Rafael Rodriguez Boix

This letter proposes a procedure to design a third-order dual-band polarization selective surface (PSS) which enables the transmission of the polarization along the $x$ axis in the lower band, and the transmission of the polarization along the $y$ axis in the upper band. The PSS is a multilayered structure in which periodic arrays of rectangular metallic patches are alternated with periodic arrays of rectangular apertures. Filtering equivalent circuits are used in the design of the PSS in both bands, and an ultra-efficient in-house Method of Moments software is employed in the design process, which is possible thanks to the simplicity of the metallization patterns of the multilayered structure. A prototype containing prepreg laminates as bonding material has been fabricated and measured. After minor adjustment of the dielectric substrate parameters, good agreement has been found between simulations and experiments. The designed PSS exhibits large frequency selectivity and angular stability up to 45$^\circ$ with respect to the normal incidence direction.

In this paper the authors describe the design of a broadband aperture-stacked patch (ASP) microstrip antenna based on a filtering equivalent circuit. The antenna consists of two stacked microstrip patches that are fed by a microstrip line through a resonant aperture. An equivalent circuit is proposed for the antenna consisting of three LC parallel resonators, out of which two resonators are inductively coupled and two resonators are capacitively coupled. The equivalent circuit is de-embedded from the antenna response by means of the least squares method, and the dimensions of the antenna are adjusted in such a way their equivalent circuit matches the response of a broadband third order filter. The reference filter is used as a mean to ensure broadband matching of the antenna. Following this design strategy, a broadband ASP antenna has been designed, fabricated and measured at a center frequency of 5.5 GHz with a bandwidth of roughly 45%.

This paper proposes the design of broadband microstrip antennas fed by differential microstrip lines. The designed broadband antennas are composed of two capacitively coupled rectangular stacked patches excited through a dog-bone shaped aperture by short-circuited differential microstrip lines. The short-circuited lines are symmetrically located with respect to the apertures so that their differential-mode (DM) naturally excites the aperture, while their common-mode (CM) is intrinsically rejected. The DM design of the antennas is based on an equivalent second-order filter circuit consisting of two capacitively coupled parallel LC resonators, which helps to ensure the DM broadband impedance matching of the antenna. Two different 2 × 2 arrays using the proposed antennas have been designed, fabricated and measured, one involving four 180° hybrids and three power dividers in the feeding network, the other involving one 180° hybrid and six power dividers. Bandwidths larger than 25%, gains around 12 dBi and cross-polarization below -25 dB have been achieved by the two arrays at a center frequency of 5.5 GHz.

In this paper the authors carry out a judicious application of the 2D Method of Moments (MoM) to the analysis of the scattering of plane waves by infinite conducting cylinders in the case where the cylinders show two orthogonal planes of mirror symmetry. In particular, the original MoM scattering problem is replaced by four new MoM scattering problems in which the two mirror symmetry planes behave as perfect electric conductors and/or perfect magnetic conductors. The current densities of the four new MoM problems only have to be obtained in one quarter of the cylinders cross-section, and therefore, the number of MoM matrix entries in each new problem is one sixteenth the number of MoM matrix entries in the original problem, which makes it possible to reduce the CPU time required for the solution of the original problem to roughly one fourth. Results are generated for cylinders where the cross section is a rectangle, a rhombus, an ellipse and an ogive, the one quarter CPU time reduction being confirmed in all cases

In this paper we present an efficient implementation of the spectral domain Method of Moments (SD-MoM) for the analysis of periodic multilayered structures in the case where asymmetric rooftop basis functions defined in a non–uniform mesh are used. This mesh only needs to be generated in the bounding rectangle that encloses the electric or magnetic current to be discretized. The slowly convergent double infinite summations involved in the MoM matrix entries are computed by means of four two–dimensional Non–Uniform Fast Fourier Transforms (NUFFT-2D), and the singularities and quasi-singularities appearing in the spectral functions that are subjected to the NUFFT-2D are skipped by rearranging terms and introducing eight additional one-dimensional NUFFTs (NUFFT-1D). The code implementing the NUFFT-accelerated SD-MoM approach has been used to analyze cells of frequency selective surfaces (FSSs) and reflectarray antennas (RAs). We have found that the proposed NUFFT-accelerated SD-MoM can be up to three orders of magnitude faster than the brute-force SD-MoM (direct summation of the truncated series), and around two orders of magnitude faster than commercial software CST.

This communication proves that the analysis of the scattering by a mirror-symmetric multilayered periodic structure can be replaced by the analysis of the scattering by two semi-structures with half the size in which the symmetry plane behaves either as a perfect magnetic conductor (PMC) or as a perfect electric conductor (PEC). The proof is based on the reflection properties of the electric and magnetic fields through PMCs and PECs, and it is valid for arbitrary oblique incidence. As an application of this concept, the spectral domain Method of Moments (SD-MoM) is reformulated to deal with MPSs limited by PMCs and PECs, and it is used in the design of a mirror-symmetric multilayered linear to circular polarization (LP-to-CP) converter. The results obtained with SD-MoM are validated by comparison with commercial software CST. Numerical simulations show that the CPU time required by both SD-MoM and CST in the analysis of half the LP-to-CP converter limited by PMC and PEC is between 30 and 42 per cent smaller than that required by the analysis of the complete LP-to-CP converter, which shows the numerical advantage gained in exploiting the symmetry when it is present.

In this paper, glide symmetry is applied to design common-mode rejection filters based on defected ground structures with bandstop response. To this aim, complementary split-ring resonators are chosen as the basic components for common-mode rejection. To illustrate the advantages of using glide symmetry, three implementations are studied and compared. The results reveal that glide symmetry offers the best performance in terms of common-mode rejection level and fractional bandwidth. Furthermore, glide symmetry barely affects the integrity of the differential mode. A prototype of each of the considered symmetries has been designed, simulated, and tested for practical validation. Good agreement is observed between the simulated and measured results, experimentally demonstrating the advantages of glide symmetry.

Two new compact balanced-to-balanced diplexers composed of two multiband balanced bandpass filters in a multilayer configuration are proposed in this letter to perform dual- and tri-band responses. The balanced bandpass filters are based on the use of magnetically coupled open-loop resonators. The magnetic coupling results in a strong inherent common-mode rejection, greater than 40 dB within all the dual-band diplexer passbands and greater than 30 dB for the tri-band diplexer passbands. All passbands in both diplexers are close to each other and well separated thanks to the presence of several transmission zeroes between them. Operating frequencies have been selected to be within the L band, used for many applications such as mobile services or satellite navigation. Specifically, the dual-band diplexer passbands are located at 1.08/1.58 GHz and 1.3/1.8 GHz with fractional bandwidths of 7/5.2 % and 7.4/5.5 %, while the tri-band diplexer passbands are located at 1.7/2.2/2.79 GHz and 1.97/2.37/2.95 GHz with fractional bandwidths of 4.1/4.6/3.5 % and 5.6/4.6/3.7 %. Measurements of two different prototypes are provided to validate the obtained simulation results, illustrating in this manner the usefulness of the proposed design methodology.