I made a pcb using AD9136, ADRF6720 and a gain block as a TX chain.
I made some test for different kind of scenario. Below is an example for 20MHz LTE (not the full frame) sampled at 983.04MHz. LO is at 2109.28MHz and LTE carrier is at 2140MHz (30.72MHz from LO).
I use the cancellation registers from DAC and ADRF6720 to reject the image. In this scenario, the best I can get is -60dBc with batwing on the image.
I have two questions:
1 - Do I need to implement DSP to improve the image rejection?
2 - Does the batwing on the image come from the delays between I and Q or is it the cancellation coefficients that are not frequency dependent?
Thanks for your help.