A Bandpass Filter Based on Dielectric Layers with a Strip Conductor Subwavelength Grating at Their Interfaces
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A Bandpass Filter Based on Dielectric Layers with a Strip Conductor Subwavelength Grating at Their Interfaces B. A. Belyaeva,b,c,*, V. V. Tyurneva, A. S. Voloshina,b,c, An. A. Leksikova, R. G. Galeevc, and Academician V. F. Shabanova,c Received June 30, 2020; revised June 30, 2020; accepted July 10, 2020
Abstract—The design of a multilayer bandpass filter has been investigated, in which each of the half-wavelength resonators consists of two dielectric layers with outer strip conductor gratings in the form of square grids and inner ones in the form of square patches. The grids serve as mirrors with specified reflective properties, which ensure optimal couplings of the outer resonators with free space and optimal coupling between the resonators. The patch gratings make it possible to tune the resonator eigenfrequency during the filter synthesis. The efficiency of the quasi-static calculation of the frequency response for the layered structure is shown for the case of a lattice period smaller than the wavelength in the dielectric and much smaller than the layer thickness. Since the calculation does not require much computing power, the parametric synthesis of the device can be performed on a conventional personal computer. The measured characteristics of the prototype of the synthesized third-order filter with a fractional passband width of ∼10% and a central passband frequency of ∼10.6 GHz are in good agreement with the calculation. The proposed design allows one to fabricate multilayer panels radio transparent in a certain frequency band for hiding microwave antennas. Keywords: frequency response, return loss, passband filter, insertion loss DOI: 10.1134/S1028335820090013
At present, the features of transmission and reflection of electromagnetic waves falling onto structures consisting of dielectric layers with strip conductor periodic structures (2D gratings) formed on their surfaces are intensively being studied [1–4]. The interest in such structures is due to the possibility of their use to create frequency selective surfaces serving as bandpass filters operating in the ranges from decimeter to submicron wavelengths. Strip elements forming a 2D periodic structure, for example, metal patches or metal grid cells, exhibit the properties of parallel or series oscillating circuits, which allows one to create bandpass filters using multilayer structures consisting of interacting resonant structures. It is important that, at high frequencies, the unloaded Q factor of strip resonators decreases with a decrease in the skin depth and an increase in the value of the substrate roughness effect. Therefore, the multilayer filters based on the strip conductor resonant structures have a relatively high passband loss.
The filter designs in which the dielectric layers serve as high-Q resonators and the 1D or 2D strip conductor structures formed on their surfaces work as mirrors with a specified reflectivity have the much lower loss [5, 6]. To expand the high-frequency stopband in such structures, the strip struc
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