Waveguide Dispersion Tailoring by Using Embedded Impedance Surfaces

The capability to tailor the dispersion and the cut-off frequency of waveguides is of importance, as these essential parameters govern the operating frequency range and the waveguide dimension. Here, we propose the concept of substrate-integrated impedance surface (SIIS) that enables arbitrary control of propagation characteristics of closed-shape waveguides. Specifically, we develop a theoretical framework for the simplest form of SIIS constituted by a one-dimensional array of blind vias, which is equivalent to a homogenized surface capacitance embedded in the waveguide. We theoretically and experimentally demonstrate that loading a substrate-integrated waveguide (SIW) with a capacitive SIIS can effectively reduce its cut-off frequency, regardless of the transverse dimension of the SIW. In addition, a SIIS-loaded SIW exhibits several intriguing phenomena, such as the slow-wave guiding properties and the local field concentration. This SIIS-loading technique may open up new possibilities for miniaturization of various waveguide-based components and for enhancement of their uses in microwave sensing and nonlinear functions.

Figure 1

The general concept and structure of SIIS. (a) Schematics of the standard waveguide (top) and the SIIS-loaded waveguide (bottom); λ_eff represents the effective wavelength in the waveguide channel. (b) The top, cross-section, and longitudinal views of a SIIS-loaded SIW. (c) Equivalence of SIIS to a 2D impedance surface, formed by currents induced on the blind-vias array and their images.

Figure 2

Theoretical surface capacitance of the SIIS shown in Fig. 1 and the comparison of the analytical and numerical dispersion curves of the SIIS-loaded SIW: (a) Theoretical surface capacitance of the SIIS vs the gap g (p = 1 mm). (b) Theoretical surface capacitance of the SIIS vs the period p (g = 0.5 mm). Propagation constant vs frequency for a SIIS-loaded SIW with (c) p = 1 mm and a variable g, and (d) g = 0.5 mm and a variable p; here, the dashed and solid lines are obtained from the analytical model [Eqs. (1) and (10)] and numerical simulation, respectively.

Figure 3

Photographs of the SIIS-loaded SIW and the standard SIW.

Figure 4

Experiment demonstration of the SIIS-loaded waveguide with different geometric parameters. Simulation (dashed lines) and measurement (solid lines) results for (a) transmission coefficients (S₂₁) and (b) real part of propagation constant of the SIIS-loaded SIW in Fig. 3, with different values of g (p = 1.6 mm). (c),(d) are similar to (a),(b), but for the SIIS-loaded SIW in Fig. 3, with different values of p (g = 1 mm).

Figure 5

Distributions of electric field intensity. Distributions of electric field intensity in (a) cross-section view and (b) longitudinal-section view for the SIIS-loaded SIW at 7 GHz. (c),(d) are similar to (a),(b), but for the standard SIW. Normalized electric field intensity for the rectangular waveguide, the standard SIW, and the SIIS-loaded SIW (with g = 0.5 and 0.2 mm) along the (e) x axis and (f) y axis.