Flat Antenna Research Articles

Matched and wideband flat lens antennas using symmetric graded dielectrics.

Matched and wideband flat lens antennas using a two-dimensional symmetric graded dielectric (SGD) are considered. An explicit relation for refractive index of this type of antenna is presented. This design relation is obtained in two steps. The variations of refractive index are determined first in the radial direction and then in the axial direction. Additionally, reflector-lens antennas are introduced using two-dimensional SGD. The validity of design methodology is verified by simulation.

Assessment of LTCC-Based Dielectric Flat Lens Antennas and Switched-Beam Arrays for Future 5G Millimeter-Wave Communication Systems

This paper presents the design, low-temperature co-fired ceramics (LTCC) fabrication, and full experimental verification of novel dielectric flat lens antennas for future high data rate 5G wireless communication systems in the 60 GHz band. We introduce and practically completely evaluate and compare the performance of three different inhomogeneous gradient-index dielectric lenses with the effective parameters circularly and cylindrically distributed. These lenses, despite their planar profile antenna configuration, allow full 2-D beam scanning of high-gain radiation beams. A time-domain spectroscopy system is used to practically evaluate the permittivity profile achieved with the LTCC manufacturing process, obtaining very good results to confirm the viability of fabricating inhomogeneous flat lenses in a mass production technology. Then, the lenses performance is evaluated in terms of radiation pattern parameters, maximum gain, beam scanning, bandwidth performance, efficiencies, and impedance matching in the whole frequency band of interest. Finally, the performance of the three lenses is also experimentally evaluated and compared to a single omni-directional antenna and to a ten-element uniform linear array of omni-directional antennas in real 60 GHz wireless personal area network indoor line-of-sight (LOS) and obstructed-LOS environments, obtaining interesting and promising remarkable results in terms of measured received power and root-mean-square delay spread. At the end of this paper, an innovative switched-beam antenna array concept based on the presented cylindrically distributed effective parameters lens is also introduced and completely evaluated, confirming the potential applicability of the proposed antenna solution for future 5G wireless millimeter-wave communication system.

Polarization-dependent bi-functional metasurface for directive radiation and diffusion-like scattering

In this paper, we design a bi-functional metasurface with different spatial distribution of reflection phase responses depending on the incident polarization. The metasurface with a thickness of only 0.067 λ0 (λ0 is the working wavelength) is constructed by unit cells composing two orthogonal I-shaped metallic structures, and the reflection phase for x- and y-linearly polarized incidence can be independently controlled by the geometric parameters. The metasurface can work as a flat parabolic reflector antenna with a maximum gain reaching about 22 dBi around 9.5 GHz, when it is illuminated by the x-polarized feed source of an offset open-ended waveguide antenna. Meanwhile, designed with randomly distributed reflection phases, the proposed metasurface can behave as an electromagnetic (EM) diffusion-like surface, which is capable of suppressing the backward scattering in a broadband from 8.5 GHz to 14 GHz for y-polarized incidence. By this strategy of EM functionality integration, a metasurface reflector antenna equipped with stealth technique to achieve simultaneously high gain and low backward scattering is obtained. Finally, experiments have been carried out to demonstrate this design principle, which agree with the simulation results. The proposed metasurface could offer a promising route for designing EM devices with polarization-dependent multi-functionalities.

Wideband and Large Coverage Continuous Beam Steering Antenna in the 60-GHz Band

A wideband and continuous beam steering flat antenna is proposed in the 60-GHz band. The antenna consists of two layers and is made of two parts: 1) a feeding network and 2) a slotted plate. The relative rotation movement between the two antenna parts generates a phase gradient across the radiating part, and a continuous beam is generated in the upper hemisphere. The mechanical movement between the two antenna parts is facilitated by the use of gap waveguides; therefore, no electrical contact is needed between the two metallic parts. To validate the antenna concept, an antenna has been designed and fabricated in the 60-GHz band. Good agreement has been obtained between the simulations and the measurements. The antenna field of view is up to ±60°. The antenna bandwidth is up to 13% for VSWR <2. The loss within the antenna structure is estimated to be around 0.86 dB.

