FreeLists / si-list / [SI-LIST] Antenna currents and digital Ground

["davidpauljones2003" <davidpauljones2003@xxxxxxxxx>]

Hello friends,
I am working on a wireless device and will try to simplify my query 
as much as I can.
I am working on a multi-layer PCB with digital on one side and RF 
circuits on the other. The Digital circuits have their own ground 
plane and the RF circuits also have their own ground plane. The two 
Ground planes are solid and entirely overlap eachother. The PCB stack 
up is therefore as follows; Digital-Digital-Digital Ground-Power 
plane-RF to digital connections-RF Ground-RF-RF (1-2-3-4-5-6-7-8).
There is one shield covering all of the digital circuits on the top 
of the PCB and one on the bottom covering all of the RF circuits.
I propose to stitch RF and Digital grounds around the perimeter of 
the PCB (which is also the boundary of the top and bottom shields) to 
form a Faraday cage. I also intend to stitch the ground planes 
together wherever a signal traverse between the two Ground planes.
I may also flood internal layers and stitch them to both grounds in 
order to improve isolation from one side of the PCB to the next. 
I believe this strategy will reduce emissions from my PCB and help to 
isolate high frequency harmonic content from the digital circuits 
signals from my sensitive RF circuits. 

This leads me to the question of the antenna ground. Here is where I 
need some help/advice;
I believe the whole ground system constitutes the antenna ground.
Where will the antenna currents predominantly flow? 
Will this be on the outside of the shield around the antenna feed 
point?
Since all the Grounds overlap and are stitched together, will the 
(high harmonic) digital return currents drown the small antenna 
currents or degrade the radiated sensitivity of my receiver ?
Should I avoid stitching together my digital and RF Ground planes 
close to the antenna?

Thankyou for your time,
David


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