I am using SystemVue (from keysight) software to simulate. I have a source which gives me a signal and source thermal noise which is -173dBm/Hz at room temperature. Now when I pass this through a hybrid 90. i am getting the same noise floor at two outputs, i.e., -173dBm/Hz and the signal is degrated by 3 dB at each output (which makes sense because it has divided the signal equally to two ports of the hybrid-90).
Then i am passing it to two-way 90 degree combiner so my signal level is increased by 3 dB at output of combiner but the noise floor remains same. Why it remains same? shouldn't the noise also added up by 3dB?
both the hybrid 90 and splitter are lossless.