Showing papers in "IEEE Transactions on Antennas and Propagation in 2015"

Ultrawideband and High-Efficiency Linear Polarization Converter Based on Double V-Shaped Metasurface

Abstract: In this paper, a double V-shaped metasurface that can efficiently convert linear polarizations of electromagnetic (EM) waves in wideband is proposed. Based on the electric and magnetic resonant features of a single V-shaped particle, four EM resonances are generated in a V-shaped pair, leading to significant bandwidth expansion of cross-polarized reflections. The simulation results show that the proposed metasurface is able to convert linearly polarized waves into cross-polarized waves in ultrawideband from 12.4 to 27.96 GHz, with an average polarization conversion ratio (PCR) of 90%. The experimental results are in good agreement with the numerical simulations. Compared to published designs, the proposed polarization converter has a simple geometry but an ultrawideband and hence can be used in many applications, such as reflector antennas, imaging systems, remote sensors, and radiometers. The method can also be extended to the terahertz band.

A High-Efficiency Broadband Rectenna for Ambient Wireless Energy Harvesting

Abstract: This paper presents a novel broadband rectenna for ambient wireless energy harvesting over the frequency band from 1.8 to 2.5 GHz. First of all, the characteristics of the ambient radio-frequency energy are studied. The results are then used to aid the design of a new rectenna. A novel two-branch impedance matching circuit is introduced to enhance the performance and efficiency of the rectenna at a relatively low ambient input power level. A novel broadband dual-polarized cross-dipole antenna is proposed which has embedded harmonic rejection property and can reject the second and third harmonics to further improve the rectenna efficiency. The measured power sensitivity of this design is down to $- {\bf 35}\;{\bf dBm}$ and the conversion efficiency reaches 55% when the input power to the rectifier is $- {\bf 10}\;{\bf dBm}$ . It is demonstrated that the output power from the proposed rectenna is higher than the other published designs with a similar antenna size under the same ambient condition. The proposed broadband rectenna could be used to power many low-power electronic devices and sensors and found a range of potential applications.

Checkerboard EBG Surfaces for Wideband Radar Cross Section Reduction

Abstract: Electromagnetic band-gap (EBG) structures have noteworthy electromagnetic characteristics that include their reflection phase variations with frequency. This paper applies this unique reflection phase property to alter the direction of the fields scattered by a radar target to reduce its radar cross section (RCS). This redirecting of the scattered fields occurs when a surface is covered with a checkerboard of alternating EBG structures, and results in a wider frequency band RCS reduction. RCS reduction compared to a PEC surface of 10 dB can be realized over 60% frequency bandwidth. Simulations of monostatic and bistatic RCSs of two dual EBG checkerboard surfaces, square and hexagonal, are compared with those of equal-sized PEC ground planes. The simulated monostatic RCS is also compared with measurements. Both $\bf{TE}^{\bf{z}}$ and $\bf{TM}^{\bf{z}}$ polarizations for oblique incidence are considered. Excellent agreement is obtained between simulated and measured patterns, for both the square and the hexagonal EBG checkerboard surfaces. An approximate analytical expression is provided as a guideline for a 10-dB RCS reduction of a dual EBG checkerboard surface compared to that of a PEC.

Modulated Metasurface Antennas for Space: Synthesis, Analysis and Realizations

Abstract: This paper presents design and analysis methods for planar antennas based on modulated metasurfaces (MTSs). These antennas operate on an interaction between a cylindrical surface-wave (SW) excited by an isotropic TM radiator, and an MTS having a spatially modulated equivalent impedance. The MTS is realized by using sub-wavelength patches printed on a grounded slab, thus resulting in a structure with light weight and compact volume. Both features are appealing characteristics for space applications. This paper introduces for the first time an impedance-based amplitude synthesis of the aperture field distribution and shows several new examples of antennas for space applications obtained in recent research projects financed by the European Space Agency.

