Anders Vstberg [email protected] 08-790 44 55
Lecture 6: Antennas Anders Vstberg Dipole antenna Half-wave dipole
Quarter-wave dipole
Gain 1,64 = 2.15 dBi Linear Polarisation Quarter-wave dipole
Conducting plane below a single quarter wave antenna. Acts like a
half-wave dipole L=l/2 I L=l/4 I Corner Reflectors Multiple images
results in increased gain
Example: G=12 dBi Images l/2 Driven Element Yagi-antenna 3-30
element and a gain of 8-20 dBi
Loop-antenna Linear Polarisation Gain 1,76 dBi
Parabolic antenna Effective area Ae = hp d2/4 h=0.56 [Stallings,
2005] Helical antenna Normal mode Axial mode
Characterization of Fading
Small Scale Fading (Based on multipath time delay spread) Small
Scale Fading (Based on Doppler spread) Frequency non-selective
(Flat) Fading Frequency Selective Fading Fast Fading Slow Fading BW
of signal < BW of symbol Tm < Ts BW of signal > BW of
symbol Tm > Ts High Bd Td < Ts Channel variations faster than
base band signal variations Low Bd Td > Ts Channel variations
slower than base band signal variations [Rappaport, 1996]
