Hi everybody,
I have problems simulating IIP3 of an N-path filter. My bandpass filter is clocked with FLO=1GHz and I define two sines with Freq1=1.15GHz and Freq2=1.3GHz at the input port to simulate IIP3 using qpss analysis. The power of both these sines is PowerRF=-30dBm. I have doubts about choosing the correct "1st Order Harmonic" and "3rd Order Harmonic" under "Direct Plot Form". This form has following options for the 3rd order harmonic
            FLO          Freq1         Freq2
1GHz      2             -2              1
1GHz      1              0              0
1GHz      0              2              -1


and following options for the 1st harmonic
                    FLO           Freq1         Freq2
1.15GHz         2              -3               2
1.15GHz         1              -1               1
1.15GHz         0               1               0
1.15GHz         -1              3               -1

1.3GHz           1               -2               2
1.3GHz           0                0                1
1.3GHz           -1               2                0

I think I must choose 0 2 -1 for the 3rd order harmonic and either 0 1 0 (1.15GHz) or 0 0 1 (1.3GHz) for the 1st one, however the result is about +8dBm while in the the reference paper it is +21dBm!!! I cannot find any reason for this difference, I should mention that all the parameters are the same for my simulation and the simulation of the paper.
Interestingly, choosing 0 1 0 for 1.15GHz gives somewhat different results than choosing 0 0 1 for 1.3GHz.
I would appreciate if anybody helps me with this problem.