Showing papers on "Reflective array antenna published in 2014"

Wideband Radar Cross Section Reduction of Slot Antennas Arrays

Abstract: A comprehensive analysis aimed at reducing the radar cross section (RCS) of array antennas, preserving at the same time their radiating performance, is presented. A microstrip slot array is considered as a test case to illustrate the proposed strategy for radar cross section reduction (RCSR). It is shown that a remarkable reduction of the radar signature can be accomplished over a frequency band as wide as two octaves by employing an array of periodic resistive elements in front of the radiating apertures. The monostatic and bistatic RCS of the proposed structures are investigated both for normal and oblique incidence. Different arrangements and geometries of the periodic resistive pattern are thoroughly analyzed showing the benefits and the drawbacks in terms of antenna gain and level of the scattered fields. Furthermore, the use of metallic parasitic elements for enhancing the antenna gain is considered, and the scattering phenomena caused by their presence are addressed, taking into account the appearance of grating lobes. The antenna designs are also analyzed by resorting to a bidimensional color plot presenting the variation of the reradiated field both in frequency and spatial domain. The guidelines illustrated by the proposed examples can be easily applied to other antenna architectures.

Scalable RF Energy Harvesting

Abstract: This paper discusses harvesting of low-power density incident plane waves for electronic devices in environments where it is difficult or impossible to change batteries and where the exact locations of the energy sources are not known. As the incident power densities vary over time and space, distributed arrays of antennas with optimized power-management circuits are introduced to increase harvested power and efficiency. Scaling in array size, power, dc load, frequency, and gain is discussed through three example arrays: a dual industrial-scientific-medical band Yagi-Uda array with a low-power startup circuit; a narrowband 1.96-GHz dual-polarized patch rectenna array with a reconfigurable dc output network designed for harvesting base-station power; and a broadband dual-polarized 2-18-GHz array with multi-tone performance. The efficiency of rectification and power management is investigated for incident power densities in the 1-100-μW/cm2 range.

A Wideband Sequential-Phase Fed Circularly Polarized Patch Array

Abstract: This communication presents a wideband circularly polarized (CP) 2 × 2 patch array using a sequential-phase feeding network. By combining three operating modes, both axial ratio (AR) and impedance bandwidths are enhanced and wider than those of previous published sequential-fed single-layer patch arrays. These three CP operating modes are tuned and matched by optimizing the truncated corners of patch elements and the sequential-phase feeding network. A prototype of the proposed patch array is built to validate the design experimentally. The measured -10-dB impedance bandwidth is 1.03 GHz (5.20-6.23 GHz), and the measured 3-dB AR bandwidth is 0.7 GHz (5.25-5.95 GHz), or 12.7% corresponding to the center frequency of 5.5 GHz. The measured peak gain is about 12 dBic and the gain variation is less than 3 dB within the AR bandwidth.

Dual-Band Wide-Angle Scanning Planar Phased Array in X/Ku-Bands

Abstract: A novel planar dual-band phased array, operational in the X/Ku-bands and with wide-angle scanning capability is presented. The design, development and experimental demonstration are described. A new single-layer crossed L-bar microstrip antenna is used for the array design. The antenna has low-profile architecture, measuring only $0.33\lambda \times 0.33\lambda $ , at the low frequency band of operation, with flexible resonance tuning capability offered by the use of a plate-through-hole and field-matching ring arrangement. A 49-element planar (7 $\,\times \,$ 7) array demonstrator has been built and its performance validated, exhibiting good agreement with full-wave simulations. The dual-band array supports a large frequency ratio of nearly 1.8:1, and also maintains good sub-band bandwidths. Wide-angle scanning up to a maximum of 60 $^{\circ}$ and 50 $^{\circ}$ are achieved at the low and high frequency bands of operation, respectively.

