Corrugated Surface and Metal Pad or High-Impedance Surface

Corrugated Surface

A corrugated surface is a metal slab into which a series of vertical slots are cut. The slots are narrow so that many of them fit within one wavelength across the slab. Each slot can be regarded as a parallel plate transmission line, running down into the slab, and shorted at the bottom.

If the slots are one quarter-wavelength deep, then the short circuit at the bottom is transformed by the length of the slots into an open circuit at the top end. Thus the impedance at the top end is very high. In this situation the surface impedance is capacitive and transverse magnetic (TM) surface waves are forbidden. Furthermore, a plane wave polarized with the electric field perpendicular to the ridges will appear to be reflected with no phase reversal. Corrugated surface is shown in figure 4.3.

Fig. 4.3: Corrugated metal surface

   Metal Pad or High-Impedance Surface

A more effective and compact approach, compared to the corrugated surfaces, which makes use of a triangular or square lattice of metal pads connected to ground with vias, has been recently proposed and applied in to enhance the gain of planar antennas. These structures are the first realization of planar compact electromagnetic crystals with a complete stop-band in the microwave range. This type of structure with a triangular lattice of hexagonal metal plates and square vias to ground is shown in figure 4.4.

Figure 4.4: Periodic metal connected to ground with via holes to yield high-impedance surface.