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SIW: Advantages and Disadvantages of Substrate Integrated Waveguides

siw waveguide rf components microwave devices substrate

This page explores the pros and cons of SIW, or Substrate Integrated Waveguide technology.

What is SIW?

As illustrated in the figure below, an SIW (Substrate Integrated Waveguide) structure consists of three layers: top and bottom ground planes with a dielectric layer sandwiched in between. A metallic via array (a series of holes) is placed between these two planes.

SIW-Substrate Integrated Waveguide

Microwave devices like filters, antenna arrays, power dividers, directional couplers, phase shifters, and transitions are often designed and manufactured using SIW structures because of the numerous advantages it offers.

Advantages of SIW (Substrate Integrated Waveguide)

Here are the key benefits of using SIW technology:

  • Higher Power Handling: SIW structures can handle significantly more power compared to other planar transmission line technologies.
  • Lower Radiation Losses: Radiation losses are minimized in SIW designs, leading to more efficient signal transmission.
  • Lower Fabrication Cost: Manufacturing various RF components using SIW structures can be more cost-effective.
  • High-Density Integration: SIW facilitates the high-density integration of discrete components directly onto the structure.
  • Reduced Conductor Loss: The use of metal in SIW design helps to minimize conductor losses.

Disadvantages of SIW (Substrate Integrated Waveguide)

Despite its benefits, SIW also has certain drawbacks:

  • Leakage Losses: Leakage losses can be substantial and depend on the separation between the via holes on the top planes. Careful design is necessary to mitigate this.
  • Dielectric Losses: The use of a dielectric material within the waveguide structure introduces dielectric losses compared to air-filled rectangular waveguides. These losses are frequency-dependent, so mmWave (millimeter wave) applications of SIW require careful consideration.
  • Cutoff Frequency: Due to its waveguide structure, SIW exhibits a lower cutoff frequency. This can limit its performance at lower frequencies.