Polarization is one of the basic properties of electromagnetic waves conveying valuable information in signal transmission and sensitive measurements. Conventional methods for advanced polarization control impose demanding requirements on material properties and attain only limited performance. We demonstrated ultrathin, broadband, and highly efficient metamaterial-based terahertz polarization converters that are capable of rotating a linear polarization state into its orthogonal one. On the basis of these results, we created metamaterial structures capable of realizing near-perfect anomalous refraction. Our work opens new opportunities for creating high-performance photonic devices and enables emergent metamaterial functionalities for applications in the technologically difficult terahertz-frequency regime.

Terahertz Metamaterials for Linear Polarization Conversion and Anomalous Refraction

Utilization of electromagnetic band-gap (EBG) structures is becoming attractive in the electromagnetic and antenna community. In this paper, a mushroom-like EBG structure is analyzed using the finite-difference time-domain (FDTD) method. Its band-gap feature of surface-wave suppression is demonstrated by exhibiting the near field distributions of the electromagnetic waves. The mutual coupling of microstrip antennas is parametrically investigated, including both the E and H coupling directions, different substrate thickness, and various dielectric constants. It is observed that the E-plane coupled microstrip antenna array on a thick and high permittivity substrate has a strong mutual coupling due to the pronounced surface waves. Therefore, an EBG structure is inserted between array elements to reduce the mutual coupling. This idea has been verified by both the FDTD simulations and experimental results. As a result, a significant 8 dB mutual coupling reduction is noticed from the measurements.

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Microstrip antennas integrated with electromagnetic band-gap (EBG) structures: a low mutual coupling design for array applications

This paper provides a comprehensive review of the domain of physical layer security in multiuser wireless networks. The essential premise of physical layer security is to enable the exchange of confidential messages over a wireless medium in the presence of unauthorized eavesdroppers, without relying on higher-layer encryption. This can be achieved primarily in two ways: without the need for a secret key by intelligently designing transmit coding strategies, or by exploiting the wireless communication medium to develop secret keys over public channels. The survey begins with an overview of the foundations dating back to the pioneering work of Shannon and Wyner on information-theoretic security. We then describe the evolution of secure transmission strategies from point-to-point channels to multiple-antenna systems, followed by generalizations to multiuser broadcast, multiple-access, interference, and relay networks. Secret-key generation and establishment protocols based on physical layer mechanisms are subsequently covered. Approaches for secrecy based on channel coding design are then examined, along with a description of inter-disciplinary approaches based on game theory and stochastic geometry. The associated problem of physical layer message authentication is also briefly introduced. The survey concludes with observations on potential research directions in this area.

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Principles of Physical Layer Security in Multiuser Wireless Networks: A Survey

Metasurfaces: From microwaves to visible

Mathematical Handbook for Scientists and Engineers

Many modern satellite and terrestrial point-to-point communications systems use circular polarization (CP) wave propagation in order to maximize the polarization efficiency component of the link budget. Therefore, in an undergraduate electromagnetics syllabus, an introduction to the topic of circular polarization is necessary to promote an understanding of the propagation aspects of modern communications system design. Students new to the antennas and propagation discipline often have difficulty in grasping the concept of CP; therefore, in this paper, the essential aspects of this topic are reinforced by a tutorial description of CP in terms of wave propagation, antenna properties, and measurement techniques. A simple laboratory-based project is described that requires the design, fabrication, and measurement of a crossed dipole antenna. The measured input impedance and radiation patterns are correlated with theory to highlight the conditions necessary to support CP wave propagation. By combining basic electromagnetic concepts with a series of simple intuitive laboratory experiments, the students can more easily visualize, and hence understand, CP wave propagation and its use in communications systems design.

Understanding and measuring circular polarization

The authors propose a solution to the surface conduction problem in silicon monolithic microwave integrated circuits (MMIC's). An LPCVD polycrystalline silicon layer is deposited over the surface of a high-resistivity silicon wafer which is then covered with a silicon dioxide layer. The polycrystalline silicon layer effectively removes, through traps, any free electrons or holes that may have been induced at the oxide-silicon interface. The CPW lines with 1.25-/spl mu/m aluminum metallization on passivated HRS substrates have an attenuation loss at 30 GHz of only 1.08 dB/cm.

Low-loss CPW lines on surface stabilized high-resistivity silicon

In order to formalize and extend on previous ad-hoc analysis and synthesis methods a theoretical treatment using vector representations of directional modulation (DM) systems is introduced and used to achieve DM transmitter characteristics. An orthogonal vector approach is proposed which allows the artificial orthogonal noise concept derived from information theory to be brought to bear on DM analysis and synthesis. The orthogonal vector method is validated and discussed via bit error rate (BER) simulations.

A Vector Approach for the Analysis and Synthesis of Directional Modulation Transmitters

A retrodirective antenna system (1) for receiving an incoming signal (15) from an object (13) and directing an outgoing signal (11) back to the object (13), comprising two or more transceiver cells (3), each of which receives a part of the incoming signal, produces a phase conjugate output signal, which output signals from the cells combine to form an outgoing signal (11) directed back to the object (13), wherein each transceiver cell (3) comprises an antenna component (7) which detects the part of the incoming signal, a processor which receives the part of the incoming signal and produces first and second same-side, sideband (SB) signals of the part of the incoming signal, a phase shift system comprising a first phase element which receives the first SB signal and outputs a SB signal having a first phase, and a second phase element which receives the second SB signal and outputs a SB signal having a second phase which is in quadrature with the first phase, and an IQ modulator comprising an I input port, a Q input port and a phase adjuster, which receives the SB signal having the first phase on the I input port and the SB signal having the second phase on the Q input port, or receives the SB signal having the first phase on the Q input port and the SB signal having the second phase on the I input port, and phase adjusts the SB signals to produce an output signal which is the phase conjugate of the part of the incoming signal.

Retrodirective antenna systems

Numerical simulations are used to study the electromagnetic scattering from phase agile microstrip reflectarray cells which exploit the voltage controlled dielectric anisotropy property of nematic state liquid crystals (LCs). In the computer model two arrays of equal size elements constructed on a 15 mum thick tuneable LC layer were designed to operate at center frequencies of 102 GHz and 130 GHz. Micromachining processes based on the metallization of quartz/silicon wafers and an industry compatible LCD packaging technique were employed to fabricate the grounded periodic structures. The loss and the phase of the reflected signals were measured using a quasi-optical test bench with the reflectarray inserted at the beam waist of the imaged Gaussian beam, thus eliminating some of the major problems associated with traditional free-space characterization at these frequencies. By applying a low frequency AC bias voltage of 10 V, a 165deg phase shift with a loss 4.5-6.4 dB at 102 GHz and 130deg phase shift with a loss variation between 4.3-7 dB at 130 GHz was obtained. The experimental results are shown to be in close agreement with the computer model.

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Vincent Fusco

Papers

Understanding and measuring circular polarization

Low-loss CPW lines on surface stabilized high-resistivity silicon

A Vector Approach for the Analysis and Synthesis of Directional Modulation Transmitters

Retrodirective antenna systems

Design and Measurement of Reconfigurable Millimeter Wave Reflectarray Cells With Nematic Liquid Crystal