A review on planar printed structures that are based on Matryoshka-like geometries is presented. These structures use the well-known principle of Matryoshka dolls that are successively nested inside each other. The well-known advantages of the planar printed technology and of the meandered nested Matryoshka geometries are combined to generate miniaturized, multi-resonance, and/or wideband configurations. Both metal and complementary slot structures are considered. Closed and open configurations were analyzed. The working principles were explored in order to obtain physical insight into their behavior. Low-cost and single-layer applications as frequency-selective surfaces, filters, antennas, and sensors, in the microwave frequency region, were reviewed. Potential future research perspectives and new applications are then discussed.

A modeling of the resonant behavior of a continuously reconfigurable frequency selective surface, FSS, is described in this paper. The FSS is based on four arms star geometry and its reconfigurability is achieved by the use of varactors. FSS, four arms star geometry and varactor principles are explained. Considering available a set of measured or numerical data, with frequency responses for different varactor capacitance values, the FSS equivalent circuit is stablished. Then, the varactor capacitance effect is included and the resonant behavior can be easily determined. After stablished, the FSS equivalent circuit can be applied even for a different varactor. In order to validate the proposed modeling, the equivalent circuit of a reconfigurable FSS using the varactor SMV1231 (0.466 pF ≤ Cv ≤ 2.35 pF is obtained. The equivalent circuit results are compared to numerical (ANSYS) and measured results, verifying a good agreement. Following, for the same geometry, the equivalent circuit is applied to a reconfigurable FSS using the SMV1234 varactor (1.32 pF ≤ Cv ≤ 9.63 pF) and once more a good agreement between the results is observed, indicating the applicability of the proposed modeling, which is especially attractive for optimization process.

In this paper, a compact matryoshka DGS using dielectric resonator (DR) is proposed. Despite the use of dielectric resonators to obtain band-stop frequency response not being a new idea, the proposed compact matryoshka DGS is an original contribution, since only recently the matryoshka geometry was used in DGS applications. Furthermore, a numerical analysis of the positioning of the DR is presented, which makes it possible to determine the region of the DGS for which the minimum resonant frequency is reached, and the resonant frequency range that can be obtained. To the best of the authors’ knowledge, this numerical analysis is an unpublished result, even more so, for the matryoshka DGS. The matryoshka geometry was described, including initial design equations. To verify the expected characteristics (miniaturization, selectivity, and resonant frequency tunability), two compact matryoshka DGSs (DGS1 and DGS2) were designed using a high permittivity ceramic (MCT-115) as DR. The obtained numerical and experimental results showed good agreement, and the initial design equations proved to be applicable, which allows new dimensions to be determined for other resonant frequencies, according to the application requirements. Resonant frequencies ranging from the maximum value to 33% (DGS1) and 27% (DGS2) were achieved, depending on the DR position. Considering λ ₀ the wavelength in free space, corresponding to the resonant frequency, DGS1 and DGS2 achieved an occupied area of 0.04λ ₀ ×0.04λ ₀ , and 0.05λ ₀ ×0.05λ ₀ , respectively, a good miniaturization. The proposed compact matryoshka DGS may be especially attractive for applications that require a very selective band-stop frequency response. If a wider band-stop is required, the proposed DGS can be cascaded.