How does a rectangular waveguide work?
A rectangular waveguide is a hollow metal pipe that propagates electromagnetic waves in TE and TM modes above a cutoff frequency. The dominant TE10 mode has cutoff fc = c/(2a), where a is the broad inner dimension. WR-90 (a = 22.86 mm) has fc ≈ 6.56 GHz and a recommended band of 8.2–12.4 GHz (X band).[1]
What are guide wavelength and impedance?
Above cutoff, λg = λ0/√(1 − (fc/f)²), longer than free space; phase velocity exceeds c while group velocity is below c. The TE wave impedance is ZTE = η/√(1 − (fc/f)²), with η ≈ 377 Ω.[1]
Why use waveguide instead of coax?
- Lower loss, especially at mmWave.
- Much higher power handling (no center conductor, air dielectric).
- Used for radar, satellite feeds, high-power transmitters and test at 110 GHz and above.
Drawbacks: limited bandwidth (about 1.25–1.9 fc is the usual single-mode operating range), bulk, and cost.
What are standard WR sizes?
| Designation | Inner a (mm) | Recommended band (GHz) |
|---|---|---|
| WR-284 | 72.14 | 2.60–3.95 |
| WR-137 | 34.85 | 5.85–8.20 |
| WR-90 | 22.86 | 8.20–12.40 |
| WR-62 | 15.80 | 12.4–18.0 |
| WR-42 | 10.67 | 18.0–26.5 |
| WR-28 | 7.11 | 26.5–40.0 |
| WR-15 | 3.76 | 50–75 |
| WR-10 | 2.54 | 75–110 |
The WR number is the broad dimension in hundredths of an inch.
What are substrate-integrated waveguides?
SIW forms a waveguide in a PCB using two rows of plated vias as side walls, giving waveguide-like low radiation in planar form; it is common in mmWave filters and antenna feeds.
Frequently asked questions
What is the cutoff of WR-90?
About 6.56 GHz for TE10.
Can waveguide pass DC?
No; it is a high-pass structure.
Why is waveguide band limited?
Below 1.25 fc loss and dispersion rise; near 2 fc the next mode (TE20) propagates.
See also
References
Online sources accessed October 21, 2026; printed works cited by edition. See all sources.
- “Microwave Engineering, 4th ed.”. D. M. Pozar, Wiley. 2012.