Electronics > RF, Microwave, Ham Radio

Ultra low insertion loss SPDT 1.4GHz RF switch

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srce:
I'm looking for an ultra low insertion loss SPDT RF switch for 1.4GHz.

Can anyone recommend anything better than an Infineon BGS12PN10? Insertion loss is given as around 0.17dB at 1.4GHz.

Input power is very low, Z0=50Ohm, can supply any voltage and cost not really important either.

MartinL:
What are you trying to do? Whatever it is, if it depends on getting better than 0.17dB loss in a switch, then I think you probably need a different approach. That's already pretty spectacularly low. It's getting down to the range where, even if you found a part whose datasheet claimed a lower figure, I'd be surprised if you were able to reliably measure a difference between them that would be distinguishable from the noise of individual manufacturing variations between units and boards.

Here's an electromechanical one with SMA ports and a 12V solenoid drive for $127 - but it still only promises to get you down to 0.15dB: https://www.digikey.com/en/products/detail/radiall-usa-inc/R570312000/10521679

srce:

--- Quote from: MartinL on October 21, 2021, 12:43:12 pm ---What are you trying to do? Whatever it is, if it depends on getting better than 0.17dB loss in a switch, then I think you probably need a different approach.

--- End quote ---
A switch for a Dicke Switch radiometer. The switch goes in front of the LNAs so minimising loss is critical. Any ideas for a different approach?

MartinL:
Hmm, interesting. Not a topic I'm familiar with I'm afraid.

But poking around the literature a bit, I see this paper which proposes the use of a "dual path" LNA, such that no separate switch is needed:

Looking at the circuit proposed, it's basically just two separate frontend LNAs, simultaneously connected to the input of a second stage LNA, with only one powered up at a time.

They're working on-chip at 100GHz, but I don't see why the same approach couldn't be applied in a board level design at 1.4GHz.

The presence of the inactive LNA would have some effect on the load impedance seen by the active one, and the source impedance seen by the next stage. But it should be possible to design a matching network in the middle such that everything sees the correct impedance when either one of the two LNAs is active. You would want to choose LNAs with suitable shutdown behaviour - ideally a high output impedance when off.

Joel_Dunsmore:
I think ADI has some MEMs switches that could work but your application should be extremely low power so there are likely lots of candidates.    I think PIN will be lower loss than FET switches, I can't tell the technology of the Infineon switch.  We have such as switch in the Fieldfox but I don't know the technology.  In fact we have it in the PNA-X but we found the improvement using it wasn't worth the trouble (you have to know the temperature very well of the load side of the switch, and our instrument drift was lower than the temperature drift). I'll ask and write back.  will this be room temperature of cryo?

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