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A simple method to achieve multi-focus and pattern manipulation in antenna near field (NF) is proposed in this study, whose effectiveness is then validated by measurements based on different transmit-array antennas. The radiating aperture is divided into several regions and each region corresponds to one assigned focal point, thus achieving multi-focusing performance. Then, the superposition principle is employed and constrains the multiple foci into a certain area to get a contoured pattern. Three examples are investigated. Ant-A presents four balanced focal spots simultaneously, while Ant-B presents two unbalanced foci. A square flat-top field pattern is obtained for Ant-C. Three-dimensional printing technology is employed to fabricate these lenses, resulting in a low cost and light weight. Measured results coincide well with the numerical design and simulation. The proposed method provides a simple and effective alternative for NF power redistribution and owns great value in such applications as radio-frequency identification, wireless power transmission, millimetre-wave imaging etc. [ABSTRACT FROM AUTHOR]

The authors propose the design of a compact mechanically frequency and pattern reconfigurable patch antenna. The frequency tuning is achieved by changing the positions of two adjustable shorting screws which are used to modify the length of the antenna radiating patch. Simulated and measured results are carried out to validate the proposed approach. When the screws are symmetrically positioned, the measured operating frequency can be tuned from 2.95 to 5.16 GHz without degrading the radiation characteristics over the entire comparatively wide measured tuning range of 54.5%. The antenna main radiating beam can be tilted from θ = 0° to θ = 30° when the screws are asymmetrically positioned. The measured gains and efficiencies range from 3.01 to 5.53 dBi and 68 to 74%, respectively. The overall antenna size is only 0.39λ0 x 0.39λ0 x 0.02λ0. [ABSTRACT FROM AUTHOR]

A compact dual-band patch antenna with independent tuning of both frequencies is introduced. The frequency agility is achieved by inserting two varactor diodes into the radiating patch, while the antenna miniaturisation is realised by shorting one patch edge using metallised vias. Simulated and measured results are in good agreement. Measurements reveal that the two operating bands can be tuned separately without any frequency shifting and with high stability and similar unidirectional radiation patterns during the tuning process. The measured tunable ranges of the lower and upper bands are 27.95% (from 2.4 to 3.18 GHz) and 28.27% (from 4.1 to 5.45 GHz), with measured peak gains and efficiencies of [3.23 dBi, 65%] and [3.42 dBi, 62%], respectively. The antenna presents comparatively wide tuning ranges with similar unidirectional radiation patterns, has a miniaturised size, and uses a simple direct current bias circuit. Thus, it can be easily integrated and used in different wireless systems. [ABSTRACT FROM AUTHOR]

A novel composite phase-shifting transmission line (TL) with designable characteristics is presented, which can be used to achieve arbitrary phase of the transmission coefficient at any required frequency with a certain length of the TL. An empirical formula is given of the relationship between the phase and physical length of the composite TL at a required frequency. A sample of 0 phase-shifting TL is designed in details, and is verified by the full-wave simulation. At the required frequency of 5 GHz, the amplitude of S21 is equal to -0.23 dB with a phase of -0.467°. The electric length is only 0.21λ0, which has been decreased by 68.5% compared to the conventional microstrip line. Using the proposed composite TL, an antenna array is designed with two radiation patches excited by the novel series feed-line. The detailed procedure of such design is presented. The lowest reflection coefficient is exactly achieved at the required frequency of 5 GHz. The maximum radiation is obtained at θ0 = O°, which indicates that the 0 phase-shifting TL works very well. The sample is also fabricated and good agreements between simulation and measurement results are obtained. [ABSTRACT FROM AUTHOR]

An efficient method is presented to design the evanescent wave amplification exactly by cascading two layers of periodic series-shunt capacitors and inductors, which simulate a bilayer of magnetic and electric plasmas. Based on the presented method, equivalent lumped parameters of circuit structures are retrieved, from which the evanescent-wave amplification (EWA) is obtained at a designed frequency. Full-wave simulations show that the relative offset of the EWA frequency is less than 0.1%. The structure has been fabricated and measured, and the measurement results have good agreements with the simulation results. The proposed method can be used to design other periodic circuit structures, and the exact design of EWA can be used in the fabrication of novel components. © Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 1870–1873, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23501 [ABSTRACT FROM AUTHOR]

