Rectangular Waveguide
Understanding Rectangular Waveguide
Rectangular waveguide is the gold standard transmission line for frequencies above 1 GHz when loss and power handling are critical. Its enclosed metallic structure provides complete shielding and very low loss, making it preferred for high-performance radar, satellite, and test equipment systems.
Rectangular Waveguide Properties
- Dominant mode: TE10. Electric field perpendicular to the wide wall.
- Cutoff frequency: f_c = c/(2a). Only the wide dimension matters for TE10.
- Usable bandwidth: f_c to 2*f_c (before TE20 propagates). Standard sizes use 1.5:1 ratio.
- Impedance: Z_TE10 = 377/sqrt(1-(f_c/f)^2) ohms. Frequency-dependent.
Common WR Sizes
| WR Size | Band | Freq Range |
|---|---|---|
| WR-284 | S-band | 2.6-3.95 GHz |
| WR-137 | C-band | 5.85-8.2 GHz |
| WR-90 | X-band | 8.2-12.4 GHz |
| WR-42 | Ka-band | 18-26.5 GHz |
| WR-10 | W-band | 75-110 GHz |
Frequently Asked Questions
What is rectangular waveguide?
A hollow metallic tube with rectangular cross-section. Dominant TE10 mode has cutoff at c/(2a). Usable bandwidth 1.5:1. Lowest loss, highest power handling, and best shielding of any transmission medium.
Why is a=2b the standard aspect ratio?
Making a=2b maximizes the bandwidth before the next mode (TE20) appears. The TE20 cutoff is c/a. With a=2b, the TE01 cutoff is c/(2b) = c/a = same as TE20. This gives the widest single-mode bandwidth.
When should I use waveguide instead of coax?
Waveguide when: frequency > 18 GHz (coax loss too high), power > 1 kW (waveguide handles more), lowest-loss connection needed, or best shielding required. Coax when: compact size, broadband operation, and flexibility are more important.