I have a transmitter project to implement. Part of the project is to combine an in-phase and an out of phase (90 degree difference) signal with a center frequency at 3.5GHz. I figured I could implement a 90 degree hybrid combiner as in [this paper.]?https://www.hindawi.com/journals/ijmst/2014/854346/) using a transmission line design.
Is there another way to implement the power combiner without a transmission line? Like, for example, through a polyphase filter? I understand that a polyphase filter should work in theory but I couldn't find a paper that implements this design which made me skeptical about the feasibility of the design using the polyphase.
Another thing that I am confused about is the following:
I understand that quarter wavelength transmission line depends on the operating frequencies greatly, and in the design the frequency changes from the operating frequency as seen in the simulation. Wouldn't the transmission line NOT be a quarter wavelength anymore if it deviates from the operating frequency? (I know that we are setting the quarter wavelength based on the operating frequency.)