Lenses are commonly used to reduce the profile and enhance radiation properties
of horn antennas. To this purpose, metallic as well as metamaterial lenses have
been successfully employed in the past showing a clear gain enhancement and
shortening of the horn antenna (D. Ramaccia, et al., IEEE Trans. Antennas
Propag., 61, 2929-2937, 2013). The aim of this work is to implement a highfrequency
metamaterial lens-antenna based on a fishnet structure which promises
improved impedance matching compared to dielectric lenses.
Here, we show a metamaterial fishnet lens-antenna that enhances the antenna gain
when it is coupled to the aperture of a modified H-plane sectorial horn showing
also good matching in a narrow bandwidth. The fishnet consists in a pair of
perforated metallic 0.089λ0-thick plates separated by a gap of 0.133λ0. The unit
cell of each perforated plate is 0.535λ0 × 0.892λ0 and is perforated with a circular
aperture of diameter 0.446λ0. The fishnet matches the aperture of the H-plane
sectorial horn dimensions which are 5.89λ0 wide and 0.892λ0 high. Hence, it
consists of a row of 11 unit cells, see Figure. The antenna is designed to work at
53.5 GHz. For given aperture dimensions a wide flare angle such as the one
employed here means a low profile horn antenna (i.e. a shorter horn length). The
semi-angle flare of the horn is 75º and this implies a horn length of 1.31λ0. The
system was simulated using the commercial software CST MWSTM. Results show
good matching at 53.5 GHz, and a realized gain enhancement within a 1 GHz
bandwidth, with a gain peak of 15.8 dB at 53.5 GHz (see Figure). A standard Hplane
sectorial horn with a 5.16λ0 long and 30º semi-angle flare provides the same
gain, which means that our design is about 74% shorter although it works in a
narrower bandwidth. Gain is enhanced at the expense of bandwidth. Nevertheless,
results show another range between 58 GHz and 60 GHz where gain is also
enhanced. Experimental verification of the findings is now in progress.