HMC7044(HMC7043) spurious of finput/2

I have a question about the divider in the "output channel" of HMC7044(HMC7043).
The Condition:
  Input external clock to FIN pin and select External VCO.
  The external clock frequency(fin) : 2.4GHz, +6dBm
  Output MUX selection : Channel Divider Output
  Corse Digital Delay .. OFF, Channel Divider Ratio .. 1

The image of fin/2(1.2GHz, -42.15dB) appears in the above condition.


When I change Output MUX Selection to "fundamental", this image is drastically reduced (< -66.17dB).


This fin/2 image increases the spurious for High-Speed ADC(AD9689) and our customer should reduce this image but he needs delay function too.

Q1. What is the cause of this fin/2 image when the divider set to 1?
      (Our customer wants to know the mechanism of occurring f/2 image.)
Q2. Do you have a workaround to reduce this fin/2 image while using the divider on divide ratio=1?

Best regards,

y_suzuki

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