MATLAB: What does phase rotation in the RF Blcokset example mean

Question

I have the following question for this example:

https://www.mathworks.com/help/simrf/examples/getting-started-with-rf-modeling.html

1) The example mentions this:

"Notice that at 2.45GHz it introduces a phase rotation of approximately -58 degrees."

What does the phase rotation relative to? What phase is rotated? How do you tell it is -58 degrees?

2) The example mentions this:

"Notice that due to the phase rotation introduced by the S-parameter block, the complex input signal is partly downconverted on the I and on the Q branch, and thus the output power on the two branches is different. "

Why phase rotation will downconvert when there is phase rotation? This might be clear once I understand what the phase rotation is.

Answer 1

The SAW filter S-parameters introduces phase rotation of 58 degrees at 2.45GHz. This is the S21 component representing the effect on the signal going though the filter. The other S components also introduce phase rotations at that frequency, but, since the system is matched, only the S21 component affects the signal reaching the IQ demodulator (downconvertor). Over all, usually filters introduce phase rotation due to signal delay in the filter. The phase rotation affects how the signal is distributed between the I (real) and Q (imaginary) component at the RF frequency. Once the signal is downconverted to DC (later in the chain), the I and Q components are separated into two branches and the effect of the rotation makes the power on the branches different.