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A simple, high gain, and dual-polarized patch antenna array for Wi-Fi 6/6E application is proposed in this communication. Different from the conventional feeding method, the patches are driven by coupling dipoles that are printed on the same board. The dipoles are specially designed to be T-shaped to adjust the impedance matching. Broadband covering both 5 and 6 GHz bands of Wi-Fi 6/6E is achieved. The feeding circuit is easily integrated on the board with only parallel dual line utilized. A prototype is fabricated and tested to validate the concept. The measured and simulated results are in good agreement. The measured bandwidth with $S_{11} < -10$ dB for two ports are 5.12–7.50 and 5.15–7.50 GHz with the isolation higher than 30 dB. Moreover, the measured gains are higher than 9.76 and 9.61 dBi for two ports over the operating band with a peak value of 12.05 dBi. The proposed antenna array shows great potential in the application of Wi-Fi mesh. [ABSTRACT FROM AUTHOR]

A broadband and omnidirectional coverage dual-antenna pair with horizontally polarized (HP) radiation for Wi-Fi 6/6E application is presented in this article. The dual-antenna pair is composed of two open cavity antennas (OCA) with the apertures partially sealed. By sealing the aperture partially, the dimension of the proposed half-OCA (HOCA) is reduced dramatically without changing the matching bandwidth and the radiation performance. Compared with other OCAs with the omnidirectional radiation, the proposed dual-antenna pair realizes omnidirectional coverage in azimuth plane by the back-to-back combination of two unidirectional OCAs, which also makes the antenna have multiple-input multiple-output (MIMO) performance. Besides, a broadband covering both 5 and 6 GHz bands of Wi-Fi 6/6E is also achieved. A prototype was fabricated and tested to validate the concept. In well agreement with the simulated results, the measured bandwidth with $S_{11} < -10$ dB for two ports are 5.03–7.35 GHz and 5.09–7.53 GHz, respectively, with the isolation higher than 22.67 dB. Besides, the measured gain > 5 dBi and ECC < 0.05 are achieved over the operating band. The proposed antenna shows great potential in the Wi-Fi 6/6E application. [ABSTRACT FROM AUTHOR]

This article describes a compact dual-polarized endfire antenna array for fifth-generation (5G) millimeter-Wave (mm-Wave) mobile application. The dual-polarized endfire antenna element is constructed by a compact open-ended cavity with cavity mode for vertical polarization (VP) radiation and open-slot mode for horizontal polarization (HP) radiation. With the integrated design of VP and HP elements, the proposed antenna shows a much more compact size compared to existing schemes. To enhance the bandwidth of low-profile VP radiation, a slot is etched on the cavity to create a new mode for dual-resonance response, realizing a wide bandwidth of 24.5–29.5 GHz for both polarizations. In addition, radiation pattern modification techniques are employed to achieve good endfire beams with a high front-to-back ratio for both polarizations, thus enabling a high peak gain of 10.3 and 11.3 dBi for VP and HP, respectively. A wide beam scanning range of ±50° with realized gain above 7 dBi is realized at 27 GHz for both polarizations. In virtue of compact size, wide bandwidth, high gain, and good spatial coverage, the proposed design strategy is promising for future 5G mm-Wave mobile phones. [ABSTRACT FROM AUTHOR]

A high-gain low-profile leaky-wave antenna (LWA) for vertically-polarized (VP) fixed-beam endfire radiation is proposed in this article. The LWA is composed of two back-to-back half-mode waveguides with grooves etched at the margins of both radiation edges. By etching grooves, the phase velocity of the traveling wave can be tailored to slower than the wave velocity in free space for fitting the Hansen–Woodyard condition. Compared with periodic LWAs, the proposed antenna continuously radiates at two symmetric apertures, contributing to a high endfire gain. A prototype is fabricated and tested to validate the concept. The measured and simulated results are in good agreement. A simulated gain of 14.29 dBi and a measured gain of 13.37 dBi are achieved within an antenna length of $3.05\lambda _{0}$. Moreover, a measured overlapping bandwidth of 2.74–3.17 GHz (14.3%) is realized with $S_{11} < - 10$ dB and gain variation less than 3 dB. To the best of the authors’ knowledge, the proposed VP endfire LWA realizes the highest aperture efficiency and shows great advantages in high gain, low profile, and wide bandwidth. [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]

