I am new in RF recently i made a pcb design which includes some antenna they are meant to transmit data at 5GHz and 1.5GHz(GPS). My problem lies on GPS when the 5GHz antenna starts transmitting, the GPS signal strength degrades gradually and losing the GPS validation. when stop 5GHz antenna the GPS again recives signal suddenly. All the time i can't able to remove 5GHz because it place an important role in the application. About my GPS antenna it is from taoglas AP.17E GPS/GALILEO 1 Stage Active Patch and it is placed on board using 2 side adhesive.

 

I have not met this effect You write, but very similar. At very high reactive power capacitors the thermics depend mostly of dielectric material tan(fi), what may variate between 0,05 to FR-4 (normal) glass-textolite and similar for FR-2, up to 0,0001 for best kind of Duroid(TM) teflon-based PCB materials from Rogers.inc. Them are not very cheap, at least with a factor of 20 of "normal", but it is solely best choice for GHz range signals where the loss and neighbour larger signal caused dissipation may be the disturbing very much.
My advice No1 - change the pcb material to better. Advice No2 - check the induced fields, probably the ground-jobs may fix this appropriately. Just dig... for a surplus walls, better gnd points, kill the current loops etc etc. The advice 3 - check the Q-factor of input chains - probably that is a whole reason alone.