Planar Dual-Band Wide-Scan Phased Array in X-Band

Abstract: The design of a planar dual-band wide-scan phased array is presented. The array uses novel dual-band comb-slot-loaded patch elements supporting two separate bands with a frequency ratio of 1.4:1. The antenna maintains consistent radiation patterns and incorporates a feeding configuration providing good bandwidths in both bands. The design has been experimentally validated with an X-band planar 9 × 9 array. The array supports wide-angle scanning up to a maximum of 60 ° and 50 ° at the low and high frequency bands respectively.

Dual-Band Dual-Polarized Compact Bowtie Antenna Array for Anti-Interference MIMO WLAN

Abstract: Smart antennas have received increasing interest for mitigating interference in the multiple-input-multiple-output (MIMO) wireless local area network (WLAN). In this paper, a dual-band dual-polarized compact bowtie dipole antenna array is proposed to support anti-interference MIMO WLAN applications. In the antenna array, there are 12 antennas, six for horizontal polarization and six for vertical polarization. In order to achieve dual linear polarizations and beam switching, six horizontal antennas are placed in a sequential, rotating arrangement on a horizontal substrate panel with an equal inclination angle of 60 ° to form a symmetrical structure, while the other six antennas for vertical polarization are inserted through slots made on the horizontal substrate panel. Furthermore, six pairs of meandered slits are introduced to reduce the mutual coupling between horizontal antennas in the lower band. A prototype of the array with a dimension of 150 × 150 × 60 mm3 is manufactured and exhibits the characteristics of high isolation, good front-to-back ratio, and average gains of 4.5 and 5 dBi over the 2.4- and 5-GHz band, respectively. The MIMO performance of the array is analyzed and evaluated by mutual coupling, the total active reflection coefficient (TARC) and the envelope correlation coefficient. The anti-interference capability of the array is also investigated by the experiment.

Design and Evaluation of Pattern Reconfigurable Antennas for MIMO Applications

Abstract: In recent years, reconfigurable antennas have been sought to improve the performance of multiple-input multiple-output (MIMO) wireless communication systems. Their ability to dynamically reconfigure their radiation pattern adds diversity in a manner that is not possible with fixed antennas. This paper investigates the performance benefits provided by pattern reconfigurable receiving antennas with uniform beam steering capability. Their potential performance is first estimated using simulations, and for the first time, the effect of uniform beam steering on MIMO system performance is evaluated in a real indoor channel using two electrically steerable passive array radiator (ESPAR) antennas. Performance comparison is made against a pair of monopole antennas using a hardware bit error rate (BER) test-bed that incorporates statistical spatial averaging in order to assess performance improvements in a more realistic way, and analyze the effect of antenna diversity on the overall system performance. The MIMO-ESPAR system reduces BER with certain pattern combinations and excels in capacity evaluations. The ESPAR antennas improve the spatially averaged channel capacity by as much as 37% at 10 dB transmit SNR, and gain an additional 1 bit/s/Hz in peak capacity at 10 dB receive SNR from diversity gain alone. These improvements make pattern reconfigurable antennas promising options in MIMO-related applications.

77-GHz Multi-Channel Radar Transceiver With Antenna in Package

Abstract: This paper presents the design of a directional folded dipole antenna integrated in an embedded wafer level ball grid array (eWLB) package, the comparison of different antenna designs and the influence of the silicon die and neighboring antennas within the package to the radiation behavior. The co-integration of the antenna and the silicon-based monolithic microwave integrated circuit (MMIC) in a system in package (SiP) approach is a convenient solution to suppress lossy radio frequency (RF) transitions and to simplify the design and the manufacturing of radio frontends significantly. The proposed SiP is focused on 77-GHz automotive radar applications. The MMIC contains the 77-GHz signal source and a transceiver with amplifier and mixer. The gain of different antennas in different constellations within the package is shown.

Wideband antenna array for Simultaneous Transmit and Receive (STAR) applications

Abstract: A wideband antenna array for Simultaneous Transmit and Receive (STAR) applications is presented. The design is comprised of a ring array of TEM horns, and a monocone at the array's center. When the array is phased with the first order circular mode, it is isolated from the monocone. Thus, the array may be used in reception while the monocone is used in transmission, or vice versa. The array and monocone both produce quasi-omnidirectional patterns in the azimuthal planes. Simulations suggest that the design operates across an 8.4 : 1 bandwidth. This wide bandwidth is possible through the use of a novel capacitive feed employed in the TEM horn array.

