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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]

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]

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]

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]

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]

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 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 $6 \times 6$ 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]

ABSTRACT A microstrip-fed conventional annular ring slot (ARS) antenna with linear polarization (LP) is initially studied. To generate two orthogonal degenerate modes for circular polarization (CP) radiations, two identical meandering perturbation slots (MPS) are symmetrically loaded into the ARS. By further incorporating a PIN diode switch across each MPS, the proposed antenna can switch between left-hand CP (LHCP), right-hand CP (RHCP), and LP. All three polarizations have shown good impedance bandwidth and broad CP bandwidth that can satisfy the wireless local area network (WLAN) 2.4-GHz operating band (2400-2480 MHz). Furthermore, desirable gains of 1.8-2.0 dBi and 2.40-2.84 dBic are also exhibited at LP and LHCP/RHCP, respectively. © 2015 Wiley Periodicals, Inc. Int J RF and Microwave CAE 26:110-120, 2016. [ABSTRACT FROM AUTHOR]

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]

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]

A compact size (15 × 40 mm2) microstrip-fed printed planar inverted-F antenna (PIFA) for mobile applications operating in the GSM/DCS/PCS/UMTS/WLAN and WiMAX bands is proposed. The main structure of this antenna is simply a double-folded PIFA with two wide open-ended radiating sections. By tuning the dimensions of the shorter open-ended section, optimum impedance matching can be achieved, while additional slits loaded to the longer open-end section are for the inclusion of universal mobile telecommunications system band. To allow shifting of the higher frequencies modes so that a wide impedance bandwidth from 5 to 6 GHz can be achieved, the technique of adjusting the position of the shorting post horizontally along the ground plane is also introduced. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53:2952-2960, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26429 [ABSTRACT FROM AUTHOR]

A novel microstrip-fed polygon slot antenna with dual-band operation for WLAN (Wireless Local Area Network) applications in the 2.4/5.2/5.8 GHz bands is proposed. The polygon slot is formed by embedding two right-angle triangular ground patches into both upper-corners of the rectangular slot. To allow the excitation of three resonant modes located exactly around 2.4, 5.2, and 5.8 GHz bands, besides tuning the length of the hypotenuse of the triangular ground patches, an L-shaped slit is also loaded into the rectangular radiating element. The design of this proposed antenna via simulation is illustrated in detail, and typical experiments were performed on the fabricated prototype. From the experimental results, the lower band measured along VSWR 2:1 operates from 2.36 to 2.63 GHz, while a broad upper band from 4.98 to 6.8 GHz is also observed. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53:1394-1398, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26018 [ABSTRACT FROM AUTHOR]

A compact size planar microstrip-fed monopole antenna designed for mobile handset applications is proposed. To operate at global system for mobile communication (GSM)/global positioning system/digital communication system/personal communication system/universal mobile telecommunications system and 2.4-GHz wireless local-area network bands, a hybrid technique of joining the horizontal section of a T-monopole to an open-loop back coupling strip and loading a pair of monopole slot into the ground plane is used. Two operating bands are observed (along 3:1 VSWR) with the lower band covering only the GSM application, while the wide upper operating band covers the remaining applications. The effects on the antenna performances by tuning the various vital parameters have also been studied. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53:910-915, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.25889 [ABSTRACT FROM AUTHOR]

A novel coplanar equilateral triangular-ring slot antenna with dual frequency operation is proposed for WLAN (Wireless Local Area Network) system in the 2.4/5.2/5.8 GHz operating bands.Impedance matching for both lower and upper operating bands at 2.4 and 5.8 GHz, respectively, are achieved by capacitively loading the inner triangular patch. To excite the 5.2-GHz band, two T-shaped slits are inserted into the triangular patch. The design flow of this antenna is clearly illustrated, and a prototype was constructed and experimentally investigated. Good radiation patterns and stable gain variation are measured for all operating bands. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52:2775-2780, 2010; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.25601 [ABSTRACT FROM AUTHOR]

The characteristics of circular-polarization (CP) square-ring microstrip antennas loaded with superstrate are studied in this paper. Firstly, several CP antenna prototypes with various substrate thicknesses and inner-slot sizes are designed, and they are excited by a coupling-strip feed in order to overcome the high-impedance problem of the square-ring microstrip antenna. Then, superstrates with different thicknesses and permittivities are attached to the antenna prototypes in order to evaluate their effects on the CP performances. The experimental results show that the effects are more obvious for the square-ring microstrip antenna with a larger inner-slot size. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 47: 567–570, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21231 [ABSTRACT FROM AUTHOR]