A compact multiband NRI-TL metamaterial-loaded planar antenna for heart failure monitoring

A compact, planar antenna is proposed, which uses negative-refractive-index transmission-line (NRI-TL) metamaterial loading in order to achieve multiband operation with orthogonal pattern diversity in different bands. The antenna occupies a small footprint, which is a key requirement for its future use in a heart failure monitoring system. It is shown that by employing two metamaterial unit cells as the main radiators, this produces a dipolar mode at 1.43 GHz and 1.92 GHz and an orthogonal folded monopole mode at 4.18 GHz. The associated -10 dB bandwidths around each of these frequencies are 24 MHz, 57 MHz and 372 MHz, while the corresponding gain and radiation efficiency are 0.82 dBi (71%), 1.27 dBi (75%) and 2.13 dBi (90%), respectively. The total size of the antenna is 30 × 36 × 1.59 mm³, while the height of each radiating arm is only 5 mm.