---
title: "Waveguide vs transmission line"
subject: "Electromagnetism"
chapter: 6
key: "semester_3/electromagnetism:waveguide-advantages-over-transmission-line"
source: https://www.bctengineer.com/q/semester_3/electromagnetism/waveguide-advantages-over-transmission-line
site: BCT Engineering
---

# Waveguide vs transmission line

Electromagnetism · Chapter 6: Wave guides

- Asked in: 2075 Chaitra, 3 marks; 2075 Asoj, 1 marks; 2074 Asoj, 4 marks (asked 3 times)
- Video: [WAVEGUIDES VS TRANSMISSION LINES](https://www.youtube.com/watch?v=jU0uUU0-F54) — ECE by MVK
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_3/electromagnetism/waveguide-advantages-over-transmission-line
- Whole chapter: https://www.bctengineer.com/md/semester_3/electromagnetism/chapter-6

## Question

What are the advantages and disadvantages of waveguides when compared with transmission lines? (Differentiate between transmission line and waveguide.)

## Short answer

Waveguides offer lower loss, higher power handling, and no radiation at microwave frequencies but are bulky, operate only above cut-off, are dispersive, and harder to install. Transmission lines support TEM from DC, are compact, non-dispersive, but have higher attenuation at high frequencies.

## Answer

A **waveguide** is a hollow metal tube (usually rectangular or circular) that guides electromagnetic waves along its length through reflections from its inner walls. A **transmission line** has two or more conductors and carries a TEM wave.

#### Advantages of waveguides

- Very low power loss: no dielectric between conductors, so only small wall (copper) loss.
- High power-handling capacity: no centre conductor, and the large cross-section avoids voltage breakdown.
- Less attenuation at microwave frequencies (above about 3 GHz) than coaxial cable.
- Simple, strong construction with no radiation losses and good screening.

#### Disadvantages

- Bulky, heavy and costly, especially at lower frequencies (a is of the order of λ/2).
- Operate only above a cut-off frequency, so they cannot carry DC or low frequencies.
- Dispersive: the phase and group velocities vary with frequency.
- Rigid, hard to install, and need special couplings and bends.

#### Differences

| Point | Transmission line | Waveguide |
|---|---|---|
| Conductors | Two or more | Single hollow conductor |
| Mode | TEM | TE and TM (no TEM) |
| Cut-off | None; works from DC | Cut-off frequency exists |
| Frequency | DC to a few GHz | Microwave, above about 1–3 GHz |
| Loss at microwave | Higher | Lower |
| Power handling | Low | High |
| Dispersion | Non-dispersive (ideal) | Dispersive |
| Size and cost | Small, cheap | Large, expensive |

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. Why can waveguides handle high power with low loss?
   A. No dielectric between conductors and no centre conductor, with a large cross-section avoiding breakdown
   B. Because they are heavy
   C. Because they operate at DC
   D. Because they are TEM
   Answer: A. Only small wall losses remain and breakdown is unlikely. (Key point: Low loss and power)

2. Why can a waveguide not carry DC or low frequencies?
   A. It has only one conductor and no power
   B. It is non-dispersive
   C. It supports only TEM
   D. It has a cut-off frequency, below which waves are evanescent
   Answer: D. Cut-off sets a minimum frequency, with dimension a of the order of lambda/2. (Key point: Cut-off)

3. Which statement correctly contrasts a transmission line and a waveguide?
   A. Both carry TEM
   B. The waveguide carries TEM and is cheaper
   C. A transmission line carries TEM and is non-dispersive; a waveguide carries TE/TM modes and is dispersive
   D. The transmission line has a cut-off, the waveguide does not
   Answer: C. Line: two conductors, TEM, no cut-off. Waveguide: single conductor, TE/TM, cut-off, dispersive. (Key point: Differences)

## Related in Electromagnetism

- [Distortionless line and telephone lines](https://www.bctengineer.com/question.md?key=semester_3%2Felectromagnetism%3Adistortionless-line-telephone) — Electromagnetism, chapter 5
- [Derive input impedance of transmission line](https://www.bctengineer.com/question.md?key=semester_3%2Felectromagnetism%3Aderive-input-impedance-line) — Electromagnetism, chapter 5
- [Line at 120 MHz, γ v Z0](https://www.bctengineer.com/question.md?key=semester_3%2Felectromagnetism%3Aline-120mhz-primary-constants) — Electromagnetism, chapter 5
- [Lossless line, L Z0 β Γ](https://www.bctengineer.com/question.md?key=semester_3%2Felectromagnetism%3Alossless-line-velocity-capacitance-30pf) — Electromagnetism, chapter 5
- [Two-wire 40 Ω line, input and output voltage](https://www.bctengineer.com/question.md?key=semester_3%2Felectromagnetism%3Atwo-wire-40-ohm-line-voltages) — Electromagnetism, chapter 5
- [Line with 50+j50 load, first maximum, power](https://www.bctengineer.com/question.md?key=semester_3%2Felectromagnetism%3Aline-50-j50-load-first-maximum) — Electromagnetism, chapter 5

## Related in other subjects

- [Band applications and microwave transmission lines](https://www.bctengineer.com/question.md?key=semester_7%2Frf_and_microwave_engineering%3Aband-applications-transmission-lines) — RF and Microwave Engineering, chapter 1
- [Skin effect in transmission lines](https://www.bctengineer.com/question.md?key=semester_4%2Fpower_system_analysis_i%3Askin-effect-brief) — Power System Analysis I, chapter 4
- [Transmission line behavior at low and microwave bands](https://www.bctengineer.com/question.md?key=semester_7%2Frf_and_microwave_engineering%3Atransmission-line-low-vs-microwave) — RF and Microwave Engineering, chapter 1
- [TE vs TM mode in circular waveguide](https://www.bctengineer.com/question.md?key=semester_7%2Frf_and_microwave_engineering%3Acircular-waveguide-te-vs-tm) — RF and Microwave Engineering, chapter 4