How to eliminate self-oscillating from a Colpitts oscillator?

I design a Colpitts oscillator f=2GHz.But the output is 500MHz and its harmonics.is this self oscillating?how to eliminate it?

I think there should be some parasitic capacitors ( and inductors) in your circuit. You should use the components that it can be operates at GHz frequencies. And You carefully design the pcb layout of the circuit.