1,721,512 research outputs found
A Frequency Selective Radome With Wideband Absorbing Properties
Full text linkA frequency selective radome is presented, acting as a pass band filter at a given frequency band, while behaving as an absorber above the transmission band. The pass band behavior is obtained by a metallic FSS realized through a compact interdigitated Jerusalem cross element characterized by a very large rejection band. The metallic FSS is used as the ground plane of a thin wideband absorber based on resistive high-impedance surfaces within the total reflection band. The outer absorber reduces the signature of the antenna system when the radome is illuminated by out of band signals. The resistive FSS which comprises the absorber is designed so to minimize losses within the transmitting band of the radome. The composite structure is thoroughly analyzed by an efficient equivalent circuit approach and by full-wave numerical simulations
Design of subwavelength tunable and steer-able Fabry-Perot/leaky wave antennas
No full textThe design of a thin tunable and steerable Fabry-Perot antenna is presented. The subwavelength structure is analyzed both by an efficient transmission line model and by full-wave simulations. The tunable antenna consists of a low profile resonant cavity made up of a Partially Reflecting Surface (PRS) placed in close proximity of a tunable high-impedance surface. The active ground plane is synthesized by loading the high-impedance surface with varactor diodes. Such design allows both tuning the high-gain operational frequency and obtaining a beam steering/shaping for each resonant frequency. The transmission line model here presented includes averaged analytical expressions for modelling the tunable high-impedance surface and the frequency selective surfaces. All the theoretical speculations are verified by full-wave simulations on a finite size structure
A hybrid finite-element finite-difference time-domain (FE/FDTD) technique for solving complex electromagnetic problems
No full textA hybrid finite-element finite-difference time domain (FE/FDTD) technique for solving complex electromagnetic problems is presented in this letter. The method combines the computational simplicity of the structured FDTD scheme with the versatility as well as flexibility of the finite-element method (FEM) and enables us to accurately model curved geometries and those with fine features. Numerical results that illustrate the accuracy of the method are included in the letter
Closed-Form Analysis of Reflection Losses in Microstrip Reflectarray Antennas
Full text linkMicrostrip reflectarray antennas consist of a grounded quasi-periodic array of printed elements able to compensate the phase displacement of a non-coherent electromagnetic excitation generated by a feeder. The design of reflectarray antennas is usually accomplished by tracing the reflection phase diagram of the periodic version of the printed surface, which is analogous to a high-impedance surface (HIS). Reflection losses of this periodic structure are here analyzed through a simple equivalent transmission line model. The analytical expressions of the surface impedance offered by a HIS (real and imaginary part) as a function of the imaginary part of the dielectric permittivity of the substrate are derived through well justified approximations. Some useful practical examples are then presented both for verifying the accuracy of the derived closed-form expressions and for studying the effect of the geometrical and electrical parameters of the periodic surface on the reflection losses. The dependence of the input impedance on the capacitance associated with the printed pattern is highlighted, demonstrating that highly capacitive elements (tightly coupled subwavelength elements) are preferable for minimizing reflection losses
A novel subgridding scheme based on a combination of the finite-element and finite-difference time-domain methods
No full textA simple and versatile local mesh refinement scheme, based on the hybridization of the finite-element (FE) and the finite-difference time-domain (FDTD) algorithms, is presented in this letter. The scheme achieves considerable flexibility in subgridding by using a transition region between the coarse and fine FDTD grids, meshed according to an unstructured grid, and solved by means of the FE method in TD. An interpolation scheme in the time domain, which allows the use of different time steps in the coarse and fine mesh regions, is included in the paper
A Parallel Iteration-Free MoM Algorithm based on the Characteristic Basis Functions Method
No full text
- …