High-Gain Filtering Patch Antenna Without Extra Circuit

Abstract: This paper presents a novel kind of patch antenna with high-selectivity filtering responses and high-gain radiation performance. The proposed antenna is mainly composed of a driven patch and a stacked patch, with its entire height being ${0.09\lambda }$ . Three shorting pins and a U-slot are embedded in the driven patch to enhance out-of-band suppression levels and skirt selectivity near the lower band-edge, whereas the stacked patch provides a sharp roll-off rate at the upper band-edge and also an enhanced gain. Without using extra filtering circuits, the proposed antenna exhibits a quasi-elliptic boresight gain response with three radiation nulls. For demonstration, an antenna is implemented covering the LTE band (2.3–2.7 GHz). The antenna achieves an average gain of 9.7 dBi within passband, and out-of-band suppression levels of more than 21 dB.

General Metasurface Synthesis Based on Susceptibility Tensors

Abstract: A general method, based on susceptibility tensors, is proposed for the synthesis of metasurfaces transforming arbitrary incident waves into arbitrary reflected and transmitted waves. The proposed method exhibits two advantages: 1) it is inherently vectorial, and therefore better suited for full vectorial (beyond paraxial) electromagnetic problems; 2) it provides closed-form solutions, and is therefore extremely fast. Incidentally, the method reveals that a metasurface is fundamentally capable to transform up to four independent wave triplets (incident, reflected, and refracted waves). In addition, this paper provides the closed-form expressions relating the synthesized susceptibilities and the scattering parameters simulated within periodic boundary conditions, which allows one to design the scattering particles realizing the desired susceptibilities. The versatility of the method is illustrated by examples of metasurfaces achieving the following transformations: generalized refraction, reciprocal and nonreciprocal polarization rotation, Bessel vortex beam generation, and orbital angular momentum multiplexing.

Metamaterial-Based Low-Profile Broadband Aperture-Coupled Grid-Slotted Patch Antenna

Abstract: A metamaterial-based broadband low-profile grid-slotted patch antenna is presented. By slotting the radiating patch, a periodic array of series capacitor loaded metamaterial patch cells is formed, and excited through the coupling aperture in a ground plane right underneath and parallel to the slot at the center of the patch. By exciting two adjacent resonant modes simultaneously, broadband impedance matching and consistent radiation are achieved. The dispersion relation of the capacitor-loaded patch cell is applied in the mode analysis. The proposed grid-slotted patch antenna with a low profile of $0.06 \lambda_{0}$ ( $\lambda_{0}$ is the center operating wavelength in free space) achieves a measured bandwidth of 28% for the $\vert{\text{S}_{{11}}}\vert$ less than $-{10}\;\text{dB}$ and maximum gain of 9.8 dBi.

Compact UWB Monopole Antenna for Automotive Communications

Abstract: This communication presents a bandwidth-enhanced, compact, monopole antenna with modified ground plane for modern automotive ultra wide-band (UWB) applications The proposed antenna has hybrid geometry and is constructed using half circular ring and half square ring The ground plane of the fundamental radiator is curved and defected to improve the VSWR bandwidth An extended ground stub is added to further enhance the bandwidth to suit the modern automotive requirements The designed antenna covers 31–109 GHz frequency spectrum with ${\mathrm {VSWR}} \leq {2}$ This antenna can be conveniently placed inside the shark fin housing or it can be printed along with the existing print circuit board (PCB) electronics nullifying the need for dedicated location for in-car communications Furthermore, a simple two-port multiple input multiple output (MIMO) antenna is constructed and its diversity performance is estimated The prototype is fabricated and tested for impedance and radiation characteristics