This article presents a pattern-reconfigurable saber-like antenna with low wind drag for the onboard communication application, under the requirement of upper hemispherical coverage. The compact antenna mainly consists of a segmented loop and a $\Pi $ -shaped polygon, which are closely integrated for compact size. By controlling the OFF/ON states of a p-i-n diode embedded in the segmented loop, the proposed antenna can be operated at dipole/monopole modes. An upper hemispherical coverage area can be achieved since broadside and omnidirectional patterns are obtained at dipole and monopole modes, respectively. To validate the design strategy, a prototype was fabricated and tested. A good agreement between the simulated and measured results is achieved. The measured −8 dB reflection coefficient common bandwidth of two modes is from 2.16 to 2.63 GHz with the relative bandwidth of 19.6% while keeping a smaller size of $30.5\times 32.5\times 0.6$ mm3 ($0.24\,\,\lambda _{0} \times 0.26 \lambda _{0}\times 0.005 \lambda _{0}$ , $\lambda _{0}$ is the free-space wavelength at the center frequency). We portend that the proposed design scheme, with merits of low wind drag, metal ground compatibility, and upper hemispherical coverage, has the potential for airborne application. [ABSTRACT FROM AUTHOR]

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 communication presents a dual-mode dipole antenna for impedance bandwidth improvement. In our approach, an electrically small loop (ESL) resonator is properly loaded to compress the operating frequencies of first- and third-order modes. With the existence of ESL, the third-order mode shifts to its first-order mode to obtain a wide bandwidth with stable polarization and radiation patterns, due to the fact that ESL is equivalent to an orthogonal magnetic dipole at the third-order mode. To validate the design strategy, a prototype was fabricated and tested. Omnidirectional radiation pattern in H-plane is achieved over the entire operating band from 2.94 to 3.89 GHz while keeping a smaller size of $0.45\lambda _{0}\times 0.17\lambda _{0} (\lambda _{0}$ is the wavelength in free space at the center frequency). Good agreement has been obtained between measurement and simulation. [ABSTRACT FROM AUTHOR]

In this letter, a novel high-gain leaky-wave endfire antenna is proposed. By utilizing an air substrate parallel strip line, which is periodically disturbed by the radiating elements, such as the feedline, the phase constant of the antenna approaches the phase requirement of the Hansen–Woodyard (H–W) condition. By optimizing the size of the radiating element, which is dipole element, an approximately constant aperture distribution is obtained by the antenna. Thereby, with the characters similar to the H–W endfire antenna around the center frequency and moderate phase constant over the operating bandwidth, the antenna achieves a high gain, narrow beamwidth, and stable endfire radiation pattern. With the radiating aperture length of two wavelengths, the antenna generates the measured gain of 12.5 dBi at the center frequency of 5 GHz, operating bandwidth of 20.8%, and measured 1 dB gain bandwidth of 16.2%. Fabricated by metal, the antenna may be an attractive substitute for the long-distance communication applications, especially for the systems where cost and power capacity are important. [ABSTRACT FROM AUTHOR]

A broadband and high-gain endfire antenna array fed by an air-substrate parallel strip line is proposed in this communication. It has a simple and planar structure consisting of multiple dipole radiating elements and one parallel strip line. By utilizing the center-fed dipole working between the first and third resonances as the radiating element, the antenna array could obtain stable radiating capability over a broad bandwidth. Fed by an air-substrate parallel strip line working on the TEM mode, the antenna array achieves a moderate phase constant, which is helpful for realizing stable endfire radiation. The radiating element separation is optimized to eliminate the high-order spatial harmonics, ensuring single beam radiation. Fabricated by thin copper plates, the merits of the antenna array include lightweight, low cost, and easy fabrication. According to the measured results, the antenna array has a good match and a stable endfire radiation pattern over the operating band from 4 to 10.5 GHz with the measured gain varying from 10.1 to 13.5 dBi. [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, the novel compact tightly arranged pairs are employed to form a $4 \times 4$ multiple-input-multiple-output (MIMO) system and an $8 \times 8$ MIMO system operating at 3.4–3.6 GHz for fifth-generation (5G) mobile phones. Each tightly arranged pair is composed of a bent monopole and an edge-fed dipole with a compact size of $7 \times 12$ mm2. The orthogonal-mode method is presented to mitigate the mutual coupling of the tightly arranged pairs without any external decoupling structure. With the help of the orthogonal mode, isolation performances across the desired band of the $4 \times 4$ MIMO system and the $8 \times 8$ MIMO system are better than 20 and 17 dB, respectively, with the elements closely spaced. The measured efficiencies are 51.7%–84.5%/49%–72.9%, and the measured envelope correlation coefficients are less than 0.06/0.07 for the $4 \times 4/ 8 \times 8$ MIMO system. The proposed MIMO systems provide a promising solution to compact 5G MIMO mobile phone antennas with good isolation and diversity performance. [ABSTRACT FROM AUTHOR]

