Inductive coupled coil is an antenna structure that can easily realize multiple resonant frequencies with planar structure for MHz band wireless capsule endoscopic (WCE) communication. However, since one resonant frequency is generated by one coil, the antenna size is large when designing multi-band antennas. In this paper, the antenna matching circuit is modified to be a series circuit with an LC tank so that one coil can generate two resonant frequencies. For the receiving antenna, this improvement can reduce half the number of coils and achieve smaller antenna size. For the transmitting antenna that is difficult to use multiple coils due to the strict size constraints of the WCE, this improvement can achieve two resonant frequencies through one coil. In order to evaluate the feasibility and whether this improvement will reduce the antenna transmission performance, a single-coil dual-band antenna operating in the MHz band is designed and manufactured, and the simulated and measured reflection and transmission coefficients are evaluated by a biological tissue equivalent phantom. By comparing with the previously proposed antenna results, it can be known that the transmission performance is not deteriorated, indicating that the improvement is feasible for the WCE transmitting and receiving coil antennas.
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