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This article presents a wideband orthogonal-mode dual-antenna pair with a shared radiator for fifth-generation (5G) multiple-input multiple-output (MIMO) metal-rimmed smartphones. The wideband decoupling property of the dual-antenna pair is realized by the combination of the orthogonal monopole/dipole modes in the lower band and the orthogonal slot/open-slot modes in the higher band. With the orthogonal-mode design scheme, the dual-antenna pair shows a wide impedance bandwidth of 3.3–5.0 GHz and a high isolation of more than 21.0 dB across the entire band without using any external decoupling structures. By arranging four such dual-antenna pairs at two side edges of the smartphone, an $8 \times 8$ MIMO system is fulfilled. Both the simulation and measurement results show that the proposed $8 \times 8$ MIMO system could offer an isolation of better than 12.0 dB and an envelope correlation coefficient of lower than 0.11 between all ports. The measured average antenna efficiencies are 74.7% and 57.8% for the two antenna elements of the dual-antenna pair. We portend that the proposed design scheme, with merits of shared radiator, wide bandwidth, and metal rim compatibility, has the potential for the application of future 5G smartphones. [ABSTRACT FROM AUTHOR]

This paper presents a planar omnidirectional multiple-input multiple-output (MIMO) antenna with pattern phase diversity. The profiles of conventional dual-polarized omnidirectional MIMO antennas are too high to be planar integrated due to the limited bandwidth of vertical-polarized element. Therefore, a dual-channel horizontal-polarized MIMO antenna is proposed for the planar integration of omnidirectional MIMO antenna. The antenna is formed with four-element folded dipole array, and a compact feed network with two sets of 90° progressive phases is employed to feed the two channels with shared elements, thus the antenna can be integrated into a sheet of substrate with an ultralow profile of 0.8 mm. Although the polarization and radiation pattern (amplitude) of the two colocated channels are the same with each other, a high isolation is still achieved as a result of the orthogonal pattern phase. A prototype was fabricated to validate the performance. The measured highest isolation between two channels is 31.7 dB, and −10 dB isolated bandwidth is 2.29–2.57 GHz (11.7%) with S11 < −14 dB and envelope correlation coefficient less than 0.05, which shows a good diversity performance. Therefore, the proposed dual-channel antenna gives a feasible solution for the planar integration of the omnidirectional MIMO system. [ABSTRACT FROM AUTHOR]

In this communication, a dual-polarized 36-element ($3 \times 6 \times 2$) magnetic current array antenna is designed without using complex feeding network. Instead, a pair of differential feeds is adopted to excite the overall dual-polarized array within a low profile. Such a simple feeding strategy is achieved by using the TM90 mode of a microstrip antenna, which is loaded by $3 \times 4$ identical half-wavelength slots for each polarization. In this configuration, an in-phase $3 \times 6$ element single-polarized magnetic current array is achieved for high gain, but with narrow bandwidth due to the high-order mode. By trivially 90° rotating and combining, the proposed dual-polarized, high-gain, and low-profile magnetic current array is designed, constructed, and measured. Within a total size of $2.92\lambda _{0}\times 2.92\lambda _{0}\times 0.085\lambda _{0}(\lambda _{0}$ is the free-space wavelength at the center frequency), the measured maximum gain is 15.5 dBi, also with the merits of low profile, low sidelobes, simple feeding, and high port isolation, exhibiting promising usage in MIMO and diversity applications. [ABSTRACT FROM AUTHOR]

This paper presents a novel high-gain endfire slot antenna array fed by air-substrate microstrip line. It has a simple and compact structure consisting of a copper strip and two copper sheets. Designed based on the slot antenna array, the antenna could be embedded into a large metallic platform. The surface wave above the antenna radiates the energy to free space. Fed by the air-substrate microstrip line, the antenna works on the TEM mode. Therefore, the antenna obtains a suitable phase constant to realize stable endfire radiation pattern and could be designed by a long structure to realize high endfire gain. Because all of the antennas are designed by metal, it has the characteristics of high strength, easy fabrication, and low cost. With the radiating aperture of 3.5 wavelength, the antenna achieves a measured endfire gain of 11.81 dBi. The measured 1 and 3 dB gain bandwidths reach 4.5% and 8.4%, respectively. Good matching and stable endfire radiation pattern are obtained over the entire operating band from 3.75 to 4.15 GHz. [ABSTRACT FROM AUTHOR]

