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This letter presents a circularly polarized (CP) discrete lens with large operating bandwidth and optimized thickness. A wideband polarization-twisting unit cell, which enables the polarization agility of the lens at a pixel level, is developed using the magnetoelectric-dipole-based transmissive element. By comprehensively utilizing the rotation freedom of the probes at the transmitting and the receiving layers as well as incorporating additional dielectric-coating layer, an over-2-bit CP discrete lens is achieved, demonstrating a wide axial ratio (AR) bandwidth, an improved antenna gain, and a well-controlled lens thickness. A maximum gain of 21.5 dBic and an overlapped 3 dB gain and AR bandwidth of 47% are experimentally achieved with the designed 0.66-λ0-thick, 256-element discrete lens.

A millimeter-wave 4 × 4 magnetoelectric (ME) dipole antenna array using a packaged microstrip line feed network is proposed. This antenna array features a wide impedance bandwidth of more than 50% and small back radiation. Each ME dipole element is excited by an L -shaped probe and each L -shaped probe is connected to the packaged microstrip line through a small hole in the ground plane. The packaged microstrip line forms the whole corporate feed network for the antenna array. The entire antenna structure is realized by multiple printed circuit boards (PCBs), which is low in material cost and easy in fabrication. The results demonstrate that the proposed antenna array enables the impedance bandwidth of 51.5%, high gain up to 20.3 dBi, and stable broadside radiation pattern with small back radiation over the operating frequencies. The array is suitable for the 5G application.

A circularly polarized (CP) water patch antenna is proposed in this letter. Both the patch and the ground plane are composed of distilled water. The water patch is in square shape with two diagonal truncated corners for generating CP radiation pattern. A metallic L-shaped probe is employed as the feeding portion. The entire configuration had been accomplished by a 3-D printed plastic container. Measured results show that the proposed CP water patch antenna can achieve a wide impedance bandwidth of 29%, a 3 dB axial-ratio (AR) bandwidth of 8.0%, a left-hand circular polarization gain up to 3.05 dBic, and a maximum radiation efficiency of 48% over the operating band. This presented design aims to demonstrate the feasibility of using distilled water to form the CP patch antenna. Besides, some parametric studies have also been carried out to investigate the performance characteristics, which significantly provide the design guideline for a range of CP water patch antenna designs in the future.

A wideband and optically transparent water patch antenna with a broadside radiation pattern is presented. Both the patch and the ground plane are composed of distilled water, enclosed by the transparent plexiglass container. Air is utilized as the middle substrate so that highly optical transparency can be achieved with low-cost materials. A metallic L-shaped probe is employed in the air substrate to excite the water patch. The performance turns out that a wide impedance bandwidth of 34.9% (from 1.61 to 2.29 GHz with standing wave ratio (SWR) < 2), the maximum gain of 6.6 dBi and a radiation efficiency up to 75% can be achieved.

A wideband dual-polarized stacked patch antenna with optical transparency is proposed in this letter. The traditional metal plates are replaced by transparent conductive films made by printing metal meshes with sheet resistance of 0.5 Ω/sq to single side of polyethylene terephthalate. The planar conductive layers are separated by substrates made by transparent polymethyl methacrylate plates. The majority of the antenna area has a high optical transparency. A wide impedance bandwidth is realized by applying stacked round microstrip patches. The disk probes provide good impedance matching as well as a small occlusion area. Measurement results show the antenna exhibits an impedance bandwidth of 19% (2.4–2.9 GHz, ${{\bf VSWR}} ) for both ports. The radiation efficiency is around 75%. The optical transparency is nearly 70% throughout the visible spectrum for the majority of the antenna. The antenna has a stable unidirectional radiation pattern with low cross polarization $({ and low back-radiation level across the operating frequency band.

A dual linearly polarized endfire antenna, excited by an E-plane 180° 3 dB hybrid coupler, is reported for millimeter-wave applications. The radiator is constructed by two stacked open-ended substrate integrated waveguides (SIWs). A slope-shaped slot is employed to the common metallic layer of the two SIWs, operating as a polarizer. Experimentally, the proposed antenna achieves an impedance bandwidth (SWR < 2) from 32 to 40 GHz for both the vertical and horizontal polarizations. The port isolation keeps above 14.5 dB over almost the whole operating band. Besides, the proposed antenna is compact and obtains symmetrical radiation patterns, therefore being suitable for array designs.

