- 2068 Baisakh · 3 marks
Short note: Waveguides
Short answer
A waveguide is a hollow conducting tube that guides microwaves via wall reflections, supporting only TE and TM modes above a cutoff frequency; the dominant mode is TE10. It is dispersive (v_p > c, v_g < c), offers low loss and high power, but is bulky and cannot transmit DC. Widely used in radar, satellite, and microwave links.
Write a short note on waveguides.
A waveguide is a hollow, conducting tube (rectangular, circular or elliptical) used to guide electromagnetic waves, mainly at microwave frequencies (about 1 to 100 GHz). The wave travels along the guide by repeated reflection from the inner walls.
Key features:
- Modes: only TE (E_z = 0) and TM (H_z = 0) modes; a hollow guide cannot support TEM.
- Cut-off: each mode propagates only above its cut-off frequency f_c = (c/2)√[(m/a)² + (n/b)²]; the dominant mode in a rectangular guide is TE₁₀ with f_c = c/2a.
- Dispersion: guide wavelength λ_g = λ₀/√(1 − (f_c/f)²), v_p = c/√(1 − (f_c/f)²) > c, v_g = c√(1 − (f_c/f)²) < c, and v_p v_g = c².
- Impedance: Z_TE = η/√(1 − (f_c/f)²), Z_TM = η√(1 − (f_c/f)²).
Advantages: very low loss, high power handling, good shielding. Disadvantages: bulky and costly, no DC or low-frequency transmission, dispersive.
Applications: radar, satellite and microwave links, feed lines to horn and dish antennas, microwave ovens, and connections between microwave components.
✓ Answer checked by Claude Opus 5.5 (high effort)