How does this circuit resonance?

Hi
is there anyone who help me?
I have a equivalent circuit.I want to know that How does this circuit resonance?or at all,my circuit is a resonant circuit?
thanks

In your schematic there are two inductors and two capacitors shown.
One of the resonant circuits comprises the capacitor (the two shown in series) in series with an inductor (two shown in series).
Depending on the shunt resistors, the resonant circuit Q-factor can vary. With a small shunt resistor across one of the two inductors, resonance frequency may shift up, with a high shunt value, down.

what is diode function in this circuit?

You never indicated what is the equivalent circuit for. You should know what the diodes stand for