Search

We study how nanophotonic structures can be used for determining the position of a nearby nanoscale object with subwavelength accuracy. Through perturbing the near-field environment of a metasurface transducer consisting of nano-apertures in a metallic film, the location of the nanoscale object is transduced into the transducer’s far-field optical response. By monitoring the scattering pattern of the nanophotonic near-field transducer and comparing it to measured reference data, we demonstrate the two-dimensional localization of the object accurate to 24 nm across an area of 2 × 2 μm. We find that adding complexity to the nanophotonic transducer allows localization over a larger area while maintaining resolution, as it enables encoding more information on the position of the object in the transducer’s far-field response.

This letter deals with a study of aperiodically ordered textured (mushroom-type) high-impedance surfaces (HISs), and their possible application as artificial-magnetic-conductor groundplanes for low-profile directive antennas. In this framework, results from full-wave simulations are presented in order to characterize the electromagnetic response (in terms of impedance matching, directivity, and surface-wave suppression) of selected configurations based on representative categories of aperiodic tilings, and compare them with those of standard periodic HISs. © 2008 IEEE.

A leaky-wave slot array antenna fed by a dual offset Gregorian reflector system is realized by pins in a parallel plate waveguide. The radiating part of the antenna is composed by parallel slots etched on one side of the same parallel plate waveguide. The dual offset Gregorian reflector system is fed by an arrangement constituted by two vias and a grid, also constituted by pins. Also this feed arrangement realizes a leaky type of radiation, this time inside the parallel plate waveguide. A prototype of the antenna has been designed, manufactured and successfully tested. The low profile, low cost and high efficiency of the antenna render it suited for a variety of radar or telecom applications. Index Terms--Leaky-wave antennas (LWA), millimeter-wave antennas, planar antennas, reflector antennas.

The performance of multibeam focal plane arrays feeding a single aperture is usually reduced due to conflicting requirements on the feed elements. Dense packing is usually required to minimize the beam separation, while typically large feed apertures are needed to provide the high feed directivity to reduce spillover losses from the reflector. In this paper the use of dielectric super-layers to shape the radiation pattern of each feed is demonstrated. The shaping is obtained by exciting, according to design, a pair of TE/TM leaky waves. The spillover from the reflector is reduced without physically increasing the dimensions of each single element aperture. A prototype of a feed array composed of 19 waveguides arranged in a hexagonal lattice was designed, manufactured and tested. The measured embedded patterns provided an increase of the edge of coverage gain, with respect to the free space case, of at least 0.6 dB in an operating bandwidth (BW) of [approximately equal to] 12%. Moreover when reactive loading of adjacent feeds is adopted the increase in the edge of coverage with respect to the free space case was demonstrated to be larger than 1.6 dB over a 3% BW. Index Terms--Leaky wave antennas, leaky waves, reflector antenna feeds, reflector antennas.

The impact of mutual coupling between neighboring radiators in an imaging array configuration in the presence of a dielectric super-layer is investigated. The super-layer generally aims at increasing the directivity of each element of the array. However, here it is shown that the directivity of the embedded element patterns are reduced by a high level of mutual coupling. Thus a trade off between directivity enhancement and close packing of the array elements must be found depending on the bandwidth and the pattern requirements. Index Terms--Electromagnetic bandgap (EMB) materials, leaky waves (LWs), leaky wave (LW) antennas, reflector antenna feeds.

A modular technique originally proposed for waveguide junctions, the multimode equivalent network approach based on the integral equation formulation (IEMEN), is extended to the analysis of multilayer Frequency Selective Surfaces integrated with waveguide array antennas. This technique represents each layer and transition between layers in terms of a generalized impedance or admittance matrix, obtained directly from the solution of an integral equation with reduced kernel. Thanks to the adopted formulation, the integral equation needs to be solved only in a limited set of frequency points. The IEMEN method is validated by comparison with results available in literature. Index Terms--Admittance matrix, antenna phased arrays, frequency selective surfaces (FSS), impedance matrix, periodic structures.

We describe the use of electromagnetic bandgap (EBG) super-layers to improve the shape of reflectors illumination function. Following an investigation of the leaky wave pole singularities of the EBG Green's function, the shape of the radiation patterns of small apertures in ground planes are optimized. The maximization of the reflector aperture efficiency can be obtained by properly tuning the super layers geometrical parameters. A prototype of such feed has been designed, manufactured and tested. The results indicate that the inclusion of the EBG, increases the aperture efficiency of the feed+reflector system to values higher than 80%, over a 10% bandwidth. These low profile feeds are compatible with printed circuit board and/or integrated technology. Index Terms--Aperture efficiency, electromagnetic bandgap (EBG) materials, leaky waves, reflector antenna feeds.