D-band on-chip higher-order-mode dielectric-resonator antennas fed by half-mode cavity in CMOS technology

Abstract: In this paper, on-chip higher-order-mode dielectric-resonator antennas (DRAs), fed by a half-mode-backed cavity structure using standard CMOS technology, are presented. With the dominant cavity mode (half-TEz100), the half-mode cavity-feeding structure provided a high antenna radiation efficiency. The dielectric resonators (DRs) were designed to operate at higher-order modes (TEx?13, TEx?15) to enhance the antenna gain. At around 135 GHz, the proposed antennas demonstrated measured gains of 6.2 dBi and 7.5 dBi for the TEx?13 and TEx?15 modes, respectively, with corresponding simulated radiation efficiencies of 46% and 42%. Both antennas had a measured impedance bandwidth of 7%. The proposed antennas not only accomplished high gain without occupying a large chip area, but also maintained comparable or even improved cost performance and simplicity over other on-chip antennas.

Dual-Polarized Partially Reflective Surface Antenna With MEMS-Based Beamwidth Reconfiguration

Abstract: A partially reflective surface (PRS) antenna design enabling 1-bit dynamic beamwidth control is presented. The antenna operates at X-band and is based on microelectromechanical systems (MEMS) technology. The reconfigurable PRS unit cell monolithically integrates MEMS elements, whose positions are chosen to reduce losses while allowing a considerable beamwidth variation. The combined use of the proposed PRS unit cell topology and MEMS technology allows achieving low loss in the reconfigurable PRS. In addition, the antenna operates in dual-linear polarization with independent beamwidth control of each polarization. An operative MEMS-based PRS unit cell is fabricated and measured upon reconfiguration, showing very good agreement with simulations. The complete antenna system performance is rigorously evaluated based on full-wave simulations and the unit cell measurements, demonstrating an 18° and 23° variation of the half-power beamwidth in the E-plane and the H-plane, respectively. The antenna radiation efficiency is better than 75% in all states of operation.

Low Side-Lobe Circularly-Polarized Phased Arrays Using a Random Sequential Rotation Technique

Abstract: A novel technique is presented for sidelobe and axial ratio control of circularly-polarized phased array antennas. Although our new random sequential rotation (RSR) concept uses a regular periodic array grid, it provides similar properties as randomly-spaced array antennas. In this way, a wideband behavior is provided, without the appearance of grating lobes. In addition, the gain is maximized, since a uniform amplitude distribution is used. A 4 GHz prototype consisting of 16 aperture-coupled microstrip antennas with a beamformer was developed to demonstrate the basic properties of RSR array antennas. Although the element spacing is much larger than half a wavelength, well-controlled sidelobes are provided, even in the worst-case diagonal plane. The measured cross-polarization level at 4 GHz is below -20 dB at a 20-degree scan angle in the diagonal-plane.

Backhaul radio with an aperture-fed antenna assembly

Abstract: Directive gain antenna elements implemented with an aperture-fed patch array antenna assembly are described. A feed network for the aperture-fed patch array may include offset apertures and may also include meandering feed lines. Scalable aperture shapes and orientations that can be used with antennas operating at any frequency and with dual orthogonal polarizations are also disclosed. Directive gain antenna elements implemented with arrays of orthogonal reflected dipoles are also described with optimal feed networks and parasitic elements to achieve desired directive gain characteristics. Such arrayed dipole antennas feature dual orthogonal polarizations with assembly tabs that lower cost and improve reliability. Backhaul radios that incorporate said antennas are also disclosed.

