Gain antenna and communication system

The invention relates to a gain antenna and a communication system. The gain antenna includes an LC series resonance circuit and an LC parallel resonance circuit; the LC series resonance circuit is used for communicating with a reader and is provided with a first inductor ls and a first capacitor Cs which are in series connection; and the LC parallel resonance circuit is connected in series with the LC series resonance circuit, is used for communicating with an implanted biosensor tag, and is provided with a second inductor lp and a second capacitor Cp which are in parallel connection. The gain antenna is used for increasing a communication distance between the reader and the implanted biosensor tag.