple structure and small size have good radiation performances in both lower and higher bands. Details of the proposed antenna are presented.

Small-Size LTE/WWAN Tablet Device Antenna With Two Hybrid Feeds

A 16-antenna array disposed in the smartphone for the LTE MIMO operation in the 3.5-GHz band (3400 ∼ 3600 MHz) is presented. The array is fabricated by disposing four quad-antenna linear (QAL) arrays along two long side edges of the system circuit board of the smartphone. The QAL array has a planar structure occupying a small area of 3 mm × 50 mm. Two QAL arrays spaced 20 mm are disposed along each side edge. Acceptable antenna performances and ECC (envelope correlation coefficient) values are obtained for the antennas in the array. The calculated ergodic channel capacities of the 16-antenna array in a 16 × 16 MIMO system reach about 66 ∼ 72 bps/Hz with a 20-dB signal-to-noise ratio. The obtained results of the 16-antenna array are presented.

16-Antenna array in the smartphone for the 3.5-GHz MIMO operation

A simple, decoupled dual-inverted-F antenna (DIFA) formed by two inverted-F antennas (IFAs) with a decoupling chip inductor is presented. The open ends of the two IFAs face to each other and are connected by the decoupling chip inductor. The DIFA has a planar structure and is easily fabricated on a thin dielectric substrate. Good isolation between the two IFAs can be obtained, owing to an equivalent bandstop circuit formed by the decoupling chip inductor and the equivalent distributed capacitor between the open ends of the two IFAs. For the tablet computer application in the 3.6-GHz LTE band (3.4–3.8 GHz), the DIFA with a decoupling chip inductor of 39 nH occupies a small size of 20 × 4 mm2 on a 0.8-mm thick FR4 substrate. The two IFAs in the DIFA almost require no isolation spacing, thereby leading to the compact structure and small size. Details of the proposed DIFA are described, and its multi-input multioutput performance is discussed. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:2189–2194, 2015

Dual‐inverted‐F antenna with a decoupling chip inductor for the 3.6‐GHz LTE operation in the tablet computer

A promising small-size WLAN antenna suitable to be mounted along the hinge of the ultrabook computer with metal housing is presented. The antenna is formed by a two-branch structure of a monopole strip and a loop strip. The antenna has attractive features of low profile and wideband operation. In addition, by using the closed resonant path provided by the loop strip, possible coupling of the proposed antenna with nearby conducting elements for frequencies over the 2.4 GHz band can be expected to be decreased. Also, when the antenna is operated in the 5.2/5.8 GHz band, the loop strip is not at resonance and can serve as a shielding element for the monopole strip. This can also lead to decreased possible coupling of the proposed antenna with nearby conducting elements over the 5.2/5.8 GHz bands.

Li-Yu Chen

Papers

8-antenna and 16-antenna arrays using the quad-antenna linear array as a building block for the 3.5-GHz LTE MIMO operation in the smartphone

Small-Size LTE/WWAN Tablet Device Antenna With Two Hybrid Feeds

16-Antenna array in the smartphone for the 3.5-GHz MIMO operation

Dual‐inverted‐F antenna with a decoupling chip inductor for the 3.6‐GHz LTE operation in the tablet computer

2.4/5.2/5.8 GHz WLAN antenna for the ultrabook computer with metal housing