liletian,

This is called a "lead lag" network. works as a poormans transformer, but only over a narrow band.  from left to right the first two caps and the inductor are for "I'm guessing" transforming the IC's impedance to the lead lag circuit.  the lead lag circuit works simply to a +90 degree phase shift to one leg and a -90degree to the other, and since the output being differential is 180 degrees out of phase then at the common point the phase while be such that the two signals add inphase.  The lead-lag may not be the best choice when an antenna is the load since the impedance presented to it probably will result in a wider loss since it will vary the frequency at which the phase shift occurs degrading the output power due to phase imbalance as well as matching loss.

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