A new structure of horizontally polarized (HP) antenna array is presented for azimuthal omnidirectional coverage. The proposed antenna array is engineered by breaking the fringing field symmetry along the typical parallel strip-lines, which is implemented by loading field-block structures alternatively and periodically. In physics, the blocking structures constrain the fringing fields inside, producing a series of rectangular open cavities operating at the \rmTM1n0 ( $n = 0.5$ ) mode. Counterintuitively, these asymmetric open cavities are able to generate an omnidirectional radiation pattern in the $E$ plane with horizontal polarization, similar to the linear magnetic current array. In order to verify the design strategy, a five-unit center-fed cascaded cavity array is fabricated and tested. The measured bandwidth is 120 MHz (5.83–5.95 GHz) with reflection coefficient lower than −10 dB. The HP omnidirectional pattern at 5.9 GHz provides a gain variation of 1.94 dB ranging from 6.7–8.64 dBi. [ABSTRACT FROM PUBLISHER]

This communication proposes a compact single-feed dual-mode antenna for active radio-frequency identification (RFID) tag application. The proposed antenna consists of a slotted patch on an FR4 substrate, a feeding microstrip line, and a foam spacer with a volume of only 60\;\textmm \times 50.3\;\textmm \times 6\;\textmm ($0.48{{\lambda}_0} \times 0.40{{\lambda}_0} \times 0.048{{\lambda}_0}$, where ${{\lambda}_0}$ is the wavelength at the center frequency). It operates as a dipole in free space and as a patch when placed on a metallic surface. A prototype that can provide an impedance bandwidth of 390 MHz (2.28–2.67 GHz) in free space and 470 MHz (2.32–2.79 GHz) on a metallic surface is built and measured. The measured radiation patterns, peak gains, and radiation efficiencies in these two scenarios are provided. [ABSTRACT FROM PUBLISHER]

In this communication, we have proposed a compact planar antenna for isotropic radiation pattern in a wide operating band. The proposed antenna consists of four sequential rotated L-shaped monopoles that are fed by a compact uniform sequential-phase (SP) feeding network with equal amplitude and incremental 90^\circ phase delay. Based on the rotated field method, a full spatial coverage with gain deviation less than 6 dB is achieved in a wide operating band from 2.3 to 2.61 GHz, also with well-impedance matching. A prototype of the proposed antenna has been built and tested. The measured results, including the reflection coefficient, gain, and radiation patterns, are analyzed and compared with the simulated results. [ABSTRACT FROM PUBLISHER]

This paper presents the successful design and physical realization of a wideband MNG-TL dipole antenna. An artificial mu-negative transmission line (MNG-TL) structure is realized by employing periodically loaded parallel-plate lines. It is known that the current reversal, which occurs at frequencies much beyond the dipole natural frequency, disturbs the omnidirectional radiation pattern in the azimuth plane. The MNG-TL has a unique property to support a zero propagation constant (\beta =0) with non-zero group velocity at the zeroth-order resonance. Due to the unique property of an infinite wavelength, the current distribution of the dipole antenna can be improved. Furthermore, the MNG-TL dipole is also useful to achieve a wide impedance bandwidth. A prototype of the proposed MNG-TL dipole is fabricated and measured. It can provide a wide effective bandwidth of about 1.55 GHz (1.85–3.40 GHz) with VSWR 2:1 (S11< -10 dB) impedance matching and stable omnidirectional radiation patterns in the azimuth plane. [ABSTRACT FROM PUBLISHER]

