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A low‐profile wideband 8‐antenna array for future 5G New Radio (5G NR) mobile devices is studied. Each array element has a size of 16.85 mm × 4.6 mm, and the height of the frame is only 5 mm. The array element is composed of a driven element coupled‐fed by a T‐shaped feeding element and a shorting element. The driving element and the shorting element enable the antenna to obtain dual resonance modes, while the T‐shaped feeding structure can improve the impedance matching. The 10‐dB impedance bandwidth (3.27–4.24 GHz) of the proposed 8‐antenna array can completely cover the 5G Sub‐6GHz NR Band n77/n78. The measured antenna efficiency of each array element was higher than 50%. Good isolation of >13 dB was achieved between adjacent array elements due to the introduction of a modified decoupling structure. Besides achieving a desirable ECC of <0.06, the calculated channel capacities of the 8 × 8 multiple‐input multiple‐output system working across the bands of interest can reach up to 38.8 bps/Hz. [ABSTRACT FROM AUTHOR]

A coplanar waveguide (CPW) fed polarization reconfigurable antenna for WLAN 2.4 GHz operation is studied. To achieve reconfiguration between left‐hand circular polarization (LHCP), right‐hand circular polarization (RHCP), and linear polarization (LP) with broad CP and LP operating bandwidths, the technique of switching only two PIN diodes embedded between the CPW feeding line and an open square‐ring radiating element is introduced. As the radio frequency (RF) and direct current (DC) signals must be fed from the same feeding line (input port), during the experiment, an additional Bias‐Tee element is introduced to the input port for combining the two signals. [ABSTRACT FROM AUTHOR]

In this article, a wideband low‐profile endfire circularly polarized (CP) antenna using magnetoelectric dipole is proposed. Designing a wideband electric dipole element is easy and well‐studied in the literature. However, designing a compact wideband magnetic dipole element is still a challenge. In this paper, the impedance bandwidth (IBW) of the magnetic dipole is enhanced by reducing the resonance frequency of higher‐order mode half‐TE310 with the help of rectangular slots placed at the null of mode half‐TE310. By combining the resonance frequency of mode half‐TE110 and mode half‐TE310, the magnetic dipole can yield a larger IBW (6.86–7.67 GHz, 11.14%) with smaller planar dimensions of 1.259λ0 × 0.363λ0 × 0.038λ0 (λ0 is the free space wavelength at the centre frequency). To generate a wideband endfire CP wave, a horizontally polarized electric dipole with a feed line is combined with the vertically polarized magnetic dipole. The measured IBW and axial ratio bandwidth (ARBW) are 11.65% and 12.02%, respectively, with a measured peak endfire gain of 5 dBic. The overall dimension of the proposed wideband low‐profile endfire CP antenna is 1.11λ0 × 0.66λ0 × 0.033λ0. [ABSTRACT FROM AUTHOR]

In the modern era of wireless Internet of Things designing a planar antenna at relatively low frequency (P-band) with positive gain and high efficiency is exacting task. In this letter, a planar P-band microstrip antenna (a simple rectangular patch of size 0.16λ0×0.20λ0×0.01λ0, smaller than classical quarter-wave patch) for wireless underground sensor network (WUSN) is proposed. The proposed structure yields high gain with the judicious use of four shorting vias, which are collocated along the side edges of the patch with a composite substrate (dielectric-artificial magnetic conductor). The results shows that the designed antenna resonates at 413 MHz with gain and efficiency of 3.1 dBi and 75%, respectively, with a 10 dB impedance bandwidth of 2% (408–416 MHz) [ABSTRACT FROM AUTHOR]

Because the width of antenna elements exceeds half of the air wavelength, resulting in too large element spacing, the scanning angle of traditional endfire circularly polarized (CP) antenna array is usually less than 60°. In order to solve the above problem, a CP quasi-Yagi antenna element is proposed in this letter, whose width is less than half of the air wavelength. Further, an 1 × 8 endfire CP antenna array is designed. Because the element spacing is about half a wavelength, the scanning angle of the proposed endfire CP antenna array can reach 60°. Moreover, the axial ratios of all beams are less than 3 dB in the scanning angle range of (0°, 60°). The final measured results are basically consistent with the simulated results [ABSTRACT FROM AUTHOR]

