Adding/Subtracting two microwave signals
I have two signals A and B at 10 GHz. I want to get C=A-B. How do I go about. I do not want to use any active devices. Basically I can always phase shift B by 180 degrees using an extra λ/2 length of transmission line and then add it to A. The question is how to "ADD" two signals. I am looking basically at a microstrip implementation of the same. Will simply joining the two transmission lines work ? Looking forward to replies. Thanks for your time.
-svarun
To add two signals, you can use "Wilkinson power divider" to do it. But its input becomes output, vice versa. "Microwave Engineering" from Pozar mentioned its theory in detail.
You don't have to use λ/2 transmission line.
Use 180-hybrid coupler, e.g., rat-race coupler.
You can get C(=A-B) signal directly.
B.R.
Actually, i am not sure if i understand your question. Are A and B at the same frequency, 10GHz? If so, for the getting C=A-B, do you already know the phase of the two signals, A and B? If you use extra λ/2 length of transmission line, you have to make sure they have the same phase before the signals are input to this network. It is the same case for you to "add" the two signals. You only need to combine, by a Wilkinson power divider, the two signals with 180 out of phase or in phase when you want they are substracted or added, respectively.
Hi WalterChan,
The two signals are indeed at the same frequency and indeed phase matched at the input. I think Wilkinson power divider can be a sloution to my problem. I need to read more on its design from Pozar though. Thanks to all for the replies.
-svarun
Hi ,
you can use rat-race coupler , I desinged that in practice
Regards
Any "180 degree hybrid coupler" of which a rat race can be one, or a "magic tee" in waveguide terms, will have two inputs and two outputs. The two outputs offer a "sum" and "diference" of the two inputs at their respective port.
Wilkinson power divider consists of a lumped resistor. For a fully planar solution, you can search in IEEExplore, where lots of paper report novel structures of power divider/combiner realized in pure microstrip form.