Amit M. Patel

A Printed Leaky-Wave Antenna Based on a Sinusoidally-Modulated Reactance Surface

A simple procedure for designing a sinusoidally-modulated reactance surface (SMRS) that radiates at an arbitrary off-broadside angle is outlined. The procedure allows for nearly independent control of the leakage and phase constants along the surface. Printing an array of metallic strips over a grounded dielectric substrate is discussed as a way to practically implement the theoretical SMRS. A method of mapping the gaps between metallic strips to a desired surface impedance is presented as an efficient alternative to mapping methods used in the past. A printed leaky-wave antenna with a sinusoidally-modulated surface reactance is designed using the procedure mentioned above. The TM-polarized antenna radiates at 30° from broadside at 10 GHz, and exhibits an experimental gain of 18.4 dB. Theoretical, simulated, and experimental results are presented.

Modeling and Analysis of Printed-Circuit Tensor Impedance Surfaces

Analysis of a printed-circuit tensor impedance surface (PCTIS) is presented. The surface consists of a periodic, subwavelength-patterned metallic cladding printed over a grounded dielectric substrate. First, the dispersion equation for an idealized tensor impedance boundary condition is derived by expressing the field in terms of TE and TM waves. A similar method is then used to find the dispersion equation of the PCTIS consisting of a tensor sheet impedance, which models the metallic cladding, over a grounded dielectric substrate. In addition, a method for extracting the tensor sheet impedance of a periodic, metallic cladding printed over a grounded dielectric substrate, is reported. It involves performing two normal-incidence scattering simulations using a full-wave electromagnetic solver. The method is strictly valid when the ground plane is sufficiently far from the metallic cladding to avoid evanescent-wave interactions. By combining the tensor sheet extraction method with the dispersion equation, the full dispersion characteristics of the PCTIS are analytically predicted in the homogenous limit. The results are verified through full-wave eigenmode simulations.

Transformation Electromagnetics Devices Based on Printed-Circuit Tensor Impedance Surfaces

A method for designing transformation electromagnetics devices using tensor impedance surfaces is presented. The method is first applied to idealized tensor impedance boundary conditions (TIBCs), and later to printed-circuit tensor impedance surfaces (PCTISs). A PCTIS is a practical realization of a TIBC. It consists of a tensor impedance sheet, which models a subwavelength patterned metallic cladding, over a grounded dielectric substrate. The method outlined in this paper allows anisotropic TIBCs and PCTISs to be designed that support tangential wave vector distributions and power flow directions specified by a coordinate transformation. As an example, beam-shifting devices are designed, using TIBCs and PCTISs, that allow a surface wave to be shifted laterally. The designs are verified with a commercial full-wave electromagnetic solver. This work opens new opportunities for the design and implementation of anisotropic and inhomogeneous printed-circuit or graphene-based surfaces that can guide or radiate electromagnetic fields.

Effective Surface Impedance of a Printed-Circuit Tensor Impedance Surface (PCTIS)

The surface impedance and dispersion equation of a printed-circuit tensor impedance surface (PCTIS) are derived using a modified transverse resonance technique. A PCTIS consists of a subwavelength-patterned metallic cladding over a grounded dielectric substrate. The metallic cladding is analytically modeled as a tensor impedance sheet. An explicit expression is derived for the effective surface impedance of the PCTIS using a transmission-line approach. First, the surface-impedance expression is found for a printed-circuit scalar impedance surface using the transverse resonance technique. Next, a modified transverse resonance technique is applied to an idealized tensor impedance boundary condition (TIBC) to find its dispersion equation. Finally, the analysis of the printed-circuit scalar impedance is combined with that of the idealized TIBC to find the tensor surface impedance and dispersion equation of a PCTIS. A discussion of the principal axes and the propagation of TM and TE waves is provided. The special case of electrically thin PCTISs is also analyzed and discussed.

The Effects of Spatial Dispersion on Power Flow Along a Printed-Circuit Tensor Impedance Surface

In this communication, expressions for the group velocity and the direction of power flow along an idealized tensor impedance boundary condition (TIBC) and a printed-circuit tensor impedance surface (PCTIS), are found. A PCTIS consists of a patterned metallic cladding over a grounded dielectric substrate. The patterned metallic cladding is modeled by a tensor impedance sheet. Expressions for the surface impedance of a TIBC and a PCTIS are reviewed. From these expressions, the group velocity and direction of power flow are derived as a function of transverse wave vector. A PCTIS exhibits spatial dispersion due to the electrical thickness of its substrate while a TIBC does not. As a result of this spatial dispersion, a PCTIS can have the same surface impedance as a TIBC for a given transverse wave vector, but a different direction of power flow. The expressions for direction of power flow along a TIBC and a PCTIS are verified with a full-wave electromagnetic solver.

Transformation electromagnetics devices using tensor impedance surfaces

A method for designing transformation electromagnetics devices using tensor impedance surfaces (TISs) is presented. The method allows anisotropic TISs to be designed that can support tangential wave vector distributions and power flow directions specified by a coordinate transformation. A beam-shifting device is designed using an anisotropic surface that allows a surface wave with a Gaussian profile to be shifted laterally at 10 GHz. The design is verified with a commercial full-wave solver. This work opens new opportunities for the design and implementation of surfaces that can guide or radiate electromagnetic fields.

A printed leaky-wave antenna with a sinusoidally modulated surface reactance

In this paper, a printed leaky-wave antenna with a sinusoidally modulated surface reactance (SMRS) is reported. The TM polarized antenna consists of metallic strips with periodically varying gaps printed on a grounded dielectric substrate. The designed antenna radiates at thirty degrees from broadside at 10 GHz, and exhibits a gain of 14.7 dB. Theoretical, simulation, and experimental results are shown. A design procedure allowing for an arbitrary radiation angle is outlined.

Analytical modeling of a printed-circuit tensor impedance surface

Analysis of a printed-circuit tensor impedance surface is presented. The printed-circuit impedance surface consists of a periodic, subwavelength-patterned metallic cladding over a grounded dielectric substrate. It is analytically modeled as a tensor sheet impedance over a grounded dielectric substrate, and its dispersion equation is found. In addition, a method for extracting the tensor sheet impedance of an arbitrarily patterned metallic cladding is reported. The extraction method involves performing two normal-incidence scattering simulations with a full-wave solver, and does not require prior knowledge of the principle axes of the surface. By combining the tensor sheet extraction method with the dispersion equation, the full dispersion characteristics of the periodic structure can be analytically predicted within the homogenous limit. The results are verified through full-wave eigenmode simulation.

Dispersion analysis of printed-circuit tensor impedance surfaces

Dispersion analysis of a printed-circuit tensor impedance surface is presented. The tensor impedance surface consists of a periodic, subwavelength-patterned metallic cladding over a grounded dielectric substrate. It is analytically modeled as a tensor sheet impedance over a grounded dielectric substrate. Its dispersion equation and an expression for the group velocity are found. In addition, a method for extracting the tensor sheet impedance of an arbitrarily patterned metallic cladding using a full-wave solver is reported. By combining the extraction method with the dispersion equation, the full dispersion characteristics of the periodic structure can be analytically predicted within the homogenous limit. The results are verified through full-wave eigenmode simulation.

Experimental results with bistatic SAR tomography

This paper gives a quick overview of inversion methods for bistatic tomographic processing. The methods are tested over simulated and real data. The real data has been acquired from a set of indoor experiments carried out in the Radiation Laboratory (RadLab), at the University of Michigan. A scale model with a house, some trees and a rough surface on the ground has been built to reproduce an urban scenario.