A
microstrip periodic structure behaves like a magnetic screen near
resonance. Defined as a ratio of strength of a
reflected to strength of an incident electric field, a reflection coefficient
value equals +1 at a resonance. Far from resonance the reflection coefficient
is close to –1 and a microstrip structure behaves like a dielectriccoated
ideal metal screen. It is possible to design a microstrip periodic structure
formed of curved narrow particles which when stretched are much longer than
the structure periods. As a result resonance occurs on the wavelength that
is much longer than the array periods. 

The frequency dependence of reflection coefficients
of a microstrip array formed by Cshaped metal particles near the lowest
resonance frequency is shown in the Figure below as an example. The
parameters of the strip are a=4 mm, f =15 degrees, 2w=0.5 mm. Array periods are
identical and are 10 mm long, substrate permittivity is 3 and substrate
thickness equals to 1.5 mm. The surface admittance where Ohm tends to zero
at the resonant frequency. Thus the surface of array is a high impedance
surface. A linear polarized along ydirection normal incident wave is
reflected by microstrip array of Cshaped particles at resonant frequency in
the same way as a surface of ideal magnetic. 


References Prosvirnin
S.L., Analysis of electromagnetic wave scattering by plane periodical array
of chiral strip elements, Proceedings of 7th Intern. Conf. on Complex
Media “Bianisotropics98”, Technische Universitat Braunschweig, Germany,
36 June 1998, p. 185188. Prosvirnin S.L.,
Transformation of polarization when waves are reflected by a microstrip array
made of complexshaped elements, Journal of Communications Technology and
Electronics, 1999, vol. 44, no. 6, p. 635639. Russian version: Просвирнин С.Л., Преобразование поляризации при отражении волн микрополосковой решеткой из элементов сложной формы, Радиотехника и электроника, 1999, т.44, 6, 681686. 