13 Adding Individual VSWR Values

Kathrein T. Wulff 08/2002

VSWR Calculation

Kathrein-Werke KGRosenheimPO Box 10 04 44Phone:+ 49 (0)8031 184 - 0Fax: +49 (0)8031 184 [email protected]

Torsten Wulff

Kathrein-Werke KGRosenheimGermany

www.kathrein.dePhone: +049 8031 184 - 0

VSWR Calculation

Rule of Thumb Calculation

Advanced Calculation

Conclusion

Site Calculations

Improper Calculation

Adding different VSWR values


How to add different VSWRs

VSWR, Antenna1.5

VSWR, Feeder Cable / Jumper Cable1.1

Total VSWR???

VSWR Calculation



Conclusion

Site Calculations




VSWR Calculation

How to add VSWR values

Re-calculate the reflection coefficient out of a given VSWR value

Add two reflection coefficients to recover a new reflection coefficient

Re-calculate VSWR value out of the new reflection coefficient

n

nn VSWR 1

1 - VSWR r +=

21total r r r +=

total

totaltotal r - 1

r 1 VSWR +=

VSWR Calculation



Conclusion

Site Calculations




VSWR Calculation

Which values are required to calculate the overall VSWR of a site installation?

VSWR, Antenna

VSWR, Feeder Cable

Insertion loss, Feeder Cable

VSWR Calculation



Conclusion

Site Calculations




VSWR Calculation

Example of an improper calculation

VSWR, Antenna (1.5)

VSWR, Feeder Cable (1.1)

VSWR 1.1 + VSWR 1.5 = VSWR 1,66 (worst case)This equals a return loss of 12.2 dB

This calculation considers a lossless cable and is incorrect for a site measurement!

VSWR Calculation



Conclusion

Site Calculations




VSWR Calculation

Rule of thumb calculation

VSWR, Antenna (1.5) Cable attenuation 3 dB (one way)

VSWR 1.5 = 14 dB return loss

Total cable attenuation: 2 x 3 dB insertion loss plus 14 dB = 20 dB

20 dB return loss equals a VSWR of 1.22

This calculation considers a lossy cable witha perfect impedance match!

VSWR Calculation



Conclusion

Site Calculations




VSWR Calculation

Example of an advanced site calculation

VSWR, Antenna (1.5)

VSWR, Cable Connector (1.1)

Jumper cable attenuation of 0.5 dB (one way)

Cable attenuation 2.5 dB (one way), return loss considered of being better than VSWR 1.05

VSWR, Cable Connector (1.1)


VSWR CalculationExample of an advanced site calculationVSWR, Antenna (1.5) + VSWR, Cable Connector (1.1)Calculate the total VSWR at the end of the cable to the antenna:VSWR 1.5 + VSWR 1.1 = VSWR total 1,65VSWR 1.65 = 12.2 dB return loss

Jumper CableAdd the cable attenuation twice, since the signal has to pass the cable up to theantenna and down to the connector. Add this attenuation to the upper return loss:12.2 dB + 1 dB = 13.2 dB

Feeder CableAdd the cable attenuation twice13.2 dB + 5 dB = 18.2 dB

Re-calculate the new VSWR value out of the new return loss:18.2 dB = VSWR 1.28

VSWR measurement at the input connector - WORST CASE CALCULATION !Add connector VSWR to VSWR of antenna-cable-assembly:VSWR site = VSWR 1.28 + VSWR 1.1 = 1.45 = 14.8 dB return loss


VSWR Calculation

Conclusion

A rule of thumb site calculation is being considered as

an appropriated step to get an idea about the

expected VSWR performance!

Run this calculation prior to a site measurement.


VSWR Calculation

VSWR 1.5 versus VSWR 1.3

VSWR 1.5 1.4 1.3Missmatch loss (dB) 0.18 0.13 0.08

A difference of only 0.1 dB results comparing a VSWR of 1.5 versus a VSWR of 1.3

- 0.1 dB equals a increased loss of 2%

This value is insignificant small and marginal!

VSWR Calculation



Conclusion

Site Calculations




VSWR Statement

Conclusion

VSWR of better 1.5 is required for- broadband antennas- antennas with adjustable electrical down tilt

All major antenna suppliers are focused on broadband IMT 2000/UMTS antennas

VSWR of 1.5 is the world wide standard

VSWR Calculation



Conclusion

Site Calculations



13 Adding Individual VSWR Values

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