Suppose a PCB antenna or chip antenna is integrated onto a board design with a wireless IC, e.g. a Zigbee or Bluetooth module.
What are some guidelines regarding clearance/keepout area on the PCB that one should allocate surrounding the anteanna, so as to ensure effective transmission and reception?
Example: In the following image of a PCB (pulled from Google images), there is a USB connector situated fairly close to the PCB antenna:
I presume since RF design is a very significant field, there must be both theory- and practice-based rules of thumb regarding this (I understand there are a lot of case-based factors that play a role, so this question is only to scout for some generic helpful suggestions).
How far should the clearance be maintained? E.g., is it critical to maintain more than 10 mm of clearance area horizontally out from each end of the antenna?
In which axial/angular directions is the clearance most important? E.g., I presume the Fresnel Zone plays a role here, so is there a cone or certain maximum angle within which the clearance is most pertinent?
Which of the following are most critical to "keep out" in the keepout area?
- large metallic objects such as header pins or USB connectors, etc.
- ground copper pour
- any copper traces whatsoever
- all of the above?