Periodic Array Antenna Research Articles

Metamaterial-Loaded 16-Printed Log Periodic Antenna Array for Microwave Imaging of Breast Tumor Detection

This article presents printed log periodic antennas with metamaterials for use in microwave imaging. A single layer of epsilon negative (ENG) metamaterial (MTM) array (1 × 6) of the unit cell is on the radiating patch. Adding a single negative metamaterial structure enhances the properties of far-field antennas, such as radiation pattern and gain, both of which are vital for breast imaging. Two frequency bands exhibit negative permittivity: 3–3.3 GHz and 3.6–4.5 GHz. In the operating band, the proposed antennas have achieved a maximum gain of 5.5 dBi and impedance bandwidth of 3 GHz (2–5 GHz) with a reflection coefficient less than −10 dB. At the lowest operating frequency of 2 GHz, the electrical dimensions of this designed antenna are 0.34λ × 0.26λ × 0.01λ. All 16 transceiver antennas are arranged vertically in a circular pattern around the phantom, each acting as a transmitter and the rest as receivers. The system design is carried out with the electromagnetic simulators CST and HFSS. After receiving the extracted data, the data are postprocessed using the MATLAB software and the delay multiply and sum (DMAS) imaging algorithm. Based on the reconstructed image, it is evident that the MTM-loaded antenna-based imaging system can detect many undesired tumors inside the breast phantom.

Radiation Pattern Synthesis of the Coupled almost Periodic Antenna Arrays Using an Artificial Neural Network Model

This paper proposes radiation pattern synthesis of almost periodic antenna arrays including mutual coupling effects (extracted by Floquet analysis according to our previous work), which in principal has high directivity and a large bandwidth. For modeling the given structures, the moment method combined with the generalized equivalent circuit (MoM-GEC) is proposed. The artificial neural network (ANN), as a powerful computational model, has been successfully applied to antenna array pattern synthesis. Our results showed that multilayer feedforward neural networks are rugged and can successfully and efficiently resolve various distinctive, complex almost periodic antenna patterns (with different source amplitudes) (in particular, both periodic and randomly aperiodic structures are taken into account). An ANN is capable of quickly producing the synthesis results using generalization with the early stopping (ES) method. Significant advantages in speed and memory consumption are achieved by using this method to improve the generalization (called early stopping). To justify this work, several examples are shown and discussed.

Modified 16-Quasi Log Periodic Antenna Array for Microwave Imaging of Breast Cancer Detection

In this paper, an effective system for microwave imaging of breast tumor detection using modified 16-planar log periodic antenna (PLPA) array is presented. The modified PLPA operates in the band from 2 to 5 GHz with stable directional patterns in the end-fire direction. Once the results of a single antenna element have been validated, the design is extended to include 16 antenna elements. All 16 transceiver antennas are vertically placed around the phantom in a circular manner where one antenna acts as a transmitter and the rest work as receivers. Delay and Sum (DAS) algorithm is used for post processing the acquired scattered signals from the sensors to reconstruct the image of the breast and to identify the existence of breast tumors. The electromagnetic simulators CST and HFSS are used to design the system, while MATLAB is used to process the data. The developed PLPA array-based microwave imaging system performs admirably, making it one of the most effective systems for detecting tumor cells.

Ultrasensitive critical-state of upconversion nanoparticles assembled on plasmonic antenna arrays for rapid and accurate determination of NH3

Plasmon enhanced upconversion luminescence has drawn extensive attention due to its advances in the fields of optical sensors, bio-detection and medical diagnosis. However, the coupling state between plasmon and upconversion emission is never clearly revealed. Here, we report a novel critical state in plasmon coupled upconversion nanoparticles (UCNPs) that has a long lifetime and is highly stimuli-responsive. The critical state is generated through the precise control over the coupling between plasmonic local field and optical near field. Platinum (Pt) film with thickness of ~7 nm is deposited on photonic crystals to form a periodic plasmonic antenna arrays. UCNPs with inert shells are embedded in plasmonic antenna arrays with a tunable plasmon coupling distance via the thickness control of inert shells. An ultrasensitive critical state is observed for the coupling distance of ~10 nm between Pt film and NaGdF4:Yb/Er luminescent core, accompanied with light confinement by NaYF4/NaGdF4 heterojunction shells. This critical-state can be employed as an ultrasensitive route for fluorescent detection of NH3 and the lowest detection of 0.47 ppm can be achieved that is about 34 times lower than ever reported.