THE RATIO OF THE HARMONICS LEVELS OF THE SCATTERED FIELD IN NONLINEAR LOCATIONS

The article discusses about the advantages of using the methods of nonlinear location in the field of technical protection of information. It is shown that searching for radio electronic equipment as a nonlinear scattered (NS) efficiently implement the Non Linear Junction Detector (NLJD). The efficiency of NLJD associated with the choice of thresholds of the ratio of the received multiple harmonics levels. It becomes relevant analytical estimation of the optimal values of the thresholds of identification, with considering the power level of the probing signal of NLJD and the non-linear effective square of scatterer of mortgaged devices. It is advisable to use the simulator of mortgaged device on the basis of two-way flat spiral antenna with semiconductor diode in the load. Working on the simulator in the microwave field from NLJD leads to deformation of the current-voltage characteristics of the diode. During the investigations, it was found that the overestimation of threshold is only suitable to mask for high-power NLJD radiation in probing the LDCs with a small non-linear effective square of scatterer. The threshold is a criterion of reliable identification of inefficient for low-power NLJD radiation in probing the NS with the big non-linear effective square of scatterer.

A compact printed multistubs loaded resonator rectangular monopole antenna design for multiband wireless systems

In the present article, a compact triple-band multistubs loaded resonator printed monopole antenna is proposed. The antenna consists of a quarter wavelength two asymmetrical inverted L-shaped stubs to excite two resonant modes for 3.5/5.5 GHz bands and one integrated horizontally T-shaped stub with inverted long L-shaped stub to excite resonant mode for 2.5 GHz band. By loading these stub resonators along y-axis with distinct gaps, the antenna resonates at three frequencies 2.57/3.52/5.51 GHz covering the desired bands while keeping compact size of 24 × 30 mm2 (0.2 λ0 × 0.25 λ0). The proposed antenna is fabricated on Rogers RT/duroid 5880 substrate with thickness 0.79 mm and its performance experimentally verified. The measured results reveal that the antenna has the impedance bandwidths of about 210 MHz (2.50-2.71 GHz), 260 MHz (3.37-3.63 GHz), and 650 MHz (5.20-5.85 GHz), for 2.5/3.5/5.5 GHz WiMAX and 5.2/5.8 GHz WLAN band systems. The antenna provides omnidirectional radiation patterns and flat antenna gains over the three operating bands. In addition, the design approach and effects of multistubs resonator lengths on the operating bands are also examined and discussed in detail.

Metamaterial Demonstrates Both a High Refractive Index and Extremely Low Reflection in the 0.3-THz Band

Communication and imaging in the terahertz waveband have advanced rapidly in offering industrial applications. However, optical elements such as collimated lenses in the terahertz waveband are bulky compared with the wavelength due to the lack of naturally occurring substances with a high refractive index and low loss. It is essential to miniaturize optical elements in the terahertz waveband for industrial application. Metamaterials consisting of subwavelength structures can arbitrarily control permittivity and permeability and provide a range of refractive indices. Here, we demonstrate a metamaterial with both a high refractive index and extremely low reflection consisting of symmetrically aligned paired cut metal wires with 18,800 units on the front and back surfaces of a dielectric substrate. Measurements by terahertz time-domain spectroscopy (THz-TDS) confirm a high effective refractive index of 6.66 + j0.123, extremely low reflection power of 1.16%, and the unprecedented high figure of merit (FOM = |n real/n imag|) of above 300 in the 0.3-THz band. Components with such specifications would enable miniature, high-performance optical elements in the terahertz waveband such as ultrathin flat antennas with high directivity. Further, the concept of the metamaterial with both a high refractive index and extremely low reflection potentially offers a wide range of attractive applications such as solid immersion lenses and cloaking devices.

