Anders Vstberg vastberg@kth.se 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]