# Chirality in guided-wave structures and printed-circuit antennas: Theory and applications

#### Abstract

Electromagnetic chirality, which describes the role of chirality or handeness in electromagnetics, is exhibited in chiral materials. Isotropic chiral materials can be described electromagnetically by the constitutive relations D = $\varepsilon\sb{\rm c}$ E + i$\xi\sb{\rm c}$ B and H = i$\xi\sb{\rm c}$ E + B/$\mu\sb{\rm c}$ where $\varepsilon\sb{\rm c}$, $\mu\sb{\rm c}$, and $\xi\sb{\rm c}$ are the permittivity, permeability and chirality admittance of the medium, respectively. Here, we introduce the concept of chirality into guided-wave structures and printed-circuit antenna technology. We develop the theory of chirowaveguides which consist of conventional waveguides containing chiral materials. We apply this theory to the cases of perfectly conducting parallel-plate, circular, and rectangular chirowaveguides. Novel features such as mode bifurcation and hybrid modes are discussed. We then extend our analyses to waveguides with open boundaries and investigate the electromagnetic properties of grounded and ungrounded chiral slabs. In particular, we determine the modes of electromagnetic waves in a grounded chiral slab (surface-wave and radiation modes), and introduce sources to model chirostrip antennas which consist of microstrip antennas with their substrates and/or superstrates replaced by chiral layers. We investigate the canonical cases of a line and a dipole antennas on top of grounded chiral slabs and show that, under certain circumstances, the surface wave power for a line source can be reduced and the radiation efficiency increased. We also present the radiation properties of line and dipole chirostrip arrays and study the effect of chirality on the sidelobe levels of these arrays. We then consider the more realistic finite-length chirostrip antenna and investigate its radiation properties such as current distribution, radiation patterns, input impedance, bandwidth, efficiency and mutual coupling between two such antennas. We find that a compromise has to be made between a wider bandwidth and a lower efficiency as compared with the nonchiral case. We also show that, due to chirality, the main beam of the radiation pattern is rotated around the axis normal to the slab. We finally show that, when chiral materials are used for the substrates, the mutual coupling between two finite-length chirostrip antennas is generally reduced. A whole host of applications of chiral materials in guided-wave structures and microstrip antennas are also addressed.

#### Subject Area

Electrical engineering

#### Recommended Citation

Pelet, Philippe Francois Louis, "Chirality in guided-wave structures and printed-circuit antennas: Theory and applications" (1991). Dissertations available from ProQuest. AAI9125731.
https://repository.upenn.edu/dissertations/AAI9125731

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