We show how the design of integrated arrays can significantly benefit from planar circularly symmetric (PCS) electromagnetic band gap (EBG) structures. Using this technology, a phased array that scans up to 40[degrees] in one dimension and that is characterized by relatively large bandwidth (BW [approximately equal to] 15%) is designed, manufactured and tested. The specific advantages coming from the use of PCS-EBGs are two fold. On one hand the losses associated to surface waves are significantly reduced. On the other hand each element of the array has a larger effective area that leads to a higher gain for the complete array when compared with a standard technology. Additional benefits are the low cross-polarization levels, the good front to back ratio considering that the antenna does not include a backing reflector, and the low profile. Index Terms--Electromagnetic band gap (EBG), phased arrays, printed technology, surface waves.

This paper describes a design strategy to achieve the maximum bandwidth and efficiency for a printed slot antenna surrounded by EBGs. First the dielectric constant and the thickness of the dielectric slab that guarantees an acceptable front to back radiation ratio is identified. Then electromagnetic bandgap (EBG) structures are designed to achieve the optimal bandwidth (BW) while obtaining high surface wave efficiency in the radiating half space. To achieve this goal the wave interaction between the slot and the EBG structures is investigated in depth and clearly described. For the case of Planar circularly symmetric (PCS) EBGs the maximum of radiation BW is shown to occur when the distance between the central antenna and the EBG is approximately half wavelength of the first surface wave, [[lambda].sub.sw]/2. Index Terms--Electromagnetic bandgap (EBG), planar circularly symmetric electromagnetic bandgap (EBG), planar printed antennas, slot antennas, surface waves, wideband antennas.

Problem matched basis functions are proposed for the method of moments analysis of printed slot coupled microstrips. The appropriate equivalent currents of the integral equation kernel are represented in terms of two sets of entire domain basis functions. These functions synthesize on one hand the resonant behavior of slots, microstrips or dipoles and on the other hand the field in proximity of the feeding source and of the discontinuities. In order to define these basis functions, canonical geometries are identified, whose Green's functions have been found in semi-analytical form. The accuracy and the effectiveness of the method in terms of convergence rate and number of unknowns is demonstrated by comparison with a standard fine meshing full-wave analysis. The method is extremely convenient for large arrays, where the subwavelength details should be treated together with large global dimensions. Since the proposed solution is independent of the dimensions of these details, it provides dramatic reduction of the number of unknowns and improvement of condition number. Index Terms--Entire domain basis functions, Green's functions, method of moments (MoM).

A novel type of leaky-wave antenna is presented. Differently from previously reported leaky-wave antennas, it is characterized by a constant beam direction over a very wide range of frequencies. The radiation originates at a slot etched at the interface between air and a dense dielectric, which is shaped to form a cylinder of elliptical cross sections of decreasing dimensions. Two prototypes have been designed, manufactured, and tested. The measurements are in very good agreement with the expectations, demonstrating the potentials of the leaky lens concept to realize integrated transmitters or receivers that are extremely broadband and directive. Index Terms--Broad-band antennas, leaky waves, lens antennas, slot antennas.

This paper discusses the design and analysis of planar circularly symmetric (PCS) electromagnetic band gap (EBG) structures for reducing the surface waves excited by printed antennas on dense dielectric substrates. The key advantage of the circularly symmetric geometries is that a surface wave generated by a source located at its center experiences the same band gap effect in all radial directions. To obtain simple design rules of the PCS-EBGs for the optimization of the bandwidth, an equivalence is established between 2-D-EBGs and PCS-EBGs. Integrated planar printed antennas with bandwidths up to 20% are designed, manufactured and tested. Index Terms--Circular structures, dispersion diagrams, electromagnetic band gap (EBG), printed antennas, surface waves.

In this paper, we present the analysis of periodic arrays on cylindrical surfaces using open-ended waveguide radiators loaded with radomes and frequency selective surfaces (FSS). The multilayer structure can be used to obtain a filtering behavior by properly choosing the radomes and the size of the FSS apertures. The effect of the gradual cutoff properties of the cylindrical waves is also addressed and the design of a number of filtering structures including one or two FSS is presented. Index Terms--Conformal arrays, Floquet's theorem, frequency selective surfaces (FSS), gradual cutoff, radome.

In this paper, we present an efficient integral equation formulation based on a multimode equivalent network (MEN) approach for the analysis of phased arrays on cylindrical surfaces using open-ended waveguide radiators. In addition to theory, experimental data are also presented showing very good agreement with simulated results. Index Terms--Conformal arrays, edge conditions, Floquet's theorem, multimode equivalent network (MEN).

We have developed a rigorous full-wave analysis technique capable of characterizing quasiplanar travelling wave structures, constituted of multilayer dielectrics and conductors of finite thickness, also taking into account dielectric and conductor losses. We have studied boxed embedded microstrips and another complex passive structure, namely the T-gate TW-FET, devoting particular attention to the distribution of current inside the metallization. All structures considered were simulated by means of a desktop computer. We have tested our program by comparing our results with experimental data of embedded microstrips and employed it for the characterization of planar and T-type gates of the FET's without bias.