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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 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 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]

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]

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]

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]

A single open-slot antenna for long term evolution (LTE)/ wireless wide area network (WWAN) operation is proposed for smartphone applications. To achieve dual-band operation, the narrow open-slot is fed by a simple 50- $\Omega$ vertical feedline with two horizontally protruded feeding structures. To further attain good impedance matching for these two operating bands, an L-shaped metallic plate is used. From the measured results, good antenna efficiencies of more than 40% are demonstrated across the LTE/WWAN operation in the 698–960 MHz and 1710–2690 MHz bands. [ABSTRACT FROM PUBLISHER]

A wideband antenna with ±45° dual polarization is proposed. The antenna is mainly comprised of four printed trapezoidal metal walls standing on a ground plane that forms a 3-D open square aperture cavity structure with tapered cut on the four wall edges. The metal walls are fed by two orthogonally positioned (±45°) feeding networks, forming two pairs of dipole arms. Because of the excited magnetic-electric resonances, wide bandwidth can be achieved. The proposed antenna is fabricated, and the measured results show that it has an impedance bandwidth of 56% (1.62–2.87 GHz) for VSWR < 1.5. In addition, isolation of larger than 30 dB is also exhibited across the bandwidth between the two feeding ports. Because the proposed antenna has a hollow inside structure, it is a good candidate for multiband sharing aperture antenna element. Furthermore, it has a simplified fabrication process and is suitable for outdoor base station antennas that require VSWR < 1.5. [ABSTRACT FROM PUBLISHER]

This paper proposes a waveguide-stripline series–corporate hybrid feed technique to ease the feed-network design for dual-polarized antenna arrays. The hybrid feed network consists of a stripline series feed network and a waveguide-stripline corporate feed network, incorporating both of their advantages in one application. Furthermore, the design can efficiently simplify the manufacturing and packaging process without any bonding postprocess. The proposed technique is realized on an $8 \times 8$ dual-polarized antenna array, and the expected performances are verified by measurement. Experimental results show that the antenna array can operate in a wide bandwidth of 13.2% with more than 40 dB isolation for dual polarization. Cross polarizations at the center frequency of 15.2 GHz are below −27 dB, and the achievable aperture efficiency is 80% for both the polarizations. This hybrid feed approach can be considered as a promising solution for efficient feed-network applications. [ABSTRACT FROM PUBLISHER]

A $6 \times 6$ wideband antenna array with ±45° dual polarizations is proposed. To achieve good radiation efficiency, cavity antenna is used in this work as the basic element. Feeding probes and strip line feeding networks are printed on general PCB substrate. The feeding circuits for exciting different polarizations are stacked and multilayer substrate step structure is used. Here, strip line to downward SMA connector transitions is also designed, which aids in integrating the proposed array with T/R modules located below and extending it to larger phased array. The antenna array is fabricated and measured. Simulated and measured impedance and radiation performances are also given and compared. The proposed antenna arrays show wide bandwidth of 30% from 10.9 to 14.8 GHz, and isolation of higher than 33 dB is also exhibited across the bandwidth. Furthermore, symmetrical patterns and cross-polarizations of below −25 dB are also demonstrated. [ABSTRACT FROM PUBLISHER]

A microstrip-fed reconfigurable eccentric annular ring slot (EARS) antenna with switchable polarization is proposed. To generate orthogonal circular polarization (CP) radiations, two identical perturbation slots (PSs) are loaded below the eccentric ring-shaped slot. By incorporating a PIN diode switch across each PS, the proposed antenna can switch between left-hand CP (LHCP), right-hand CP (RHCP), and linear polarization (LP). All three polarizations have shown good impedance bandwidth and broad CP bandwidth that can cover the WLAN 2.4 GHz operating band (2400–2480 MHz). Furthermore, desirable gains of 2.49–2.82 dBi and 2.94–3.24 dBic are also exhibited at LP and LHCP/RHCP, respectively. [ABSTRACT FROM PUBLISHER]

A square-shaped microstrip RFID tag antenna designed for 915 MHz band is proposed. The antenna is capacitively excited by a dual-offset coupling feed network with one of the feed lines a quarter-wavelength longer than the other. By selecting appropriate dimensions for the coupled lines and feed-lines, along with desirable coupling distance between the coupled line and square patch, the input impedance of the proposed tag antenna can be easily controlled, which results in excellent impedance matching. Moreover, by incorporating the dual-offset feed technique with the method of embedding a cross slot of unequal arm lengths into the square patch, the bandwidth of the circularly polarized (CP) operation can be enhanced. The measured 6-dB return-loss bandwidth of the tag antenna is 25 MHz (902–927 MHz), and its corresponding 3-dB axial-ratio (AR) bandwidth is 20 MHz (903–923 MHz). Further experimental results show that the proposed tag antenna can provide slightly better reading range and gain when mounted on a large metallic surface. [ABSTRACT FROM PUBLISHER]

The design of a simple UHF (ultrahigh frequency) RFID (radio frequency identification) reader antenna that operates within the 900 MHz band (902–928 MHz) is studied. To generate circular polarization (CP) radiation, a novel method of loading a semicircular slot into the main circular radiating patch is proposed. To allow optimum impedance matching with enhanced CP bandwidth, the L-shaped probe-feed technique is employed in this design. From the experimental results, besides achieving a gain level of more than 7 dBic, the proposed antenna can also yield an impedance bandwidth (10-dB return loss) from 880 to 1100 MHz, while good CP performances between 901 to 930 MHz are exhibited. To further validate the experimental results, parametric studies are also carried out via simulation. [ABSTRACT FROM PUBLISHER]