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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]

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 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 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]

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 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]

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]

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]

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 microstrip-fed circular ring slot antenna (CRSA) with a fundamental mode at 2.45 GHz is initially studied. To suppress the additional harmonic modes excited by the ring slot, a single inverted U-shaped slot (or defected ground structure, DGS) is integrated into the CRSA. Through this, harmonic suppression over a wide bandwidth (approximately between 3 and 9 GHz) is achieved. This DGS can also be applied to other microstrip-fed ring slot antennas, such as square and triangular ring slot antennas. [ABSTRACT FROM PUBLISHER]

The design of a switchable microstrip-fed half annular ring slot antenna for multi-frequency operation is proposed. By incorporating three switches along the meandered tuning stub that is loaded on top of the half circular patch located within the circular slot, easy reconfigurability of four frequency bands over a frequency ratio of approximately 1.7:1 can be achieved. Furthermore, the proposed antenna structure does not require additional DC biasing circuit. Simulation and measurement results have demonstrated that the four frequency bands can exhibit good impedance matching, stable radiation patterns and desirable gains. [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]

This study designed a 2\,\times\,2 circular disc array antenna with omnidirectional radiation pattern and polarization diversity. Each disc element was located above a circular slot fed by an L-shaped strip, in which the switching between two orthogonal linear polarizations (LP) and circular polarization (CP) were realized by controlling two pin diodes. To allow conical beam for all polarization senses, a meticulously designed cross-shaped feeding network is proposed, and besides showing a sufficient 10 dB return loss bandwidth that covers the 2.4 GHz band of WLAN operation, good cross-polarization level (XPL) were measured when the array operated in all available polarization senses. [ABSTRACT FROM PUBLISHER]

Two novel array antennas (3 \times 2 and 3 \times 3) with broadband and high gain characteristics are proposed for the application of WiMAX base station. To maintain the same electric current intensity with identical phase for each array element, an asymmetrical feed-network which composed of microstrip T- junctions with 2:1 power ratio, quarter-wavelength impedance transformers, and 180^\circ phase shifters are devised, which in turn exhibits a desirable gain of more than 17 dBi at boreside direction for the proposed array antennas. Furthermore, by embedding a U-slot into all array elements, enhanced operating bandwidth measured along 14-dB return loss can be achieved, so that the WiMAX band operating between 3.3 and 3.8 GHz can be covered. [ABSTRACT FROM PUBLISHER]

A square patch passive RFID tag antenna designed for UHF band is presented in this article. To achieve compact size and circular polarization (CP) radiation, the square patch is embedded with a cross slot, while an L-shaped open-end microstrip line linked to a tag-chip and terminated by a shorting pin is capacitively coupled to the patch. By selecting an appropriate length for the microstrip line and its coupling distance with the radiating element, easy control on the input impedance of the proposed tag antenna which leads to excellent impedance matching is achieved. The measured 10-dB return-loss bandwidth of the tag antenna is 50 MHz (904–954 MHz), while its 3-dB axial-ratio bandwidth is 6 MHz (922–928 MHz). Further experiment shows that the tag antenna can provide better reading range when mounted on a metallic surface. [ABSTRACT FROM PUBLISHER]