The arguments to the interp1 call are incorrect. The first two should be reversed, since the interpolation is over frequency.
Try this —
freqHz = [20.51 21.97 23.44 24.9 26.37 27.83 29.3 30.76 32.23 33.69 35.16 36.62 38.09 39.55 41.02 42.48 43.95 45.41 46.88 48.34 49.8 51.27 52.73 54.2 55.66 57.13 58.59 60.06 61.52 62.99];
phaseDeg = [142.97 120.69 90.32 67.07 50.38 28.25 5.72 -15.26 -29.47 -49.75 -68.85 -93.73 -119.85 -136.02 -145.41 -161.94 -179.65 174 155.32 132.26 112.73 94.44 78.02 64.64 58.87 62.91 66.56 51.86 41.99 36.01];
freqHzTarget = [20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50];
% phaseDegInterpolated = interp1(phaseDeg, freqHz, freqHzTarget); % Original
phaseDegInterpolated = interp1(freqHz, phaseDeg, freqHzTarget); % Corrected
phaseDegUnwrapped = unwrap(deg2rad(phaseDeg));
phaseDegInterpolatedUnwrapped = unwrap(deg2rad(phaseDegInterpolated));
figure
semilogx(freqHz, phaseDegUnwrapped, freqHzTarget, phaseDegInterpolatedUnwrapped)
This appears to be the desired result!
.
