Figure 4: Power spectrums before (TOP) and after calibration (Bottom) with 300 MHz LTE carrier. Click image to enlarge.
The calibration signal was kept unchanged and the LTE carrier center frequency swept from 50 MHz to 400 MHz in order to assess the frequency behaviour. The resulting image rejection, as shown in Figure 5, shows that at least 30 dB dynamic range improvement is maintained across the two first Nyquist zones. As expected, the image rejection decreases with frequency limited by the contribution of the bandwidth error which is not corrected.
Figure 5: Image rejection versus the LTE carrier center frequency with fixed
calibration signal. Click image to enlarge.