Dual-band circularly polarized flat antenna with plano convex and concave slots for RFID readers

This article has proposed a circularly polarized dual-band antenna with unidirectional pattern operating at the bandwidth frequencies of 920–925 MHz and 2.40–2.48 GHz for radiofrequency identification (RFID) readers. The proposed antenna structure is of a radiating patch with a single feeder and two pairs of plano convex and concave slots. This work has innovated and utilized the convex and concave slotting technique to generate the circular polarization. The simulated results showed that the dual-band antenna is of circular polarization (CP) and unidirectional radiation pattern with the 3 dB axial ratio and the respective gains of 1.31 and 1.36 dBic for the experimental lower and upper bandwidth frequencies. An antenna prototype was subsequently fabricated and tests performed. The simulated and measured results are in good agreement, rendering the proposed dual-band antenna with plano convex and concave slots suitably applicable to the ultrahigh frequency and microwave RFID readers.

A Microwave Free-Space Method Using Artificial Lens with Anti-reflection Layer

This paper describes a microwave free-space method using flat artificial lens antennas with anti-reflection layer. The lens antenna is made of an artificial material of metal particle. Comparing with our previous study, Anti-reflection (AR) layers are supplemented to the lens in this study to obtain a wave matching on the air-lens interface. The improved lens is in a disk shape of 50 mm diameter and 5.9 mm thickness. The lens is applied in a free-space setup, in which it is set in front of a patch antenna resonating at 15 GHz to get a high gain. The free-space setup is used to measure microwave attenuation and phase shift through a sawdust sample. The experimental results show that the multiple-reflection in the free-space method becomes small, because the reflection on air-lens interface has been reduced. The proposed AR lens antenna is flat and very small in the size. It is possible to construct a very compact and low cost free-space setup using the improved lens.

The nonlinear radar testing on the reliability of the objects’ identification

The nonlinear radar testing using a single wideband simulator of the laying device is considered. It is shown that the simulator on the basis of the flat two-armed spiral antennas with semiconductor diode in the load has a thermal sensitivity to electromagnetic field. The energy dissipation of the probe signal leads to deformation of the current-voltage characteristics (CVC) of the diode composed of the simulator. Parameter $\gamma$ is introduced as the degree of closeness to the equilibrium state of the diode. It characterizes the degree of CVC deformation during sensing. According to the experimental data normalized approximating function (NAF) depending on the parameter $\gamma$ is obtained. The phenomenon of a lens identification attribute inversion using NAF is investigated. It consists in changing the ratio between the levels of second and third harmonics response signal to the opposite value. The acquisition of unmasking properties of the structure "metal-oxide-metal" by simulator is identified. The maximum frequency distribution of the unmasking sign inversion occurrence depending on the normalized voltage value of operating point displacement of the diode composed of the simulator is received. It is suggested to capture the unmasking sign inversion of the simulator to judge the reliability of embedded devices detection and identification by the ability of nonlinear radar.

Simultaneous Generation of Pseudo-Bessel Vortex Modes with a RLSA

This letter shows that it is possible to simultaneously generate, in the microwave frequency band, several pseudo-Bessel beams having an azimuthal field variation, characteristic of vortex modes, by making use of a single flat antenna. Specifically, a radial line slot array has been designed to prove the concept. The design benefits of a Butler matrix network to provide the correct phase progression along the azimuthal coordinate, and it makes use of a holographic approach to assure the required aperture field distribution.

Evaluation of ion current density distribution on an extraction electrode of a radio frequency ion thruster

The radial distributions of ion current density on an ion extracting electrode of a radio frequency (RF) ion thruster (RIT) with an inductive plasma source were obtained using probe diagnostics of the RF xenon plasma. Measurements were carried out using a plane wall probe simulator and the VGPS-12 Probe System of Plasma Sensors Co. At xenon flow rate q = 2 sccm plasma pressure was 2 · 10−3 Torr, incident RF generator power varied in the range Pg = 50−250 W with RF power absorbed by plasma up to Pp = 220 W. Ion current densities were determined using semi- and double-logarithmic probe characteristics by linear extrapolations of their ion branches to probe floating potentials. The same parameters were also measured in undisturbed plasma by a classic cylindrical probe. They exceeded plane probe data by more than two times, showing the effectiveness of plasma sheath reproduction of the RIT ion extracting electrode by the plane wall probe simulator. Slight non-uniformity of the resulting plasma distributions and simplified RIT model design showed that the studied device with flat antenna coil and ferrite core could be considered as a promising prospect for RITs of new generation.

