Читать книгу Introduction To Modern Planar Transmission Lines - Anand K. Verma - Страница 202

Medium #2 could be a conducting medium, with the intrinsic impedance, For a PEC medium, σ → ∞ , η₂ → 0.The PEC has infinite permittivity, i.e. ε → ∞. Using equation (5.1.3a), the interface provides the total reflection with the reflection coefficient Γ = − 1; i.e. a phase reversal for the reflected component. The total tangential electric field at the interface (x = 0⁻) is zero. There is no field in the medium #2. The total electric field, using an equation (5.1.6a), in medium #1 is,

(5.1.13)

The expression (5.1.13) shows the formation of a standing wave in the medium #1, without any traveling wave. The standing wave for the H_z field component can be easily obtained. At the PEC surface, the E_y‐field is zero, and H_z‐field is at maximum.

The total reflection at the interface also occurs for η₂ → ∞ , i. e. for μ → ∞. In this case, medium #2 acts as a PMC, and it offers Γ = + 1. The PMC has infinite permeability, i.e. μ → ∞. Again, a standing wave is formed in the medium #1, with E_y‐field maximum at the interface; while H_z is zero. The PMC is a hypothetical medium. However, it is realized on the periodically loaded surface as an artificial magnetic conductor (AMC) over a band of frequencies. The interface can also totally reflect the wave if the interface offers either inductive or capacitive impedance. In this case, the interface is a RIS. The periodic surfaces are discussed in chapter 20. These are widely used in the modern microwave and antenna engineering. The PEC, and PMC surfaces, forming the idealized rectangular waveguides, are discussed in chapter 7.