A Multiband Slot Antenna for GPS/WiMAX/WLAN Systems

Abstract: The design of a four-band slot antenna for the global positioning system (GPS), worldwide interoperability for microwave access (WiMAX), and wireless area network (WLAN) is presented. The antenna consists of a rectangular slot with an area of ${\mathbf{0}}.{\mathbf{37}}{\lambda _g} \times {\mathbf{0}}.{\mathbf{14}}{\lambda _g} = {\mathbf{48}} \times {\mathbf{18}}\;{\bf m}{{\bf m}^{\mathbf{2}}}$ (where ${\lambda _g}$ is the guide wavelength), a $T$ -shaped feed patch, an inverted $T$ -shaped stub, and two $E$ -shaped stubs to generate four frequency bands. The radiating portion and total size of the antenna are less than those of the tri-band antennas studied in literature. Parametric study on the parameters for setting the four frequency bands is presented and hence the methodology of using the design for other frequency bands is proposed. The multiband slot antenna is studied and designed using computer simulation. For verification of simulation results, the antenna is fabricated and measured. The simulated and measured return losses, radiation patterns, realized peak gains, and efficiencies of the antenna are presented. Measured results show that the antenna can be designed to cover the frequency bands from 1.575 to 1.665 GHz for the GPS system, 2.4–2.545 GHz for the IEEE 802.11b&g WLAN systems, 3.27–3.97 GHz for the WiMAX system, and 5.17–5.93 GHz for the IEEE 802.11a WLAN system. The effects of the feeding cable used in measurement and of the cover are also investigated.

Low-Profile Broadband Circularly Polarized Patch Antenna Using Metasurface

Abstract: A low-profile single-feed circularly polarized (CP) patch antenna using metasurface is proposed for broadband operation. The antenna is comprised of a truncated corner square patch sandwiched between a lattice of $4 \times 4$ periodic metal plates and the ground plane. Surface waves propagating on the metasurface are excited in the proposed structure. This phenomenon generates additional resonances and minimum axial ratio (AR) points for the radiating structure, consequently broadening the impedance-matching and AR bandwidths of the antenna. The final prototype, with an overall size of $32\;{\text{mm}} \times 32\;{\text{mm}} \times 3\;{\text{mm}}$ ( $0.58{\uplambda}_{\text o} \times 0.58{\uplambda}_{\text o} \times 0.056{\uplambda}_{\text o}$ at 5.5 GHz), was fabricated and tested. The measurements resulted in a $\vert{S}_11 \vert bandwidth of 4.70–7.48 GHz (45.6%) and a 3-dB AR bandwidth of 4.9–6.2 GHz (23.4%). In addition, the antenna yielded a good broadside left-hand CP radiation with a small gain variation (7.0–7.6 dBic) and a high radiation efficiency ( ${>} 90$ %) within the operational bandwidth.

Compact MIMO Antenna for Portable UWB Applications With Band-Notched Characteristic

Abstract: A multiple-input-multiple-output (MIMO) band-notched antenna with a compact size of only $22 \times 36\;\mathrm{mm}^2 $ is proposed for portable ultrawideband (UWB) applications. The antenna consists of two square monopole-antenna elements, a T-shaped ground stub, a vertical slot cut on the T-shaped ground stub to reduce mutual coupling, and two strips on the ground plane to create a notched frequency band. Simulation and measurement are used to study the antenna performance in terms of impedance matching, isolation between the two input ports, radiation pattern, efficiency, peak gain, and envelope correlation coefficient. Results show that the antenna can operate from 3.1 to more than 11 GHz with a notched band in 5.15–5.85 GHz. In the center notched frequency, the efficiency drops to 7%, indicating a good interference suppression performance. The mutual coupling is less than $- 15\;\mathrm{dB}$ and the envelope correlation coefficient is less than 0.1. The performances of the MIMO antenna when installed on a PCB with a standard size, with an USB connector and device housing, are also studied. Results show that the proposed MIMO antenna is a good candidate for portable UWB applications.

X-Band Phase-Gradient Metasurface for High-Gain Lens Antenna Application

Abstract: We propose a high-gain transmitting lens antenna by employing layered phase-gradient metasurface (MS). The MS is engineered to focus the propagating plane wave to a point with high efficiency. An X-band patch antenna is placed at the focal point of the MS as a feed source, and then the quasi-spherical wave emitted by the source is transformed to plane wave. Due to the successful conversion of quasi-spherical wave to plane wave, the beam width of the patch antenna has been decreased 66° and the gain has been enhanced 11.6 dB. The proposed lens antenna not only opens up a new route for the applications of phase-gradient MS in microwave band, but also affords an alternative for high-gain antenna.