This paper presents a novel compact meta-structure, which is characterized by left-handed properties. In the novel structure, two linear arrays of metallic vias and short-stub inductors are used to generate shunt inductors besides the series interdigital capacitors. Compared with conventional composite right/left-handed transmission-line structures, the new structure has weaker coupling to other components and is easily controlled by adjusting the shunt inductance and series capacitance to produce different left-handed properties. Due to the isolation of two via arrays, the proposed structure can also be transplanted directly from the microstrip system to the coplanar-waveguide system. We have proposed an efficient procedure to retrieve the equivalent propagating modes for both forward and backward waves based on the matrix pencil method, which provides an easy way to study the propagation characteristics. Using such a meta-structure, a series of super-wide bandpass filters are designed and fabricated at different frequency bands. Good agreements between simulation and experiment results have been achieved, and good performance in passbands and stopbands has been observed with a relative 3-dB bandwidth larger than 70%. For easy design of such super-wide bandpass filters, an experienced formula is given between the physical size and the center frequency of the 3-dB passband, which can be used to redesign any filters at other frequency bands. [ABSTRACT FROM AUTHOR]

Microwave components with nonlinear phase responses are developed using a simplified composite right/left-handed (CRLH) transmission-line (TL) structure without the series capacitance or the shunt inductance. Using such a simplified CRLH structure, arbitrarily dual-band microstrip components have been realized in compact sizes such as a quarter-wavelength short-circuited stub and dual-band branch-line couplers. Simulation and measurement results are given to demonstrate the efficiency and good performance of the proposed components. For the quarter-wavelength short-circuited stub based on the simplified CRLH-TL structure without the series capacitance, it has been shown that the insertion loss is less than -0.1 dB. For the arbitrarily dual-band branch-line coupler, experiment results exhibit that $21 and $31 are larger than -3.6 dB, the isolations are smaller than -30 dB, the return losses are smaller than -20 dB, and the phase differences are within 90° ± 1.8°. [ABSTRACT FROM AUTHOR]

We propose a metamaterial particle which is composed of a dielectric block with a thin metallic rod screwed inside. By adjusting the height of rod inside the dielectric block, we can control the effective medium parameters of a periodic structure composed of the particles. An experiment is presented to retrieve the effective medium parameters, which have good agreements with those from simulation results. Using the unique property of the tunable particles, gradient metamaterial lenses are easily designed to deflect and focus the incident plane waves. [ABSTRACT FROM AUTHOR]

An analogue phase shifter with a constant low insertion loss (IL) and compact size is proposed. It consists of two quarter wavelength transmission lines and three tunable reflective loads. The theoretical analysis to maximise the relative phase shift, reduce the IL and the IL variation of the phase shifter is presented explicitly, which provides performance estimation and design guidance for this class phase shifter. A circuit with a size of 0.12λg × 0.21λg is designed and fabricated to verify the theory. The simulated and measured results are in good agreement. The measurement shows that the relative phase shift of the proposed phase shifter is 186° at 1.97 GHz. The average IL is 0.79 dB with a very small IL variation which is just 0.02 dB. [ABSTRACT FROM AUTHOR]

A modulatable electromagnetically induced transparency (EIT) is achieved using a slotted circle ring structure. The circle ring structure is used to induce a polarisation-independence resonance with a low Q factor, while the slot is etched to obtain a polarisation-dependence resonance with a high Q factor. The EIT effect is obtained when the two resonances have nearby resonant frequencies but with different Q factors. As both resonant modes are excited by the external field independently, different coupling strength is achieved simply by adjusting the polarisation angle. Then the transmission of EIT is successfully modulated. The design concept is well validated both by simulation and measurement. [ABSTRACT FROM AUTHOR]

Surface plasmon can lead to wave propagation not only along the surface as a dielectric waveguide but also in the normal direction to the surface because of the evanescent-wave amplification by metamaterial. In this letter, the authors design a surface plasmon structure to implement the electric and magnetic plasma resonances in microwave regime. Near the plasma resonant frequency, they directly observe the strong surface plasmon by experiments. The evanescent waves can be transmitted in an exponentially increasing and decreasing distribution, which is the evanescent-mode propagation by the tunneling effect. [ABSTRACT FROM AUTHOR]

The S-parameter retrieval has proved to be an efficient approach to obtain electromagnetic parameters of metamaterials from reflection and transmission coefficients, where a slab of metamaterial with finite thickness is regarded as a homogeneous medium slab with the same thickness [D. R. Smith and S. Schultz, Phys. Rev. B 65, 195104 (2002)]. However, metamaterial structures composed of subwavelength unit cells are different from homogeneous materials, and the conventional retrieval method is, under certain circumstances, not accurate enough. In this paper, we propose an advanced parameter retrieval method for metamaterial slabs using an inhomogeneous model. Due to the coupling effects of unit cells in a metamaterial slab, the roles of edge and inner cells in the slab are different. Hence, the corresponding equivalent medium parameters are different, which results in the inhomogeneous property of the metamaterial slab. We propose the retrievals of medium parameters for edge and inner cells from S parameters by considering two- and three-cell metamaterial slabs, respectively. Then we set up an inhomogeneous three-layer model for arbitrary metamaterial slabs, which is much more accurate than the conventional homogeneous model. Numerical simulations verify the above conclusions. [ABSTRACT FROM AUTHOR]