In this letter, a simple wideband magnetoelectric (ME) dipole antenna with a defected ground structure (DGS) is proposed and investigated. The dimensions of the pair of the quarter-wavelength patch antennas and the half-wavelength electric dipole antennas are changed to extend the impedance bandwidth. A DGS is used for impedance matching, which is novel in the ME dipole antenna design. A prototype of the proposed antenna is designed, fabricated, and measured. On combining impedance bandwidth and radiation pattern, measured results show that the proposed ME dipole antenna achieves an operating bandwidth of 86.9% (1.38–3.5 GHz) for ${{\vert S}}_{11}\vert , and a stable gain of 7.2 ± 1.2 dBi is realized. A low cross-polarization level and low backlobe radiation level are found across the operating bandwidth.

A circular-polarization-reconfigurable complementary antenna with compact size is presented. The proposed antenna has a low-profile planar structure that exhibits an omnidirectional circularly polarized (CP) radiation pattern achieved by combining a printed electric dipole and a quarter-wave shorted microstrip patch. By manipulating the dc biasing voltages, the operation of the antenna can be switched between left-hand circular polarization and right-hand circular polarization. Moreover, by using the meandering line methodology, the lateral dimension of the printed electric dipole is reduced by 25% compared to the conventional design. A prototype of the proposed structure is designed and fabricated for potential use in multifunction application. Measured results are in good agreement with simulation. The CP radiation feature and polarization reconfigurability are also sustained by measurement.

A single-feed wideband polarization-reconfigurable magneto-electric dipole antenna is presented in this letter. A bent cross dipole with one p-i-n diode inserted into each of its four arms is utilized to excite the antenna. The proposed antenna can be reconfigured to provide a pair of orthogonal linear polarizations by controlling the ON/OFF states of four p-i-n diodes. A prototype of the proposed antenna is designed, fabricated, and measured. An overlapped impedance bandwidth (S 11

A three-element linear magneto-electric (ME) dipole array is proposed to realize beamwidth reconfiguration for base stations. The reconfiguration between narrow and wide beamwidth is realized by varying the phase of the excitation current of the middle element. A practical prototype was designed, fabricated, and measured. Measured results show that about 15% overlapped impedance bandwidth for ${\vert{{ S}_{11}}\vert , symmetrically unidirectional radiation patterns with low cross polarization and low back-radiation are achieved for the antenna array operated at different modes. The half-power beamwidth in the E-plane maintains a mean value of 72 $^\circ $ with 2 $^\circ $ in variation, while the beamwidth in the H-plane can be switched between the small value of 37 $^\circ $ and the large value of 136 $^\circ $ across the frequency band. The proposed antenna is a suitable candidate for base stations with enhanced traffic capacity.

A novel low-profile magneto-electric dipole antenna is proposed and investigated. The antenna utilizes an obtuse-triangular structure to work as a magnetic dipole, which reduces the antenna thickness to ${0.097 {\lambda}_0}$ (where ${{\lambda }_0}$ is the free-space wavelength at the center frequency). A prototype with ground plane size of around $1{{\lambda }_0} \times 1{{\lambda }_0}$ is fabricated and measured. Measurement result shows that the proposed design achieves an impedance bandwidth of 28.2% (1.67–2.22 GHz) for ${{\rm SWR} . A stable gain of $9.2 \pm 1.1\ \hbox{dBi}$ is realized. The antenna has a unidirectional radiation pattern with low cross polarization ( $ ) and low back-radiation level ( $ ) across the operating frequency band.

A single-feed circularly polarized (CP) patch antenna at L-band is designed and built using the recently developed U-slot loaded patch technique. With the presence of the U-slot, the antenna fabricated on a high-dielectric-constant (er = 10.02) substrate achieves a reasonable axial-ratio bandwidth. At the operating frequency of 1.575 GHz, the size of the patch is 0.13λo × 0.13λo, while the ground size is 0.315λo × 0.315λo and the thickness of the substrate is 0.05λo. The measured gain is 4.5 dBi, and axial-ratio bandwidth is 3.2%.

This letter presents a new circularly polarized patch antenna with loaded shorting elements to achieve symmetric broadside radiation and size reduction. The loaded elements are parasitic to the driven patch, but are shorted to the ground plane. Conventionally, shorting pins or walls are a common technique for reducing the size of the antenna. However, deterioration in broadside radiation with high cross-polar level occurs. The proposed shorting elements provide a solution for size reduction of the radiating patch while maintaining good broadside radiation pattern. Since the radiating patch is effectively shorted to the ground at the operating frequency, it is designated as a virtually shorted patch antenna (VSPA).

