Abstract-Conventionally, radiofrequency (RF) coils used for magnetic resonance imaging (MRI) are electrically small and designed for nearfield operation. Therefore, existing antenna design techniques are mostly irrelevant for RF coils. However, the use of higher frequencies in ultrahigh field (UHF) MRI allows for antenna design techniques to be adapted to RF coil designs. This study proposes the use of parasitic scatterers to improve the performance of an existing 7T MRI coil called the single-sided adapted dipole (SSAD) antenna. The results reveal that scatterers arranged in a Yagi fashion can be applied to reduce local specific absorption rate (SAR) maxima of a reference SSAD by 40% with only a 6% decrease in the propagated B1 + field at the tissue depth of 15 cm. The higher directivity of the proposed design also decreasing the coupling with additional elements, making this antenna suitable for use in high density arrays. These findings show the potential of parasitic scatterers as an effective method to improve the performance of existing radiative MRI coils.Index Terms-Magnetic resonance imaging, electromagnetic propagation in absorbing media, specific absorption rate, YagiUda antennas.

Spatial diversity is a popular multiple antenna system technique, due to simplicity in implementation. However, its application has thus far been limited to systems where the electrical separation between adjacent antennas typically exceeds half a wavelength. This is because a more compact design induces higher antenna correlation and impedance mismatch, which results in lower diversity gains. In this paper, the performance of a compact multiband diversity antenna is investigated in both simulations and measurements. The dual-antenna structure is designed for the future WCDMA bands of WCDMA850, WCDMA1800 and 3G EU (UMTS), where the antenna separation at the WCDMA850 band is 0.24*wavelength. The measured results indicate that an average effective diversity gain of 7.3 dB at the 1% probability level can be achieved for the three bands