--- title: "Frequency bands of waves and rays" subject: "RF and Microwave Engineering" chapter: 1 key: "semester_7/rf_and_microwave_engineering:frequency-bands-waves-rays" source: https://www.bctengineer.com/q/semester_7/rf_and_microwave_engineering/frequency-bands-waves-rays site: BCT Engineering --- # Frequency bands of waves and rays RF and Microwave Engineering · Chapter 1: Introduction - Asked in: 2073 Bhadra, 3+5 marks - Video: [Electromagnetic Spectrum Explained - Radio, Microwave, Infrared, Visible Light, UV, X-ray, Gamma Ray](https://www.youtube.com/watch?v=C4os2eqc8Y4) — Illustrate to Educate - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_7/rf_and_microwave_engineering/frequency-bands-waves-rays - Whole chapter: https://www.bctengineer.com/md/semester_7/rf_and_microwave_engineering/chapter-1 ## Question Classify signal frequency in different bands of waves and rays. What are the advantages and disadvantages of using microwave signal? ## Short answer The spectrum is classified from ELF/VLF through radio, microwave (UHF/SHF/EHF), infrared, visible, ultraviolet, X-rays and gamma rays; microwaves are 300 MHz to 300 GHz. Advantages include large bandwidth, high antenna gain, satellite use and low noise; disadvantages include line-of-sight requirement, rain attenuation above 10 GHz, expensive components and biological hazards. ## Answer #### Classification of signal frequencies into waves and rays The electromagnetic spectrum, from low to high frequency: | Band / name | Frequency | Wavelength | |---|---|---| | ELF / VF / VLF | 3 Hz–30 kHz | 100,000 km–10 km | | LF (long wave) | 30–300 kHz | 10–1 km | | MF (medium wave) | 300 kHz–3 MHz | 1 km–100 m | | HF (short wave) | 3–30 MHz | 100–10 m | | VHF | 30–300 MHz | 10–1 m | | UHF (microwave) | 300 MHz–3 GHz | 1 m–10 cm | | SHF (microwave) | 3–30 GHz | 10–1 cm | | EHF (mm-wave) | 30–300 GHz | 10–1 mm | | Infrared rays | 300 GHz–400 THz | 1 mm–750 nm | | Visible light | 400–790 THz | 750–380 nm | | Ultraviolet rays | 790 THz–30 PHz | 380–10 nm | | X-rays | 30 PHz–30 EHz | 10 nm–10 pm | | Gamma rays | above 30 EHz | below 10 pm | The "waves" (radio, up to EHF) are used for communication. Microwaves are 300 MHz–300 GHz. #### Advantages of microwave signals 1. Large bandwidth, so high data rates and many channels. 2. High antenna gain with small antennas (G = 4πAe/λ²). 3. Line-of-sight propagation allows frequency reuse. 4. Microwaves pass through the ionosphere, so they are used for satellite and space links. 5. Low fading and low noise. 6. Good radar resolution. 7. Compact circuits and antennas. #### Disadvantages 1. Line of sight only, so towers and repeaters are needed (about 50 km spacing). 2. Rain and gas attenuation above about 10 GHz. 3. Expensive components and precise fabrication. 4. Lumped circuit theory fails, so design is complex. 5. Transit-time effects need special devices with low efficiency. 6. Higher conductor and dielectric loss. 7. Biological hazards at high power. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Which is the correct order from low to high frequency? A. Infrared, visible, ultraviolet, X-rays, gamma B. Visible, infrared, ultraviolet, gamma, X-rays C. Gamma, X-rays, ultraviolet, visible, infrared D. X-rays, infrared, visible, gamma, ultraviolet Answer: A. Radio < microwave < infrared < visible < UV < X-ray < gamma. (Key point: Spectrum order) 2. What range do microwaves cover? A. 3 kHz to 30 kHz B. 300 MHz to 300 GHz C. 300 GHz to 400 THz D. 30 PHz to 30 EHz Answer: B. Microwaves are 300 MHz-300 GHz (lambda 1 m to 1 mm). (Key point: Microwave range) 3. What are 30-300 GHz called, with wavelengths 10-1 mm? A. VHF B. UHF C. EHF (mm-wave) D. MF Answer: C. 30-300 GHz is EHF, the millimetre-wave band. (Key point: EHF) 4. Why are towers needed about every 50 km on microwave links? A. Line-of-sight propagation B. Ground wave attenuation C. Ionospheric skip D. Low bandwidth Answer: A. Microwaves travel line of sight. 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