Gain Enhancement of Beam Scanning Substrate Integrated Waveguide Slot Array Antennas Using a Phase-Correcting Grating Cover

Abstract: In this paper, planar beam scanning substrate integrated waveguide (SIW) slot leaky-wave antennas (LWAs) are proposed for gain enhancement using a metallic phase correction grating cover. Unlike conventional Fabry-Perot (FP) cavity antennas, the proposed antenna is fed by the SIW beam scanning LWA instead of a feeding antenna. The beam scanning angle range is enlarged by meandering the entire feeding structure and the gain is enhanced by a metallic grating cover acting as a 1-D lens. Two kinds of the gratings with different metal strip parameters are designed and analyzed. The proposed antennas operating at the center frequency of 25.45 GHz are designed and experimentally verified for an automotive collision avoidance radar with a gain enhancement of about 4 ~ 6 dB. The proposed SIW LWAs have the advantages of high gain, low profile, easy fabrication and beam-scanning capability good for millimeter wave radar applications.

Synthetic Bandwidth Radar for Ultra-Wideband Microwave Imaging Systems

Abstract: A synthetic bandwidth radar as an approach to build ultra-wideband (UWB) imaging systems is presented. The method provides an effective solution to mitigate the challenges of UWB antenna's implementation with ideal performance. The proposed method is implemented by dividing the utilized UWB into several channels, or sub-bands, and designing an antenna array that includes a number of antennas equal to the number of channels. Each of those antennas is designed to have excellent properties across its corresponding channel. As part of the proposed approach, a two-stage calibration procedure is used to accurately estimate the effective permittivity of a heterogeneous imaged object at different angles and the phase center of each antenna for accurate delay time estimation. When imaging an object, each of the antennas transmits and captures signals only at its channel. Those captured signals are properly combined and processed to form an image of the target that is better than the current systems that use array of UWB antennas. The presented method is tested on breast imaging using the band 3-10 GHz via simulations and measurements on a realistic heterogeneous phantom.

Miniature directive antennas

Abstract: This paper presents the work carried out to assess the feasibility of miniature directive antennas. It is based on an analysis of the physical limits of antenna directivity in general and in particular as a function of their compact dimensions. A state of the art is done to identify and classify techniques to increase the directivity of compact antennas.

Array Antennas With Jointly Optimized Elements Positions and Dimensions Part I: Linear Arrays

Abstract: The paper describes a deterministic algorithm based on simple analytical expressions for designing linear sparse array antennas, composed of not overlapping linear sub-apertures with pre-assigned power levels, where the positions and the dimensions of the radiating elements are jointly optimized and exploited. The obtained arrays permit maximizing the aperture filling and, as a consequence, the aperture efficiency and directivity.

Dual Subwavelength Fabry–Perot Cavities for Broadband Highly Directive Antennas

Abstract: A new concept for designing broadband and subwavelength profile Fabry-Perot-type antennas is introduced. A novel multilayer periodic array design is proposed, yielding two subwavelength-profile Fabry-Perot cavities that significantly enhance the bandwidth performance of the resulting highly directive antenna. The design is based on two optimized double-layer periodic arrays of dissimilar dimensions, each double-layer array consisting of a capacitive artificial magnetic conductor (AMC) layer and an inductive partially reflective surface (PRS) layer printed on either side of a dielectric substrate. They are placed at about a quarter-wavelength distance from a ground plane and from each other. Thus, two air cavities are created with a total profile of less than λ/2. The proposed antenna has been simulated in CST Microwave Studio, achieving 18.3 dBi directivity with 8% bandwidth.

On the Use of Leaky Wave Phased Arrays for the Reduction of the Grating Lobe Level

