Abstract
Additional resonances are often introduced in an inverted-F antenna (IFA) by modifying the "F" structure, which typically makes the antenna both complex and bulky. To mitigate this problem, novel dual-/tri-band conformal capsule antennas with simple configuration are proposed in this paper by modifying the ground of the IFA and shifting the feed point. With these modifications, the IFA is miniaturized, and yet it is able to simultaneously cover the MedRadio band (401-406 MHz) and ISM bands (902-928 MHz and/or 2.4-2.5 GHz). The resulting configurations remain simple and compact despite the modifications, which is very desirable for conformal capsule type of applications. Furthermore, the impedance matching characteristics of the proposed IFAs remain stable even when a battery is added inside the capsule and the size or the position of the battery is modified. Moreover, the impedance matching of the antenna continues to remain stable even as its surrounding environment is changed. The operating principle of the proposed dual-/tri-band IFAs is discussed in detail and parametric study is carried out to investigate the characteristics of the proposed antennas. The results of this paper are expected to be helpful for designing multiband antennas in the future.