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BTC107 1 Microwaves
 

BTC107 1 Microwaves

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BTC107 1 Microwaves

BTC107 1 Microwaves

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    BTC107 1 Microwaves BTC107 1 Microwaves Presentation Transcript

    • BTC107 TV Systems & Signals Microwaves & The Electromagnetic Spectrum Martin Uren
    • The Broadcast Chain Studio OB Centre Viewer 2
    • Electromagnetic Spectrum Radio Optical Window Window Atmospheric Absorption 300 Hz 300 kHz 300 MHz 300 GHz 300 THz 300 PHz 300 EHz 300 ZHz 1000km 1km 1m 1mm 1µm 1nm 1pm 1fm L i Electric Infra g Ultra Gamma Radiowaves Microwaves X-Rays Waves Red h Violet Rays t Band Number 2 3 4 5 6 7 8 9 10 11 12 ELF ULF VLF LF MF HF VHF UHF SHF EHF THF 30 Hz 300 Hz 3 kHz 30 kHz 300 kHz 3 MHz 30 MHz 300 MHz 3 GHz 30 GHz 300 GHz 3 THz Wavelength 100 80 60 40 30 20 10 8 6 4 3 2 1 0.8 0.6 0.4 0.3 0.2 0.1 cm UHF SHF EHF Frequency 0.3 0.4 0.5 0.8 1 2 3 4 5 8 10 20 30 40 50 80 100 200 300 GHz 12 18 27 Q V W D 220 Microwave G Band P L S C X Ku K Ka U E F ? 3
    • Electromagnetic Waves  What are electromagnetic waves and how fast do they propagate?  What is relationship between frequency, speed and wavelength?  What is polarization? 4
    • Propagation in Coaxial Cable  Cable velocity ~0.66 x speed of light (c)  Cut-off wavelength = average circumference  Characteristic impedance ~138 log (R/r), where R = radius of outer, r = inner radius  What is the skin effect? 5
    • Propagation in Waveguide  Cut-off wavelength = 2 x a, a = waveguide width  Operating bandwidth: 1.25 - 1.9 x cut-off frequency, i.e. nominal frequency ~1.5 x cut-off  What is the nominal frequency for the examples? 6
    • Propagation in Waveguide 7
    • Propagation in Air Atmospheric Atmospheric Temperature Pressure (Celsius) (millibars) Press ure Temperature 140 1000 120 100 Warm Layer 80 60 40 20 10 0 -20 1 0.1 -40 0.01 0.001 -60 0 20 40 60 80 100 120 140 - 400 km Altitude 8
    • Propagation in Air  What is the ‘Radio Horizon’?  K is the Earth Radius Factor = 4/3  Effective Earth Radius = 8500km  Actual radius is 6400km  What is the Radio Horizon for a 100m high antenna? 9
    • Propagation in Air Space Wave Propagation 10
    • Antenna Gain  What is an ‘Isotropic Monopole Radiator’?  Any real antenna will have a directional response, making it better in one or more directions than an isotropic monopole radiator  This improvement is the antenna gain and is measured in dB (decibels) 11
    • Parabolic Antenna  Effective area ~n x physical area  Where n = illumination efficiency  Power gain, G = n (π D/λ)2  Where D = diameter, λ = wavelength  Beamwidth, ø ~ 24 / fD  Where f = frequency (GHz), D = diameter (m)  What is the beamwidth for f = 12GHz and D = 2m? 12