Parametric Analysis of Linear Periodic Arrays Generating Flat-Top Beams

Several synthesis techniques are available to optimize amplitude and phase excitations of periodic linear arrays to generate flat-top beams. Clearly, the optimal tapering depends on design parameters such as the array length, the number of array elements, the beam flatness, the beam width, the side lobe levels, and others. In this paper, in order to derive useful guidelines and rule of thumb for the synthesis of periodic array antennas, relations between these parameters are derived employing linear programming techniques, which guarantee optimality of the solutions. Such relations are then plotted and used in some design examples.

Gaussian Approach for the Synthesis of Periodic and Aperiodic Antenna Arrays: Method Review and Design Guidelines.

This paper presents a complete overview of the recently developed Gaussian approach for the synthesis of both periodic and aperiodic linear antenna arrays in conjunction with an exhaustive numerical investigation of the achievable performance. The position and excitation synthesis problems are jointly modeled to enable a direct mutual comparison between the two strategies. To this aim, different parameter settings are selected to analyze the results in terms of achieved beamwidth and maximum sidelobe levels as a function of the array aperture and of the number of radiating elements. The insights inferred from this numerical investigation are exploited to derive a novel first-step procedure with the purpose of enabling an antenna engineer to quickly identify the most suitable design approach, thus reducing the time required for antenna system development.

Phase change materials in photonic devices

Recent developments in reconfigurable photonic devices highly rely on the effective refractive index change enabled by phase change materials (PCMs) as either dielectric surroundings or constituting materials. This universal characteristic, tunable refractive index, is shared among various kinds of PCMs and has been successfully utilized to achieve multilevel modulations for both free-space and integrated photonics. In this Perspective, we briefly recapitulate the fundamental mechanisms of phase transitions for three dominant PCMs. The progress in integrating different PCMs with on-chip silicon photonics and periodic antenna arrays are reviewed and analyzed in parallel. We also discuss the existing problems of PCM photonics, for example, the compatibility with commercial production line, the stability issue, and accessibility of the stimuli. In the end, we provide the outlook for the improving material engineering of PCM and multi-functional PCM-based photonics devices.

Corrections to “Q-Factor and Bandwidth of Periodic Antenna Arrays Over Ground Plane”

Corrections to “<i>Q</i>-Factor and Bandwidth of Periodic Antenna Arrays Over Ground Plane”

Scattering Characteristics of Ultra-Wideband Antenna Arrays

This paper presents a study of the monostatic and bistatic radar cross-section (RCS) of three planar two-dimensionally periodic antenna arrays with the same aperture size: arrays of conductors of variable square cross-section, TEM horns, and rectangular metal waveguides. The results of numerical simulation of the arrays using the finite element method showed that, under normal plane-wave incidence, the monostatic RCS of the array of square conductors is smaller by 10…30 dB than that of the waveguide array in the frequency band wider than 10 : 1. For one linear polarization of the incident plane wave, the RCS of the array of TEM horns is close to that of the waveguide array and, for the other, it is close to the RCS of an array of conductors of variable square cross-section. With an increase in the incidence and observation angles, the difference in monostatic RCS decreases. The scattering patterns of the array of conductors of variable square cross-section for various frequencies and angles of plane-wave incidence are presented and compared with those of the waveguide array under normal incidence.

Stored Energies and Q-Factor of Two-Dimensionally Periodic Antenna Arrays

The Q-factor for lossless three-dimensional structures with two-dimensional periodicity is here derived in terms of the electric current density. The derivation in itself is shape-independent and based on the periodic free-space Green's function. The expression for Q-factor takes into account the exact shape of a periodic element, and permits beam steering. The stored energies and the radiated power, both required to evaluate Q-factor, are coordinate independent and expressed in a similar manner to the periodic Electric Field Integral equation, and can thus be rapidly calculated. Numerical investigations, performed for several antenna arrays, indicate fine agreement, accurate enough to be predictive, between the proposed Q-factor and the tuned fractional bandwidth, when the arrays are not too wideband (i.e., when $Q\geq 5$). For completeness, the input-impedance Q-factor, proposed by Yaghjian and Best in 2005, is included and agrees well numerically with the derived Q-factor expression. The main advantage of the proposed representation is its explicit connection to the current density, which allows the Q-factor to give bandwidth estimates based on the shape and current of the array element.

Two-Dimensional Periodic Dual-Polarized Over Wave Region Antenna Array

The two-dimensional periodic dual-polarized antenna array in the form of a nonuniform multiconductor line of square cross-section conductors is proposed and studied. Using the approximate theory, matching characteristics of the two-conductor line with three different laws of impedance variation are studied and the optimum law is found. Electrodynamic modeling of an infinite two-dimensional periodic array of these elements is carried out using the finite element method at different scanning modes. Using a numerical experiment, the possibility of implementing the over wave region matching mode is demonstrated for arrays of 144 (12 × 12) and 576 (24 × 24) elements: for the array of 576 elements, the working bandwidth in the cophased mode was 1 : 34; when scanning in the sector of 90°, more than 1 : 15.