Microwave dielectric stepped-index flat lens antenna

Dielectric stepped-index flat lens antennas for operation at 12 GHz are presented. A brick-shaped dielectric with a permittivity profile optimized for focusing is sandwiched between the metallic plates of an open-ended parallel-plate waveguide. A tapered slot antenna is placed at the focal point of the dielectric lens, thereby creating antennas with high directivity of 16.8 and 15.8 dBi, respectively. In the two versions of the antenna, the parallel-plate waveguide operates in TEM-mode and in the first higher-order TE-mode, respectively. The dielectric profile is realized by appropriate mixtures of alumina ceramic powder and microscopic hollow glass spheres, realizing permittivity ranging from εrel= 1.31 to εrel= 3.24. The design of the complete antennas is based on geometrical optics followed by optimizations with a full-wave electromagnetic solver. Measurements show good agreement with simulations.

Compensation of integrator time constants for electric field measurements

Rubinstein et al. (2012) [1] examined a method to compare electric fields from lightning discharges measured with analogue integrators of different time constants. The time constant distorts the waveforms and has to be corrected numerically. We have extended the work of Rubinstein et al. (2012) [1] by considering the antenna characteristics in the system equations. In this paper we focus on the compensation of the integrators time constant and present some cases and results after applying the method. Furthermore we discuss the importance of any existing offset errors. A simple approach for handling the offset will be presented. Examples and determination of continuing currents are given in section IV. Advantages of the compensation method are mentioned in the conclusion. Together with Appendix A (system equations) this paper can be seen as a reference to a profound understanding of the measurement methods of E-fields with flat plate antennas for lightning researchers.

A COMPACT AND WIDEBAND FLAT LENS ANTENNA BASED ON APERTURE COUPLED PATCHES FOR X-BAND APPLICATIONS

This paper presents a wideband and compact flat lens antenna for X-band applications. An 8×8 array of this antenna is designed and realized by using aperture coupled patches from the multilayer Frequency Selective Surface concept. The basic antenna element configuration of this design consists of two back-to-back printed patches with a common ground plane coupling. A pair of identical slots is embedded on the ground plane to provide the necessary phase error compensation between receive and transmit apertures. The lengths of the two slots are varied simultaneously to investigate how much phase shift range can be achieved with this simple design structure. The antenna elements are simulated using the electromagnetic simulation software CST Microwave Studio. A 209° transmission phase range was achieved with transmission coefficient variations of better than -2.25 dB. The gain of the feeding horn antenna used is 9 dB at 10 GHz. Upon the implementations of the lens structure, the gain of the overall antenna system has increased to 16 dB. Our simulation shows a 3-dB transmission bandwidth of around 33% could be achieved for the unit cell. Radiation pattern simulation of the antenna system shows a good symmetry between E and H-plane with a half-power beamwidth of 19.2° and 19.0° in E-plane and H-plane respectively. The gain is greater than 9 dB from 8 to 12 GHz with maximum gain of 16 dB is achieved at 10 GHz. The proposed antenna design uses a simple and less fabrication complexity mechanism for phase error correction.

BROADBAND SCATTERERS IN NONLINEAR RADAR

The problem of a single nonlinear scatterer simulator introduction for the detection of appointment parameters of nonlinear radars is solved. It is shown that for an objective comparison of nonlinear radars by appointment parameters in the real world it is necessary to take intoaccount the narrowband off-site sources and response of structures «metal-oxide-metal» radiation effect on the dissipated by nonlinear object signal. The regular simulators of scatterers included in the assembly of nonlinear radar, can not be used as reference because they are resonant. It is proposed to use a simulator of a nonlinear scatterer based on flat double-spiral antenna with non-linear matched load, as by broadband and elliptical polarization be effective absorption of the energy of the probing signal with subsequent re-emission weighty in terms of non-linear products as compared with the radiation of a narrowband off-site sources and spectral components of the response of structures «metal-oxidemetal ». Carried out in the «field» conditions, experimental studies have confirmed these benefits over the regular imitator of the proposed calibration scatterers. The measurement for nonlinear radar maximum distance detection of simulators sampling based on flat double-spiral antenna with matched nonlinear load shown a high reproducibility of parameters of scatterers, so one can use them as references.