A Compact, Wideband Circularly Polarized Co-designed Filtering Antenna and Its Application for Wearable Devices With Low SAR

Abstract: A compact circularly polarized (CP) co-designed filtering antenna is reported. The device is based on a patch radiator seamlessly integrated with a bandpass filter composed of coupled stripline open-loop resonators, which are designed together as a system. In the proposed design, the patch functions simultaneously as the radiator and the last stage resonator of the filter, resulting in a low-profile integrated radiating and filtering module with a small overall form factor of $\mathbf{0.53{\lambda _0} \times 0.53{\lambda _0} \times 0.07{\lambda _0}}$ . It is shown that the filtering circuit not only ensures frequency selectivity but also provides impedance matching functionality, which serves to broaden both the impedance and axial ratio bandwidths. The designed filtering antenna was fabricated and measured, experimentally achieving an $\mathbf{{S_{11}} , an axial ratio of less than 3 dB and a gain higher than 5.2 dBi over a bandwidth from 3.77 to 4.26 GHz, i.e., around 12.2%, which makes it an excellent candidate for integration into a variety of wireless systems. A linearly polarized version of the integrated filtering antenna was also demonstrated. In addition, further full-wave simulations and experiments were carried out to verify that the designed CP filtering antenna maintains its properties even when mounted on different positions of the human body with various body gestures. The stable impedance and radiation properties also make it a suitable candidate as a wearable antenna for off-body wireless communications.

A Novel Method for Improving Antipodal Vivaldi Antenna Performance

Abstract: Herein, a new method for improving the directivity and bandwidth of the antipodal Vivaldi antenna structure is presented. The method is based on introducing a parasitic elliptical patch in the flare aperture to enhance the field coupling between the arms and produce stronger radiation in the endfire direction. This approach improves the directivity without compromising the low frequency performance and removes the need for electrically thin dielectric substrates. The proposed antenna structure including the feeding line and transition measures $140 \times 66 \times 1.5 \text{mm}^3$ and has a peak gain $> 0\;{\text{dBi}}$ over the 2–32 GHz frequency range and ${>} 10\;{\text{dBi}}$ over the 6–21 GHz range, which is an improvement to what has been reported for Vivaldi antennas with similar size.

Miniaturized Double-Layer EBG Structures for Broadband Mutual Coupling Reduction Between UWB Monopoles

Abstract: Novel miniaturized two-layer electromagnetic band gap (EBG) structures are presented for reducing the electromagnetic coupling between closely spaced ultra wideband (UWB) planar monopoles on a common ground. The proposed EBG structures employ two closely coupled arrays, one comprising linear conducting patches and the other comprising apertures (slits) in the ground plane. The two arrays are printed on either side of a very thin dielectric layer ( $\bf{55}\;\upmu\mathrm{m}$ ) with a rotation between the elements to produce maximum coupling for miniaturizing. A microstrip line excitation is initially used for the efficient analysis and design of the slit–patch EBG structures, which are subsequently employed between two UWB printed monopoles. The proposed EBG structure has a small footprint and produces a significant reduction of the mutual coupling across the wide operating band of the UWB antennas. Simulated results and measurements of fabricated prototypes are presented.

Transmission Characteristics of a Twisted Radio Wave Based on Circular Traveling-Wave Antenna

Abstract: A traveling-wave circular loop antenna with its phase distribution along the circle of $\bm{l}\bm{\varphi}$ is demonstrated to generate the twisted radio wave. Theoretical formulations of its radiation fields are deduced in the cylindrical coordinate system and used to analyze its transmission characteristics, such as the radiation patterns, the evolution of the polarization states, and the angular momentum modes including the orbital angular momentum (OAM) modes and the spin angular momentum (SAM) modes. The prototype of a practical configuration for such antenna is proposed and conducted to validate the theoretical results. This theoretical analysis is applicable not only to radio waves but also to the whole electromagnetic spectrum.

