VSWR Calculation Adding different VSWR values VSWR Calculation Site Calculations Improper Calculation Rule of Thumb Calculation Advanced Calculation Conclusion
Kathrein-Werke KG Rosenheim PO Box 10 04 44 Phone:+ 49 (0)8031 184 - 0 Fax: +49 (0)8031 184 991
Torsten Wulff
Kathrein-Werke KG Rosenheim Germany www.kathrein.de Phone: +049 8031 184 - 0
[email protected] www.kathrein.de
© Kathrein T. Wulff 08/2002
How to add different VSWR’s Adding different VSWR values VSWR Calculation
VSWR, Antenna 1.5
Site Calculations Improper Calculation Rule of Thumb Calculation
VSWR, Feeder Cable / Jumper Cable 1.1
Advanced Calculation Conclusion
Total VSWR ???
© Kathrein T. Wulff 08/2002
VSWR Calculation How to add VSWR values •
Re-calculate the reflection coefficient out of a given VSWR value
VSWR n - 1 rn= 1 + VSWR n
Adding different VSWR values VSWR Calculation Site Calculations Improper Calculation
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r total = r1 + r2
Rule of Thumb Calculation Advanced Calculation
Add two reflection coefficients to recover a new reflection coefficient
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Re-calculate VSWR value out of the new reflection coefficient
Conclusion
VSWR total
1 + r total = 1 - r total © Kathrein T. Wulff 08/2002
VSWR Calculation Which values are required to calculate the overall VSWR of a site installation? Adding different VSWR values VSWR Calculation Site Calculations Improper Calculation Rule of Thumb Calculation Advanced Calculation
VSWR, Antenna VSWR, Feeder Cable Insertion loss, Feeder Cable
Conclusion
© Kathrein T. Wulff 08/2002
VSWR Calculation Example of an improper calculation • Adding different VSWR values
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VSWR, Antenna (1.5)
VSWR, Feeder Cable (1.1)
VSWR Calculation Site Calculations Improper Calculation Rule of Thumb Calculation
VSWR 1.1 + VSWR 1.5 = VSWR 1,66 (worst case) This equals a return loss of 12.2 dB
Advanced Calculation Conclusion
This calculation considers a lossless cable and is incorrect for a site measurement!
© Kathrein T. Wulff 08/2002
VSWR Calculation Rule of thumb calculation
Adding different VSWR values VSWR Calculation
• •
VSWR, Antenna (1.5) Cable attenuation 3 dB (one way)
VSWR 1.5 = 14 dB return loss
Site Calculations Improper Calculation Rule of Thumb Calculation
Total cable attenuation: 2 x 3 dB insertion loss plus 14 dB = 20 dB 20 dB return loss equals a VSWR of 1.22
Advanced Calculation Conclusion
This calculation considers a lossy cable with a perfect impedance match!
© Kathrein T. Wulff 08/2002
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)
© Kathrein T. Wulff 08/2002
VSWR Calculation Example of an “advanced” site calculation VSWR, 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 1,65 VSWR 1.65 = 12.2 dB return loss Jumper Cable Add the cable attenuation twice, since the signal has to pass the cable up to the antenna and down to the connector. Add this attenuation to the “upper return loss”: 12.2 dB + 1 dB = 13.2 dB Feeder Cable Add the cable attenuation twice 13.2 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 © Kathrein T. Wulff 08/2002
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.
© Kathrein T. Wulff 08/2002
VSWR Calculation VSWR 1.5 versus VSWR 1.3 Adding different VSWR values
VSWR 1.5 Missmatch loss (dB) 0.18
1.4 0.13
1.3 0.08
VSWR Calculation Site Calculations Improper Calculation Rule of Thumb Calculation Advanced Calculation
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%
Conclusion
This value is insignificant small and marginal! © Kathrein T. Wulff 08/2002
VSWR Statement Conclusion •
VSWR of better 1.5 is required for - broadband antennas - antennas with adjustable electrical down tilt
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All major antenna suppliers are focused on broadband IMT 2000/UMTS antennas
Adding different VSWR values VSWR Calculation Site Calculations Improper Calculation Rule of Thumb Calculation Advanced Calculation Conclusion
⇒ VSWR of 1.5 is the world wide standard
© Kathrein T. Wulff 08/2002
