# Post-wall waveguide

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A post-wall waveguide (also known as substrate integrated waveguide (SIW) or a laminated waveguide) is a synthetic rectangular electromagnetic waveguide formed in a dielectric substrate by densely arraying metallized posts or via-holes which connect the upper and lower metal plates of the substrate. The waveguide can be easily fabricated with low-cost and mass-production using through-hole techniques where the post walls consists of via fences. The post-wall waveguide is known to have similar guided wave and mode characteristics to the conventional rectangular waveguide with equivalent guided wavelength.

In electromagnetics and communications engineering, the term waveguide may refer to any linear structure that conveys electromagnetic waves between its endpoints. However, the original and most common meaning is a hollow metal pipe used to carry radio waves. This type of waveguide is used as a transmission line mostly at microwave frequencies, for such purposes as connecting microwave transmitters and receivers to their antennas, in equipment such as microwave ovens, radar sets, satellite communications, and microwave radio links.

A dielectric is an electrical insulator that can be polarized by an applied electric field. When a dielectric is placed in an electric field, electric charges do not flow through the material as they do in an electrical conductor but only slightly shift from their average equilibrium positions causing dielectric polarization. Because of dielectric polarization, positive charges are displaced in the direction of the field and negative charges shift in the opposite direction. This creates an internal electric field that reduces the overall field within the dielectric itself. If a dielectric is composed of weakly bonded molecules, those molecules not only become polarized, but also reorient so that their symmetry axes align to the field.

A via or VIA is an electrical connection between layers in a physical electronic circuit that goes through the plane of one or more adjacent layers. To ensure via robustness, IPC sponsored a round-robin exercise that developed a time to failure calculator.

For instance, the equivalent width of a rectangular waveguide compared to a SIW is described in the approximation:

${\displaystyle a_{RWG}=a_{SIW}-1.08(2r)^{2}/p+0.1(2r)^{2}/a_{SIW}}$

where ${\displaystyle p}$ is the distance between the posts in the post wall, ${\displaystyle r}$ describes the radius, and ${\displaystyle a_{RWG}}$ as well as ${\displaystyle a_{SIW}}$ are the widths of the rectangular waveguide and SIW respectively.