Reduction of Mutual Coupling in Planar Multiple Antenna by Using 1-D EBG and SRR Structures

Abstract: One-dimensional electromagnetic bandgap (1-D EBG) and split ring resonator (SRR) structures were inserted between two closely located monopole antennas to suppress mutual coupling. The 1-D EBG and SRR structures in these planar multiple antennas function as a reflector and wave trap, respectively. With the effect of these two structures, the mutual coupling between the two antennas is reduced by more than 42 dB and the back lobes are reduced by 6 dB. Thereby, the radiation efficiency of the antenna is also improved. The two fabricated antennas with $0.19{\lambda }_{0}$ spacing exhibit mutual coupling ( ${\mathbf{S}_{\mathbf{21}}}$ , ${\mathrm{S}_{{12}}}$ ) of less than $- {30} \mathrm{dB}$ from 2.43 to 2.54 GHz. A minimum correlation coefficient of 0.002 and maximum radiation efficiency of 82% are also demonstrated.

60-GHz Substrate Integrated Waveguide Fed Cavity-Backed Aperture-Coupled Microstrip Patch Antenna Arrays

Abstract: Cavity-backed patch antenna arrays with full corporate substrate integrated waveguide (SIW) feed networks are demonstrated at V-band for applications with the needs of high-gain antennas. A prototype of $16 \times 16$ radiating elements with a waveguide transition is fabricated by applying standard printed circuit board (PCB) facilities. A gain up to 30.1 dBi with a 3-dB gain bandwidth of 16.1%, an impedance bandwidth of 15.3% for $\mathrm{SWR} \,{ , and symmetrically broadside radiation patterns with $-40\,\mathrm{dB}$ cross-polarizations are achieved. The performance of the proposed antenna array is also systematically evaluated. The result serves as a reference for designing large antenna arrays operating at millimeter-wave frequencies.

Reconfigurable Folded Reflectarray Antenna Based Upon Liquid Crystal Technology

Abstract: A reconfigurable antenna based on the liquid crystal technology is presented in this paper. The antenna comprises a planar lower reflector with an incorporated feed at its center and a polarizing grid on top as an upper reflector. The lower reflector is utilized to collimate the beam and to twist the polarization. The polarizing grid selects the polarization for the transmission and reflects the orthogonally polarized waves toward the lower reflector. Combining reflector elements with a polarizing grid allows performing additional phase adjustment on the upper reflector for beam steering. Reconfigurability is maintained by the upper reflector, in which a liquid crystal mixture is used as a tunable substrate. The liquid crystal layer is tuned with a bias voltage configuration to obtain an appropriate phase adjustment for the beam steering. As a proof of concept, the beam steering capability of the antenna is demonstrated by steering the main beam to $-6^{\circ}$ , 0 $^{\circ}$ , and 6 $^{\circ}$ at 78 GHz. The measured gain at 78 GHz is 25.1 dB. The proposed antenna configuration is a promising candidate for reconfigurable, high-gain, low-profile, and low-cost antennas.

Cylindrical Slot FSS Configuration for Beam-Switching Applications

Abstract: A novel design for a beam-switching antenna using active cylindrical slot frequency selective surface (ACSFSS) is presented. The antenna system is composed of an omnidirectional monopole antenna and the ACSFSS, which employs a new technique of switching slot arrays. The ACSFSS is made up of 12 columns with 8 slots each, dividing the cylinder by 30 $^{\circ}$ . To steer the beam of the antenna the diodes are set off and on, so that the radiation pattern of the antenna is determined by the number of off state columns. To estimate the general dimension of the cylindrical FSS, an equivalent metallic reflector is introduced and optimized, and then parametric studies for the unit cell dimensions are discussed. The fabricated prototype works within the WLAN band, centered around 2.45 GHz, and can agilely select either a narrow-beam or wide-beam operating mode. Simulation and measurements confirm the operation of the ACSFSS antenna, with good matching and gain observed. In particular, the narrow-beam mode $-$ 3 dB beamwidth is 47 $^{\circ}$ which offers enhanced angular resolution compared with other reported beam-sweeping work.