A novel periodic leaky-wave antenna for broadside radiation with horizontally polarized omnidirectional pattern is proposed, designed and demonstrated experimentally. The objective is to achieve a horizontally polarized omnidirectional antenna array with highly directive beam. The proposed structure is based on combining the rotating electric field method and a leaky-wave antenna design. By properly designing a unit cell with a pair of crossed dipoles spaced at a distance approximately equal to \lambdag/4 at the center frequency, not only omnidirectional radiation pattern with horizontal polarization is obtained by crossed dipoles fed in phase quadrature, but also the open-stopband effect exhibited at broadside scan is significantly reduced. The analysis and design of this structure are performed on the basis of a simple equivalent network model. A finite structure formed by 16-unit cell (32-element) for broadside beam is developed at the 2.4 GHz band, which offers a horizontally polarized omnidirectional radiation pattern with enhanced gain of 9.9–10.6 dBi and measured radiation efficiency of 90% for the covering bands. [ABSTRACT FROM PUBLISHER]

An 18-port compact antenna cube is proposed in this paper. The cube, which has a volume of 0.76\,\times\,0.76\,\times\,0.76 \lambda0^{3}, provides 18 individual channels and is ideal for multiple-input multiple-output (MIMO) wireless communications. On each of the total six faces of the cube, a three-port tri-polarization antenna is installed. All antennas adopt a metal backing configuration, so the ground of all antennas forms a well shield Faraday cage, in which other functional circuits can be installed. Experimental measurements were carried out to evaluate the performance of the antenna cube in different MIMO scenarios. The results show that MIMO systems with the proposed compact antenna cube outperform those with dipole antennas which occupy the same number of RF channels but with much larger space. When a vertical 3-dipole array, a horizontal 3-dipole array and a dual polarization antenna are used in the user end (UE), respectively, the capacity of the global selected MIMO systems with antenna cube is about 2.7, 4.6, and 2.9 bits/s/Hz more than the full MIMO systems with a vertical 3-dipole array as the access point (AP) antennas. It is 1.9, 3.9, and 2.0 bits/s/Hz more than the full MIMO systems with a vertical 5-dipole array as AP antennas. The performance differences between the MIMO systems using global and simplified selection circuits are small. [ABSTRACT FROM PUBLISHER]

A conformal switchable antenna system mounted on a cylindrical surface is proposed, simulated, prototyped and measured. The antenna system is composed of several tri-polarization antennas operating at 2.4 GHz band. It is shown that this antenna system realizes a quasi-isotropic pattern without any nulls over a complete spherical surface. Specifically, it is shown that by using three tri-polarization antennas and switching among them, a complete spherical coverage could be achieved without any nulls and with a power gain larger than 2.5 dBi over more than 90 percent of a spherical surface surrounding the antenna system. Furthermore, it is shown that the performance of the antenna system does not deteriorate with the increase in the diameter of the mounting cylinder, thus facilitating the implementation of the proposed design in many applications including telemetry, satellites, and aircraft. Both simulation and experimental results of the radiation patterns are presented in this paper. [ABSTRACT FROM AUTHOR]

A dual-band dipole antenna for wireless local area network (WLAN) is designed and experimentally tested at both the 2.4 and 5 GHz (IEEE 802.11b/g and 802.11a) WLAN bands. The design procedure involves obtaining a full resonance frequency in the 2.4 GHz band and then using a matching network to achieve a secondary resonance at the 5 GHz band. It is shown that by correctly designing the dipole, the matching network can be simplified to only one series inductor. The design was experimentally verified by constructing a dipole on a FR4 board (12 mm *45 mm * 0.45 mm) and measuring its input impedance and the radiation characteristics at both bands. The measured VSWR 2:1 bandwidth in the 2.4 GHz band is 710 MHz, and the bandwidth in 5 GHz band is wider than 1 GHz. The VSWR 3:1 bandwidth is more than 3.6 GHz and it coven from 2.32 GHz to above 6 GHz. it is significant that the designed dual-band dipole maintained good radiation efficiency values at both bands. Specifically, and based on the measured radiation patterns, an efficiency value of 85% ∼ 87% is obtained at 2.4 GHz and a value in the range of 55 ∼ 64% is obtained in 5 GHz band. [ABSTRACT FROM AUTHOR]