how do i decide the number of layers on a PCB

Hello All,
I am new to the world of PCB design and have this as my first job...could someone help me? How do I decide on the number of layers that I have to use for a PCB? What parameters do I have to keep in mind? Its an RF Circuit with components operating at 2.4GHz and 900MHz. Are there any books that you can recommend to read?
Thanks

The PCB designer's bible ... Coombs' Printed Circuits Handbook

Try Amazon


Good starting point for material etc.

http://www.everythingpcb.com/

4 layers are probably enough. go to h**p://www.chipcon.com, they have some reference designs.

for your RF circuit,I used a 900MHz RF circuit use two layer,RF circuit have it special rule for PCB,number of layer is not very important,you should consider another important.

generally two layers is enough for rf circuit

You don't start a critical or sensitive design by deciding how many layers it will have.

You start by deciding the best layout for both components and traces that will give the results you want. Crosstalk, resonance, shielding, impedance control, power, frequency, etc. - all determine how wide and thick the traces will be, what material the dielectric should be, how many and where the reference planes will be, how many signal layers you might need to get the desired isolation and signal continuity, etc.

Once you have the component and trace layout determined to give the desired result, you begin to get a feel for how many layers it will take to achieve your goal. Stackup is always done in pairs of signal layers, and pairs of planes. Odd number of either will usually result in built-in stresses resulting in cupping and/or warping of the board. The stresses only get worse by soldering heat and component weight.

Follow Tanuki's advice above - get the study material and learn about the science of PCB design. In addition to the book recommended by Tanuki, I would also recommend "High Speed Signal Propagation: Advanced Black Magic" by Howard W. Johnson - it is aimed at high speed digital boards, but applies to RF work as well.

Of course, you can always do the job cheaper, with fewer layers than I might use, but the end result will be less than your best.