On the advantages of loop-based unit-cell’s metallization regarding the angular stability of artiﬁcial magnetic conductors M. E. de Cos • F. Las-Heras Received: 25 March 2014 / Accepted: 11 September 2014 / Published online: 20 September 2014 Ó Springer-Verlag Berlin Heidelberg 2014 Abstract The angular stability of artiﬁcial magnetic conductors (AMCs) with hexagonal-shaped and square- shaped, patch-based and loop-based unit-cell’s metalliza- tion is studied for comparison. The inﬂuence of the gap distance between the unit-cells’ metallization on the overall AMC angular stability, while maintaining the resonance frequency and meeting the speciﬁed bandwidth require- ments for a given dielectric substrate, is shown for the ﬁrst- time. This observed phenomenon is explained by means of a simpliﬁed equivalent circuit devised for the unit-cells under study. Experimental characterization regarding AMC’s operation bandwidth and angular stability is carried out in an anechoic chamber for an AMC with hexagonal- shaped loop-based unit-cells, since from simulation results it outperforms the other AMCs under study. 1 Introduction Metasurfaces have attracted a lot of attention from the end of the nineties due to their amazing and unique capabilities for controlling the propagation of electromagnetic waves. Among them, artiﬁcial magnetic conductors (AMCs) [1– 33] behaving as perfect magnetic conductors (PMCs) [which do not exist in nature and are dual to perfect electric conductors (PECs)] and so exhibiting in-phase reﬂection in a limited frequency band, the AMC operation band, are particularly interesting for enhancing the radiation prop- erties of antennas [7–11, 21, 22], to implement nearly perfect absorbers [12] and also in radar cross section (RCS) reduction [13]. One of the AMCs limitations is related to the operation bandwidth due to their inherent resonant behavior. This has led to many research contributions focused on trying to overcome this limitation [14, 15, 20] through speciﬁc unit- cells’ metallization geometries, using thicker dielectric substrates, reduced relative dielectric permittivity, multi- layer structures or a combination of all of them. However, it is important to keep in mind that for the aforementioned AMCs’ applications, the angular stability of the designed metasurface is also a key issue [16–34]. Both the polarization angle of the incident ﬁeld and the incidence angle under oblique incidence should be con- sidered concerning the AMC’s angular stability. For an intended application at a given frequency, a designer aims to obtain an angularly stable AMC (maximizing the angular stability margin) while preserving a suitable operation bandwidth and trying to minimize the size and to avoid increasing the complexity and cost. This work arises from an intuition based on previously obtained results [16–18] according to which the unit-cells based on hexagonal-shaped metallization geometries out- perform the square-shaped based ones concerning the angular stability while exhibiting the same or even wider AMC operation bandwidth at similar resonance frequency. These previous works were based on rather complicated hexagonal-shaped metallization such as hexagonal dipoles- based unit-cells [16, 18] and double-hexagonal loop unit- cells [17] hindering a study and modeling which could provide more general conclusions. Moreover, works con- cerning comparison in terms of AMC operation bandwidth [11] evince that the square unit-cells’ metallization over- come the circular ones. Considering all these facts, this contribution aims to study the angular stability of AMCs M. E. de Cos (&)  F. Las-Heras Area de Teorı ´a de la Sen˜al y Comunicaciones. Dpt. Ingenierı ´a Ele´ctrica, Universidad de Oviedo, Ediﬁcio Polivalente, Mod. 8, 33203 Gijo´n, Asturias, Spain e-mail: medecos@uniovi.es 123 Appl. Phys. A (2015) 118:699–708 DOI 10.1007/s00339-014-8782-8