Issues with SWR/Return Loss of Splitter in FDM System

[infinite_gbps]

splitter return loss

So let me describe by setup:

Coax Line carrying 8 signals in the range of 0.8 GHz to 2.2 GHz. Each spaced by 200 MHz.

This coax goes into a 1-to-8 Splitter. On the output (8 outputs) of the splitter there are 8 BPFs. Each filter has a different center frequency of it's particular channel.

Then there are 8 amplifiers.

Then each goes into its own mixer with corresponding LOs for down conversion to IF, etc.

My issue is that when I take the 1-to-8 splitter and terminate all 8 outputs with 50 terminations then I get really good return loss and corresponding swr at the input (S11). BUT when I put on the BPFs and terminate those outputs at 50 Ohms then my S11 (return loss) looking into the splitter again goes into the toliet.

Why is that and how can I rectify this situation if I want to use a splitter?

Secondly, if I can't use a splitter is a mux the only way? I would rather try to make the splitter work though.

I can post plots if need be.

Thanks for the help.

 

[infinite_gbps]

return loss plot

Any takers?

 

[kspalla]

swr splitters

BPF might has bad RL. It recommend to have >20dB.
It works fine for some applications with >10dB.
Check it.

 

[VSWR]

loss in splitter

1. what kind of power splitter do you use? There are many types of power splitters. A schematic diagram would be helpful.

2. what values of S11 have you measured vs frequency? A plot would be helpful, showing S11 in dB vs frequency in MHz.

3. bad return loss plot (S11) over 0.8 to 2.2 GHz at splitter input is probably caused by that each BP filter has good input return loss only within its passband. This means the power splitter will never see good match at all ports simultaneously throughout the S11 plot vs frequency.

So let me describe by setup:

Coax Line carrying 8 signals in the range of 0.8 GHz to 2.2 GHz. Each spaced by 200 MHz.

This coax goes into a 1-to-8 Splitter. On the output (8 outputs) of the splitter there are 8 BPFs. Each filter has a different center frequency of it's particular channel.

Then there are 8 amplifiers.

Then each goes into its own mixer with corresponding LOs for down conversion to IF, etc.

My issue is that when I take the 1-to-8 splitter and terminate all 8 outputs with 50 terminations then I get really good return loss and corresponding swr at the input (S11). BUT when I put on the BPFs and terminate those outputs at 50 Ohms then my S11 (return loss) looking into the splitter again goes into the toliet.

Why is that and how can I rectify this situation if I want to use a splitter?

Secondly, if I can't use a splitter is a mux the only way? I would rather try to make the splitter work though.

I can post plots if need be.

Thanks for the help.