Compact High Gain Leaky-Wave Antennas Based on Substrate Integrated Waveguide TE220 Mode

In this paper, novel compact high gain broadband leaky-wave antenna (LWA) using TE220 high-order mode is proposed. The high-order mode antenna not only possesses more compact structure with higher gain, but also simplifies the feeding network of the antenna array and relaxes processing tolerance. The radiation element consists of an SIW cavity etched with 2×2 slot array on the top surface, which is excited by a microstrip-slot coupling structure. Microstrip spoof surface plasmon polariton (SPP) is worked as a slow-wave transmission line (TL) to increase the beam scanning range of a four elements periodic array antenna. The antenna was simulated, optimized and fabricated, which verified theoretical analysis. Experimental results show that the linearly polarized (LP) beam scanning antenna has a bandwidth of 53.5% (from 12.6 GHz to 21.8 GHz) with beam scanning range from -24° to +32° and gain in the range of 10.2 dBi to 12.4 dBi. Then a linear-to-circular polarization converter is loaded to implement a circular polarization (CP) beam scanning antenna. The proposed antenna has the features of compact size, low profile, high gain, large beam scanning range and flexible polarization conversion.

W Band Imaging System Using Linear Sparse Periodic Antenna Array and Compressive Sensing for Personnel Screening

This paper presents our study on a W band imaging system consisting of a linear sparse periodic antenna array (SPA) with only 10 transmitting (Tx) and 10 receiving (Rx) elements in simulation and experiment for the purpose of personnel screening. We have devised a simplified and low cost experimental set-up using only 1 Tx and 1 Rx channels located on two scanning tracks separated by a distance to verify the proposed multi-static array imaging scheme. The simulation has taken account of the effects of track separation and measured antenna patterns. The simulation and experiment correlate quite well, indicating a resolution of about 7 mm at 1.3 m distance. Furthermore, based on the experimental data, we have investigated the compressive sensing (CS) image reconstruction as an approach for further reducing the sampling points in such a multi-static array imaging system. It is shown that using a discrete SPA-CS imaging algorithm, the images can be successfully reconstructed with the data as few as 30% of that used in the traditional holographic/synthetic aperture radar (SAR) imaging algorithm. Therefore, the CS image reconstruction is proved to be feasible for building a low-cost and fast millimeter wave imaging system.

Narrow-Width Periodic Leaky-Wave Antenna Array for Endfire Radiation Based on Hansen–Woodyard Condition

This communication presents a periodic leaky-wave antenna array with the advantages of a high endfire gain at the center frequency and a stable endfire radiation beam over the entire operating band. The antenna has a narrow width and consists of multiple monopoles located on the microstrip line. It can be fabricated by line-cutting copper strips. The antenna has a high endfire gain because it is a leaky-wave antenna designed based on the Hansen–Woodyard condition. With a length of $5.5\lambda _{0}$ and a width of $0.33\lambda _{0}$ , a measured endfire gain of 12.9 dBi is achieved at the center frequency of 5 GHz. Good matching and stable endfire radiation beams are achieved over the entire operating band from 4.5 to 5.5 GHz. Good agreement between the measurement and the simulation has been obtained.

Lens Antenna for Wide Angle Beam Scanning at 79 GHz for Automotive Short Range Radar Applications

This communication presents the design and experimental verification of a substrate integrated waveguide fed lens antenna for 79 GHz automotive radar applications. The proposed integrated lens antenna consists of a six layer cylindrical Luneburg lens illuminated by 17 source elements of substrate integrated waveguide fed by a planar log periodic dipole antenna array. The Luneburg lens is developed by using a unique foam material AirexR82 ( $\varepsilon _{r} = 1.12$ ), which is drilled and pressed to achieve the different dielectric constant needed to follow the index law inside the lens. The return loss and the radiation characteristics of the proposed integrated lens antenna are investigated and validated by measurements. A good agreement between the measured and simulated results is observed. The measured results confirm the beam scanning capability of the proposed integrated lens antenna for a wide scan angle of ±85° in azimuth plane having a maximum antenna gain of 15 dBi at 82.5 GHz and gain drop of less than 2.75 dB for the edge feeds. The estimated radiation efficiency of the antenna is found to be 67% at 82.5 GHz.