Enhanced Isolation of a Closely Spaced Four-Element MIMO Antenna System Using Metamaterial Mushroom

Abstract: A double-layer mushroom structure is proposed to enhance the interelement isolation of a four-element antenna system, wherein four closely positioned substrate-integrated cavity-backed slot (SICBS) antenna elements are configured for multiple-input multiple-output (MIMO) applications. A wall with a double-layer mushroom structure is positioned in between the four antenna elements. An antenna prototype with a ground plane size of ${\mathbf{0}}.{\mathbf{96}}\;{{\mathbf{\lambda }}_{\mathbf{0}}} \times 0.96\;{{\mathbf{\lambda }}_{\mathbf{0}}}$ ( ${{\mathbf{\lambda }}_{\mathbf{0}}}$ is the free space-wavelength at 2.4 GHz) demonstrates an enhanced interelement isolation of 16 dB for parallel-directed antenna element pairs, while the isolation of the orthogonally directed antenna element pairs remains unchanged over the operating bandwidth ( $\vert {{\mathbf{S}}_{{\mathbf{11}}}}\vert ) of 2.396 –2.45 GHz. With the enhanced isolation larger than 42 dB between each antenna element pair, the envelope correlation coefficient (ECC) is lower than 0.02 across the operating bandwidth. The simulated and measured results validate the good MIMO diversity performance of the proposed antenna system.

Multimode Resonator-Fed Dual-Polarized Antenna Array With Enhanced Bandwidth and Selectivity

Abstract: A novel design concept of multimode filtering antenna, which is realized by integrating a multimode resonator and an antenna, has been applied to the design of dual-polarized antenna arrays for achieving a compact size and high performance in terms of broad bandwidth, high-frequency selectivity and out-of-band rejection. To verify the concept, a $2 \times 2$ array at C-band is designed and fabricated. The stub-loaded resonator (SLR) is employed as the feed of the antenna. The resonant characteristics of SLR and patch as well as the coupling between them are presented. The method of designing the integrated resonator-patch module is explained. This integrated design not only removes the need for separated filters and traditional ${50}{\text - }{\Omega }$ interfaces but also improves the frequency response of the module. A comparison with the traditional patch array has been made, showing that the proposed design has a more compact size, wider bandwidth, better frequency selectivity, and out-of-band rejection. Such low-profile light weight broadband dual-polarized arrays are useful for space-borne synthetic aperture radar (SAR) and wireless communication applications. The simulated and measured results agree well, demonstrating a good performance in terms of impedance bandwidth, frequency selectivity, isolation, radiation pattern, and antenna gain.

A Broadband $\pm 45^{\circ}$ Dual-Polarized Antenna With Y-Shaped Feeding Lines

Abstract: A broadband $\pm 45^{\circ}$ dual-polarized base station antenna is proposed for 2G/3G/LTE bands. The proposed antenna has Y-shaped feeding lines to impart a wide impedance bandwidth to it, and a rectangular box-shaped reflector to enhance its stability in radiation patterns over the operating frequencies. A prototype of the proposed antenna is designed, fabricated, and tested. The measured results show achievement of impedance bandwidth of 45% for $\hbox {SWR} at both ports, port-to-port isolation $>$ 25 dB , a stable radiation pattern with 3-dB beamwidth $68^{\circ}\pm 2^{\circ}$ at H-plane and V-plane, and a stable antenna gain of 8.2 $\pm$ 0.6 dBi from 1.7 to 2.7 GHz. A broadband dual-polarized antenna array with five elements for the band is developed for base station application. Measurements show achievement of array gain of 14.8 $\pm$ 1.4 dBi, 3-dB beamwidth $66.56^{\circ}\pm 2.22^{\circ}$ at H-plane at port 1 and $64.85^{\circ}\pm 4.96^{\circ}$ at port 2 with $\hbox {SWR} over the operating frequency band. Simulation results have a good agreement with measurement ones.

