

Mixers have a wide variety of implementations; the Mini-Circuits
part you mention is a doubly-balanced diode mixer, but active ones
(BJT, FET) seem more popular in consumer receivers.  You might
call MCL; they have a nice catalog.

The universal answer for wide-coverage, theory+practice, RF design
is the _ARRL Handbook_, published by the American Radio Relay
League, the radio amateur organization.  Any technical bookstore
can order you one.  The book is superb, with lots of accessible
theory, construction projects, and generally interesting stuff.

You might also check out _Solid State Design for the Radio Amateur_
(I think), by Hayward and <someone>.  This has sharper design
and test information about subsystems like mixers.