This communication presents a novel single-fed compact circularly polarized (CP) dual-layer planar inverted-F antenna (PIFA). The proposed antenna is composed of two stacked orthogonal-orientated PIFAs which can be fabricated by elaborately folding one piece of metal plate. The two PIFAs can be excited synchronously with equally allocated power by a single probe, thus a pair of orthogonal polarizations is created. Moreover, the resonant lengths of the upper and lower PIFAs are slightly different from each other to acquire 90° phase shift between the two orthogonal polarizations. Consequently, a right-hand CP radiation is achieved, and the boresight realized gain is 3.8 dBic at the center frequency. The proposed dual-layer PIFA with two quarter-wavelength resonators provides a novel solution for the compactness of CP antennas. To validate the performance of the antenna, a prototype was fabricated and measured. The measured −10 dB impedance bandwidth and 3 dB axial ratio bandwidth are 7.4% and 1.1%, respectively, with a compact antenna volume of $0.26\times 0.22\times 0.05\,\,\lambda _{0}^{3}$. The proposed antenna is a good candidate for the 433 MHz CP active radio-frequency identification reader, and it has the merits of compact size, lightweight, high efficiency, and low cost. [ABSTRACT FROM AUTHOR]

In this communication, we propose a new type of compact and wideband coplanar waveguide (CPW)-fed microstrip antenna. Very different from traditional microstrip antennas, the proposed design has the quasi-periodic radiating aperture fed through the slot-to-CPW transition. By optimizing the geometry of the quasi-periodic aperture and the slot-to-CPW transition, the fundamental TM10 mode and antiphase TM20 mode can be efficiently excited, coupled, and matched over a broad bandwidth. We have fabricated and characterized the proposed antenna, and found a good agreement between measurement and simulation results. Our experimental results show that despite the antenna has a thickness of only $0.052\lambda _{0}$ ($\lambda _{0}$ is the free-space wavelength at the center frequency), it exhibits a −10 dB impedance bandwidth of 36.5% (3.96–5.73 GHz), a 3 dB gain bandwidth of 35.4% (4–5.72 GHz), and a maximum available gain of 10.45 dBi. Our findings may offer a feasible solution to realize wideband microstrip antennas using a single-layer substrate, with unique merits, such as low profile, low cost, and ease of fabrication. [ABSTRACT FROM AUTHOR]

This communication presents a microstrip-fed surface-wave antenna for endfire radiation. The antenna has the advantages of high endfire gain, wide endfire gain bandwidth, and stable endfire radiation pattern. It consists of a microstrip line with air media and a dielectric cuboid. The half-mode dielectric waveguide, which is made up by the dielectric cuboid and the air substrate introduced by the microstrip line, is the radiating structure of the antenna. Fed by a microstrip line, the half-mode dielectric waveguide couples the energy continuously with a moderate phase constant, which is helpful for the antenna to realize a high endfire gain and a stable endfire radiation pattern. With a low dielectric constant, the half-mode dielectric waveguide has a stable radiation performance within a wide bandwidth. With a length of 5.76 wavelength, the antenna achieves a maximum endfire gain of 13.3 dBi at 4.75 GHz. The 1 and 3 dB gain bandwidths of the antenna is 18.1% and 37.8%, respectively. Good matching is obtained from 3 to 6.5 GHz. [ABSTRACT FROM AUTHOR]

A new antenna structure is proposed to show that a single-layer magnetic current array based on the microstrip line structure can achieve a relatively uniform and large in-phase radiating aperture together with high realized aperture usage rate (RAUR). By alternatively and periodically loading the microstrip line with blocking stubs, the equivalent magnetic currents along one direction are suppressed while the currents along the other direction are left, forming a relatively uniform and in-phase 1-D magnetic current array. The electromagnetic wave is radiated into space while traveling forward along the line. By in-parallel concatenating a series of the 1-D arrays with adjacent arrays presenting mirror relations, a large in-phase radiating aperture is built with a relatively high RAUR performance. Moreover, the shorting walls at the interconnecting planes of the neighboring 1-Darrays can be removed attributing to the antenna arrangement style and the required feed network. Eight rows of the 24-element 1-D magnetic current array fed using a substrate integrated waveguide-based eight-way power divider fabricated using a single substrate board is simulated and built to demonstrate the design strategy. The prototype shows a measured bandwidth of 4.37% and a peak gain of 25.1 dBi at 20 GHz. The RAUR is 8.66/ \lambda 0^{2} , which is higher than most of the single-layer high-gain antennas. [ABSTRACT FROM PUBLISHER]

