A1-Electromagnetic signals
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Contents
⌘ Wave Propagation Parameters
Can also be called "Propagation constant". Somewhat misleading, as the propagation usually varies strongly.
Alternative names:
- Transmission parameters
- Propagation parameters
- Propagation coefficients
- Transmission constants
- Secondary coefficients
Propagation constant, symbol γ, is defined by the ratio between the amplitude at the source, and the amplitude at some distance x. Is a complex quantity, so we use α (attenuation constant) and β (phase constant) to define it. Attenuation constant, is the loss of signal, or attenuation of an electromagnetic wave travelling through a medium. Phase constant is the change in phase per meter, along the path travelled.
⌘Wave propagation and absorption mechanisms
| Band | Frequency | Wavelength | Propagation via |
| Very low frequency, VLF | 3-30 kHz | 100 - 10 km | Guided between the earth and the ionosphere. |
| Low frequency, LF | 30 - 300 kHz | 10 - 1 km | Guided between the earth and the D layer of the ionosphere. Surface waves. |
| Medium frequency, MF | 300 - 3000 kHz | 1000 - 100 m | Surface waves.E, F layer ionospheric refraction at night, when D layer absorption weakens. |
| High frequency, HF (short wave) | 3-30 MHz | 100-10 m | E layer ionospheric refraction. F1, F2 layer ionospheric refraction. |
| Very high frequency, VHF | 30-300 MHz | 10-1 m | Sporadic E propagation Extremely rare F1,F2 layer ionospheric refraction during high sunspot activity up to 80 MHz. Generally direct wave. |
| Ultra high frequency, UHF | 300-3000 MHz | 100-10 cm | Line-of-sight propagation. Sometimes tropospheric ducting. |
| Super high frequency, SHF | 3-30 GHz | 10-1 cm | Direct wave. |
| Extremely high frequency, EHF | 30-300 GHz | 10-1 mm | Direct wave limited by absorption. |
The frequencies which we use for mobile communications are ranging from 450 MHz (ICE), the old TV bands, 800-900 MHz (GSM), 1800 (GSM), 1900, 2100 MHz (UMTS), 2400 MHz (Wifi), 2650 MHz (LTE), and 5100 MHz (IEEE802.11a..). While previously frequency band were used for a specific technology, refarming started in 2012 to open for communication technologies in other bands. Examples of such refarming are LTE1800 indicating an operation of LTE in the 1800 band. Back in 2013 Apple surprised the European operators, as the iPhone came with LTE only in the 1800 band, and not, as usual in Europe, in the 2600 band.
(Source:http://en.wikipedia.org/wiki/Radio_propagation)
⌘ Further readings
- see Wave Propagation Parameters (by Joachim Tingvold)
Literature:
- Andersen, J.B., "Propagation measurements and models for wireless communications channels"
- Simon Saunders, Alejandro Aragón-Zavala, "Antennas and propagation for wireless communication systems"
- Seybold, J. S., "Introduction to RF Propagation"
- Andreas F. Molisch, "Wireless Communications"
- Andrea Goldsmith, "Wireless Communications"
- Shigekazu Shibuya, "A basic atlas of radio-wave propagation"
Keywords used:
- wireless electromagnetic propagation
- wireless electromagnetic propagation parameter
- wireless electromagnetic propagation fading
- wireless propagation refraction
- wireless wave attenuation constant