A C‐/Ka‐band circularly polarized (CP) shared‐aperture scanning antenna array has been proposed in this paper. Here, the antenna array working in the C‐band (6.48–6.52 GHz) is composed of 4 × 4 cross‐dipole antenna elements, and each cross‐dipole antenna element is fed by a 1‐to‐2 power divider with 90° phase difference, so that it can induce left/right‐hand CP wave. As for the antenna array working in the Ka‐band (27.5–28.5 GHz), it is made up of 16 × 16 CP antenna elements, in which each CP antenna element is an aperture‐coupled chamfered patch fed by substrate integrated waveguide (SIW) structure. To realize the proposed scanning array, the C‐band antenna array is set within the gap between adjacent antenna elements of the Ka‐band antenna array, and the radiation apertures of all the antenna elements are printed on the same plane. Notably, such a layout can yield good isolation performance between the C‐band antenna and the Ka‐band antenna element. From the measured results, in the C‐band, the proposed scanning array can achieve a beam scanning range of 0°–38° with axial ratio (AR) < 3 dB, a port isolation of greater than 45 dB, and a maximum gain of 18.2 dBic. On the other hand, in the Ka‐band, the proposed scanning array can yield a beam scanning range of 0°–45° with AR <3 dB, a port isolation of greater than 37 dB, and a maximum gain of 26.2 dB. [ABSTRACT FROM AUTHOR]

Two novel multisegment loops coupled ultrahigh-frequency (UHF) radio frequency identification near-field (NF) antenna with a uniform and strong magnetic field distribution over an electrically large interrogation zone are designed. Each proposed antenna is composed of eight loops, and the current distribution along the loop is kept in-phase using a segmented line. To further achieve a more uniform magnetic field, the last four loops of the two proposed antennas (ANT 1 and ANT 2) are loaded with parasitic structures. Here, a 100% detection rate is achieved by ANT 1 within an interrogation area of 370×560×105 mm3 for the bidirectional operation setup. As for ANT2, it is backed by an artificial magnetic conductor to enhance the magnetic field strength and reduce the profile with respect to a configuration with a PEC reflector plane, and it has yielded a 100% detection rate within the interrogation area of 370×560×185 mm3 for the unidirectional operation setup. The proposed ANT2 can cover the UHF band of China, the Federal Communications Commission band of North America, and European Telecommunication Standards Institute band of Europe. [ABSTRACT FROM AUTHOR]

A dual-polarized wideband omnidirectional ceiling antenna with low gain variations (GVs) for 2G/3G/LTE/5G sub-6 GHz indoor applications is presented. The vertical-polarized (VP) antenna element that is arranged in the center is composed of a pair of orthogonal semicircular plates and a top-loaded circular brass disk, whereas the horizontal-polarized (HP) antenna element is comprised of four printed dipoles with truncated corners, four arc-shaped parasitic patches around the dipoles, and a 1-to-4 power divider feeding network on the bottom. The feeding network with the “hook”-shaped stubs cooperates with the slot between the adjacent printed dipoles to improve the isolation between the VP and HP antenna elements. Furthermore, the top-loaded circular brass disk, the four arc-shaped parasitic patches, and two pairs of extended strips printed along the ±45° direction are used to reduce the GVs but broaden the operating bandwidths. Experimental results demonstrate that a wide overlapped frequency bandwidth of 74.9% (1.66–3.65 GHz) with an excellent port isolation (≥40 dB) is achieved for the aforesaid application scenarios. [ABSTRACT FROM AUTHOR]

A broadband circularly polarized (CP) slot antenna unit that is composed of a sector‐shaped radiator and an irregular pentagon slot ground plane is initially investigated. The CP characteristics are realized based on unbalanced feeding and loading of irregular slot structure. To increase the gain and yield ultrawideband operation, a 2 × 2 antenna array with a sequential rotational feeding method is introduced. To further reduce the total profile of the proposed antenna array to 0.15λ0, an artificial magnetic conductor array reflector is loaded between the antenna array and the feeding network. The measured 10‐dB impedance bandwidth of the proposed antenna array was 82.6% (8.31–20.0 GHz), and its corresponding CP bandwidth was 65.4% (8.61–16.98 GHz), and the radiation efficiency of the antenna is also higher than 80%. Besides exhibiting very good axial beams across the wide CP bandwidth, a peak gain of up to 11.1 dBic is also achieved. Thus, it is suitable for X‐band and Ku‐band satellite communication applications. [ABSTRACT FROM AUTHOR]

A circularly polarized (CP) meander loop antenna used in the unmanned aerial vehicle (UAV) satellite navigation system is proposed. The planer size of the proposed antenna is 45.6 × 38.4 mm2 and it was printed on a thin flexible substrate with a thickness of only 0.063 mm. Thus, it has the advantages of a lightweight, low profile, and ease in manufacturing. The proposed antenna design utilizes a loop antenna and has applied a perturbed element into the loop to excite two equal amplitude electric fields with a 90° phase difference, thereby exciting a good CP radiation. The measured 10‐dB impedance bandwidth of the proposed antenna was 9.3% (1.48–1.624 GHz), and its corresponding 3‐dB axial ratio (AR) bandwidth was 2.3% (1.555–1.591 GHz). The CP operating band of the proposed antenna can cover the GPS L1, Galileo E1, and Beidou B1 band (1.559–1.591 GHz). [ABSTRACT FROM AUTHOR]

