RF PCB experience
RF PCB design is complicated. I'll just sum a few thing by heart. But you should try to find some interesting literature about this suject first.
1. Try to seperate different subblocks as good as possible, and put grounded planes or traces in between (blocks the electrical field completely)
2. Use box shielding where possible
3. If you have the place on the board, put multiple ground vias in parallel.
4. Take care that every trace on the board behaves like a transmission line on the board at RF! Even bias traces should be considered carefully!
5. Use controlled impedances where you can
6. Try to seperate digital and analog circuitry. Eg if you have a hybrid PLL (DDS clock driving a PLL as reference clock), put the DDS on one side of the board and the PLL on the other side. This limits elektromagnetic coupling of noisy digital signals into the PLL loop filter
7. Filter where you can! Microstrip filters do not cost a penny more, only board space and development time ....
These are just a few things to keep in mind. But first think, then do the design!
Also, seperate different frequencies. Seperate TX and RX, make strong signal far away from receiver. Make sure microstrip line always has big GND. VCO control line need to be very careful seperated.etc.
two more points -
1. The good placement of the decoupling capacitors which will affect the total behaviours of the systems.
2. Don't cross coupling of digital and RF signal, it will cause many problems like frequency drift!
the ground through via's placement with the board and shield box's dimesion should be payed more attention because it's may cause resonance.
Use separated gnd for digital an analog gnd. i.e one gnd plane for RF . The other gnd for Analog.
pewang , how to understand the "the ground through via's placement ", and how to design the hole sizes of shielding box, for example , my boards works on GSM900 &1800 Mhz? thanks.