A Bandpass Filter Based on Dielectric Layers with a Strip Conductor Subwavelength Grating at Their Interfaces

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.