A circularly polarized (CP) meander loop antenna design for GNSS applications is presented. The antenna size is 52.5 × 52.5 × 0.76 mm3 and it is placed 10 mm above a 100 × 100 mm2 metal plane. The proposed antenna utilizes a meandered loop antenna and has applied a perturbed element into the loop to excite two equal electric fields with near 90° phase difference, thereby radiating a good CP radiation. In addition, a triangular patch is loaded to the two diagonal corners of the loop are for improving the CP performances, as well as maintaining its CP radiation even under the interference of a large metal surface beneath it. The simulated 10 dB impedance bandwidth of proposed antenna was 2.2% (1.557–1.593 GHz), and the measured one was 2.4% (1.553–1.591 GHz). The simulated and measured 3 dB AR bandwidths were 0.8% (1.57–1.583 GHz) and 1.02% (1.567–1.583 GHz), respectively. Last, the proposed antenna is suitable for GNSS application that has large metal surface/ground, such as the roof of a vehicle. [ABSTRACT FROM AUTHOR]

A compact size, coplanar waveguide (CPW) fed two‐antenna multiple input multiple output (MIMO) with high isolation and excellent impedance matching operating in n77/n78/n79 5G NR sub‐6 GHz/Wi‐Fi‐5/V2X/DSRC/Wi‐Fi‐6/INSAT‐C is proposed for future wireless applications. Each antenna element is a CPW‐fed antenna type composed of an "inverted‐A," "y‐shaped," and "small extended stub" structures. The two‐antennas are deployed in the same orientation at an edge‐to‐edge distance of 0.06λ (λ represents free‐space wavelength at 3.70 GHz) on a shared rectangular substrate having designed footprint of 0.57λ × 0.39λ. To attain high isolation of greater than 20 dB in the desired bands of interest, a novel comb‐shaped isolating structure is deployed between the two antenna elements. From the measured results, the proposed MIMO antenna has exhibited wide 10‐dB impedance bandwidth of 88.57% (3.00‐7.70 GHz), good gain above 3 dBi and efficiency larger than 78% throughout the desired operating bands. Moreover, the MIMO diversity performance metrics including envelope correlation coefficient (ECC), diversity gain (DG), mean effective gain (MEG), total active reflection coefficient (TARC), channel capacity and channel capacity loss (CCL) are also achieved. [ABSTRACT FROM AUTHOR]

This paper proposes an absorption-transmission-absorption (A-T-A) type frequency-selective rasorber (FSR) with high selectivity that is loaded above a polarization conversion structure (PCS) and applied to a circular polarization (CP) slot antenna array for ultra-wideband radar cross section (RCS) reduction. Outside the operational frequency band (out-of-band) of the antenna, the energy of the incident electromagnetic (EM) wave is directly absorbed by the FSR, whereas from within the operational frequency band (in-band) of the antenna, the incident EM wave penetrates the FSR and irradiates it on the PCS placed on the lower layer of the FSR structure, which meets the phase cancellation condition and is diffused at the same time, thereby realizing the in-band RCS reduction. Due to the lower insertion loss in the passband, higher quality factor (Q value) in the transmission band, and wider absorption band, the proposed FSR can minimize the gain loss (only 0.2 dB) of the CP slot antenna array and widen the RCS reduction bandwidth to 135.5% (5–26 GHz). In addition, due to the central symmetry of the FSR and PCS structures, the CP slot antenna array has monostatic RCS reduction performance for both horizontally polarized (HP) and vertically polarized (VP) incoming waves. [ABSTRACT FROM AUTHOR]

In this article, a three‐port circularly polarized (CP) multiple‐input multiple‐output (MIMO) antenna for wireless local area network (WLAN) application with pattern and polarization diversity is proposed. The proposed MIMO antenna system comprises of a broadside CP antenna element with a T‐shaped slot and two endfire CP antenna elements. Good impedance bandwidth of 16.9% and 5.5% are achieved by the broadside CP antenna and endfire CP antenna, respectively, and their corresponding axial ratio (AR) bandwidth is 7% and 10.47%. The isolation between the different antenna elements is better than 20 dB, and the polarization purity for all CP antenna is more than 25 dB along with the maximum radiation. [ABSTRACT FROM AUTHOR]

The authors propose an innovative double‐Xi‐shaped Chinese character artistic antenna backed by a high‐order‐mode cavity for 5G millimetre‐wave (mm‐wave) applications. The initial double‐Xi‐shaped microstrip antenna element is designed by using characteristic mode theory, and stable gain can be obtained across the whole 5G mm‐wave frequency band. By employing a slotted cavity with TE230 high‐order‐mode to excite 2×2 antenna subarray, a high gain of 13.2 ± 0.8 dBi and a high isolation better than 45 dB without additional feeding networks can be simultaneously achieved. To further improve the gain for reliable transmission, a 4×4 dual linearly polarised (LP) antenna array is also designed and fabricated. Measured results show that a wide frequency bandwidth of 11.45% (24.7–27.7 GHz) with a peak gain of 19.2 dBi and a high isolation of 33 dB is realised for the dual LP antenna array. The proposed method provides a simple and efficient prediction‐theory way to design artistic antenna for the first time, which solves the problem of designing specific‐shaped antenna without theoretical support. [ABSTRACT FROM AUTHOR]

