Dear Eric,

Thank you for your help. I have a question for you how to write the specs for harmonic rejection,spurious (In/Out of band ) and image frequency rejection for a down converter ? Is there any calculations involved in this ? Please send any literature which related to the above.

Regards,
SRIKANTH

In the last 10 years I've not thought much about the specs for downconverters (e.g C band or Ku band down to 70 MHz).  We used to use whatever kit was supplied by reputable manufacturers.  I rather thought that such devices were now near obsolete, now that L band is so common as an earth station IF.

I suggest you look at the specification of competitors equipment and search the internet for relevant documents regarding the design of downconverters. Google for terms like .. direct down conversion receiver design.
Sample documents:
https://iroi.seu.edu.cn/prepare/Meeting/File/SODC/F/SODC/biltzer.pdf
https://focus.ti.com/lit/ds/symlink/trf371109.pdf
https://notes-application.abcelectronique.com/052/52-39543.pdf

If you say much more specifically what you are trying to do maybe someone else help please do so.

Best regards, Eric