MEMS-reconfigurable metamaterials and antenna applications

This paper reviews some of our contributions to reconfigurable metamaterials, where dynamic control is enabled by micro-electro-mechanical systems (MEMS) technology. First, we show reconfigurable composite right/left handed transmission lines (CRLH-TLs) having state of the art phase velocity variation and loss, thereby enabling efficient reconfigurable phase shifters and leaky-wave antennas (LWA). Second, we present very low loss metasurface designs with reconfigurable reflection properties, applicable in reflectarrays and partially reflective surface (PRS) antennas. All the presented devices have been fabricated and experimentally validated. They operate in X- and Ku-bands.Comment: 8 pages; 8 figures; International Journal of Antennas and Propagatio

Realizing Tunable Inverse and Normal Doppler Shifts in Reconfigurable RF Metamaterials

This work is supported by the National Basic Research Program (973) of China (No.2011CB922001), and National Natural Science Foundation of China (No.11234010

Low-Profile Metamaterial-Based Adaptative Beamforming Techniques

In this chapter, we will review recent research advances on beamforming and spatial multiplexing techniques using reconfigurable metamaterials (MTMs) and metasurfaces. This chapter starts by discussing basic principles and practical applications of transmission line-based metamaterials and planar metasurfaces, followed by their active versions that enable novel smart antennas with beam steering and beamshaping functions. We include detailed descriptions of their practical realizations and the integration with circuits and the radio-frequency (RF) frontend, which are used to adaptively and dynamically manipulate electromagnetic radiation. We summarize the state-of-the-art MTM/metasurface-based beamforming techniques and provide a critical comparison for their uses in the RF-to-millimeter-wave range in terms of cost, reconfigurability, system integratability and radiation properties. These techniques are expected to pave the way for the massive deployment of communication, radar, remote sensing and medical and security imaging systems

A Miniaturized Printed Circuit CRLH Antenna-based Hilbert Metamaterial Array

With the development of communication systems and antennas, various challenges arise that require antennas of small size with enhanced performance. Metamaterials (MTM) defects introduced a considerable solution to such a challenge. Therefore, in this paper, a lightweight with low profile antenna is designed based on a novel design of a Composite Right/Left-Handed CRLH-MTM Hilbert array. The proposed CRLH-MTM unit cell consists of a T-symmetric CRLH unit cell conjugated to the 3rd-order Hilbert on the ground plane through a T-stub structure to enhance the gain-bandwidth product. CST-MWS is used to stimulate and design the proposed antenna structure. The antenna parameters are optimized to evaluate the antenna performance in gain and S11. As a result, the antenna can operate forward and backwards with a large scanning angle ranging from +34o to -134o with changing frequency, and dual-band extended from 3.3GHz to 4.2GHz 4.86GHz 5.98GHz with a maximum gain of 7.24dBi and 3.74dBi, respectively. The beam steering is achieved by trough controlling the switching operation of PIN diodes. As a result, the antenna can scan up to 8° from 34° to 42° at 3.5GHz with constant gain along with the operating range

Analysis, design, and implementation of a reconfigurable fractal volumetric left-handed metamaterial

At the present time, one of the greatest goals to exploit the advantages of Volumetric Left-handed Metamaterials (LHM) is overcoming their very narrow operational bandwidth. This thesis proposes two schemes to efficiently solve this difficulty: 1) a mechanism which reconfigures, at will, the frequency the LHM operates at, and 2) a novel arrangement of Split Ring Resonators (SRR) based on the Sierpi\u0144ski carpet fractal pattern with two SRR sizes. Reconfigurability is implemented by cutting two splits of different widths in each ring of the SRRs. These SRRs are simulated with switches in the ON and OFF states inside an ideal simulation environment implemented in the electromagnetic modeling software HFSS where the reflection and transmission coefficients are calculated. Through simulations, each size of SRR is independently optimized and shown to have a broad frequency range where its resonance can be selected from. The two SRRs are subsequently combined in a single structure according to the Sierpi\u0144ski carpet fractal pattern. This structure is simulated again to obtain a new frequency response with two resonance frequencies near each other. A thin-wire structure is designed and coalesced with the fractal structure which results in a LHM with two transmission bands. Finally, prototypes are fabricated by mechanically etching high-frequency laminates, and tested using standard techniques. Experimental results demonstrate that the fabricated LHM is characterized by two well-defined left-handed transmission bands. Both experimental and theoretical results show a good agreement in predicting the resonances of the complex LHM structure