Classical microstrip patch antenna fabricated on a dielectric substrate suffers from poor gain, efficiency, and high cross polarization due to the automatic excitation of TM0 surface wave. It also radiates strong fields along the horizon which is susceptible to multiple-input–multiple-output (MIMO) or array configurations. In view of this, a separate class of circular microstrip antenna known as the reduced surface wave (RSW) circular patch antenna has been proposed with a pair of shorting strips. Unlike earlier RSW-inspired antennas that mainly confirmed their ability for the successful reduction in the mutual coupling between array elements, here, and the enhancement of radiation properties is considered. [ABSTRACT FROM AUTHOR]

A dual‐polarized antenna for the fifth‐generation (5G) array/massive multiple‐input multiple‐output (MIMO) communications is proposed in this paper. Through combining dual‐polarized differentially feeding structure and complementary magneto‐electric (ME) dipole antenna, low cross polarization (X‐pol), high gain, and isolation characteristics can be achieved by the antenna element. To take advantage of these characteristics in the array, a modified 1‐to‐16‐way H‐shaped differentially feeding network is designed to feed the 16‐element antenna array. Here, vertical cross‐shaped patches with dotted slots are arranged between adjacent ME‐dipole antenna elements to further improve the array isolation. By removing the H‐shaped differentially feeding network and the substrate at the bottom, a high‐capacity MIMO antenna system can be achieved. Measured results show that low X‐pol level of −35.7 dB and high gain of larger than 8.1 dBi can be attained by the antenna elements across the 5G frequency bands (3.3‐5.1 GHz). In addition, the antenna array has exhibited high gain of 17.3 dBi and the MIMO antenna has realized very low envelope correlation coefficient of 0.004. [ABSTRACT FROM AUTHOR]

A novel maze shaped multiband monopole antenna with a miniaturized size of only 6 × 4 × 1.6 mm3 is proposed. To further achieving excellent radiation performances across the desired operating bands, an air‐gap is set between the proposed antenna and system ground. To assess the performances of the antenna, simulations are initially carried out by loading a 1.6 mm thick nonconducting Polycarbonate material (analogous to an air‐gap) between the antenna and system ground, and a simplified equivalent circuit (EC) model of the proposed antenna is also derived. The proposed antenna has excited two different resonance frequencies, in which the lower band (fL) and upper band (fU) can yield broad 10‐dB impedance bandwidths of 6.5% (2.37‐2.53 GHz) and 16% (5.05‐5.90 GHz), respectively. Furthermore, desirable gain and radiation efficiency of 2.85 to 6.40 dBi and 57% to 85%, respectively across the two operating bands were also achieved. A practical experiment is also carried out by installing the proposed antenna into a real laptop computer (L412 Think Pad Lenovo). [ABSTRACT FROM AUTHOR]

A wideband coplanar waveguide (CPW) fed monopole antenna designed for Wi-Fi 5 and Wi-Fi 6 applications is proposed. The proposed antenna (main radiator) has a designed footprint of only 20 × 8.7 × 0.4mm³, which is composed of an oval-shaped ring radiator with three concentric rings and a double-T structure loaded with a J-shaped slot. The main novelty of this work is that the measured wideband operation of 34.5% (5.15-7.29 GHz) is contributed by only a single resonance at 6.2GHz, conforming to the bandwidth requirement of Wi-Fi 5 (5.15-5.85 GHz) and Wi-Fi 6 (5.925-7.125 GHz). Furthermore, the proposed antenna also exhibits good radiation characteristics, including a gain around 2.25 dBi, a radiation efficiency above 80%, a total efficiency above 70%, and omnidirectional radiation patterns with a low magnitude of cross polarization throughout the bands of interest. [ABSTRACT FROM AUTHOR]

In the design of ultra-high-frequency (UHF) radio frequency identification (RFID) near-field antennas, realising an antenna with electrically large size, wide frequency band, and far read range has always been a challenge. To solve these problems, a planar hexagonal broadband near-field antenna for UHF RFID applications is proposed and investigated. The antenna structure is composed of six dipoles (resembles three sets of double-arrow structures) that are printed on the top and bottom surfaces of an FR4 substrate, forming a dual-layer (inner and outer layers) broken hexagonal loop. The 10 dB return loss bandwidth of the proposed antenna can reach up to 20.8% (856–1055 MHz), thus able to cover the entire European Telecommunication Standards Institute and Federal Communication Commission system operating bands. Since the current distribution along the loop is kept in a single direction and the length of each dipole is ∼1/2 wavelength (λ), strong and uniform z-component magnetic field distribution with an 18 cm read range can be obtained in the near-field zone of the antenna. As the proposed near-field antenna has a planar size of 175 mm × 175 mm, it is suitable for multi-system and wide-range RFID applications. [ABSTRACT FROM AUTHOR]