Abstract: Dielectric superlayers can be used to reduce the grating lobe levels in thinned phased arrays, i.e., arrays with large periodicities. In this contribution we show how the mutual coupling impacts the active impedance and the roll-off of the embedded patterns necessary to achieve the grating lobe angular filtering in this type of arrays. The reduction of the grating lobes in the thinned array radiation pattern depends on the dielectric superlayer constant. The larger the dielectric constant the higher the attenuation of the grating lobe will be. However, this can only be obtained at the cost of an increased mutual coupling. This mutual coupling will impact on the embedded patterns reducing the actual roll-off that can be achieved. Several 11 × 11 phased arrays with different dielectric superlayers are studied in order to establish the maximum useful permittivity as a function of the mutual coupling level. We show that antenna elements based on dielectric superlayers leading to mutual coupling levels larger than -20 dB suffer from a loss of directivity in the embedded pattern and a loss of gain in the phased array because of the highly resonant active impedance. As a reference we also compare the performances of the 11 × 11 leaky wave phased array with an 11 × 11 phased array of standard conical horns. We show that an increase in the gain of more than 2.2 dB over all the frequency and scanning ranges is obtained in the leaky wave array with respect to the reference horn array. The leaky wave array leads to a reduction of the grating lobe of more than 10 dB.

Theory of ESPAR Design With Their Implementation in Large Arrays

Abstract: A generalized formulation as well as a simple design approach is presented for electronically steerable parasitic array radiators (ESPAR). Based on the presented design procedure, a low-cost rectangular dielectric resonator parasitic phased array antenna is designed. An E-plane linear dielectric resonator phased array coupled to symmetric narrow slot apertures is investigated. The driven element is mutually coupled to the parasitic elements and reactive loads are utilized to control the phase to achieve a particular beam scanning direction. The use of low-cost reactive loads instead of expensive conventional phase shifters allows for more economic fabrication. Based on this design, a five elements planar array is designed and measured. In addition, a large array using ESPAR subarrays is presented.

Broadband near-field filters for Simultaneous Transmit and Receive in a small two-dimensional array

Abstract: In order to enable Simultaneous Transmit and Receive (STAR), it is essential to provide high isolation between antenna elements. A novel technique is presented here in which tunable resonators are used in the near-field of an array of antennas to provide transmission zeros in the coupling between antennas. By using two sets of tunable resonators between each set of adjacent antennas, it is possible to significantly increase the bandwidth of the isolation provided relative to previous topologies used to give isolation between planar antennas.

Antenna Coupling Effects for Space-Time Radar Waveforms: Analysis and Calibration

Abstract: In this paper, we investigate the impact of mutual coupling between the antenna array elements on the performance of a multiple-input multiple-output (MIMO) radar with colored waveform transmission (collocated coherent MIMO system). Simulation results confirm the decrease in system performance when antenna mutual coupling is taken into account. A dedicated scan-dependent calibration technique is proposed for elimination of the coupling effect. The experiments with a real X-band antenna array validate the coupling analysis and the calibration procedure presented in this paper.

Miniaturized Reconfigurable Multiband Antenna For Multiradio Wireless Communication

Abstract: This paper introduces a general methodical approach for designing frequency reconfigurable antennas. This method was successfully used to design a novel coplanar waveguide (CPW)-fed slot frequency reconfigurable antenna capable of operating at four preselected frequency bands distributed over a wide frequency range from ~ 59.5 MHz to ~ 1000 MHz (i.e., ~ 4 octaves of bandwidth) while keeping its overall size as small as possible. To add reconfigurablility to the antenna, optimally-designed and electronically-controllable PIN diode-loaded slots were used to strategically manipulate the flow of current path and consequently change the characteristics of the antenna. Designing for the lowest operating frequency (59.5 MHz), capacitor-loaded meandered slot lines and reconfigurable matching network were implemented to keep the size of the antenna as small as possible. The resulting overall size of the antenna is only 0.06λL×0.06λL where λL is calculated at 59.5 MHz. The measurement results verified that the antenna successfully operates at 59.25-59.75 MHz, 314-398 MHz, 430-496 MHz, and 792-950 MHz, all with an almost omnidirectional pattern and an acceptable gain.

