Dual-band implantable antenna with circular polarisation property for ingestible capsule application

A novel capsule antenna with dual-band performance and small occupation of inner capsule space is proposed. The antenna is designed by combining rigid Rogers substrate with flexible polyimide, which takes full utilisation of capsule inner surface and the system ground for implanted electronics. The antenna structure is based on two identical orthogonal strips, each connected with one conformal L-strip. In addition, a shorting pin is introduced, bringing in a fundamental resonance at 1.4 GHz industrial, scientific and medical (ISM) band with linear polarisation. Besides, with the adoption of the shorting pin, two extra resonant modes are excited and split in higher band, generating two orthogonal electric fields with equal amplitude and p/2 phase difference; therefore, covering another ISM band at 2.45 GHz with circular polarisation property. Finally, the simulation results show a wide impedance bandwidth of 16.2% at 1.4 GHz ISM band (for | S11| < -10 dB), and a broad axial ratio (AR) bandwidth of 34.8% at 2.45 GHz ISM band (for | S11| < -10 dB and AR < 3 dB), with dual-band operation further validated by measurement result.