1. Anders Västberg vastberg@kth.se 08-790 44 55
Lecture 6: Antennas
Anders Västberg

2. 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

3. Corner Reflectors Multiple images results in increased gain
Example: G=12 dBi
Images
l/2
Driven
Element

4. Yagi-antenna 3-30 element and a gain of 8-20 dBi

5. Loop-antenna Linear Polarisation Gain 1,76 dBi

6. Parabolic antenna
Effective area
Ae = hp d2/4
h=0.56
[Stallings, 2005]

7. Helical antenna Normal mode Axial mode

8. 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]