A tri-polarized antenna with diverse radiation characteristics is proposed in this paper. This design mainly consists of two pairs of loop radiating dipoles and an omnidirectional monopole antenna element, which are used for the fifth generation (5G) and vehicle to everything (V2X) communications, respectively. By adding eight pairs of inverted L-shaped patches with unequal sizes around the proposed dipoles, wide beamwidths in both E- and H-planes can be obtained across the desired lower and upper frequency bands. Furthermore, by employing eight fork-shaped microstrip stubs to combine the circular monopole antenna element and the L-shaped patches, the flare angle of the conical beam can be increased to 180 $^{\circ }$ , which results in gain enhancement in the azimuth plane. Finally, the proposed loop radiating dipoles are excited by a pair of symmetrical differentially-fed feeding lines. Consequently, high port isolation for the proposed loop radiating dipoles as well as low gain variations for the monopole antenna element can be achieved. Measured results show that the impedance bandwidths of 32.84 $\%$ (2.8–3.9 GHz) and 18.18 $\%$ (4.5–5.4 GHz) can be achieved for the 5G communications. Wide half power beamwidths (HPBW) of larger than 103 $^{\circ }$ in E-plane and 91 $^{\circ }$ in H-plane can be achieved across the operating bands. In addition, a bandwidth of 5.5 $\%$ (5.82–6.15 GHz) with gain of 2.47 $\pm$ 0.69 dBi in the azimuth plane can also be obtained for V2X communications. [ABSTRACT FROM AUTHOR]

A low‐profile wideband dual‐polarized antenna with high gain, low gain variations, and low cross‐polarization for the fifth generation (5G) indoor distribution system is proposed. By using circular‐thread vase‐shaped structure, a low profile of 0.23λ0 (λ0 is the free‐space wavelength at the starting frequency) as well as low gain variation feature can be achieved by the vertically polarized (VP) radiating element. An eight‐way power divider network is employed to feed the horizontally polarized (HP) dipoles so that wideband performance is obtained. Here, eight pairs of arc‐shaped parasitic strips are used to broaden the bandwidth, and eight pairs of director elements are introduced to enhance the gain and reduce the gain variations. In addition, the protruded stubs that are extended from the circular ground plane will help to reduce the cross polarization in the VP direction. Measured results show that a bandwidth of 46.5% (3.3‐5.3 GHz) (S11 < −10 dB) with a gain of 0.85 ± 0.35 dBi, and another bandwidth of 85.0% (2.5‐6.2 GHz) with a gain of 4.75 ± 1.75 dBi can be realized in the HP and VP directions, respectively. Furthermore, high isolation (>27 dB) and low cross polarization (<−24 dB) can also be attained. Therefore, the proposed antenna is a good candidate for 5G indoor distributed system. [ABSTRACT FROM AUTHOR]

A multiple-input–multiple-output (MIMO) antenna array for broadband 5G new radio (5G NR) metal-frame smartphone applications is proposed. The MIMO antenna array is realized by loading eight identical antennas (Ant1–Ant8) into the metal frame of the smartphone to form an eight-antenna array for the sub-6 GHz 8 × 8 MIMO system. Each antenna element is a slot antenna type that is composed of an L-shaped open slot and a 50 Ω microstrip feedline, and good impedance matching in the upper frequency band can be achieved by loading a tuning stub to the feedline. The 10 dB impedance bandwidth of the proposed eight-antenna array can cover the 5G NR Bands n77/n78/n79 and wireless local area network (WLAN) 5 GHz band. Besides demonstrating desirable antenna efficiency of 50%–82% and envelope correlation coefficient of <0.11, the isolations between adjacent array elements are also >12 dB. At 20 dB signal-to-noise ratio (SNR), the calculated peak channel capacity of the proposed eight-antenna array applied to an 8 × 8 MIMO system is 43.93 b/s/Hz. [ABSTRACT FROM AUTHOR]

A low-profile differentially fed dual-polarized antenna with high gain and isolation is proposed for fifth-generation (5G) microcell communications. By introducing two pairs of symmetrical meandering conductors to connect both ends of the radiating cross slots, a compact-size antenna with wide bandwidth can be achieved. By further adopting an artificial magnetic conductor-backed (AMC) reflector that is arranged below the radiating patches with a distance of 6 mm, the antenna profile can be reduced from $0.25\lambda _{c}$ to $0.13\lambda _{c}$ (where $\lambda _{c}$ is the free-space wavelength at the center frequency), while both the gain and frequency bandwidth are also enhanced. Furthermore, owing to the orthogonal differentially fed structure, the antenna element displays a high port isolation of 37 dB. Finally, by meticulously designing the feeding network, much narrower beamwidth can be yielded, and hence, the unidirectional gain is further improved. The measured results show that a lower-frequency bandwidth of 13.5% (3.26–3.73 GHz) with a gain of 15.7 ± 0.1 dBi and upper-frequency bandwidth of 7.6% (4.68–5.05 GHz) with 15.55 ± 0.05 dBi gain can be obtained by the proposed antenna array. In addition, port isolation better than 28 dB and stable radiation patterns can be achieved. With the aforementioned characteristics, the proposed antenna is a good candidate for future 5G microcell communications. [ABSTRACT FROM AUTHOR]

