# B2-Antennas

Wiki for ITS

## ⌘ B2-Antennas

Building .... Networks
History, Now and Future
History
Pioneers: Maxwell, Hertz,...
1G, 2G,... 5G networks
Frequencies and Standards
Future Challenges
A-Basics of Communication
Electromagnetic Signals
Digital communication: Signal/Noise Ratio
Signal strength and Capacity: Shannon
B-Antennas and Propagation
Free Space Propagation
Multipath Propagation, Reflection, Diffraction
Attenuation, Scattering
Interference and Fading (Rayleigh, Rician, …)
Mobile Communication dependencies
C-Propagation models
Environments (indoor, outdoor to indoor, vehicular)
Outdoor (Lee, Okumura, Hata, COST231 models)
Indoor (One-slope, multiwall, linear attenuation)
D-System Comparison
Proximity: RFID, NFC
Short Range: ZigBee, Bluetooth, ANT+,...
WLAN/Wifi/802.11...
Mobile: GSM, UMTS, IMT-A (WiMAX, LTE)
E-Mobility
Mobile Network mobility
IP mobility
F-Network Building
5G and Future Networks
5G Heterogeneous Networks
Basic Internet
Video Distribution Networks
Coverage simulations
Coverage simulations
Traffic simulations
Network Capacity simulations
Building .... Networks

Keywords: Antennas, Hertz Dipol, Antenna Gain

## ⌘ B2-Antenna Basics

The gain is the radiation intensity of an antenna into the main direction as compared to an isotropic antenna (omnidirectional). For a perfect antenna without any losses, the gain G will be identical to the directivity D.

$D = D_{main}/D_{isotropic}$

$D_{rad} = \frac{4\pi F_{max}(\theta,\varphi)}{\int_0^{2\pi} \int_0^{\pi} F(\theta,\varphi)sin(\theta)d\theta d\varphi}$

## ⌘ Antenna pattern

If the antenna pattern is known, then the gain can be easily calculated.

• Isotropic antenna = point source: $G_s=0 \mathrm{dB}$
• Hertz Dipol = Short dipol: $G_s=1,5=1,76 \mathrm{dB}$
• $\lambda/2$-Dipol: $G_s \approx 1,64=2,15 \mathrm{dB}$
• draw electrical field of dipole
• Aperture antennas: $A_{eff}=e_{ap}A_{phys}$, with $e_{ap}= 0.65...0.75 (0.85)$, leads to gain of $G_s= A_{eff}\frac{4\pi}{\lambda^2}$
• examples of reflector antennas (effective aperture)

## ⌘Example:

Gain calculation for a $\lambda/2$-antenna calculate the gain of a $\lambda/2$ antenna, given that the electrical field can be described as:

$E(\vartheta) = -j \frac{\pi l}{c \lambda} \sin{(\vartheta)} I_0 \frac{e^{-j\omega t}}{r}$

Practical measurement of antenna gain: Compare the value of the electromagnetic field in the main direction of radiation with the gain of an isotropic antenna (or the gain of a known antenna). Best interaction is for antennas with length l approx lambda/2 ... lambda. Examples are provided for stubb antennas on GSM phones and typical WLAN 802.11b antennas.

Calculate the gain of a lambda/2 antenna, given that the electrical field of the antenna is given through a sin(theta) relation

Doubling antenna gain (+3 dB) will decrease the antenna pattern by a factor of two. This might cause mobile phones to fall outside of the radiation range.

## ⌘Example

What happens if I move from 2.4 Unik/GHz (802.11b) band to 5.1 Unik/GHz (802.11a)?

• Free space propagation
• antenna gain
• total power budget
• other factors?

Increase frequency from 2.4 to 5.2 Unik/GHz will yield to an additional free-space attenuation of 5.5 dB. If the same antennas are used, then this attenuation will be overcompensated by the antenna gain of both the transmit and the receive antenna.

However, the antenna characteristic will change significantly when doubling the frequency. Assuming that no mismatch occurs at the antenna feed, the width of the antenna beam will be reduced by a factor of two (relation lambda/l). This means that if receive and transmit antennas don't point towards each other, significant antenna gain loss might be seen.

### Antenna interaction

• from antenna design, what have we learned?
• which length/area is best (as compared to $\lambda$ to interact with an electromagnetic wave)?