Substrate Integrated Waveguide
Understanding SIW
SIW bridges the gap between traditional rectangular waveguide and planar transmission lines. It provides waveguide-like performance (high Q, low radiation, high isolation) in a standard PCB manufacturing process, enabling low-cost mmWave components.
| Antenna Type | Gain (dBi) | Beamwidth | Bandwidth |
|---|---|---|---|
| Dipole | 2.1 | 360° (H) | Moderate (~10%) |
| Patch | 5-8 | 60-90° | Narrow (2-5%) |
| Horn | 10-25 | 10-60° | Wide (>50%) |
| Parabolic | 25-45 | 1-10° | Wide |
SIW Design
- Via rows: Two rows of metallic vias form the sidewalls. Via diameter and spacing must prevent leakage (spacing < lambda_g/5).
- Width: Determines cutoff frequency. SIW width = conventional waveguide width minus corrections for via effects.
- Integration: Transitions from SIW to microstrip or GCPW enable connection to active devices.
SIW Advantages
- Fabricated in standard PCB/LTCC process.
- Higher Q than microstrip (enclosed structure).
- Better isolation than microstrip (shielded).
- Compatible with surface-mount components.
Frequently Asked Questions
What is SIW?
SIW implements a rectangular waveguide in a PCB using via rows as sidewalls and copper layers as broad walls. It provides waveguide-like performance (high Q, shielding) in a low-cost planar format. Widely used 10-300 GHz.
What are the advantages of SIW over microstrip?
SIW provides higher Q (lower loss for resonant structures), better shielding (less coupling between adjacent circuits), lower radiation loss, and better power handling. The trade-off is larger size than microstrip and limited impedance range.
How is SIW connected to microstrip?
A tapered microstrip-to-SIW transition provides wideband coupling. The microstrip tapers into the SIW aperture, exciting the TE10-like mode. Transition insertion loss of 0.1-0.3 dB is typical.