how to design LC tank for adf7021 freq 80mhz ???
For optimum performance, you may follow the reference design schematics closely from the ADF7021DBX Eval Note. But since your requirement is 80MHz which is not on the available evaluation board models, you may use the free tool, the SRD Design Studio (https://www.analog.com/en/design-center/landing-pages/001/adisimsrd-design-studio.html) to aid you in designing.