Square Loop and Slot Frequency Selective Surfaces Study for Equivalent Circuit Model Optimization

Abstract: This paper presents a parametric study of square loop and square slot frequency selective surfaces (FSSs) aimed at their equivalent circuit (EC) model optimization. Consideration was given to their physical attributes, i.e., the unit cell dimensions and spacing, substrate thickness and dielectric properties, for several frequencies and plane wave incident angles. Correlation analysis and evaluation of the influence of physical related input parameters on the FSS performance are presented. Subsequent optimization factor for the square loop classical EC model is analyzed, and a novel EC model formulation for the square slot FSS is proposed. The performance of the proposed EC model was assessed against results obtained from appropriate electromagnetic (EM) simulations, based on a root-mean-square error (RMSE) criteria. Results demonstrate the validity of the optimized EC model, in which good estimations of the frequency response of FSS structures were obtained. Significant reduction of the resonant frequency offsets, in the order of 650 (from 910 to 260) and 460 (770 to 310) MHz, was obtained for square loops and square slots, respectively. The models were further validated against measurements performed on two physical FSS prototypes inside an anechoic chamber at 2.4 GHz. Relatively good agreement was obtained between measurements of real FSS prototypes and results obtained with the EC model. Finally, this work is sought to provide the necessary refinement of elementary models for further studies with more complex and novel FSS structures.

Circular Polarization Wide-Angle Beam Steering at Ka-Band by In-Plane Translation of a Plate Lens Antenna

Abstract: A simple mechanical beam steering antenna concept is proposed for ground mobile terminals of Ka-band satellite and high altitude platform (HAP) providing broadband access services. The wide-angle elevation beam steering is achieved by in-plane translation of a thin offset flat lens in front of a stationary primary feed while full azimuth coverage is obtained by simple 360° rotation of the lens. A new strategy is also proposed to reduce the effective F/D of the focusing system and consequently the total antenna height without increasing beam distortion: a second small flat lens is added on top of the primary feed to create a virtual focus located well below the feed phase center. The challenge is to conciliate high gain both with wide beam scanning and reduced antenna height. Design rules are presented for this antenna concept along with a 27.3-dBi gain fabricated example for the up-link Ka-band (29.5–30 GHz), with circular polarization, 0° to 50° elevation scan, better than 2.8-dB scan loss and an effective F/D of only 0.55. Both lenses are 3.35-mm thick, formed by a suitable assembly of phase shifting unit cells with less than 0.4 dB of transmission loss in simulation. The main lens dimensions are $195\;\text{mm} \times 145\;\text{mm}$ and its weight is 215 g. Total antenna height, including the feed is 84 mm.

A Novel Dual-Band, Dual-Polarized, Miniaturized and Low-Profile Base Station Antenna

Abstract: In this paper, a novel dual-band, dual-polarized, miniaturized and low-profile base station antenna operating in the frequency bands of 820–960 and 1710–2170 MHz is designed. Elements are arranged such that high-frequency elements are embedded in low frequency elements to reduce volume. A baffle is used to reflect the transmitted power density in the forward direction and also improve isolation between elements. Therefore, surrounding isolation baffles and rectangular baffles are appended around high-frequency elements and low-frequency elements, respectively. The diameter of the proposed antenna cover is only 200 mm, which is smaller than the existing antenna diameter of 280 mm. Compared with the other commonly used antennas, the proposed antenna also has some advantages such as concealment and low profile using a tubular form of radome, which can easily integrate the proposed antenna with the surrounding environment. The measured results verify that the proposed antenna meets the stringent design requirements: voltage standing wave ratio (VSWR) is less than 1.3, the isolation is greater than 30 dB, and the pattern parameters also meet telecommunications industry standards.