Wideband Dielectric Lens Antenna With Stable Radiation Patterns Fed by Coherent Array of Connected Leaky Slots

Abstract: A broadband reflector feed is presented, which consists of a dielectric extended hemispherical lens fed by a connected array of leaky-wave slots. The slot elements are coherently combined to generate directive radiation patterns that mostly illuminate the central part of the lens, the most efficient one. The array is capable of producing secondary patterns with almost constant -10 dB beamwitdh over a 3:1 bandwidth. This allows efficient illumination of the reflector over a wide frequency range. Performance is estimated in terms of amplitude taper and phase error losses at the reflector, yielding efficiency of about 80% over the entire 3:1 bandwidth. Although the envisaged applications are in the terahertz (THz) and mm-wave frequency bands, a low-frequency prototype demonstrator has been tested in the 4 to 12 GHz band, for experimental validation of the concept.

Novel Parasitic Micro Strip Arrays for Low-Cost Active Phased Array Applications

Abstract: In this paper, a novel idea is proposed to construct low-cost phased arrays by using the multi-port property of array elements. The operating principles are illustrated and explained in detail. A three-element patch subarray with a periodic lattice is conceived according to the proposed idea. In the subarray, one patch antenna with multiple ports is designed as an active element which is directly fed through the excitation port by a feeding network. The other two parasitic patches are fed by the coupling ports of the active element. Good agreements between simulations and measurements of a two-subarray phased array prototype successfully verify the proposed idea. Then, comparisons to a conventional phased array are performed to highlight its advantages, e.g., high aperture efficiency and low cost. Finally, a second design example is given for more references.

An optically controlled phased array antenna based on single sideband polarization modulation

Abstract: A novel optically controlled phased array antenna consisting a simple optical beamforming network and an N element linear patch antenna array is proposed and demonstrated. The optical beamforming network is realized by N independent phase shifters using a shared optical single sideband (OSSB) polarization modulator together with N polarization controllers (PCs), N polarization beam splitters (PBSs) and N photodetectors (PDs). An experiment is carried out. A 4-element linear patch antenna array operating at 14 GHz and a 1 × 4 optical beamforming network (OBFN) is employed to realize the phased array antenna. The radiation patterns of the phased array antenna at −30°, 0° and 30° are achieved.

Design of cylindrically conformed metal reflectarray antennas for millimetre-wave applications

Abstract: Conformal metal reflectarray antennas on the surface of a cylinder are designed for millimetre-wave applications. All depths of metal grooves in the reflectarrays are specially manipulated for high-gain conformal reflectarray antennas. There is a good agreement between simulated and experimental radiation performance results for two different ‘sagittas’. The proposed conformal reflectarray antennas can be a helpful choice for applications requiring high-gain antennas on curved platforms.

Ground-coupled antenna array for step-frequency GPR

Abstract: This paper describes a new broadband ground coupled antenna array for step-frequency GPR operating continuously over the frequency range from 200 MHz - 3 GHz. The broad frequency range makes the array suitable both for high resolution shallow imaging and deeper investigations where efficient coupling of energy into the ground is crucial. A method for estimating penetration depth based on signal variance is described. The paper contains data examples from the new antenna array and also contains comparison with similar data from an air-coupled bowtie array. Finally, the paper discusses the benefits and disadvantages using air-coupled versus ground-coupled antennas for various applications.

Generation and detection of OAM signals for radio communications

Abstract: Orbital angular momentum radio has great potential for radio communications that require high security, spectrum efficiency and a large data rate. However, the performance of such a system, measured in terms of mode errors, is highly dependent on the alignment between the centre of the receiver array and the transmit array boresight. In addition, other impairment phenomena, such as transmit array imperfections, receiver phase errors and thermal noise can considerably degrade the performance of the orbital angular momentum radio system. In this paper, the effects caused by receive array angular and phase errors are evaluated by means of simulations. Furthermore, Monte Carlo simulations are employed to obtain the bit error rate performance of multi-level modulation orbital angular momentum radio systems.

Surface scattering antenna array

Abstract: An array of scattering and/or reflector antennas are configured to produce a series of beam patterns, where in some embodiments the scattering antenna and/or the reflector antenna includes complementary metamaterial elements. In some embodiments control circuitry is operably connected to the array to produce an image of an object in the beam pattern.