Over the past few years, there has been a huge demand to design a simple printed antenna for high-speed multimedia communication with low cost, compact size, wide band, and low copolarization (CP) to cross-polarization (XP) isolation levels. In this letter, a simple and completely planar air-gap-loaded rectangular microstrip antenna integrated with single shorting post and defected ground structures has been thoroughly investigated to obtain wide bandwidth of 58.72% (8.3–15.2 GHz) at X- and Ku-band. Besides exhibiting good broadside patterns and desirable gain (>5 dBi), good CP-to-XP isolation levels (16 dB) are also achieved. Furthermore, the proposed antenna has a low profile of 0.083 λ0. [ABSTRACT FROM AUTHOR]

An eight-antenna array with wideband operation for future 5G New Radio mobile devices is studied. Each array element is composed of an inverted-F antenna with shorting branches and parasitic elements. The driving element (monopole structure) and the shorting element (inverted-L branch and inverted-C branch) enable the antenna to obtain multiple modes, whereas the parasitic element, open slit, and stub can improve the impedance matching. The 6 dB impedance bandwidth of the proposed eight-antenna array can completely cover the 5G Sub-6 GHz NR frequency Bands n77/n78/n79, which include the 5G band of U.S. (3.55–4.2 GHz), China, EU, and Japan (3.6–4.2 GHz and 4.4–4.9 GHz), as well as the LTE Band 46 (5.15–5.925 GHz). From the measured results, the isolation between adjacent array elements is lower than 10 dB and its corresponding envelope correlation coefficient is also lower than 0.1. [ABSTRACT FROM AUTHOR]

A fully dielectric packaged liquid patch antenna based on liquid metal alloy is presented. In this letter, there are two hollow cavities embedded in a dielectric box, including a rectangular cavity placed at the upper portion acting as the radiating element, and a nonplanar cavity with a central groove under the radiating element serving as the ground plane. The antenna is realized by a three-dimensional printing technique, alleviating assembly tolerance, and uncertainties from a printed-circuit-board approach, which would degrade an antenna performance. The radiating element and the ground plane are fully metallized by filling liquid metal alloy. Unlike traditional liquid antennas, the liquid packaging antenna is completely metallized by conductive liquids, which does not contain any solid metals. The proposed antenna is designed to operate at 5.2 GHz. Results show that the proposed liquid patch antenna produces a satisfactory impedance matching, and a good agreement between simulation and measurement in terms of radiation characteristics is achieved at the desired frequency. [ABSTRACT FROM AUTHOR]

In this paper, a compact building block composed of a slot antenna and a loop antenna is proposed. The slot antenna and the loop antenna share a rectangular clearance, which improves the compactness of the building block effectively. Although the slot and the loop have overlapped completely, the proposed building block exhibits good isolation (better than 19 dB) without any external decoupling structure. Four such building blocks are used to implement a compact eight-port multiple-input multiple-output (MIMO) array operating at 3.5 GHz band (3.4–3.6 GHz) for fifth-generation (5G) metal-rimmed smartphone applications. The proposed eight-antenna MIMO array exhibits good isolation of better than 16 dB across the whole operating band. The measured efficiencies of the proposed MIMO array were between 59% and 73%, and its corresponding measured envelope correlation coefficients (ECCs) were better than 0.05. Furthermore, the calculated channel capacity of the proposed MIMO array with 20 dB signal-to-noise ratio (SNR) was about 38.2–39.8 bps/Hz across the desired bands (3.4–3.6 GHz). The measured results confirm that the proposed MIMO array is a good candidate for 5G terminals. [ABSTRACT FROM AUTHOR]

An 8-element dual-band multiple-input–multiple-output (MIMO) antenna operating in the 5G New Radio band n77 (3300–4200 MHz) and 5 GHz band (4800–5000 MHz) in mobile handsets is presented. The 8-element MIMO antenna is formed by employing four sets of dual-antenna arrays (DAAs) that are symmetrically printed along the two long side–edge frames of the smartphone. Each DAA is composed of two double-branch monopoles and a T-shaped decoupling stub, in which good mutual coupling reduction can be realized via the decoupling structures. Furthermore, the decoupling structures can also aid in improving the impedance matching of the array units for achieving wideband operation. [ABSTRACT FROM AUTHOR]

