Gurkan Gok

Tensor Transmission-Line Metamaterials

Transmission-line (TL) metamaterials possessing effective material parameters that are diagonal in the Cartesian basis have been previously studied. In this paper, TL metamaterials with arbitrary full tensors are introduced and analyzed. An approximate tensor analysis of the proposed metamaterials is first developed. Bloch analysis is then used to verify the approximate analysis and derive exact dispersion equations and impedance relations. Finally, simulation results are presented that validate the analysis and show the utility of this new class of metamaterials. The ability to design tensor metamaterials such as these is crucial to the practical implementation of novel devices derived through transformational optics/electromagnetics.

Full-Wave Verification of Tensor TL Metamaterials

In this letter, the propagation characteristics of tensor transmission-line (TL) metamaterials are verified through full-wave analysis. They are a new class of TL-based metamaterial that can have arbitrary material tensors. Full-wave simulations are reported, which demonstrate that planar anisotropic metamaterials with full 2 × 2 magnetic tensors and scalar permittivity values can be designed and implemented in microstrip technology. The reported metamaterials will open new opportunities in the design of microwave devices based on transformation optics.

A Printed Beam-Shifting Slab Designed Using Tensor Transmission-Line Metamaterials

We present the design and implementation of a beam-shifting slab (a transformation electromagnetics device) using tensor transmission-line metamaterials. A beam-shifting slab is an anisotropic, homogeneous and reflectionless slab which laterally displaces the electromagnetic field transmitted through it. The experimental beam-shifting slab consists of printed metamaterial unit cells exhibiting anisotropic effective material parameters, while the surrounding medium consists of printed isotropic unit cells. The measured and simulated field patterns within the beam-shifting slab and the surrounding media are compared and show excellent agreement. Simulation and experimental results demonstrate that radiation from a cylindrical source is shifted upward by 5.28 unit cells due to the presence of the beam-shifting slab. Furthermore, the wide-band frequency response of the slab is experimentally studied. The reported experimental results verify the theory behind tensor transmission-line metamaterials and demonstrate their utility in the design of transformation electromagnetics devices at microwave frequencies.

Alternative Material Parameters for Transformation Electromagnetics Designs

A method to find alternative material parameters for 2-D transformation electromagnetics (EM) devices is presented. The alternative material parameters support exactly the same field pattern as the original ones of the transformation EM device. The same method is extended to design dual functional transformation EM devices that combine the characteristics of two separate transformation devices into one. Analytical calculations are shown and the results are verified through the full-wave simulation of well-known transformation EM devices: an electromagnetic field rotator and a cylindrical electromagnetic field concentrator. Although the transformation EM devices possessing alternative material parameters only work for a particular illumination direction, the method presented will find application in the design of antennas and beam-forming networks with a fixed feed position.

A printed antenna beam former implemented using tensor transmission-line metamaterials

This paper presents the implementation of an antenna beam former using tensor transmission-line (TL) metamaterials. Unit cells exhibiting both isotropic and anisotropic effective material parameters are utilized in the design. The beam former produces a uniform power density and a uniform phase profile at its output. The device includes a printed beam former, an antenna flare and seven feeds. The designed antenna beam former has planar input/output faces and has dimensions 2.97λ0×5.94λ0 at the operating frequency of 8.25 GHz. Measurement results show that the beam former exhibits a scan capability between -33° and +33°, a gain of 8.55 dB, and HPBW of 11.70°.

A physical explanation for the all-angle reflectionless property of transformation optics designs

In this paper, the all-angle reflectionless property of transformation optics devices is analyzed, and a physical explanation is provided for it. To this end, plane wave propagation through a planar boundary separating two homogenous, lossless magnetically anisotropic media is studied. The general form of material parameters enabling an all-angle reflectionless transmission of electromagnetic waves through the boundary is derived. Similarities are drawn between this general form of all-angle reflectionless material parameters and those observed in transformation optics designs. The findings are verified through full-wave simulation. Furthermore, a physical explanation as to why the general form of anisotropic material parameters are reflectionless for all angle of incidences is provided. This work provides an intuitive understanding of the inherent reflectionless property of transformation optics devices, and may find applications in designing reflectionless media to control electromagnetic waves without the use of coordinate transformations.

Controlling the phase and power flow of electromagnetic fields

A method for controlling the phase progression and power flow of electromagnetic fields within a region of space is presented. The method describes how to design 2D inhomogeneous, anisotropic media based on desired spatial distributions of the wave vector and Poynting vector direction. Plane-wave relations in anisotropic media and an optimization process are used to find the required material parameters.

A beam-shifting slab implemented using printed, tensor TL metamaterials

This paper presents the implementation of a beam-shifting slab (a transformation optics device) using tensor transmission-line (TL) metamaterials. The slab consists of printed unit cells exhibiting anisotropic effective material parameters, while the surrounding medium consists of printed isotropic unit cells. The measured electric field patterns within the beam-shifting slab and the surrounding media show close agreement with simulation. The results experimentally verify the anisotropic properties of tensor TL metamaterials and open new opportunities to design transformation optics devices at microwave frequencies.