Bidirectional Coupler from Directional Couplers

Question

new to RF engineering.

I want to build a wideband bi-directional coupler because commercial ones are quite expensive. I decided to build one from two wideband directional couplers (SEDC-10-63+).

Directional couplers are 4 port devices, one being the isolated port. For the above coupler, the termination of the isolated port to 50 Ohm happened already internally, leaving me with three ports:

1. Input
2. Output
3. Coupled

For a four port device I could chain two devices after another, terminating the corresponding port with 50 Ohms myself. However, I could not find non-terminated ones for such wide bands. So, as the termination has already taken place internally, I am wondering if I can do something like the following:

That is: Chaining two directional couplers output-to-output in order to build a bidirectional coupler.

My feeling says this should work, as Input and Output should be directly connected and the coupling itself exhibits directivity.

But I am very curious to hear if I am missing something here. Can you build bidirectional couplers like this?

Best regards, Marvin

Answer 1

As you note, most (all?) couplers are bidirectional internally, and one side of the bridge is simply terminated.

This is fine to do, as long as the doubled insertion loss, and bandwidth reduction, are acceptable.