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This is something of a basic question, but don't want to assume prior to buying an expensive switch.

Are microwave (think up to 20GHz) switches typically reciprocal?

When reading specification sheets, they are normally very specific in mentioning 1 input and 2 outputs. I am interested in alternating between two inputs and feeding to one output.

My guess is that a SPDT switch will work for this no problem (it would for DC/lower frequencies,) but assumptions like that don't always play out at higher frequencies.

Anyone able to help?

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  • \$\begingroup\$ CMOSonSapphire switches from the likes of Peregrine tend to be reciprocal. Check power handling differences betweenports. \$\endgroup\$
    – Neil_UK
    Nov 24, 2021 at 22:14
  • \$\begingroup\$ Mechanical switches should be but sometimes are optimized for one direction. Some designs are in fact purposely build to be unidirectional to avoid signal reflection coupling. If the datasheet talks about inputs and outputs assume you can only use in that direction unless the manufacturer confirms otherwise \$\endgroup\$
    – Lorenzo Marcantonio
    Nov 25, 2021 at 7:08

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In general, NO, they are not reciprocal (except for some unintended reverse leakage), unless they are specifically designed for that use. I'm talking about solid state switches.

On the other hand, if the switch were made from a mechanical device then it could be reciprocal.

And you (or someone) can design a solid state microwave switch that mimics a SPDT mechanical switch (2 inputs, 1 output). Or a SP3T switch, or DPDT, or whatever switch configuration you want. It's just a matter of how the underlaying switching devices (FETs for example) are connected and controlled.

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  • \$\begingroup\$ Nitpick: there's nothing inherently unidirectional about FETs in general; MOSFETs that have a separate body connection, as well as any type of JFETs, can work in either direction just fine. And signal flows just fine backwards through a normal MOSFET (with body tied to source) too, you just can't turn it off properly. \$\endgroup\$
    – Hearth
    Nov 24, 2021 at 16:49
  • \$\begingroup\$ Well, if you can't turn it off then it's not much of a switch? But your point is well taken. I'll update my answer to be a bit more explicit. \$\endgroup\$
    – SteveSh
    Nov 24, 2021 at 16:53
  • \$\begingroup\$ Thanks! So solid state switches are a no go. What would you think about electromechanical switches (like ie.rs-online.com/web/p/rf-switches/2240545)? These have a coil physically move parts in and out of contact. \$\endgroup\$
    – NAP_time
    Nov 24, 2021 at 16:53
  • \$\begingroup\$ @SteveSh My point was more about the JFETs, which I understand are very commonly used to switch RF signals--the bit about MOSFETs leaking in reverse was just an addendum. \$\endgroup\$
    – Hearth
    Nov 24, 2021 at 16:55
  • \$\begingroup\$ @NAP_time Solid-state switches can be made to be reciprocal! They just aren't necessarily. Electromechanical switches, on the other hand, are always reciprocal. \$\endgroup\$
    – Hearth
    Nov 24, 2021 at 16:56

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