A novel dual-polarized magneto-electric dipole antenna excited by two -shaped strips is presented. The antenna achieves a common impedance bandwidth of 65.9% (SWR < 2) at both input ports. The antenna has excellent performance in isolation, which is more than 36 dB between the two input ports, and the gain of the antenna is about 9.5 dBi. The radiation pattern and bandwidth over the operating frequency band are very stable.

A newly developed patch antenna, designated as the folded feed L-slot folded patch antenna, is presented in this letter. It consists of an L-slot folded patch that is shorted to the ground plane by a metallic wall and is fed by a folded structure. The patch has profile of 0.24lambda and length of 0.4lambda, where lambda is the free-space wavelength at the center frequency of its operating bandwidth. This antenna has impedance bandwidth of 133.3% (0.72 to 3.60 GHz) for SWR les 2, which is the largest value that can be achieved by a shorted wall patch antenna in the literature. As the proposed antenna can achieve such wide impedance bandwidth, it is very suitable for the multiband wireless communication systems nowadays.

A unidirectional antenna with loaded dielectric substrate composed of two shorted-circuited rectangular patches and a printed Gamma-shaped probe feed operated at 2.5 GHz is presented. The antenna is fully filled with dielectric substrate isinr = 2.65. The height of the antenna is only 18 mm. A wide impedance bandwidth of 45.3% (SWR les 2) is achieved. The average gain is about 6.7 dBi. The antenna performance can be improved by introducing of a metallic wall. The backlobe is reduced from -11.1 to -20.1 dB at the lower frequency.

A 2 times 1 dual-polarized L-probe stacked patch antenna array is presented. It has employed a novel technique to achieve high isolation between the two input ports. The proposed antenna has a 14-dB return loss bandwidth of 19.8%, which is ranged from 0.808 to 0.986 GHz, for both ports. Also, it has an input port isolation of more than 30 dB and an average gain of 10.5 dBi over this bandwidth. Moreover, its radiation patterns in the two principal planes have cross-polarization level of less than -15 dB within the 3-dB beamwidths across the passband. Due to these features, this antenna array is highly suitable for the outdoor base station that is required to cover the operating bandwidths of both CDMA800 and GSM900 mobile communication systems.

A dual-polarized shorted bowtie antenna integrated with a cross dipole is presented. The electric cross dipole is added to generate a symmetric radiation pattern and to compensate the high back radiation due to the shorted patches. This novel dual-polarized antenna is designed for the existing DCS, PCS, and 3G mobile communication systems working between 1.71 and 2.17 GHz. Stable and symmetric radiation patterns at slanted plusmn45deg polarization have been obtained over the operating frequency bands. Measured isolation between the two input ports is over 28 dB. The gain of the proposed antenna is also stable with frequency. The average is about 6.6 dBi

A novel design of miniature embedded antenna for mobile handset based on hierarchical genetic algorithms (HGA) with method of moments (MoM) is presented in this letter. The proposed antenna consists of a patterned patch and ground with shorting pins, the number, and locations of which are optimized by GA, with a total volume within 18 $,times,$ 43 $,times,$8 $ mm^3$ . It can provide wide bandwidth to cover operating bands for modern mobile communications, including global system for mobile communication (GSM), digital communication system (DCS), personal communication system (PCS), and universal mobile telecommunication system (UMTS) bands. The details of the design are discussed and the simulation results are compared with experiments.

By combining a horizontal planar dipole and a vertically oriented folded shorted patch antenna, a new low-profile magneto-electric dipole antenna is presented. The antenna is simply excited by a coaxial feed that works as a balun. A prototype was fabricated and measured. Simulated and measured results agree well. An impedance bandwidth of 45.6% for ${\rm SWR}\leq 1.5$ from 1.86 to 2.96 GHz was achieved. Stable radiation pattern with low cross polarization, low back radiation, and an antenna gain of 8.1 $\pm$ 0.8 dBi was found over the operating frequencies. The height of the antenna is only $0.169\lambda$ (where $\lambda$ is the free-space wavelength at the center frequency). In addition, the antenna is dc grounded, which satisfies the requirement of many outdoor antennas.

