both 90deg and 180deg coupler can be used for balanced amplifier design. The condition is when you used a 90deg splitter, you need 90deg combiner; and when you are using 180deg splitter, you need a corresponding 180deg combiner.
For both design, input and output reflection can be canceled theoretically. but for real situations, this is hard to obtain in band edges. But totally speaking, the return loss for both input and output are better than unbalanced design.
the typical 180 deg coupler is rat-race coupler, you can check any textbook for the information of it; the rat-race couplers are used in balanced amplifier design for its wide band and better matching / isolation performance;
I used such design previously; the only problem is that the PCB layout is troublesome
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发表于 2008-11-24 20:04:16
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