A dual-loop antenna with massive-input–massive-output (MIMO) operation within the fourth-generation Long Term Evolution (LTE) bands for smart glasses applications is proposed. The 2 × 2 MIMO antenna array is formed by converting the glasses frame into two symmetrical single-loop antenna structures and using the glasses “temple” region as a common ground plane. For each single-loop antenna to excite four resonant modes so that it can yield a desirable −6 dB impedance matching across the desired low band (LB), 824–960 MHz, and high band (HB), 1710–2690 MHz, of LTE operations, a simple matching circuit is loaded into the open section of the loop antenna. Further measurements show good efficiency and isolation across the LB and HB for the dual-loop antenna. Finally, the calculated envelope correlation coefficient and ergodic channel capacity of the 2 × 2 MIMO antenna are also discussed. [ABSTRACT FROM AUTHOR]

A dual-band dual-polarized stacked microstrip antenna with high-isolation and band-notch characteristics is proposed. The proposed antenna is comprised of three layers of substrate. To obtain high isolation between two input ports, a pair of orthogonal differentially driven feeding lines are printed on the top side of the bottom layer. To yield the desired lower- and upper-frequency bandwidths for 5G microcell communications, two sets of $2\times 2$ radiating patch arrays are printed on the second and top layer substrates, respectively. Compared with the conventional microstrip antenna, besides demonstrating a smaller size of $0.48\times 0.48\times 0.085\,\,\lambda _{0}^{3}$ , the proposed antenna has also exhibited higher isolation of better than 40 dB and higher gain of >8 dBi. Finally, a novel technique of arranging four meander lines that connects the four array elements printed on the second layer substrate is proposed to achieve an adjustable band-notch characteristic. [ABSTRACT FROM AUTHOR]

A useful method to transform the smartphone metal cover into an antenna booster for near-field communication (NFC) antenna installed in a full metal cover (FMC) smartphone is proposed. In this proposed work, by properly embedding a series capacitor into a meticulously selected location within the metal cover, strong coupling between the NFC antenna coil and the metal cover will be generated, which mitigates the reverse eddy current induced on the metal cover. Because of that, the performance of the NFC antenna (located below a narrow horizontal slot-loaded metal cover) is substantially improved, as compared to a reference stand-alone NFC antenna in free-space conditions. To verify this proposed methodology, an ordinary single-turn coil reference NFC antenna 1 (ref 1) and a 3-turn coil reference NFC antenna 2 (ref 2) are initially designed via simulation, followed by the conducting of several typical experiments on these two reference antennas. Finally, the two reference prototype NFC antennas that have utilized this method for a single horizontal slot-loaded FMC are also certified by the Europay, MasterCard, and Visa (EMV) test. [ABSTRACT FROM AUTHOR]

A hepta-band antenna with high efficiency, small clearance, and simple structure for metal-rimmed smartphones is proposed in this letter. The proposed antenna occupies only 71 × 5 mm2 of the total clearance, and it is mainly composed of a system ground, a metal rim with two gaps, and two shorting strips. The theory of characteristic modes is used to analyze the entire structure. All resonant characteristic modes (CMs) in the target frequency are traced, and their characteristic current distributions are analyzed. By using an L-shaped capacitive exciter, three CMs are excited at the lower bands, and an inverted L-shaped branch is utilized for improving the impedance matching at higher bands. The measured 6 dB impedance bandwidths were 800–1000 and 1700–2780 MHz, respectively, and they can cover seven operating bands. The measured efficiencies were 62%–85.7% at the lower band and 66.9%–91% at the higher band. [ABSTRACT FROM AUTHOR]

In this paper, multiband antennas based on a single ring slot are proposed for 4G/5G smartphone applications. The basic structure of the antenna is consisted of a large metal ground and an unbroken metal rim, in which a single 2 mm-wide ring slots is realized between the metal ground and rim. Here, a reconfigurable 4G antenna (820–960 and 1710–2690 MHz) is initially devised by loading multiple grounded stubs and a simple dc controlling circuit with varactor diode into the upper section of the ring slot. To further cover the sub-6 GHz spectrum (3400–3600 MHz) for future 5G communications, a four-element multi-input multi-output (MIMO) slot antennas configuration is designed by utilizing the lower section of the ring slot. A prototype antenna was fabricated, and good agreement is shown between the measured and simulated results. Due to the advantages such as multiband operation, MIMO configuration for 5G communications, high isolation, and compact structure, the proposed antenna design is attractive for 4G/5G smartphones. [ABSTRACT FROM AUTHOR]

In this paper, a novel decoupling method without adding any decoupling structure is investigated, and it is able to apply to multiple-input and multiple-output (MIMO) antenna designs with dual and multiple elements. The decoupling mechanism applied in here is to change the electrical length of the radiators to manipulate the radiation pattern for obtaining pattern diversity and good isolation simultaneously. The design mechanism and procedures for realizing pattern diversity are presented. To validate the proposed method, a two-element monopole antenna array with inverted-L elements is initially studied with the isolation better than 20 dB. Next, a four-element MIMO antenna utilizing two different types of monopole elements is proposed to further verify the feasibility of the proposed decoupling method. Finally, an eight-element MIMO antenna operating at 3.5 GHz is implemented with a compact total size of $40\times 100$ mm2, and the measured isolations between two elements are better than 15 dB. Envelope correlation coefficient and channel capacity are calculated to evaluate the MIMO performance, and good results are obtained. The target application of the proposed design is for laptop, small cell base station, or WiFi box with multiple elements. [ABSTRACT FROM AUTHOR]

