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Transverse Permittivity Gradient (TPG) Superstrates or Lens: A Critical Perspective

This paper presents a quantitative comparison of superstrates with transverse permittivity gradient (STPG) when used in RCAs, as compared to stand-alone lens configurations. RCAs with TPG superstrates are often compared with lens antennas, considering the apparent structural similarity between the two. However, these two classes of antennas present inherent differences in terms of characteristics as well as principle of operation. Detailed comparisons are carried out using full-wave simulations. It was found that nearly 50% reduction in 3dB bandwidth was observed when a TPG superstrate was used as a lens antenna, as opposed to in an RCA.