A Reconfigurable Partially Reflective Surface (PRS) Antenna for Beam Steering

Abstract: The design of a novel partially reflective surface (PRS) antenna with the capability of beam steering is presented in this paper. The beam steering is realized by employing a reconfigurable PRS structure to achieve a changeable reflection phase as well as using a phased array as the source to excite the PRS antenna. A prototype antenna including the biasing network is fabricated and measured. It achieves a consistent beam steering from – 15° to 15° with respect to the broadside direction across an overlapped frequency range from 5.5 to 5.7 GHz with measured realized gains over 12 dBi. Good agreement between the simulated and measured results for the input reflection coefficients and radiation patterns is achieved, which validates the feasibility of the design principle. Compared with other beam steering PRS antennas, the proposed one enables a larger beam steering angle with comparable gains, requires a simpler biasing network, and is more compact.

A Dual-Loop Antenna Design for Hepta-Band WWAN/LTE Metal-Rimmed Smartphone Applications

Abstract: A simple direct-fed dual-loop antenna capable of providing hepta-band WWAN/LTE operation under surroundings of an unbroken metal rim in smartphone applications is proposed. The greatest highlight of this proposed antenna is that it provides a simple and effective multiband antenna solution for an unbroken metal-rimmed smartphone. The unbroken metal rim with 5 mm in height embraces the system circuit board of 130 $\, \times \,$ 70 mm $^{2}$ . Two no-ground portions of 10 $\, \times \,$ 70 mm $^{2}$ and 5 $\, \times \,$ 70 mm $^{2}$ are set on the top and bottom edge of the system circuit board, respectively. In-between the two separate no-ground portions, there is a system ground of 115 $\, \times \,$ 70 mm $^{2}$ connected with the unbroken metal rim via a small grounded patch which divides the unbroken metal rim into two strips. Finally, a dual-loop antenna is formed by combining the inner system ground and two strips. This proposed dual-loop antenna is capable of covering GSM850/900/DCS/PCS/UMTS2100/LTE 2300/2500 operating bands. Detailed design considerations of the proposed antenna are described and both experimental and simulation results are also presented and discussed.

A Wideband High-Gain High-Efficiency Hybrid Integrated Plate Array Antenna for V-Band Inter-Satellite Links

Abstract: A wideband high-gain high-efficiency hybrid integrated plate array antenna for inter-satellite links is presented in this paper This antenna consists of microstrip patches, substrate integrated waveguide (SIW) and waveguide power dividers A novel feeding structure is proposed to excite the microstrip sub-array with a wideband characteristic The radiation efficiency of SIW arrays with different sizes is compared by experiment The hybrid SIW-waveguide feeding topology is optimized to realize high efficiency, low cost and compact configuration at the same time The array antenna is fabricated through standard multi-layer PCB process and milling technology Measured results demonstrate about 146% of reflection coefficient bandwidth ( $\vert {\rm S}_{11}\vert dB) in the frequency band of 57–66 GHz The gain fluctuates less than 3 dB within the same band The 1 dB gain bandwidth is 81% within the frequency band of 59–64 GHz The maximum gain is 392 dBi at 59 GHz with the efficiency of 41%

Dual-Band Textile MIMO Antenna Based on Substrate-Integrated Waveguide (SIW) Technology

Abstract: A dual-band textile antenna for multiple-input–multiple-output (MIMO) applications, based on substrate-integrated waveguide (SIW) technology, is designed. The fundamental SIW cavity mode is designed to resonate at 2.4 GHz. Meanwhile, the second and third modes are modified and combined by careful placement of a via within the cavity to enable wideband coverage in the 5-GHz WLAN band. The simple antenna topology can be fabricated fully using textiles in a planar form, ensuring reliability and comfort. Numerical and experimental results indicate satisfactory antenna performance when worn on body in terms of impedance bandwidth, radiation efficiency, and specific absorption ratio (SAR). In order to validate its potential for MIMO applications, two elements of the proposed SIW antenna are arranged in six configurations to study the performance in terms of mutual coupling and envelope correlation. It is observed that the placement of the shorted edges of the two elements adjacent to each other produces the lowest mutual coupling and consequently the best envelope correlation.