Compact wideband frequency reconfigurable metamaterial antenna design

This paper presents the design of compact wideband frequency reconfigurable metamaterial (MTM) antenna. The design is based on the idea of obtaining single and multi-bands in wideband metamaterial antenna within the range of bandwidth. This is achieved by introducing capacitive slots which neutralize inductive properties and generate left handed capacitive parameter. The three series slots in the patch contribute for bandwidth enhancement while two PIN Diode Switches provide multi-bands operation. Computer Simulation Technology (CST) software is used to determine the operation and effectiveness of the proposed antenna. The approach has several notable merits which include improvement of spectrum utilization, minimize spectrum congestion, interference and provide bands selectivity. From the simulation results, it was found that, bandwidth was improved to 2.8 GHz which is equivalent to 82% fractional bandwidth. Also, it can switch to seven different frequency bands of operation with only two number of switches. The realized peak gain is 2.44 dBi and 3.15 dBi at 2.4 GHz and 5.0 GHz respectively with average efficiency of 95%. The antenna can be utilized for wireless communication and cognitive radio application

Metamaterial antennas for cognitive radio applications

Cognitive radio is one of the most promising techniques to efficiently utilize the radio frequency (RF) spectrum. As the Digital Video Broadcasting-Handheld (DVB-H) band is targeted (470-862 MHz), the size of the antenna becomes challenging. Metamaterial concept is used as a miniaturization technique. Two antennas are designed, fabricated and measured. The first one achieved multiband operation by loading it with a metamaterial unit cell. These bands are controlled by engineering the dispersion relation of the unit cell. The second one, which is a 2-lumped elements loaded antenna, achieved wideband operation through the entire DVB-H band with a planar size of 5×2 cm^2. A model is proposed to explain, through simple numerical simulations and an optimization algorithm, the behavior of these component loaded antennas (which are equivalent to metamaterial inspired electrically small antennas)

Antennas using left handed transmission lines

The research described in this thesis is concerned with the analysis and design of conventional wire antenna types, dipoles and loops, based on the left-handed transmission line approach. The left handed antennas have a unique feature that the wavelength of the induced current becomes shorter with decreasing frequency. The left handed transmission line concept can be extended to construct reduced-size dipole or loop antennas in the VHF frequency band. The use of higher order modes allows orthogonal polarisation to be obtained, which is thought to be a feature unique to these antennas. Efficiency is a key parameter of left handed antennas as the heavy left handed loading increases the resistive loss. A study of the efficiency of small dipole antennas loaded with a left-handed transmission line is specially described, and the comparison with conventional inductive loading dipoles. In a low order mode, the efficiency of L-loading dipole is better with low number of unit cell. If the number of cell increases, CL-loading presents comparable and even better performance. In a high mode the meandered left handed dipole gives the best efficiency due to the phase distribution, presenting orthogonal polarization as well. The optimized dipole loaded with parallel plate capacitors and spiral inductors presents the best performance in impedance and efficiency, even better than the conventional inductive loading. A planar loop antenna using a ladder network of left handed loading is also presented. Various modes can be obtained in the left handed loop antenna. The zero order mode gives rise to omnidirectional patterns in the plane of the loop, with good efficiency. By loading the loop with active components, varactors, a tunable left handed loop antenna with a switchable radiation pattern is implemented. The loop gives an omnidirectional pattern with a null to z axis while working in an n = 0 mode and can switch to a pattern with a null at phi = 45° in the plane of the loop in an n = 2 mode