A broad-band dual-polarization patch antenna fed by L-shaped probes at the patch corners is presented. A coupled line directional coupler mounted at the back of the ground plane is used to enhance the isolation between the L-probes to a large extent. Through using the coupler to feed the L-probes, the isolation between the input ports is 34 dB over the GSM900 operating bandwidth, which has enhanced by 14 dB. By using two plastic spacers of 0.1/spl lambda//sub o/ in height to support the patch in the air, an impedance bandwidth of 18% (for S/sub 11//spl les/-14 dB), and an average gain of 7 dBi can be obtained for both ports. The far field patterns are stable across the passband. This antenna can potentially be used as a GSM900 base station antenna.

A compact two-element antenna with both pattern and polarization diversities and high isolation for 2.4 GHz WLAN application is reported. The antenna is composed of a low-profile monopole and a pair of inverted-L antennas fed by 180deg out-of-phase excitations. A prototype is fabricated and the measured S-parameters and radiation patterns are presented. The measured isolation is better than 29 dB across the required bandwidth. The envelope correlation coefficient, the mean effective gains and the diversity gain are calculated to evaluate the diversity potential of the proposed antenna.

A wideband unidirectional antenna element composed of a magnetic dipole and an electric dipole is designed. Simulated and measured results are presented. The antenna achieves an impedance bandwidth of 91% (SWR < 2). Due to the complementary nature of the antenna and the incorporation of a modified grounded structure, the antenna has a relatively stable broadside radiation pattern with low cross-polarization and low back-lobe radiation over the operating band. The gain of antenna is about 9.3 dBi.

A novel, horizontally polarized, conical-beam antenna is proposed. The antenna is low in profile (H = 0.1867lambdao) and has about 38% impedance bandwidth (SWR < 2) and average antenna gain of 5 dBi. The radiation patterns are stable across the operating band. Good agreement between simulated and measured results is observed.

A new dual-band vertical patch antenna for broadside radiation is described. The antenna is fed by a proximity-coupled probe, which maintains the advantages of the original single-band vertical patch antenna, such as small size, wide bandwidth and simple structure. The achieved bandwidths are 7% and 26%, respectively, at the lower and upper frequency bands.

This paper presents the design and testing of a wide-band monopolar wire-patch antenna. The proposed antenna consists of a circular patch that is shorted to the ground plane by four copper wires and is fed by an L-probe at its center. For the patch height and patch radius of 0.092 and 0.179 free space wavelengths at 0.893 GHz, this antenna possesses a 14-dB return loss bandwidth of 27.1%, which is 9 times wider than that of similar type of antenna reported in the literature. Also, it has an average gain of 2.6 dBi and monopole-like radiation patterns over this bandwidth. As this antenna has wide impedance bandwidth and relatively small size, it is very suitable for the indoor mobile communication systems.

This letter presents a novel dual-band patch antenna developed by combining the folded-patch and U-slot techniques. The electrical length of the antenna is 0.147 wavelengths at the center frequency of the lower band. The lower band of the antenna ranges from 2.400 to 2.480 GHz, while the upper band covers both frequency bands from 5.150 to 5.350 GHz and 5.725 to 5.875 GHz with an average gain of 2 dBi. It is suitable for short-range wireless applications.

A novel technique that improves the performance of a conventional quarter-wave patch antenna is proposed. Two different geometries (U-slot and L-slit) are investigated experimentally. With the inclusion of a folded inner small patch, we achieve impedance bandwidths of 53% and 45% for the U-slot and L-slit, respectively, for a voltage standing wave ratio less than 2. Radiation patterns are stable across the whole operating frequency bands.

A low-profile equilateral-triangular dielectric resonator antenna (DRA) of very high permittivity is excited by a disk-loaded coaxial aperture. The loading disk is placed centrally on the aperture of a 50 /spl Omega/ subminiature version A (SMA) connector for impedance matching. The measured return loss, radiation patterns, and antenna gain of the proposed configuration are presented.

A wideband vertical patch antenna (VPA) is depicted, which is devised from fractal antenna technology. By using a dual-Koch loop structure, a wideband VPA with 42% bandwidth and 8 dBi gain at the center frequency is designed and tested. Symmetrical broadside patterns are obtained at the passband.

A small wide-band patch antenna with double shorting walls is presented. By employing two shorting walls and an additional aperture on the upper patch of a folded patch feed antenna, a 0.365/spl lambda//sub 0/ patch antenna with impedance bandwidth of more than 70% (VSWR/spl les/2) is achieved experimentally. Measured radiation patterns and gain across the frequency band are given.