This paper presents an overview of integrated optics routing and coupling devices based on multimode interference. The underlying self-imaging principle in multimode waveguides is described using a guided mode propagation analysis. Special issues concerning the design and operation of multimode interference devices are discussed, followed by a survey of reported applications. It is shown that multimode interference couplers offer superior performance, excellent tolerance to polarization and wavelength variations, and relaxed fabrication requirements when compared to alternatives such as directional couplers, adiabatic X- or Y-junctions, and diffractive star couplers. >

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Optical multi-mode interference devices based on self-imaging: principles and applications

A survey of microstrip antenna elements is presented, with emphasis on theoretical and practical design techniques. Available substrate materials are reviewed along with the relation between dielectric constant tolerance and resonant frequency of microstrip patches. Several theoretical analysis techniques are summarized, including transmission-line and modal-expansion (cavity) techniques as well as numerical methods such as the method of moments and finite-element techniques. Practical procedures are given for both standard rectangular and circular patches, as well as variations on those designs including circularly polarized microstrip patches. The quality, bandwidth, and efficiency factors of typical patch designs are discussed. Microstrip dipole and conformal antennas are summarized. Finally, critical needs for further research and development for this antenna are identified.

Microstrip antenna technology

The extensive development of electronic systems and telecommunications has lead to major concerns regarding electromagnetic pollution. Motivated by environmental questions and by a wide variety of applications, the quest for materials with high efficiency to mitigate electromagnetic interferences (EMI) pollution has become a mainstream field of research. This paper reviews the state-of-the-art research in the design and characterization of polymer/carbon based composites as EMI shielding materials. After a brief introduction, in Section 1, the electromagnetic theory will be briefly discussed in Section 2 setting the foundations of the strategies to be employed to design efficient EMI shielding materials. These materials will be classified in the next section by the type of carbon fillers, involving carbon black, carbon fiber, carbon nanotubes and graphene. The importance of the dispersion method into the polymer matrix (melt-blending, solution processing, etc.) on the final material properties will be discussed. The combination of carbon fillers with other constituents such as metallic nanoparticles or conductive polymers will be the topic of Section 4. The final section will address advanced complex architectures that are currently studied to improve the performances of EMI materials and, in some cases, to impart additional properties such as thermal management and mechanical resistance. In all these studies, we will discuss the efficiency of the composites/devices to absorb and/or reflect the EMI radiation.

Polymer/carbon based composites as electromagnetic interference (EMI) shielding materials

A compact representation is given of the electric- and magnetic-type dyadic Green's functions for plane-stratified, multilayered, uniaxial media based on the transmission-line network analog along the aids normal to the stratification. Furthermore, mixed-potential integral equations are derived within the framework of this transmission-line formalism for arbitrarily shaped, conducting or penetrable objects embedded in the multilayered medium. The development emphasizes laterally unbounded environments, but an extension to the case of a medium enclosed by a rectangular shield is also included.

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Multilayered media Green's functions in integral equation formulations

The finite-element method (FEM) is a full-wave numerical method that discretizes the variational of a functional. The evolution of this method within the scope of electromagnetics traces back to the solving of two classes of problems, namely, the eigenmode problems and the deterministic problems. If we try to use some examples to illustrate the most typical and the most complete techniques with the most complete solution, the eigenmode problem of a dielectrically loaded waveguide and the wave propagation in a three-dimensional (3D) discontinuous waveguide are good candidates representing the eigenmode and the closed-domain solutions, respectively. As for the open-domain scattering problem and radiating problems, the authors consider the essential and key parts are presented in solving the 3D scattering problems. For this reason, we will illustrate the theoretical basics, the critical solving techniques and the typical skills involved in FEM through solving of the above three specific problems. At the end of this chapter, we will also briefly review the FEM solution for some other problems.

Finite-Element Method

Electromagnetic waves and curved structures

A spatial domain mixed-potential integral equation method is developed for the analysis of microstrip discontinuities and antennas of arbitrary shape. The algorithm is based on roof-top basis functions on a rectangular and triangular mixed grid and analytical evaluation of the quadruple moment integrals involved. The algorithm has been successfully implemented into an accurate, efficient, and versatile computer program. The numerical results agree with the measured ones very well. >

Electromagnetic modeling of passive circuit elements in MMIC

Integrals arising in the Wiener-Hopf solution for wide microstrip antennas are approximated in closed form for the case of an electrically thin substrate. The resulting expressions are used to obtain simple, closed-form expressions for resonant frequency and unloaded radiation Q for rectangular microstrip patch antennas which are valid when commonly used quasi-static formulas no longer hold. Numerical comparisons show significant shifts in resonant frequencies as compared with existing theories.

The thin-substrate approximation for reflection from the end of a slab-loaded parallel-plate waveguide with application to microstrip patch antennas

This investigation concerns a TEM wave obliquely incident onto the open end of a parallel plate wave guide with a truncated upper plate. The lower plate as well as the dielectric slab between the two plates is assumed to extend out indefinitely in order to support the propagation of at least one surface wave mode. Reflection from the wave guide opening is determined as a function of incident angle via a dual Wiener-Hopf formulation. It is found that total reflection, i.e., a reflection coefficient with magnitude equal to unity, is possible for incident angles greater than the critical angle associated with the lowest-order surface wave mode of the grounded dielectric slab. The field external to the parallel plate wave guide in this case becomes completely evanescent in the cross-sectional plane perpendicular to the plane of incidence, which is determined by the propagation direction of the incident wave and the edge of the upper plate. It is shown that the phase of the reflection coefficient thus obtained can be used to construct the modal equation for the fundamental mode(s) of a wide microstrip.

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Total and partial reflection from the end of a parallel‐plate waveguide with an extended dielectric slab

The antenna problem consisting of exciting an infinitely long horizontal thin wire with an arbitrary distribution of impressed electric field along the axis of the wire is discussed. The special case of excitation by a delta function voltage source is solved. The current on the antenna is found as a sum of two residue (discrete) contributions and two branch integration (continuous) contributions. The far field and orthogonality properties of both the discrete and continuous modes are discussed. Finally, expressions are given for the current on the antenna. From this current the input conductance of the antenna can be obtained.

David C. Chang

Papers

Electromagnetic waves and curved structures

Electromagnetic modeling of passive circuit elements in MMIC

The thin-substrate approximation for reflection from the end of a slab-loaded parallel-plate waveguide with application to microstrip patch antennas

Total and partial reflection from the end of a parallel‐plate waveguide with an extended dielectric slab

Excitation of an infinite antenna above a dissipative earth