Frequency Selective Surfaces With Multiple-Strip Group Elements

In this letter, a new group of elements of double and triple strips are proposed. Instead of a single perfectly conducting strip, a group of multiple strips constitutes a unit cell. In this case, the group is periodic, not the individual elements. The fraction of electromagnetic power reflected (reflectance) and transmitted (transmittance) of a new type of freestanding frequency selective surface (FSS), made of the group of elements per periodic cell, is examined theoretically for transverse magnetic (TM) polarization. The electric field integral equation (EFIE) technique with the subdomain overlapping piecewise sinusoidal (PWS) basis functions are employed to compute the unknown current coefficients induced on the metallic elements. It is observed that the spectral characteristic of single-strip FSS is enhanced by using periodic group cells. There exist transmission bands that allow full energy transfer for unequal lengths of double and triple strips. Double and triple resonances appeared in the event of unequal strip lengths. Since it is observed multiple resonances, the structure can be used in multiband antenna applications and subreflector systems. The computed results of strip FSS are compatible with the measured and calculated results in literature.