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Antenna System VSWR/Return Loss Calculation
I have a question about how to calculate VSWR/ReturnLoss of a hybrid
antenna/feed line sysem which include bottom jumper, pressure window, wave guide, upper jumper and antenna? I list the parameters of all the components as bellow for an actual instance: VSWR InsertionLoss Antenna 1.06 Antenna Radome 1.01 0.4 Top Jumper 1.03 0.09 Waveguide 1.06 2.36 Pressure Window 1.01 Bottom Jumper 1.03 0.09 Could somebody help me get the ReturnLoss/VSWR at the end of Bottom Jumper for the entire system? Thanks. |
Antenna System VSWR/Return Loss Calculation
On Jan 21, 11:07*am, wrote:
I have a question about how to calculate VSWR/ReturnLoss of a hybrid antenna/feed line sysem which include bottom jumper, pressure window, wave guide, upper jumper and antenna? I list the parameters of all the components as bellow for an actual instance: * * * * * * * * * * * * * * * * *VSWR * *InsertionLoss Antenna * * * * * * * * * * 1.06 Antenna Radome * * * *1.01 * * * *0.4 Top Jumper * * * * * * * *1.03 * * * *0.09 Waveguide * * * * * * * * 1.06 * * * *2.36 Pressure Window * * * 1.01 Bottom Jumper * * * * * 1.03 * * * *0.09 Could somebody help me get the ReturnLoss/VSWR at the end of Bottom Jumper for the entire system? *Thanks. The problem is that you need more information than you have here. Let's reduce this to the case of just two components, a load that shows a 1.10:1 VSWR relative to the system reference resistance (commonly 50 ohms), and a transmission line that shows a 1.10:1 VSWR at the "input" end when terminated with the system load resistance at the other end. But the 1.10:1 can represent either of two resistances, or any of an infinite set of reactance + resistance that represent a constant magnitude but arbitrary phase angle reflection coefficient. For example, with a system reference resistance of 50 ohms, the 1.10:1 SWR load might be 55 ohms. And the transmission line might be 90 electrical degrees of 52.45 ohm line (well within tolerance for RG-8 type 50 ohm line); it would show 1.10:1 SWR with a 50 ohm load. But if you put the 55 ohm load at the end of that line, you'd measure 1.00:1 SWR at the input end of the line. On the other hand, the line could just as well have been 90 electrical degrees of 47.58 ohm line, which would also show a 1.10:1 SWR with a 50 ohm load at the far end; but if you put your 55 ohm load on that line, you'd see a 1.21:1 SWR at the input end of the line. In this example, I've just used things that evaluate to pure resistances; in practice, they could also include reactance. So in summary, without more information about each component, you can't arrive at an unambiguous answer to your question. You really should characterize each one-port in the system with its S11, and each two-port with its full S-matrix; then you have enough information, ASSUMING no other coupling than at the ports you used to characterize each piece. But even that's not always the case--and commonly isn't the case for antenna systems. Cheers, Tom |
Antenna System VSWR/Return Loss Calculation
wrote in message
... I have a question about how to calculate VSWR/ReturnLoss of a hybrid antenna/feed line sysem which include bottom jumper, pressure window, wave guide, upper jumper and antenna? I list the parameters of all the components as bellow for an actual instance: VSWR InsertionLoss Antenna 1.06 Antenna Radome 1.01 0.4 Top Jumper 1.03 0.09 Waveguide 1.06 2.36 Pressure Window 1.01 Bottom Jumper 1.03 0.09 Could somebody help me get the ReturnLoss/VSWR at the end of Bottom Jumper for the entire system? Thanks. You need to fully characterize each component with 2 port S parameters. You can then determine the cascaded parameters by the use of T parameters. You need a vector network analyzer to acomplish this. The procedure is described in HP's application note AN-154 "S parameter Design", available at: http://www.hpmemory.org/ressources/resrc_an_01.htm# Regards, Frank |
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