A differentially driven dual-polarized high-gain stacked patch antenna is presented in this letter. Two-layer stacked patches are adopted to increase the impedance bandwidth of the antenna. Each of the two stacked patches is inserted with four shorting posts for enhancing the antenna gain. To validate the proposed design, a prototype was meticulously fabricated and tested. The simulated and measured results of the antenna show fractional impedance bandwidths of greater than 19% for differential reflection coefficients less than −10 dB and a high isolation level between the two polarizations ($ \vert S_{dd21}\vert $ larger than 35 dB). The antenna gain of up to 11 dBi was also measured for the two ports. Furthermore, a good agreement of radiation patterns between simulation and measurement with the cross-polarization levels lower than −16 dB over the whole operating frequency band is achieved. [ABSTRACT FROM AUTHOR]

In this study, a low-profile ultrahigh frequency (UHF) radio-frequency identification (RFID) tag antenna designed for wristbands in healthcare applications is proposed. The radiator is based on the open-slot cavity technique that is composed of a slotted patch (double-T slots) loaded onto a flexible open cavity. The proposed slotted design can easily allow the tag’s input impedance to be tuned to the complex impedance of typical UHF RFID chips. The proposed tag antenna has a size of 86 mm × 25 mm × 1.6 mm (0.26λ0×0.07λ0×0.004λ0) at 915 MHz, and it can yield a maximum reading range of 8 m (stand alone in free-space condition), 6.6 m (when placed on the human wrist in free-space condition), and up to 3 m (when placed on the human wrist in a crowded condition). [ABSTRACT FROM AUTHOR]

A dual-polarized aperture-coupled magnetoelectric (ME) dipole antenna is presented in this paper. The feeding network is based on substrate-integrated coaxial lines (SICLs). To describe the effect of the SICL on improving the isolation, the ME dipole with another two different feeding configurations, microstrip lines and striplines, respectively, is compared. As such, the coupling between the transmission lines is tremendously reduced and the isolation between the two input ports of different polarization is enhanced. An antenna prototype is fabricated and tested, exhibiting good performances, including an isolation level of higher than 30 dB between the two input ports and gains of more than 9.5 dBi. Besides, the proposed design is capable of achieving stable directional radiation patterns with cross-polarization levels lower than −22 dB and back radiation levels lower than −24 dB. [ABSTRACT FROM AUTHOR]

A simple internal antenna design for wireless wide-area network/long-term evolution (LTE) operations is investigated, and it can be incorporated into a mobile phone that has an unbroken metal rim of height 5 mm. The proposed antenna is mainly composed of two parallel slots (dual loop) embedded on the system ground, and by feeding them with an L-shaped coupled feedline with matching networks, good excitation of multiple loop resonant modes can be obtained, which is capable of covering the GSM850/900 (824–960 MHz), DCS/PCS/UMTS2100, and LTE2300/2500 (1710–2690 MHz) operating bands. In addition, the feasibility of realizing decoupled multiantennas ( $2 \times 2$ multi-in multi-out antenna system) is also demonstrated, and its performances are acceptable for smartphone applications. [ABSTRACT FROM PUBLISHER]

A near-field communication (NFC) dual-loop antenna with a miniaturized size of 15\,\, \text mm \times 25 \,\,\text mm is initially proposed for full metal-cover smartphone applications. To achieve a small clearance zone on the metal cover, a small rectangular slot of size 8 \,\,\text mm \times 16\,\, \text mm is loaded into the metal cover. To allow good inductive coupling, the NFC antenna is only 0.37 mm beneath the center of the rectangular slot. Because of that, the direction of the eddy current induced on the metal cover will be the same as the dual-loop NFC antenna. It is noteworthy that the prototype NFC antenna integrated with a single rectangular slot loaded full metal cover was certified by the Europay, MasterCard, and Visa test. [ABSTRACT FROM PUBLISHER]

The design of a novel practical 28 GHz beam steering phased array antenna for future fifth generation mobile device applications is presented in this communication. The proposed array antenna has 16 cavity-backed slot antenna elements that are implemented via the metallic back casing of the mobile device, in which two eight-element phased arrays are built on the left- and right-side edges of the mobile device. Each eight-element phased array can yield beam steering at broadside and gain of >15 dBi can be achieved at boresight. The measured 10 dB return loss bandwidth of the proposed cavity-backed slot antenna element was approximately 27.5–30 GHz. In addition, the impacts of user’s hand effects are also investigated. [ABSTRACT FROM AUTHOR]