An Accurate Modeling Technique for Periodic Antenna Arrays—Experimental Validation

In the context of large periodic antenna arrays, a modelling technique implementation and its experimental validation on a 16-element array are presented. This passive array is designed to radiate linear polarization in Ka-band (19.7- 20.2 GHz). It is a preliminary step of the modelling of a much larger array of 1024 radiating elements. Existing antenna arrays simulation techniques allow the representation of an infinitely surrounded unit cell through periodic boundary conditions. However, large arrays can be difficult to model accurately. A new wideband modelling technique for large periodic antenna arrays is used to reconstruct the scattering matrix of the 16-element array. This technique is based on periodic reconstruction and requires only small calculation volumes. Results obtained with this technique are then compared to full-wave results. Finally, experimental results are presented and a comparison between measurements, full-wave calculation and periodic reconstruction is done.

Ultrasensitive molecular absorption detection using metal slot antenna arrays.

We theoretically study the transmission reduction of light passing through absorptive molecules embedded in a periodic metal slot array in a near infrared wavelength regime. From the analytically solved transmitted light, we present a simple relation given by the attenuation length of light at the resonance wavelength of the slot antennas with respect to the spectral width of the resonant transmission peak. This relation clearly explains that the control of the transmission reduction even with very low absorptive materials is possible. We investigate also the transmission reduction by absorptive molecules in a real metallic slot antenna array on a dielectric substrate and compare the results with finite difference time domain calculations. In numerical calculations, we demonstrate that the same amount of transmission reduction by a bulk absorptive material can be achieved only with one-hundredth thickness of the same material when it is embedded in an optimized Fano-resonant slot antenna array. Our relation presented in this study can contribute to label-free chemical and biological sensing as an efficient design and performance criterion for periodic slot antenna arrays.

Near Field Properties and Plasmonic Effects of a Periodic Bowtie Antenna Array Embedded in a Substrate with Different Depths

 Abstract—We numerically investigate the near field properties and plasmonic effects of a periodic bowtie antenna array which is embedded in a substrate with different depths by means of finite element method with three-dimensional calculations. The electromagnetic modes obtained from the embedding cases are quite different from that of air background case of the same size, resulting in an intensity enhancement and a redshift phenomenon. We find that the embedded depth of the bowtie antenna in a silica substrate is an important parameter which can influence the field enhancement and the position of peak resonant wavelengths. The near-field intensity becomes less intense and the spectrum of peak resonances red-shifted as the embedded depth is increased.

ANALYSIS OF A WIDE SPECTRAL RANGE PLASMONIC OUTLINE BOWTIE ANTENNA RANGING IN 0.3-5.0 μm

We numerically analyze a broadband plasmonic outline bowtie antenna over a large parameter space by means of finite element method with three-dimensional calculation. The antenna is composed of a pair of triangular gold with outline shape placed in close proximity to each another. We show how the structural parameters affect the antenna resonance conditions, such as peak resonances wavelengths, electric field intensities, propagation properties, component field and total field distributions, charge densities and electrical filed stream lines at spectral points of interest. In addition, the characteristics of transmittance spectral of a periodic antenna array corresponding to the bonding mode and anti-bonding mode are investigated as well. Simulation results show that it is possible to tune an antenna with a constant length over a wide spectral range (ranging in 0.3–5.0μm or more range) while maintaining a constant antenna dimension, reduce the antenna footprint by a factor of 4.98, and increase the gap enhancement by 23%. This article has been removed from the website on January 3, 2013, because it has been found to violate plagiarism rule of our journal. Received 18 October 2012, Accepted 16 November 2012, Scheduled 7 December 2012 * Corresponding author: Yuan-Fong Chau (yfc01@uch.edu.tw).

Periodic Leaky-Wave Antenna Array With Horizontally Polarized Omnidirectional Pattern

A novel periodic leaky-wave antenna for broadside radiation with horizontally polarized omnidirectional pattern is proposed, designed and demonstrated experimentally. The objective is to achieve a horizontally polarized omnidirectional antenna array with highly directive beam. The proposed structure is based on combining the rotating electric field method and a leaky-wave antenna design. By properly designing a unit cell with a pair of crossed dipoles spaced at a distance approximately equal to λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</sub> /4 at the center frequency, not only omnidirectional radiation pattern with horizontal polarization is obtained by crossed dipoles fed in phase quadrature, but also the open-stopband effect exhibited at broadside scan is significantly reduced. The analysis and design of this structure are performed on the basis of a simple equivalent network model. A finite structure formed by 16-unit cell (32-element) for broadside beam is developed at the 2.4 GHz band, which offers a horizontally polarized omnidirectional radiation pattern with enhanced gain of 9.9-10.6 dBi and measured radiation efficiency of 90% for the covering bands.