Antenna o How much RF energy the antenna
can radiate or emit? n This is due to its radiation resistance
(Rr) (resistive characteristic of the antenna – imaginary part: jX)
n The ohmic resistance (Ro)of the antenna acts as physical resistance, converting energy to heat)
o Radiate Power Pt: I2xRr
RF Current at the feedline
Radiation Pradiated
ZL
Zo
Zin
Power Forward
Power Reflected
Remember How Electromagnetic Waves Work o So if waves travel what happens when they hit an
object? n RF signal creates disturbances in the media n Some of the signal reflects when the standing wave hits an
object (some get observed) o Reflected wave (BLUE) o Incident wave (RED) o Resulting Standing wave (BLACK)
http://www.walter-fendt.de/ph14e/stwaverefl.htm
Between source and Antenna
Voltage Standing Wave Radio (VSWR) o Determines loss of forwarded radiation due to returned power
n Note that the loss can be compensated by high power àDamage the transmitter
o VSWR results from mismatched impedance o To calculate the VSWR, first calculate the reflection coefficient:
o VWSR is represented as VWSR:1; n e.g., 3:1 assuming reflection coefficient is 0.5 – represent how
much mismatch we have! o Based on VWSR we can determine the power loss
n http://www.microwaves101.com/calculators/872-vswr-calculator
http://www.antennex.com/preview/vswr.htm
Voltage Standing Wave Radio (VSWR) o Determines loss of forwarded radiation due to returned power o VSWR results from mismatched impedance o The loss can be compensated by high power
n Damage the transmitter o To calculate the VSWR, first calculate the reflection coefficient:
o VWSR is represented as VWSR:1; e.g., 3:1 assuming reflection coefficient is 0.5
o Based on VWSR we can determine the power loss n Verify these values: http://www.skyworksinc.com/uploads/
documents/VSWRreturn.pdf
http://www.antennex.com/preview/vswr.htm
§ What is minimum value of COR? § Short: CORà -1 § Open: CORà 1
§ What is the maximum value of VSWR? § Shortà Zero § Openà Infinity
Voltage Standing Wave Radio (VSWR) o Determines loss of forwarded radiation due to returned power o VSWR results from mismatched impedance o The loss can be compensated by high power
n Damage the transmitter o To calculate the VSWR, first calculate the reflection coefficient:
o VWSR is represented as VWSR:1; e.g., 3:1 assuming reflection coefficient is 0.5
o Based on VWSR we can determine the power loss n Verify these values: http://www.skyworksinc.com/uploads/
documents/VSWRreturn.pdf
http://www.antennex.com/preview/vswr.htm
§ What is minimum value of COR? § Short: CORà -1 § Open: CORà 1
§ What is the maximum value of VSWR? § |Γ|=1àInfinity § |Γ|=0à1
We want COR = 0 à VSWR = 1
Return Loss o The return loss of a load is merely the
magnitude of the reflection coefficient expressed in decibels
Example o Consider VSWR of 3:1
n Find COR n Find Return Loss (dB) n Find Mismatch Loss (dB)
http://www.microwaves101.com/calculators/872-vswr-calculator
Examples Bounce Diagram
L/2
t=0; V1 5 ns
2.5 ns
V1.ΓL=-6.67 10ns
7.5 ns
15 ns
12.5 ns
V1.ΓL. Γg= -6.67/3=-2.2
V1.ΓL. ΓL. Γg=0.74 20ns
25 ns 0.23469
2.5 ns
7.5 ns
12.5 ns
17.5 ns
22.5 ns
20
20-6.67 =13.33
13.33-2.2 =11.13
11.13+0.74= 11.87
Time Response Voltage V(z=0.5,t)
Stables
Assume Vg=60V ; Rg = 100; Zo= 50; L = 1 meter; Vp=2C/3
Introduction to Power Budget – A simple Example o Assume the following:
n Transmitter is transmitting 100mW on channel 1, 802.11b n A, C, D connectors each have a loss of -3dB n Transmitter antenna has an active gain of +12dB n The two antennas are 124 meters away from one another n Ignore the attenuation of the coax cable
o Answer the following n The power in Watts as Receiver Y receives. n Assuming the sensitivity of the receiver antenna is -5dBm, will Y
receive the transmitted information properly?
TransmitterX
Coax Cable
A C D ReceiverY
d
Do it!
802.11b Frequency Band o In the United States and Canada there are 11 channels available for
use in the 802.11b 2.4GHz WiFi Frequency range. This standard is defined by the IEEE.
1 2.401 2.412 2.423 2 2.404 2.417 2.428 3 2.411 2.422 2.433 4 2.416 2.427 2.438 5 2.421 2.432 2.443 6 2.426 2.437 2.448 7 2.431 2.442 2.453 8 2.436 2.447 2.458 9 2.441 2.452 2.463 10 2.446 2.457 2.468 11 2.451 2.462 2.473
http://www.moonblinkwifi.com/2point4freq.cfm