Tunable antenna design by metamaterial structures operating at S band

Un “metamaterial” por su definición ampliamente aceptada es una estructura construida artificialmente que obtiene sus propiedades materiales de su estructura en lugar de la composición de su material intrínseco. El ámbito de los materiales ha ganado mucha atención dentro de la comunidad científica en la última década. Con los continuos avances y descubrimientos conducen al camino de las aplicaciones prácticas; los metamateriales han ganado la atención de las empresas de base tecnológica y los organismos de defensa interesados en el uso de dispositivos de próxima generación. Las superficies selectivas en frecuencia (FSS) son una variedad potente de metamateriales que, dependiendo de la geometría de la superficie, se pueden utilizar para diseñar propiedades de radiación específicas tales como la emisión direccional, emisión polarizada circular y lineal, y la selectividad espectral. Los elementos de la FSS pueden ser tanto elementos metálicos sólidos como elementos metálicos con aberturas, y en los diseños tradicionales, la superficie selectiva en frecuencia (FSS) normalmente opera en torno a la resonancia de media longitud de onda de los elementos. En este proyecto se va a utilizar una superficie selectiva de frecuencia (FSS) con el fin de realizar metamateriales sintonizables -una amplia clase de metamateriales controlables diseñados artificialmente, y desarrollar una antena sintonizable que trabaje a 2.4 GHz. La FSS consiste en una serie de elementos rectángulos cargados con varactores y capacitores con una película delgada de material ferroeléctrico sintonizable (BST) para el ajuste externo de los parámetros de medio efectivo. Por lo tanto se diseñan unos varactores BST que son colocados entre los elementos metálicos que conforman la FSS. El efecto de la superficie selectiva en frecuencia es estudiado en dos antenas diferentes – antena ELPOSD (End-Loaded Planar Open-Sleeve Dipole) y una antena de parche microstrip. La antena ELPOSD consiste en un dipolo plano convencional con dos elementos parásitos muy juntos, y una carga en cada extremo del dipolo. Los beneficios principales de este tipo de antenas es que, además del rendimiento similar de la antena POSD (Planar Open-Sleeve Dipole) convencional, las antenas ELPOSD pueden ser miniaturizadas. La antena parche utilizada en este trabajo es un elemento metálico cuadrado plano alimentado a través de una línea microstrip. El material ferroeléctrico Barium Strontium Titanate (BST) es un material muy bien conocido hasta el momento. Para diseñar los varactores se utiliza una película delgada de BST, junto con los capacitores interdigitales (IDCs) que se utilizan en la capa del metal. La antena general consiste en un sustrato de múltiples capas donde en una capa se encuentra la Superficie selectiva en frecuencia (FSS) sintonizable y en otra la antena dipolo o antena de parche. La capacidad de la FSS completa varía introduciendo el material ferroeléctrico BST en el varactor. Como puede verse en los resultados, variando la permitividad del material BST de 200 a 300 se consigue una variación en frecuencia de 4.15 GHz a 3.5 GHz con una distancia alrededor de 100 MHz entre frecuencias resonantes. Esto equivale a una variación de la frecuencia alrededor del 8% entre los valores de permitividad adyacentes.A “metamaterial” by its widely accepted definition is an artificially engineered structure that gains its material properties from its structure as opposed to its intrinsic material composition. The field of metamaterials has gained much attention within the scientific community over the past decade. With continuing advances and discoveries leading the way to practical applications, metamaterials have earned the attention of technology-based corporations and defense agencies interested in their use for next generation devices. Frequency Selective Surfaces (FSS) are a potent variety of metamaterials that, depending on the surface geometry, can be used to engineer specific radiation properties such as directional emission, linear and circular polarized emission, and spectral selectivity. The elements of the FSS can either be patches or apertures, and in traditional designs, the FSS usually operates around the half-wavelength resonance of the elements. In this project a Frequency Selective Surface (FSS) is used in order to realize tunable metamaterials –a broad class of controllable artificially engineered metamaterials, and develop a tunable antenna operating at 2.4 GHz. The FSS consist of an array of square patches loaded with varactors and tunable ferroelectric thin film capacitors (BST) for external tuning of the effective medium parameters. Therefore a BST varactor is designed and located between the patches of the FSS. The effect of the Frequency Selective Surface is studied in two different antennas –an End-Loaded Planar Open-Sleeve Dipole (ELPOSD) and a Square Patch. An End-Loaded Planar Open-Sleeve Dipole consist of a conventional planar dipole with two closely spaced parasitic elements, or sleeves, and loaded stubs at the end of the dipole. The main benefits of this type of antennas is that in addition to retaining similar performance to that of conventional planar open-sleeve dipole, end-loaded planar opensleeve dipole (ELPOSD) antennas can be miniaturized. The Square Patch antenna used in this work is a conventional planar square patch feed with a microstrip line. Barium Strontium Titanate (BST) is a well-known ferroelectric material and up to now. A BST thin film is used to design the varactors, along with the Interdigital Capacitors (IDCs) geometry used in the metal layer. The overall antenna consists of a multilayer substrate with tunable FSS layer and dipole or patch antenna. The capacitance of the whole FSS changes introducing the BST ferroelectric material into the varactor. As can be seen in the results, by varying the BST permittivity from 200 to 300, a variation in frequency is achieved from 1.98 GHz to 1.717 GHz with a distance around 100 MHz between resonance frequencies, which equals a variation of the frequency about 8% in the adjacent permittivity values.Ingeniería de TelecomunicaciónTelekomunikazio Ingeniaritz