Integral electrical characteristics and local plasma parameters of a RF ion thruster.

Comprehensive diagnostics has been carried out for a RF ion thruster based on inductively coupled plasma (ICP) source with an external flat antenna coil enhanced by ferrite core. The ICP was confined within a cylindrical chamber with low aspect ratio to minimize plasma loss to the chamber wall. Integral diagnostics of the ICP electrical parameters (RF power balance and coil current) allowed for evaluation of the antenna coils, matching networks, and eddy current loss and the true RF power deposited to plasma. Spatially resolved electron energy distribution functions, plasma density, electron temperatures, and plasma potentials were measured with movable Langmuir probes.

Circularly-polarized capacitively-fed UHF-RFID antenna with truncated reverse-arc shape

This article presents a circularly polarized (CP) flat antenna with truncated corners using the capacitively coupled feed technique for UHF RFID applications. A radiating plate, an air gap and a ground plane constitute the antenna. The reverse-arc shape truncated corners are utilized to generate a CP radiation and the suspended structure antenna using the capacitively coupled feed technique is adopted to enhance bandwidth. A prototype antenna was fabricated and its measured results were 13% for the bandwidth and 11.54% for the 3-dB axial ratio (AR) bandwidth. The half-power beamwidths of the left hand circular polarization on x–y and x–z planes were both greater than . The measured gain on the UHF RFID system was greater than 5.90 dBic.

An ultra flat phased array Ku-band antenna with integrated receivers in SiGe BiCMOS

A highly integrated Ku-band (10.7–12.75 GHz) planar phased array receiver of 64 antenna elements is presented. It features instantaneous reception of the full Ku-band (2.05 GHz wide) in two orthogonal polarizations with wide scan angles by using time delay instead of phase shift. The receiver is part of a system for satellite broadcast TV reception on board of moving vehicles. Two SiGe radio frequency integrated circuits (RFICs) were developed, packaged in ceramic BGAs and assembled onto a 15-layer printed circuit board (PCB) which integrates the antenna elements. An outline of the system is given along with a detailed description. It sets a new standard in integration density. The receiver has extensive analog signal processing at intermediate frequency (IF)-level. A novel bipolar implementation for true time delay is proposed, with a continuous programmable delay range of 0…80 ps with less than 2.5 ps group-delay variation in 2 GHz bandwidth (BW). The wide BW calls for a constant group-delay implementation in the IF chain. The receiver (RFIC) consumes only 132 mW per channel. Each channel has 40 dB gain.

Knee MRI under varying flexion angles utilizing a flexible flat cable antenna.

The aim of this study is to fabricate and test a novel flexible flat cable antenna (FFCA) for MRI of the knee at different flexion angles. The FFCA was made of a flat cable, a tuning/matching circuit and a signal transmission line. To test its feasibility and validity, in vitro and in vivo experiments were carried out on a 3.0 T MR scanner. The in vitro experiment suggested that the proposed FFCA could achieve a high signal-to-noise ratio (SNR) of 336, while the SNR of an eight-channel knee coil was 291, and phantom images from the FFCA are homogeneously distributed. In the in vivo experiment, the FFCA had a higher SNR of 169 in the region of interest and more than 48.5 cm of longitudinal coverage, while the corresponding values for the commercial coil were 153 and 22.5 cm. Finally, five sagittal knee images at different flexion angles were acquired. The FFCA could acquire satisfactory knee images at different flexion angles, with the advantages of simplicity, low cost, large field of view and high SNR. It may therefore be further used to improve MR image quality of the knee joint.