In this communication, an all-metal standing wave antenna array is proposed based on the microstrip transmission line. By alternatively blocking the microstrip line every half wavelength, the symmetrical equivalent magnetic currents are broken for effectively radiating. By properly tuning the blocking positions along the microstrip line, a broadside pattern is achieved with high gain. The proposed antenna is scalable along one direction to a certain level to acquire the directivity as high as about 15 dBi. More importantly, the proposed antenna array has the potential to be built only by metal without any dielectrics. The all-metal structure has the merits of being low-cost, light weight, easily fabricated, and having no dielectric losses. Based on this idea, a five-segment linear array with a center feed is designed and tested. The measured bandwidth is from 7.83 to 8.81 GHz (980 MHz, 11.78%), and the measured gain is ranging from 9.1 to 12.47 dBi. [ABSTRACT FROM AUTHOR]

A dual circularly polarized waveguide antenna with bidirectional radiations of the same sense is proposed in this communication. Bidirectional circular polarization (Bi-CP) of the same sense was obtained by two identical rectangular metal slices installed on one lateral side of the waveguide with an intersection angle of 45^\circ. These two metal slices were horizontally perpendicular to each other and vertically spaced by a quarter guided wavelength. A rat-race coupler was employed to excite the two metal slices with the same amplitude, but with a 0^\circ or 180^\circ phase difference depending on the selection of two inputs. One sense of Bi-CP was realized when the two metal slices were fed in phase and the opposite sense of Bi-CP could be obtained when they were fed out of phase. A prototype for 2.4-GHz WLAN application was tested to verify our design. The measured common bandwidth for 10-dB return loss and 3-dB axial ratio at the two feed ports was 230 MHz (9.6%, 2.29–2.52 GHz) and 210 MHz (8.6%, 2.35–2.56 GHz), respectively. The measured isolation between the two feed ports was better than 30 dB over the whole operating band. [ABSTRACT FROM AUTHOR]

In this communication, a novel approach to expand the bandwidth for the ultra-low profile wearable shorted patch is proposed and fabricated. It introduces dual-resonance to acquire 5.2% bandwidth within 0.358\lambda \times 0.358\lambda \times 0.011\lambda dimension at 430 MHz without increasing the structure complexity. By using EVA (ethylene-vinyl acetate) foam and copper gauze as the material, this dual-resonant shorted patch is light, flexible, and rigid enough for wearable application. SAR (special absorption rate) and performance after bending are simulated and analyzed to validate its reliability in wearable condition. The measurement result verifies the design concept, which can provide consistent radiation character, along with acceptable gain and efficiency in the whole working band. [ABSTRACT FROM PUBLISHER]

This communication presents a new 4-port feeding structure with sequential phase (SP) of 0^\circ, 90^\circ, 180^\circ and 270^\circ using a circularly polarized (CP) shorted loop. A 2\,\times\,2 single-fed circularly polarized corner-truncated patch array is connected to the loop's four shorting strips, which serve as 4 feeding ports with stable phase difference. By using the proposed SP feed, the axial ratio (AR) bandwidth of the array is increased to more than 7%, wider than the previous design. A prototype of the proposed antenna is built to validate the design experimentally, and a global bandwidth of 4.86–5.12 GHz is achieved (S11 <-10 dB, AR < 3 dB, and gain variation within 3 dB). [ABSTRACT FROM PUBLISHER]

A substrate integrated waveguide (SIW)-fed circularly polarized (CP) antenna array with a broad bandwidth of axial ratio (AR) is presented for 60-GHz wireless personal area networks (WPAN) applications. The widened AR bandwidth of an antenna element is achieved by positioning a slot-coupled rotated strip above a slot cut onto the broadwall of an SIW. A 4\, \times \,4 antenna array is designed and fabricated using low temperature cofired ceramic (LTCC) technology. A metal-topped via fence is introduced around the strip to reduce the mutual coupling between the elements of the array. The measured results show that the AR bandwidth is more than 7 GHz. A stable boresight gain is greater than 12.5 dBic across the desired bandwidth of 57–64 GHz. [ABSTRACT FROM PUBLISHER]

A folded loop-inverted F reconfigurable antenna for mobile phone applications is designed and the obtained results are discussed in this communication. It is shown that loop antenna mode and an inverted F antenna (IFA) mode are controlled by only one p-i-n diodes with simple bias circuit. The impedance can be matched by adopting a matching bridge for both the loop and IFA modes. In a compact volume of 60\,\times\,5\,\times\,5 mm^3, the proposed antenna operates in hepta-band, including GSM850, GSM900, GPS, DCS, PCS, UMTS and WLAN, with the return loss lower than 6 dB. A prototype of the proposed antenna is fabricated, measured, and obtained results including return loss, efficiency and gain, are presented. [ABSTRACT FROM PUBLISHER]